Latest / Daniel and Kelly’s Extraordinary Universe / Can we see planets in other galaxies?

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Can we see planets in other galaxies? · Daniel and Kelly’s Extraordinary Universe

• 0:08
  Speaker 1: Hey, Daniel, do you remember the first time you saw
• 0:10
  Speaker 1: an X ray of yourself? I do. Actually, I once
• 0:14
  Speaker 1: broke a tiny little bone in my wrist the first
• 0:17
  Speaker 1: time I went snowboarding. And were you amazed to get
• 0:19
  Speaker 1: to see the inside of your body? I was really
• 0:22
  Speaker 1: excited about it, but then I was kind of underwhelmed.
• 0:25
  Speaker 1: It was sort of like a big whitewash. It was
• 0:27
  Speaker 1: hard to actually understand like what was going on inside there,
• 0:31
  Speaker 1: but the doctor could read it right. Oh. Yeah. To
• 0:33
  Speaker 1: him it was like crystal clear. He was like, oh,
• 0:34
  Speaker 1: this bone, that bone, the other bone. He knew exactly
• 0:37
  Speaker 1: what was happening. He spotted this tiny little break. And
• 0:40
  Speaker 1: that's pretty amazing, isn't it? How you know the knowledge
• 0:43
  Speaker 1: of an experience? I how they can pull out data
• 0:47
  Speaker 1: that other people can't see. Yeah, exactly. It makes me
• 0:49
  Speaker 1: wonder how X ray astronomers see the universe. Yeah, as
• 0:54
  Speaker 1: long as they don't go snowboarding, they're probably safe. I
• 0:57
  Speaker 1: hope the universe doesn't break its wrist. I am or
• 1:15
  Speaker 1: handmade cartoonists and the creator of PhD comics. I'm Daniel.
• 1:18
  Speaker 1: I'm a particle physicist, but I'm no longer a snowboarder.
• 1:22
  Speaker 1: Where you ever, Daniel, It doesn't sound like it went well.
• 1:24
  Speaker 1: I was a snowboarder for about five minutes and then
• 1:27
  Speaker 1: I retired. But no, it didn't go well. You achieve
• 1:30
  Speaker 1: what you wanted to achieve in that area of activity
• 1:34
  Speaker 1: and then decided to focus on physics. Yeah, exactly, I
• 1:36
  Speaker 1: crossed it off the list. Well. Welcome to our podcast,
• 1:38
  Speaker 1: Daniel and Jorge Explain the Universe, a production of I
• 1:41
  Speaker 1: Heart Radio in which we don't talk about snowboarding and skiing,
• 1:44
  Speaker 1: but instead we focus our energy on trying to understand
• 1:48
  Speaker 1: the universe, the vast reaches of space, the crazy explosions
• 1:52
  Speaker 1: going on inside stars, the weird things planets are doing
• 1:56
  Speaker 1: whizzing around stars in our galaxy and other galaxies and
• 1:59
  Speaker 1: in far reaches of the universe, and we try to
• 2:02
  Speaker 1: explain all of it to you without making too many
• 2:05
  Speaker 1: banana jokes. Although there is no out there in space, right,
• 2:08
  Speaker 1: there is galactic snow. Technically there's a lot of ice. Yeah,
• 2:12
  Speaker 1: we have ice giants in our Solar System. There's a
• 2:15
  Speaker 1: huge amount of frozen water all over the Solar System
• 2:18
  Speaker 1: and all over the universe. Water turns out, is not
• 2:22
  Speaker 1: actually that rare. It's only rare to be liquid on
• 2:25
  Speaker 1: the surface of a body like it is here on Earth.
• 2:28
  Speaker 1: Who do you think will be the first person to
• 2:30
  Speaker 1: snowboard on Neptune? Probably an astronomer, definitely not me. Hopefully
• 2:37
  Speaker 1: where where a risk guard? That would be my advice,
• 2:39
  Speaker 1: because there are some crazy mountains out there and some
• 2:42
  Speaker 1: crazy different kinds of snow, Like I wonder if methane
• 2:46
  Speaker 1: snow is good for snowboarding on or not. Do you
• 2:49
  Speaker 1: think aliens have a lot of different words for snow
• 2:51
  Speaker 1: and like we do here on Earth. I don't know.
• 2:54
  Speaker 1: Maybe if aliens have a lot of wrists, then they
• 2:56
  Speaker 1: don't go snowboarding because you know, it's too easy to
• 2:58
  Speaker 1: break one. They're an increased risk. They have like eight risks,
• 3:05
  Speaker 1: increased risk risk. Well, there are a lot of interesting
• 3:09
  Speaker 1: planets and asteroids and comments out there in the universe,
• 3:12
  Speaker 1: and we've talked about a lot of the ones that
• 3:14
  Speaker 1: we can find here in our Solar System on our podcast,
• 3:17
  Speaker 1: and also we talked about finding planets in our galaxy.
• 3:22
  Speaker 1: But it's a big universe and who knows what's out
• 3:25
  Speaker 1: there beyond our galaxy? And a deep question we're always
• 3:28
  Speaker 1: asking about the universe. Is how unusual is our neighborhood?
• 3:33
  Speaker 1: You know, we spent most of the time on this
• 3:35
  Speaker 1: planet just looking in our immediate neighborhood, understanding our planet,
• 3:40
  Speaker 1: our solar system, and then wondering, is this weird or
• 3:43
  Speaker 1: is this typical? Are other stars out there? Do they
• 3:46
  Speaker 1: also have planets like ours? Or are we the only
• 3:49
  Speaker 1: solar system out there with multiple planets? Or maybe other
• 3:51
  Speaker 1: solar systems have like dozens of planets. And so in
• 3:54
  Speaker 1: the beginning, we usually just wonder and we speculate, And
• 3:57
  Speaker 1: now we're in an era where we can actually start looking. Yeah,
• 4:00
  Speaker 1: because we have spotted planets in other solar systems within
• 4:05
  Speaker 1: our galaxy. I think you know, right now we not
• 4:07
  Speaker 1: only know that there are thousands and thousands of them
• 4:10
  Speaker 1: out there, but we've also started being able to actually
• 4:13
  Speaker 1: see them and even like check the weather on them. Yeah,
• 4:16
  Speaker 1: it's really pretty amazing. We are living in an extraordinary
• 4:19
  Speaker 1: era because for thousands of years people have wondered about
• 4:22
  Speaker 1: that question, are their planets around other stars? And now
• 4:26
  Speaker 1: just in the last twenty five years, we know for
• 4:29
  Speaker 1: a fact the answer to that question, and the answers
• 4:32
  Speaker 1: are kind of exciting. Ryany tells us that there are
• 4:34
  Speaker 1: a lot of planets out there, and there are a
• 4:36
  Speaker 1: lot of them that are probably like Earth, and so
• 4:39
  Speaker 1: that's exciting to actually like know for a fact the
• 4:43
  Speaker 1: answer to questions people have been wondering about for thousands
• 4:45
  Speaker 1: of years. Yeah, but most of the ones we've seen,
• 4:48
  Speaker 1: or at least have detected so far, we've seen by
• 4:51
  Speaker 1: looking out into the stars at night, and most of
• 4:54
  Speaker 1: them are in our galaxy. Right, It's pretty much all
• 4:57
  Speaker 1: of those thousands of exo planets that we found are
• 5:00
  Speaker 1: in the Milky Way. Yeah, that's right, because the Milky
• 5:02
  Speaker 1: Way is sort of our galactic neighborhood. It's about a
• 5:05
  Speaker 1: hundred thousand light years across, and so it's the best
• 5:07
  Speaker 1: place to look at other stars because they're the ones
• 5:10
  Speaker 1: that are nearby. But then, of course our imagination reaches
• 5:13
  Speaker 1: further and wonders like, well, maybe the Milky Way is unusual,
• 5:17
  Speaker 1: Maybe the Milky Way is weird, or maybe it's typical,
• 5:19
  Speaker 1: and it makes us wonder what is it like to
• 5:22
  Speaker 1: be a planet around a star in a far away galaxy? Yeah,
• 5:26
  Speaker 1: because the Milky Way is not the only galaxy, right,
• 5:28
  Speaker 1: There are hundreds of billions of galaxies that we can
• 5:31
  Speaker 1: see or know about. There might be maybe an infinite
• 5:34
  Speaker 1: number of them. Yeah, I think the last count is
• 5:36
  Speaker 1: in the observable universe. There are more than two trillion
• 5:40
  Speaker 1: galaxies right, each with hundreds of billions of stars. And
• 5:44
  Speaker 1: as you say, that's just the observable universe, we have
• 5:46
  Speaker 1: no idea what fraction of the actual universe that is.
• 5:50
  Speaker 1: It could be literally zero volume fraction, because the universe
• 5:54
  Speaker 1: could be infinite. Yeah, and it is sort of possible
• 5:56
  Speaker 1: now that you mentioned it is it would be weird.
• 5:58
  Speaker 1: But it is maybe possible that maybe the Milky Way
• 6:01
  Speaker 1: is it is strange, right, Like, maybe our galaxy is
• 6:04
  Speaker 1: the only one that is stable enough or calm enough
• 6:08
  Speaker 1: or something enough for it to have stars with planets
• 6:12
  Speaker 1: with life and them. Yeah. Absolutely, And it's one of
• 6:14
  Speaker 1: my favorite kinds of questions because any answer to this
• 6:17
  Speaker 1: question is mind boggling. Either the Milky Way is weird
• 6:21
  Speaker 1: and it's the only one that has the conditions to
• 6:23
  Speaker 1: make these kind of planets. WHOA, that would be weird, right,
• 6:27
  Speaker 1: or it's not. And then all those other galaxies are
• 6:30
  Speaker 1: also teeming with planets, which makes the number of earthlike
• 6:34
  Speaker 1: planets in our universe a huge number. That's hard to
• 6:37
  Speaker 1: hold in your head, and it makes you really suspect
• 6:40
  Speaker 1: that the odds of life are high. Yeah, but I
• 6:43
  Speaker 1: guess the question is can we confirm news? Do we
• 6:46
  Speaker 1: know for sure there are other planets in other galaxies
• 6:50
  Speaker 1: besides the Milky Way? And so to be on the program,
• 6:52
  Speaker 1: we'll be asking the question can we find planets in
• 7:00
  Speaker 1: other galaxies far far away a long time ago? And Daniel,
• 7:04
  Speaker 1: that's literally true. Every galaxy we look at is far
• 7:07
  Speaker 1: far away and the light is coming to us from
• 7:10
  Speaker 1: a long time ago. So they're basically all the setting
• 7:13
  Speaker 1: for Star Wars. Yeah, you know, that actually did blow
• 7:16
  Speaker 1: my mind recently. I was watching the Star Wars movie
• 7:18
  Speaker 1: and you know when those words come out at the beginning,
• 7:21
  Speaker 1: a long long time ago in a galaxy far far away,
• 7:23
  Speaker 1: and it did sort of made me think about some
• 7:25
  Speaker 1: of our conversations where it's like, oh, that means, you know,
• 7:27
  Speaker 1: it's sort of happening in real time. It's just that
• 7:30
  Speaker 1: the light is just getting to us now. Yeah, well
• 7:32
  Speaker 1: it could have happened a long time ago and the
• 7:34
  Speaker 1: light could still be arriving, So you can imagine that
• 7:37
  Speaker 1: instead of watching it on your TV screen you're just
• 7:39
  Speaker 1: looking through a telescope watching these battles play out in
• 7:42
  Speaker 1: a far away galaxy. Of course, you know the events
• 7:45
  Speaker 1: have already occurred and you're just watching them. But that's
• 7:48
  Speaker 1: sort of just like watching a movie, right, and the
• 7:50
  Speaker 1: movie is totally filmed before you watch it. It's not
• 7:52
  Speaker 1: like they're acting it live or anything. But it's fun
• 7:55
  Speaker 1: to imagine. Yeah, but even a movie like Star Wars,
• 7:57
  Speaker 1: if you think about it, they only hang out in
• 7:59
  Speaker 1: one galaxy. You know, it's the Galactic Empire, the only
• 8:03
  Speaker 1: goal around the galaxy. They never go to different galaxies. Yeah,
• 8:06
  Speaker 1: that's right, And I think they use that sort of
• 8:08
  Speaker 1: as a mechanism to suggest this is impossibly distant. This
• 8:12
  Speaker 1: is some where we could never go. This is a
• 8:14
  Speaker 1: different part of the universe. Because galaxies are crazy far apart.
• 8:18
  Speaker 1: They're not just really bit right there, like fifty or
• 8:21
  Speaker 1: hundred thousand or two hundred thousand light years across. The
• 8:25
  Speaker 1: space between them is much much bigger than the size
• 8:28
  Speaker 1: of the galaxies, right. Galaxies tend to be millions of
• 8:32
  Speaker 1: light years apart. So it's like, you know, if your
• 8:35
  Speaker 1: house was out in the deep woods and the next
• 8:37
  Speaker 1: house wasn't for miles and miles away. Yeah, yeah, I
• 8:41
  Speaker 1: think galaxies are like hundreds of thousands of light years wide,
• 8:44
  Speaker 1: but there are millions of light years apart. Yeah, they're
• 8:47
  Speaker 1: like little islands. Yeah, they're like little islands. Yeah, there's
• 8:50
  Speaker 1: a lot of variation in the size of galaxies, but
• 8:52
  Speaker 1: roughly that's correct. They're like basically ten times further apart
• 8:56
  Speaker 1: than they are wide. All right, Well, then the question
• 8:59
  Speaker 1: is are their plan in those other galaxies, and if
• 9:02
  Speaker 1: there are, how could we ever find them or maybe
• 9:04
  Speaker 1: even see them. That's right, because we want to move
• 9:07
  Speaker 1: beyond just speculation. We don't want to just wonder if
• 9:10
  Speaker 1: they're there. We want actual facts, We want data, we
• 9:12
  Speaker 1: want observations, We want to know because science is not
• 9:16
  Speaker 1: just about guessing and speculating. It's about asking nature questions
• 9:20
  Speaker 1: and hearing the answers. And the best moments are when
• 9:22
  Speaker 1: those answers are a surprise. Yeah. So, as usual, we
• 9:25
  Speaker 1: were wondering how many people out there in the public
• 9:28
  Speaker 1: and in our audience know if we can find planets
• 9:31
  Speaker 1: in other galaxy. It seems to impossible. I'm gonna put
• 9:34
  Speaker 1: my money on impossible, but we'll see. So Daniel went
• 9:37
  Speaker 1: out there and solicited answers from people on the internet,
• 9:41
  Speaker 1: and so thank you everybody who participated as usual, And
• 9:44
  Speaker 1: if you would like to give a shot to answering
• 9:47
  Speaker 1: tough physics questions without any preparation, without any googling, without
• 9:51
  Speaker 1: any background knowledge, please write to us two questions at
• 9:55
  Speaker 1: Daniel and Jorge dot com. We would love to put
• 9:57
  Speaker 1: your baseless speculation on the podcast. So think about it
• 10:00
  Speaker 1: for a second. If someone as you, if you thought
• 10:03
  Speaker 1: you could find planets in other galaxies, and what would
• 10:06
  Speaker 1: you say. Here's what people had to say. I was
• 10:09
  Speaker 1: under the impression we had already found planets in other galaxies,
• 10:14
  Speaker 1: but maybe not. That does seem very far away now
• 10:18
  Speaker 1: that I think about it and say it out loud.
• 10:20
  Speaker 1: That really depends on the times, because someday we totally
• 10:26
  Speaker 1: could find those planets. For example, if we launch robotic probes,
• 10:32
  Speaker 1: maybe with self replicating capabilities, they could go on and
• 10:37
  Speaker 1: on for billion years and catalog everything they come across.
• 10:44
  Speaker 1: But since the universe is expanding, I don't think we
• 10:49
  Speaker 1: will ever be able to reach the other galaxies. Yes
• 10:54
  Speaker 1: we can. My guess is that we probably don't yet
• 10:57
  Speaker 1: have any method to tech exoplanets and other galaxies directly.
• 11:03
  Speaker 1: I would imagine that the only way to detect them
• 11:05
  Speaker 1: would be indirectly, possibly from gravitational effects on that stars. Sure,
• 11:12
  Speaker 1: eventually we can, but I don't think we can now.
• 11:15
  Speaker 1: The distances are just too far for us to see
• 11:18
  Speaker 1: the wobble of the star with the planet orbiting around it. Well,
• 11:22
  Speaker 1: I can't think of a way then with the current
• 11:26
  Speaker 1: techlorldsy we could do that, all right, A lot of
• 11:28
  Speaker 1: optimism here. Somebody just said, yes, we can see sip
• 11:33
  Speaker 1: with it was that Obama didn't sound like him? Yeah, exactly.
• 11:35
  Speaker 1: I think there's a lot of good optimism here, and
• 11:37
  Speaker 1: also some great ideas, I like, you know, launching robotic
• 11:40
  Speaker 1: probes to other galaxies, though that would take a long
• 11:43
  Speaker 1: long time for them to get there and then report back,
• 11:46
  Speaker 1: so graduate students don't propose that for your PhD. Yeah.
• 11:50
  Speaker 1: And also it seems like somebody here thought that we
• 11:52
  Speaker 1: had already found planets in other galaxies. I guess, um, Yeah,
• 11:56
  Speaker 1: it's sort of hard to remember that distinction between stars
• 11:59
  Speaker 1: in our galley sea and stars in other galaxies. And
• 12:01
  Speaker 1: remember that when you look out in the night sky
• 12:03
  Speaker 1: and you see stars, all of those stars are stars
• 12:06
  Speaker 1: in our galaxy to the naked eye, a distant galaxy
• 12:10
  Speaker 1: is too faint for you to make out the galaxy
• 12:13
  Speaker 1: by itself. It takes like a telescope or a good
• 12:16
  Speaker 1: camera and you have to like build up that light
• 12:18
  Speaker 1: over several hours or days in order to see those
• 12:20
  Speaker 1: galaxies because they are so far away. Yeah, and if
• 12:23
  Speaker 1: you do see a galaxy on a telescope or on
• 12:25
  Speaker 1: a photo, it really just looks like a little smudge
• 12:28
  Speaker 1: from Earth. Unless you have like an amazing super telescope,
• 12:31
  Speaker 1: it's really almost impossible to make out the individual stars
• 12:34
  Speaker 1: in them. For most galaxies, that's true because they're really distant.
• 12:37
  Speaker 1: For the closest galaxies, they are actually quite large in
• 12:40
  Speaker 1: the night sky, like Andromeda. If you could see it
• 12:43
  Speaker 1: it was bright enough for you to see, it would
• 12:45
  Speaker 1: be larger in the sky than the full moon. Oh really, wow,
• 12:49
  Speaker 1: I didn't know that. Yeah, it's pretty incredible. So if
• 12:51
  Speaker 1: you look at a picture of Andrameda, it's taken over
• 12:54
  Speaker 1: many many hours or sometimes many nights just to build
• 12:57
  Speaker 1: up enough photons for you to see it. It's just
• 12:58
  Speaker 1: so far away. It's not very bright, but it's huge,
• 13:02
  Speaker 1: and so it takes up a big fraction of our sky. Wow,
• 13:05
  Speaker 1: it's pretty cool. All right. Well, let's get into this
• 13:08
  Speaker 1: topic then of how we would find planets in those
• 13:11
  Speaker 1: other galaxies. And I guess we should start by maybe
• 13:13
  Speaker 1: recapping how we know about planets in this galaxy. How
• 13:17
  Speaker 1: can we possibly know there are planets around us? Yeah,
• 13:20
  Speaker 1: it's pretty cool, and these are techniques that were developed
• 13:23
  Speaker 1: again just in the last couple of decades. You know,
• 13:25
  Speaker 1: for a long time people have wondered about this, But
• 13:27
  Speaker 1: planets around other stars are hard to see because those
• 13:32
  Speaker 1: stars are pretty far away. We're talking about light years
• 13:35
  Speaker 1: and light years away, and then the planets are really
• 13:38
  Speaker 1: close to their star in comparison to the distance from
• 13:41
  Speaker 1: here to there. I've heard you say before, and I
• 13:43
  Speaker 1: like this analogy that it's sort of like looking for
• 13:46
  Speaker 1: a tennis ball around a street light on the other
• 13:49
  Speaker 1: side of the country. It's very difficult to see a
• 13:52
  Speaker 1: very small thing next to a very bright thing. Yeah,
• 13:55
  Speaker 1: because suns are pretty bright, and planets don't. They don't glow.
• 13:59
  Speaker 1: Did you reflect light? That's right, they just reflect light,
• 14:02
  Speaker 1: and so it's very very difficult to see them directly.
• 14:04
  Speaker 1: So people came up with a few really clever techniques
• 14:07
  Speaker 1: to try to deduce the presence of planets, and these
• 14:11
  Speaker 1: days we actually have a few that are pretty successful. Historically, though,
• 14:14
  Speaker 1: the first one that really worked is something called the
• 14:17
  Speaker 1: wobble method, and this is based on the idea that
• 14:19
  Speaker 1: the planet doesn't just orbit the star. The planet in
• 14:23
  Speaker 1: the star sort of orbit each other because while the
• 14:26
  Speaker 1: planet is moving around the gravity of the star, the
• 14:29
  Speaker 1: planet is also a big massive object and it tugs
• 14:32
  Speaker 1: on the star. So the planet in the star together
• 14:35
  Speaker 1: actually orbit the center of mass of those two objects.
• 14:38
  Speaker 1: What this means is that if a star has a
• 14:41
  Speaker 1: planet around it, it wobbles a little bit, It moves
• 14:44
  Speaker 1: a little bit, sort of like shakes in the sky.
• 14:46
  Speaker 1: It's not stationary relative to us, and this is something
• 14:49
  Speaker 1: we can see, So we can see the gravitational effect
• 14:53
  Speaker 1: of a planet on its star by watching it wiggle. Yeah,
• 14:56
  Speaker 1: it's pretty amazing. We tend to think of our Sun,
• 14:58
  Speaker 1: for example, as being stationary and all the planets are
• 15:01
  Speaker 1: going around it. But the Sun is actually kind of
• 15:03
  Speaker 1: wiggling and getting pulled this way and that way by Jupiter,
• 15:06
  Speaker 1: by Us, a little bit, by Mars. It's not like
• 15:09
  Speaker 1: fixing space. Yeah, it's mostly by Jupiter though, and you
• 15:12
  Speaker 1: know this is not a huge effect. It's a subtle
• 15:14
  Speaker 1: effect because the star is usually most of the mass
• 15:18
  Speaker 1: of everything in the Solar system, Like in our Solar system,
• 15:20
  Speaker 1: the Sun is of the mass of the Solar System
• 15:23
  Speaker 1: and Jupiter is about of the rest of it. So
• 15:27
  Speaker 1: if you're looking at our Solar system from really really
• 15:29
  Speaker 1: far away, you could probably detect the effect of Jupiter
• 15:32
  Speaker 1: as a little wiggle on the location of the Sun.
• 15:35
  Speaker 1: But it wouldn't be a huge effect. It's not like
• 15:36
  Speaker 1: the Sun is moving around Jupiter the same way Jupiter
• 15:40
  Speaker 1: is moving around the Sun. It's a much smaller effect
• 15:42
  Speaker 1: because the Sun has so much more mass. Yeah, okay,
• 15:45
  Speaker 1: so you can look at a star and if you
• 15:46
  Speaker 1: see a wiggle, you know that it has a planet
• 15:48
  Speaker 1: around it, But that doesn't tell you much about the
• 15:50
  Speaker 1: planet itself, right, So there are other ways to tell that. Yeah,
• 15:54
  Speaker 1: you can basically just tell the mass of the planet
• 15:56
  Speaker 1: by the amount of the wiggle. And you can't see
• 15:58
  Speaker 1: the wiggle sort of side a side, right, we don't
• 16:01
  Speaker 1: have enough angular resolution and like see stars moving at
• 16:04
  Speaker 1: that resolution. But what you can do is see the
• 16:06
  Speaker 1: wiggle sort of back and forth. Is the star moves
• 16:09
  Speaker 1: away from us and then comes closer. It changes the
• 16:12
  Speaker 1: frequency of the light that the star is sending us
• 16:14
  Speaker 1: is a little bit of a Doppler shift. So that's
• 16:16
  Speaker 1: how we see it actually wiggling. You see a wiggle
• 16:18
  Speaker 1: in the color, like the star looks a little blue,
• 16:21
  Speaker 1: a little red, a little blue, and a little it
• 16:22
  Speaker 1: and if it looks regular enough, you think, hey, there's
• 16:25
  Speaker 1: a planet there. Yeah, and that can tell you the
• 16:27
  Speaker 1: mass of the planet, because you have to know how
• 16:29
  Speaker 1: heavy the planet is to pull on the star at
• 16:31
  Speaker 1: that amount, And they'll tell you a little bit about
• 16:33
  Speaker 1: sort of the rotation of that planet around the star,
• 16:36
  Speaker 1: or at least the star's rotation around the center of mass,
• 16:39
  Speaker 1: because that affects like how long it takes to go
• 16:42
  Speaker 1: back and then forth. But it doesn't tell us something
• 16:44
  Speaker 1: really key, which is how big is the planet. And
• 16:47
  Speaker 1: we're interested in knowing like are these planets really hot
• 16:51
  Speaker 1: and dense? Are they big fluffy blobs? You know, we're
• 16:53
  Speaker 1: interested in like planets that might have life on them.
• 16:56
  Speaker 1: So this method can't tell you the radius of the planets.
• 16:59
  Speaker 1: You don't really know what's going on with the planet.
• 17:01
  Speaker 1: But yeah, there are other methods yeah, it just gives
• 17:04
  Speaker 1: you a wobbly estimate. Yeah, exactly. All right, well, let's
• 17:06
  Speaker 1: get into some of the other ways. We know that
• 17:08
  Speaker 1: there are planets in other stars in our galaxy and beyond.
• 17:12
  Speaker 1: But first let's take a quick break. All right, we're
• 17:27
  Speaker 1: talking about finding planets in other galaxies. We know there
• 17:31
  Speaker 1: are planets here under our feet and in our Solar system,
• 17:34
  Speaker 1: and we've seen thousands of planets in our galaxy, in
• 17:38
  Speaker 1: other stars in our galaxy. But the question is are
• 17:41
  Speaker 1: there planets in other galaxies? Have we seen them? Can
• 17:45
  Speaker 1: we see them? Is that impossible? What can we know
• 17:47
  Speaker 1: about them? Nothing is impossible. What we think is impossible
• 17:51
  Speaker 1: in a hundred years will be like an undergraduate research project.
• 17:55
  Speaker 1: You know. That's what I love about the progress of science.
• 17:57
  Speaker 1: Only the impossible is impossible. Yeah, what's impossible today is boring.
• 18:03
  Speaker 1: Next week it's an iPhone app and there exactly. Yeah.
• 18:06
  Speaker 1: And so we're talking about ways to learn more about
• 18:09
  Speaker 1: these planets around stars in our galaxy. Yes, and and
• 18:12
  Speaker 1: they all sort of involved looking at the star that
• 18:16
  Speaker 1: the planet revolves around. Right, that's mostly the the idea,
• 18:19
  Speaker 1: because you know, the star is so brad it's really
• 18:22
  Speaker 1: hard to see the actual planet, Yeah, exactly. So mostly
• 18:25
  Speaker 1: we're looking at the effect on the star of the planet,
• 18:28
  Speaker 1: and so one effect is that it shakes the star.
• 18:31
  Speaker 1: The other is that we can actually have a little
• 18:33
  Speaker 1: bit of an eclipse, like if it's lined up perfectly
• 18:36
  Speaker 1: so that sometimes the planet passes between us and this
• 18:40
  Speaker 1: other star, and that just you know, has to be
• 18:42
  Speaker 1: by chance that the plane of that solar system is
• 18:45
  Speaker 1: aligned to the planet passes between us and the other star.
• 18:48
  Speaker 1: It will block some of the light of that star,
• 18:51
  Speaker 1: and not completely, of course, because the planet is typically
• 18:54
  Speaker 1: much much smaller than the star, but it will pass
• 18:56
  Speaker 1: in front of it, and you will see a dip
• 18:58
  Speaker 1: in the amount of light you're getting from the star.
• 19:01
  Speaker 1: And you can see this regularly. Can go dip and
• 19:03
  Speaker 1: then back up, and dip and then back up, and
• 19:05
  Speaker 1: so that's a really good sign that there's something, some
• 19:08
  Speaker 1: sort of dark mass orbiting that star. Right. It's kind
• 19:11
  Speaker 1: of like when you're watching a movie and someone stands
• 19:13
  Speaker 1: up in front of you, you know, they temporarily kind
• 19:15
  Speaker 1: of block the light from the screen. That's kind of
• 19:18
  Speaker 1: how it is. Right, It's like a big source of
• 19:20
  Speaker 1: light and something moves in front of it you the
• 19:22
  Speaker 1: overall light from that will sort of go down, and
• 19:25
  Speaker 1: if they did that, you know, every two minutes or so,
• 19:27
  Speaker 1: you would get pretty annoyed. But that's the scenario here,
• 19:30
  Speaker 1: is that we see this regularly. So this is a
• 19:33
  Speaker 1: really awesome method, not just because it's harder to fake
• 19:36
  Speaker 1: because you're seeing this thing like happen all the time
• 19:39
  Speaker 1: you see regularly if you watch the star long enough,
• 19:41
  Speaker 1: but also because you can tell the size of the planet. Right,
• 19:45
  Speaker 1: The bigger the planet, the more light it blocks. The
• 19:47
  Speaker 1: smaller the planet, the less light it blocks. So you
• 19:50
  Speaker 1: can measure the radius of the planet, which is super
• 19:53
  Speaker 1: duper cool because if you know the mass of the
• 19:56
  Speaker 1: planet and it's radius, you can tell it's density and
• 19:59
  Speaker 1: that gives you a lot of clues about like what
• 20:01
  Speaker 1: it's made out of. Is it mostly rock? Is it iron?
• 20:04
  Speaker 1: Is it just a big loose ball of ice? Is
• 20:06
  Speaker 1: it just a fluffy collection of gas? Like that tells
• 20:09
  Speaker 1: us so much more about what the planet is, all right,
• 20:12
  Speaker 1: So that's another way to tell if a star has
• 20:14
  Speaker 1: planets around it, But that also has some negatives, right,
• 20:17
  Speaker 1: Like you can only see the planet if it happens
• 20:20
  Speaker 1: to go in front of you between you and the
• 20:22
  Speaker 1: sun and the star, and um, there are other things
• 20:25
  Speaker 1: that could maybe causing this, right, yeah, exactly, other things
• 20:28
  Speaker 1: could be passing in front of it. Doesn't have to
• 20:30
  Speaker 1: be a planet, it could be some other weird kind
• 20:32
  Speaker 1: of star, you know, like a brown dwarf for you know,
• 20:35
  Speaker 1: some sort of neutron star or something. So you don't
• 20:37
  Speaker 1: necessarily know, but you can get a lot of information
• 20:40
  Speaker 1: about the composition of it, so you can rule a
• 20:42
  Speaker 1: lot of that kind of stuff out. And this is
• 20:44
  Speaker 1: really our workhorse method. This is the method we've used
• 20:46
  Speaker 1: to find a lot of planets recently. And even though
• 20:49
  Speaker 1: you can't see every planet, you can do calculations, you
• 20:53
  Speaker 1: can extrapolate. You can say, well, if I've seen a
• 20:55
  Speaker 1: bunch of them, I know how likely it is for
• 20:57
  Speaker 1: everything to be lined up perfectly right for me to
• 21:00
  Speaker 1: see it, So I can estimate how many solar systems
• 21:02
  Speaker 1: are there out there that aren't lined up perfectly, and
• 21:05
  Speaker 1: you can make guesses about those planets. So it's pretty effective. Yeah,
• 21:08
  Speaker 1: and there's a big telescope in space that's doing most
• 21:11
  Speaker 1: of this right exactly. The Kepler Telescope is basically launched
• 21:14
  Speaker 1: just to do this and so it's just like churning
• 21:16
  Speaker 1: out these candidates. And you know, in the beginning it
• 21:19
  Speaker 1: was rare. We had like one or two and they
• 21:21
  Speaker 1: had like special fantasy names. And now there are thousands
• 21:24
  Speaker 1: of these things and more discovered every week, and so
• 21:27
  Speaker 1: now it's like a statistical game. Now we're able to
• 21:29
  Speaker 1: ask questions like how unusual is Earth? Or how weird
• 21:32
  Speaker 1: is it to have a hot jupiter that's close to
• 21:34
  Speaker 1: your star? Or how unusual is it to have nine
• 21:37
  Speaker 1: planets or eight planets? So that's really fun. Do you
• 21:40
  Speaker 1: think they will run out of names? Like I know
• 21:42
  Speaker 1: they use letters and numbers now, like you know, maybe seven, three, nine.
• 21:47
  Speaker 1: They sort of remind me of license plates, like you know,
• 21:50
  Speaker 1: all these names are just like random collections of digits,
• 21:53
  Speaker 1: and so I think they can just keep adding digits
• 21:55
  Speaker 1: and they're never going to run out of names. Do
• 21:56
  Speaker 1: you think when they get to like our two D one,
• 21:59
  Speaker 1: the will skip the number just to avoid you know,
• 22:02
  Speaker 1: infringing star Wars is right, I'm sure Disney's lawyers have
• 22:05
  Speaker 1: already written those letters, all right. So those are two
• 22:08
  Speaker 1: good ways to know if there are planets around other stars.
• 22:10
  Speaker 1: But there's also kind of a more direct way. Right,
• 22:12
  Speaker 1: Like I've seen pictures of planets around other stars, like
• 22:16
  Speaker 1: it is possible to kind of look at them, take
• 22:18
  Speaker 1: pictures of them. And now we have super powerful space
• 22:20
  Speaker 1: telescopes and clever techniques, you could actually look at fairly
• 22:24
  Speaker 1: nearby stars and see light off of those planets directly.
• 22:29
  Speaker 1: So we have like direct images, actual pictures from those
• 22:33
  Speaker 1: solar systems, and not very many of them, just a few,
• 22:35
  Speaker 1: because everything has to be like lined up just right,
• 22:38
  Speaker 1: and the planet has to be really big and kind
• 22:40
  Speaker 1: of far away from its star, and the whole star
• 22:42
  Speaker 1: has to be pretty close to us, and you have
• 22:45
  Speaker 1: to line up this coronagraph to block the life from
• 22:48
  Speaker 1: that star just right. But we've done it, and that's
• 22:50
  Speaker 1: pretty exciting. Yeah, but most of what we've done is
• 22:53
  Speaker 1: within our galaxy, and it sounds like it's already really
• 22:57
  Speaker 1: hard to see planets around other stars within our Milky
• 23:01
  Speaker 1: Way galaxy, which is our neighborhood. And so now the
• 23:04
  Speaker 1: question is, how could we possibly ever see planets around
• 23:07
  Speaker 1: other galaxies. I mean, when we look at a galaxy
• 23:10
  Speaker 1: just kind of looks like a fuzzy cloud, like a
• 23:12
  Speaker 1: fuzzy collection of stars. Yeah, the problem with all these
• 23:14
  Speaker 1: methods is that they start to fail as the star
• 23:17
  Speaker 1: gets further and further away. Right, A star that's further
• 23:20
  Speaker 1: away wobbles less, and the light that comes from it
• 23:24
  Speaker 1: is harder to look at and harder to separate from
• 23:27
  Speaker 1: the nearby stars. And so these things start to fail
• 23:30
  Speaker 1: as the stars get further away, which is why, for example,
• 23:33
  Speaker 1: we haven't even seen planets all through our own galaxy.
• 23:36
  Speaker 1: There are parts of our galaxy where we have not
• 23:39
  Speaker 1: detected any planets. The furthest planet we've ever seen is
• 23:42
  Speaker 1: about twenty seven thousand light years away, whereas the whole
• 23:46
  Speaker 1: Milky Ways a hundred thousand light years across. Right, So
• 23:49
  Speaker 1: now it seems almost impossible to imagine going to another
• 23:52
  Speaker 1: galaxy millions of light years away. But there are some
• 23:55
  Speaker 1: very cool techniques people have come up with recently that
• 23:58
  Speaker 1: will let us do this way. You said a while
• 24:00
  Speaker 1: ago that stars wobble less still further they are away.
• 24:04
  Speaker 1: Why is that wouldn't they wobble the same or is
• 24:06
  Speaker 1: it just gets lost in the noise. No, you're right, stars,
• 24:09
  Speaker 1: if they're far away, they actually wobble the same way.
• 24:11
  Speaker 1: It doesn't really matter how far away we are, and
• 24:14
  Speaker 1: of course, the sideways wobble is not what we're looking at,
• 24:17
  Speaker 1: but the back and forth wabble that's the red shift
• 24:19
  Speaker 1: and the blue shift. We could still see that for
• 24:21
  Speaker 1: stars that are further away, but they're harder to see.
• 24:24
  Speaker 1: You're looking through lots of other stars. They're further away,
• 24:27
  Speaker 1: they're more dim, and so it's just harder to study
• 24:29
  Speaker 1: these things that are further away. It's a harder to
• 24:32
  Speaker 1: make out the wiggle. Yeah, and which seemed almost impossible
• 24:34
  Speaker 1: to do this with stars in another galaxy, just because
• 24:37
  Speaker 1: it's so far away and you know they're probably drowned
• 24:41
  Speaker 1: out by all the other stars in that other galaxy.
• 24:44
  Speaker 1: But you're saying there, it is sort of possible to
• 24:46
  Speaker 1: look at planets there. Yeah. People have come up with
• 24:48
  Speaker 1: crazy ideas to do this, and so the sort of
• 24:50
  Speaker 1: three ideas that I think are pretty awesome. The first
• 24:54
  Speaker 1: one is called gravitational micro lensing, and it also uses gravity,
• 24:59
  Speaker 1: but it's not the wa hobble of the star that
• 25:01
  Speaker 1: it's using. It's looking to amplify the light of a
• 25:04
  Speaker 1: star by another star passing sort of in front of it.
• 25:09
  Speaker 1: That's kind of how we look at dark matter, right,
• 25:11
  Speaker 1: And that holds to like if we look for that
• 25:13
  Speaker 1: kind of lensing effect exactly because mass doesn't just like
• 25:17
  Speaker 1: create gravity, it actually bends space. And so if something
• 25:20
  Speaker 1: passes between us and another object, it will bend the
• 25:24
  Speaker 1: space between us and that object. So the light from
• 25:27
  Speaker 1: the object in the background gets distorted, just like if
• 25:30
  Speaker 1: you had a lens in the sky, but now it's
• 25:33
  Speaker 1: a gravitational lens. It's bent space, so it changes a
• 25:37
  Speaker 1: path of light. But you can use all of your
• 25:39
  Speaker 1: intuition for how a lens works to understand how a
• 25:42
  Speaker 1: gravitational lens work. The principles the same, even though the
• 25:45
  Speaker 1: bending mechanism is different. So what happens here is you
• 25:48
  Speaker 1: have a star in the background, and then some star
• 25:50
  Speaker 1: in the foreground passes between you and that star, and
• 25:54
  Speaker 1: as it passes right through that line between you and
• 25:56
  Speaker 1: the background star, it creates this lensing effect and it
• 25:59
  Speaker 1: just dorts the background star. That's cool, that's gravitational micro lensing.
• 26:04
  Speaker 1: But if there happens to be a planet around the
• 26:07
  Speaker 1: star that's doing the lensing, then as the planets going
• 26:11
  Speaker 1: around the star, it will change how that lens works,
• 26:14
  Speaker 1: and so it will sort of like distort the distortion
• 26:16
  Speaker 1: in a particular way, So it changes how the background
• 26:20
  Speaker 1: star looks like there'll be a wiggle in the lensing basically, right,
• 26:24
  Speaker 1: like the lensing effect will be wiggly. Yeah, exactly, Just
• 26:28
  Speaker 1: like if somebody stands in front of you in the
• 26:30
  Speaker 1: movie theater and blocks your path, if they have like
• 26:32
  Speaker 1: a little toddler running around them the whole time, they'll
• 26:35
  Speaker 1: create a different shadow, right, And so it's the same idea.
• 26:38
  Speaker 1: And if the parent is like, you know, chasing after
• 26:40
  Speaker 1: the child, you would you would notice that from the lensing, Yeah,
• 26:43
  Speaker 1: you would notice that. So it changes the pattern of
• 26:46
  Speaker 1: the brightening and the fading that you get from gravitational lensing,
• 26:49
  Speaker 1: and it doesn't in a particular way. You can even
• 26:52
  Speaker 1: enhance it, right, You can get like a flare from
• 26:54
  Speaker 1: this planet if it's just in the right spot to
• 26:57
  Speaker 1: exaggerate and enhance the light of the background are And
• 27:00
  Speaker 1: so this is pretty cool, yeah, but you still need
• 27:03
  Speaker 1: a background star to sort of see and be able
• 27:06
  Speaker 1: to like see the life from it and be able
• 27:09
  Speaker 1: to tell it a part. Can we do that? And
• 27:10
  Speaker 1: with stars and other galaxies, like can we see individual
• 27:13
  Speaker 1: stars in like Andromeda? You can't always see individual stars.
• 27:17
  Speaker 1: But you're right, you need something in the background. It's
• 27:20
  Speaker 1: not critical that you have just one star in the background, right,
• 27:22
  Speaker 1: You just need some source of light. And then you
• 27:25
  Speaker 1: need to have a model for how that light will
• 27:27
  Speaker 1: be distorted by a foreground object. And so if you
• 27:30
  Speaker 1: have some sort of source in the background, you can
• 27:32
  Speaker 1: mimic you can model how that light would be distorted
• 27:35
  Speaker 1: by gravitational lensing, even if it doesn't just come from
• 27:37
  Speaker 1: one star, even if it comes from like a background galaxy. Interesting, okay,
• 27:42
  Speaker 1: So then the star we want to measure would be
• 27:44
  Speaker 1: in another galaxy, and now we need like a light
• 27:46
  Speaker 1: source behind that other galaxy, behind that star in the
• 27:49
  Speaker 1: other galaxy, or in or outside the galaxy. It doesn't
• 27:53
  Speaker 1: have to be in that other galaxy. It can be
• 27:54
  Speaker 1: like in another galaxy, even behind it, just anywhere behind
• 27:57
  Speaker 1: the star that we want to look at. We need
• 27:59
  Speaker 1: this perfect lineup of the star we're looking at and
• 28:02
  Speaker 1: then the star behind it, so the background star can
• 28:05
  Speaker 1: get lensed by the foreground star. So that's a big disadvantage.
• 28:08
  Speaker 1: Another big disadvantage is that it usually just happens once.
• 28:12
  Speaker 1: It's like a chance thing. These two stars are not
• 28:14
  Speaker 1: like usually in a binary system or anything. So it's
• 28:17
  Speaker 1: just like by chance that one happens to pass through
• 28:20
  Speaker 1: the line of sight to the background star, which means
• 28:22
  Speaker 1: you can't repeat it. You just get like one observation,
• 28:26
  Speaker 1: and that's kind of hard to like really base the
• 28:28
  Speaker 1: claim on if you only see something once. And this
• 28:30
  Speaker 1: works with stars in other galaxies, like we can tell
• 28:33
  Speaker 1: this wiggling in the lensing for something that far away. Yeah,
• 28:37
  Speaker 1: at the end of the program, we'll talk about some examples,
• 28:39
  Speaker 1: but it really can work. And the really cool thing
• 28:42
  Speaker 1: about it is that it can detect stuff that's pretty
• 28:44
  Speaker 1: low mass because the gravitational lensing is very sensitive to
• 28:48
  Speaker 1: the mass of the planet, so you can even work
• 28:50
  Speaker 1: for like planets down to the size of Mars. Cool.
• 28:53
  Speaker 1: All right, Well that's one way. What's another way we
• 28:55
  Speaker 1: can look at planets and other galaxies? Another way it's
• 28:58
  Speaker 1: more similar to the t ends it method, and that
• 29:01
  Speaker 1: you're looking for an eclipse. Here, you have a star
• 29:04
  Speaker 1: you're looking for in the other galaxy, and you try
• 29:06
  Speaker 1: to find a star that's in a binary system with
• 29:09
  Speaker 1: something that's producing really bright X rays like a black
• 29:12
  Speaker 1: hole or a neutron star or something. Then the star
• 29:15
  Speaker 1: you're looking for sometimes will eclipse that X ray will
• 29:19
  Speaker 1: like block those X rays. And this is something we
• 29:22
  Speaker 1: can see in other galaxies because X rays are more
• 29:25
  Speaker 1: rare than other light and they're really intense, and so
• 29:28
  Speaker 1: it's possible to see these things in other galaxies. So
• 29:33
  Speaker 1: this lets us see planets around binaries, meaning like solar
• 29:36
  Speaker 1: systems with two stars in them. Yeah, exactly, if one
• 29:39
  Speaker 1: star that maybe has a planet around it, and the
• 29:41
  Speaker 1: other star is a really strong emitter of X rays
• 29:44
  Speaker 1: and maybe it's a black hole, maybe it's not a star,
• 29:46
  Speaker 1: but some really bright source of X rays, and if
• 29:48
  Speaker 1: those two things line up just right so that the
• 29:51
  Speaker 1: star you're interested in studying blocks the X rays from
• 29:54
  Speaker 1: the other one, then you can see that. You can
• 29:56
  Speaker 1: see this sort of like dip in the X ray pattern,
• 29:59
  Speaker 1: and we can tell all like you know, if we
• 30:00
  Speaker 1: if I look at a galaxy and and I send
• 30:02
  Speaker 1: some X rays, I can tell that it's coming from
• 30:04
  Speaker 1: a particular star, like we have that resolution. Yeah, because
• 30:08
  Speaker 1: X ray emitters are more rare. So there's a lot
• 30:10
  Speaker 1: of stars in the galaxy, butN not that many strong
• 30:13
  Speaker 1: X ray emitters, and so that makes it less likely
• 30:15
  Speaker 1: to happen, but it also makes it easier to separate them, right,
• 30:18
  Speaker 1: so there are fewer of these things. Also, X ray
• 30:21
  Speaker 1: emitters tend to be really really small. These they are
• 30:23
  Speaker 1: very compact objects on black hole or neutron star, and
• 30:27
  Speaker 1: so it's more precise. Right, you can like block the
• 30:30
  Speaker 1: entire X ray emitter with your star or with your planet. Cool.
• 30:35
  Speaker 1: All right, So there's one more way and in which
• 30:37
  Speaker 1: we could detect planets in other galaxies. And then let's
• 30:40
  Speaker 1: talk about what we've actually found. Have we found planets
• 30:43
  Speaker 1: in other galaxies? And what can we know about them?
• 30:46
  Speaker 1: But first let's take another quick break. All right, we're
• 31:01
  Speaker 1: talking about exo galactic exoplanets. Do I need to repeat
• 31:05
  Speaker 1: the exo or can I just say at once like
• 31:07
  Speaker 1: exo galactic planets. I think it's like sergeants at arm right,
• 31:11
  Speaker 1: it's exo galactic planets instead of planetary exo galactics or
• 31:15
  Speaker 1: something that planet planets and other galaxies that are not
• 31:20
  Speaker 1: the Milky Way where we're at. And we talked about
• 31:23
  Speaker 1: a couple of ways in which we can actually maybe
• 31:26
  Speaker 1: see these planets, and you're going to talk about the
• 31:29
  Speaker 1: last one. There's one that involves pulsars. Yeah, this is
• 31:32
  Speaker 1: my favorite one because it's super crazy in science fiction. Ee,
• 31:35
  Speaker 1: and this involves pulsars, right, And so pulsars are neutron
• 31:38
  Speaker 1: stars that give off a really really intense beam of light,
• 31:42
  Speaker 1: but they're also spinning, and if the beam is not
• 31:45
  Speaker 1: perfectly aligned with the spin, then it sort of sweeps
• 31:48
  Speaker 1: across the galaxy and gives us a pings. So every
• 31:51
  Speaker 1: time it passes across us, we see life from it,
• 31:54
  Speaker 1: and then it goes dark, and then it passes across
• 31:56
  Speaker 1: from us and it goes dark. These things are crazy
• 31:58
  Speaker 1: and amazing, but also because they're super duper precise, Like
• 32:02
  Speaker 1: they spin at a very precise speeds and they don't
• 32:05
  Speaker 1: seem to change, so we can see like a ping
• 32:07
  Speaker 1: from them and then a gap and a ping from them,
• 32:09
  Speaker 1: and the time between those pings is very very regular,
• 32:14
  Speaker 1: and so that makes them really awesome clocks. And it
• 32:16
  Speaker 1: means that we can do things like measure their speed
• 32:19
  Speaker 1: relative to the Earth, and in particular we can see
• 32:23
  Speaker 1: whether they're moving back and forth because that will change
• 32:26
  Speaker 1: how often we get the pin from them. Yeah, so
• 32:28
  Speaker 1: it's kind of like the Doppler effect, but instead of light,
• 32:31
  Speaker 1: you're looking at the frequency of the pulse are blinking, Yeah,
• 32:36
  Speaker 1: exactly when the pulsar is moving away from the Earth
• 32:39
  Speaker 1: because it's getting wobbled by a planet that's around the
• 32:41
  Speaker 1: pulse are, then the time between the pulse becomes a
• 32:44
  Speaker 1: little bit longer. And then when the pulsar swoops around
• 32:47
  Speaker 1: it's coming towards the Earth, the time between those pulses
• 32:50
  Speaker 1: gets a little bit shorter because it's sort of closer
• 32:53
  Speaker 1: to us when it emits the next pulse. So if
• 32:56
  Speaker 1: you watch the pulsars timing and you see this wiggle
• 32:58
  Speaker 1: where it's like the pulse as they're getting longer and
• 33:00
  Speaker 1: shorter and longer and shorter, that tells you that the
• 33:04
  Speaker 1: pulsar is wobbling. And because pulsars are so precise, you
• 33:09
  Speaker 1: can measure these from pulsars in other galaxies, right, And
• 33:13
  Speaker 1: pulsars are very kind of noticeable, right even within the
• 33:16
  Speaker 1: Big Gus they are. Yeah, they're very noticeable, and they're
• 33:19
  Speaker 1: sort of rare. And that's the disadvantage of this method
• 33:21
  Speaker 1: is that, like there aren't that many pulsars and so
• 33:25
  Speaker 1: you can't really like find all the planets this way.
• 33:27
  Speaker 1: But you know, if you're just looking to find a planet.
• 33:30
  Speaker 1: This is one technique. Another disadvantages that pulsars. You know,
• 33:34
  Speaker 1: they're the remnant of the death of a star. You
• 33:36
  Speaker 1: had a big star which then collapsed and made a
• 33:39
  Speaker 1: neutron star. And so it's not always likely that planets
• 33:42
  Speaker 1: will like survive this process, that they won't just get
• 33:45
  Speaker 1: like blown up when the star goes red super giant.
• 33:48
  Speaker 1: And so it's not that common to have pulsars with
• 33:51
  Speaker 1: planets around them, but it's possible. So it's a dead
• 33:54
  Speaker 1: star spinning really fast and hopefully it still has a
• 33:57
  Speaker 1: planet circling around it. That's power all enough to make
• 34:00
  Speaker 1: it wiggle, yeah, noticeably, And then then we could maybe
• 34:03
  Speaker 1: tell if there's a planet. But but again we couldn't
• 34:05
  Speaker 1: tell anything about the planet, could we. Well, we could
• 34:08
  Speaker 1: tell that if there's life on that planet, it mus
• 34:10
  Speaker 1: have had a really good sunscreen because it survived a
• 34:12
  Speaker 1: very traumatic event. Right, So it's not their on their
• 34:16
  Speaker 1: underground bunkers with their conditioning, yeah exactly, watching TV shows, yeah,
• 34:21
  Speaker 1: their Netflix and chilling on that planet. Yeah. Well these
• 34:24
  Speaker 1: are all cool ways. I guess the question now is
• 34:26
  Speaker 1: do they work? Have they worked? Have we actually found
• 34:29
  Speaker 1: planets with them? So what do we know, Daniel, have
• 34:32
  Speaker 1: we found planets in other galaxies? So we actually have
• 34:35
  Speaker 1: seen planets in other galaxies, which is so much fun
• 34:38
  Speaker 1: to say, and to know that we've achieved this huge
• 34:41
  Speaker 1: breakthrough in terms of our like actually factual knowledge about
• 34:45
  Speaker 1: stuff going on super duper far away. Right, and by way,
• 34:48
  Speaker 1: you mean like the Royal weed. I mean we've been
• 34:52
  Speaker 1: me sitting on my couch reading news articles about astronomers
• 34:55
  Speaker 1: doing the actual work. You're like, I did that, We
• 34:58
  Speaker 1: did that, we could It's like quantum mechanics, right, what's
• 35:02
  Speaker 1: the point of doing science if nobody's reading your papers?
• 35:04
  Speaker 1: And so I'm participating just by reading their papers. Does
• 35:08
  Speaker 1: the paper exist if nobody ever reads it? Exactly exactly,
• 35:12
  Speaker 1: I'm collapsing the wave function of these papers. All right,
• 35:15
  Speaker 1: So we found planets and other galaxy. Yeah, so we
• 35:17
  Speaker 1: have to that are sort of like preliminary haven't been
• 35:19
  Speaker 1: confirmed that come from gravitational lensing, and these are tough
• 35:23
  Speaker 1: because you can't repeat them, and so like it seems
• 35:25
  Speaker 1: like a planet, but who can really tell and you
• 35:27
  Speaker 1: can't really do any follow up studies. And one that
• 35:30
  Speaker 1: seems really pretty solid using the X ray eclipse method. Alright,
• 35:34
  Speaker 1: so step us through. What's the first one we found.
• 35:36
  Speaker 1: So the first one we found is from this crazy
• 35:39
  Speaker 1: system called the twin Quaysar. So remember, gravitational micro lensing
• 35:44
  Speaker 1: requires you to have something in the background. Right, you're
• 35:47
  Speaker 1: studying a star. You want to know if there's a
• 35:49
  Speaker 1: planet around it, but first you have to have something
• 35:51
  Speaker 1: behind it that's going to get gravitationally lensed by your star.
• 35:55
  Speaker 1: So it turns out that there's a quasar super duper
• 35:58
  Speaker 1: far away. Remember, a quays are is basically just a
• 36:01
  Speaker 1: huge source of light. It's very bright. It's probably the
• 36:04
  Speaker 1: accretion disk of a black hole, and all that gas
• 36:07
  Speaker 1: is really hot and giving off a lot of light,
• 36:09
  Speaker 1: so they're some of the really brightest sources in the galaxy.
• 36:12
  Speaker 1: And right between us and this quasar is another galaxy.
• 36:16
  Speaker 1: So if the quays are really far away, and between
• 36:19
  Speaker 1: us and the quasar is a galaxy that's right between it,
• 36:22
  Speaker 1: and it's gravitationally lends that quasar into two pieces, so
• 36:26
  Speaker 1: we see basically two copies of this quasar split. So
• 36:30
  Speaker 1: it's called the twin quasar because it's already sort of
• 36:33
  Speaker 1: constantly being gravitationally lens in two bits, Right, and we're
• 36:37
  Speaker 1: pretty sure it's not two quasars. We're pretty sure that
• 36:40
  Speaker 1: it's the same, but it's just a lens distortion that
• 36:43
  Speaker 1: makes it look like they're twins. Yeah, because they're basically identical,
• 36:47
  Speaker 1: and you can see correlated fluctuations in the two. So
• 36:50
  Speaker 1: sometimes you'll see something happen in the A part of
• 36:53
  Speaker 1: it and it will also happen in the B part
• 36:55
  Speaker 1: at the same time. So you're pretty confident we're seeing
• 36:58
  Speaker 1: like two images of the same ways are but we
• 37:01
  Speaker 1: can't see the actual galaxy in between, or can we Well,
• 37:04
  Speaker 1: what we can do is we can see the effects
• 37:06
  Speaker 1: of that galaxy, and so this is exactly what happened,
• 37:09
  Speaker 1: is that we saw a fluctuation in one half of
• 37:12
  Speaker 1: the twins and not in the other, and we think
• 37:15
  Speaker 1: that's an effect of the galaxy that's doing the lensing,
• 37:18
  Speaker 1: because it only appeared in one of them, and what
• 37:20
  Speaker 1: we saw was like a little dip in the light.
• 37:23
  Speaker 1: And this is consistent with some big planet in this
• 37:27
  Speaker 1: foreground galaxy, sort of like changing the lensing of the
• 37:31
  Speaker 1: quasar behind it. What that seems implausible to me. So
• 37:38
  Speaker 1: so we have a point source of light that God
• 37:42
  Speaker 1: destroyed it into two by a whole galaxy, and you're
• 37:45
  Speaker 1: saying that a tiny little planet in that galaxy can
• 37:48
  Speaker 1: affect that lensing. Hmm, that's exactly what they're claiming, And
• 37:51
  Speaker 1: again it's hard to confirm, like what they're seeing is
• 37:55
  Speaker 1: consistent with that hypothesis, but like it could also be
• 37:58
  Speaker 1: other things, right, it could be just like you're changing
• 38:01
  Speaker 1: the arrangement of the stars in that galaxy and that
• 38:04
  Speaker 1: changes the gravitational lensing, and so it's consistent, you know,
• 38:08
  Speaker 1: with the planet, but it's not a confirmed observation, right,
• 38:11
  Speaker 1: because you're saying that the whole galaxy is wiggling because
• 38:14
  Speaker 1: of this one planet. Is that what you're saying the
• 38:17
  Speaker 1: whole galaxy is shaking because of this one planet going around.
• 38:20
  Speaker 1: We're saying that the light from the quaysar is going
• 38:22
  Speaker 1: through that galaxy in a way that's sensitive to how
• 38:25
  Speaker 1: that planet is moving. And this would be a big planet,
• 38:29
  Speaker 1: so it would have to be large to affect this.
• 38:31
  Speaker 1: But yeah, you know, the photons that we're seeing our
• 38:34
  Speaker 1: gravitational lens by that galaxy, and we're saying that it
• 38:37
  Speaker 1: would be changed by the motion of this planet. But
• 38:40
  Speaker 1: how do you know it is a planet? Couldn't it
• 38:41
  Speaker 1: be like a little black hole in that galaxy? Or
• 38:43
  Speaker 1: couldn't it be a star or something wiggling? It could
• 38:46
  Speaker 1: be yeah, and it could be a rogue planet. Right,
• 38:48
  Speaker 1: So we don't really know very much. We just know
• 38:51
  Speaker 1: like something happened in this planet between us and the
• 38:54
  Speaker 1: quays are so as I said, it's not really like
• 38:56
  Speaker 1: a very well confirmed detection of an exo elactic planet.
• 39:00
  Speaker 1: It's just like an early candidate, all right. So and
• 39:03
  Speaker 1: this was back in ninety six, but we have more
• 39:05
  Speaker 1: recent events. Yeah, So then people tried to do the
• 39:08
  Speaker 1: same thing for a closer galaxy. They said, well, let's
• 39:10
  Speaker 1: look at Andromeda and Drameda is only two million light
• 39:13
  Speaker 1: years away. And what they did is they said, what
• 39:16
  Speaker 1: would it look like if we had a gravitational micro
• 39:19
  Speaker 1: lensing event in Andromeda? Now, Andrameda is pretty close when
• 39:23
  Speaker 1: it comes to galaxies, and so you can't make out
• 39:25
  Speaker 1: individual stars very well, but you can like make out
• 39:28
  Speaker 1: clusters of stars, and you can say, if one of
• 39:31
  Speaker 1: the stars in that cluster was gravitationally micro lensed by
• 39:34
  Speaker 1: another star, what would it look like? You can sort
• 39:37
  Speaker 1: of like calculate what that would look like and say oh,
• 39:40
  Speaker 1: you would get a dip or a change in the
• 39:42
  Speaker 1: brightness of the star in a certain way. Then they
• 39:44
  Speaker 1: looked for that and they saw it in Andromeda. This
• 39:47
  Speaker 1: is in two thousand nine. They see this sort of
• 39:49
  Speaker 1: like the thing that looks like a micro lensing event
• 39:52
  Speaker 1: in Andromeda, and we think it is a planet, Like,
• 39:55
  Speaker 1: how big of a planet? If it's a planet, then
• 39:57
  Speaker 1: it would have to be like six or seven time
• 40:00
  Speaker 1: the size of Jupiter right in order to cause the
• 40:02
  Speaker 1: effect that they saw, So that would be a big
• 40:05
  Speaker 1: would be a big planet. Isn't that almost a star?
• 40:07
  Speaker 1: Like put in something that big collapse into a star. Yes,
• 40:10
  Speaker 1: something much bigger than that would turn into a brown dwarf,
• 40:13
  Speaker 1: like about ten times a jupiter with the right composition
• 40:16
  Speaker 1: would turn to a brown dwarf. About a hundred times
• 40:19
  Speaker 1: the massive jupiter would turn into a star would start
• 40:21
  Speaker 1: to fuse. So this could still be a planet, but
• 40:24
  Speaker 1: we don't really know, and you know, again it can't
• 40:26
  Speaker 1: be confirmed. It was a one time thing. We saw
• 40:29
  Speaker 1: this one wiggle. It's characteristic, oh, a planet, but that
• 40:32
  Speaker 1: doesn't necessarily mean that it definitely was a planet. So
• 40:35
  Speaker 1: again it's like it's a candidate it's exciting, but you know,
• 40:38
  Speaker 1: it's not the best evidence that we have, right, But
• 40:41
  Speaker 1: it turns out that more recently, last year we got
• 40:44
  Speaker 1: a pretty good candidate. Was a difficult year, but it
• 40:48
  Speaker 1: was a pretty good year for exo galactic planets. Yeah,
• 40:52
  Speaker 1: somebody made this X ray eclipse method work. They found
• 40:56
  Speaker 1: a pair of stars that are binary system. One of
• 40:59
  Speaker 1: them is giving off a bunch of X rays and
• 41:02
  Speaker 1: the other one sometimes blocks those X rays, and it
• 41:05
  Speaker 1: blocks it in this way that you can tell that
• 41:08
  Speaker 1: there's something else going on with this star. The star
• 41:11
  Speaker 1: is doing the blocking must have something around it that's
• 41:14
  Speaker 1: changing how it's doing that eclipse, and we can see that,
• 41:18
  Speaker 1: and we can see the effect on the eclipse, and
• 41:21
  Speaker 1: so we're pretty sure that there's a planet around that star.
• 41:24
  Speaker 1: And this is in the Whirlpool Galaxy, which is like
• 41:27
  Speaker 1: twenty three million light years away in the constellation URSA Major.
• 41:33
  Speaker 1: So something is emitting X rays and something is blocking
• 41:37
  Speaker 1: it regularly, and we can see the eclipse and then
• 41:41
  Speaker 1: we can see variations in that eclipse. Right, if it
• 41:43
  Speaker 1: was just an eclipse from another star, you would see
• 41:46
  Speaker 1: a regular pattern, but we see a pattern on top
• 41:48
  Speaker 1: of that which means there's something orbiting that star changing
• 41:52
  Speaker 1: how it's eclipsing it, and from that pattern we can
• 41:55
  Speaker 1: tell actually some really interesting information about the planet. We
• 41:59
  Speaker 1: think it's like just about the size of Saturn, maybe
• 42:01
  Speaker 1: a little bit smaller, and it orbits that other star
• 42:04
  Speaker 1: around ten times the orbital radius of the Earth around
• 42:08
  Speaker 1: the Sun, so ten au. Wow, that's crazy precise. It
• 42:12
  Speaker 1: seems like a lot of detailed information about something so
• 42:14
  Speaker 1: far away. Yeah. Well, because we can take repeated measurements, right,
• 42:18
  Speaker 1: so we can study these patterns, we can understand the
• 42:20
  Speaker 1: period of this thing. We can look at all the
• 42:22
  Speaker 1: dips and the flips and the wiggles, and so that's
• 42:25
  Speaker 1: what gives you a lot more confidence that this really
• 42:27
  Speaker 1: actually is a big object orbiting that star and to
• 42:30
  Speaker 1: make these kinds of measurements. So this technique is much
• 42:33
  Speaker 1: better than gravitational micro lensing because it allows for repeated observations.
• 42:38
  Speaker 1: But I guess these would be planets orbiting weird things
• 42:41
  Speaker 1: like maybe not a railar star, but like a black
• 42:43
  Speaker 1: hole or a neutron star. Right, Like the source has
• 42:46
  Speaker 1: to be something special, Well, it has to be a
• 42:48
  Speaker 1: little weird because it has to be in a binary system.
• 42:50
  Speaker 1: You can have a pretty normal star with a planet
• 42:52
  Speaker 1: around it, but then you have to be in a
• 42:54
  Speaker 1: binary system with something that's giving off X rays, so
• 42:57
  Speaker 1: you can then eclipse those X rays. So like our
• 43:00
  Speaker 1: star wouldn't be visible from the Whirlpool galaxy using this
• 43:03
  Speaker 1: technique because our star is not in a binary system
• 43:06
  Speaker 1: with a neutron star or with the black hole giving
• 43:09
  Speaker 1: off a bunch of X rays right right. So it
• 43:11
  Speaker 1: feels like a lot of these really distant methods for
• 43:15
  Speaker 1: other galaxies only seem to work in really strange situations. Yeah,
• 43:19
  Speaker 1: you know what I mean. Like, we can find planets
• 43:20
  Speaker 1: in our galaxy pretty much any star we can sort
• 43:23
  Speaker 1: of check to see if it has planets, But in
• 43:26
  Speaker 1: other galaxies we have to rely on these weird kind
• 43:29
  Speaker 1: of phenomenons or arrangements. It is so far we don't
• 43:32
  Speaker 1: have a way to just check all the stars in
• 43:34
  Speaker 1: the galaxy. No, we definitely, and even for the ones
• 43:36
  Speaker 1: in our galaxy, right, And it comes down to coming
• 43:39
  Speaker 1: up with clever ideas. But that's what I love about
• 43:41
  Speaker 1: astronomy is that they have to come up with these
• 43:44
  Speaker 1: clever ideas. They think, well, this seems impossible. What if
• 43:48
  Speaker 1: there was a really weird configuration and this happened to
• 43:50
  Speaker 1: be attached to that which would swing around this other thing. Oh,
• 43:53
  Speaker 1: then maybe we could figure it out, and then you know,
• 43:55
  Speaker 1: then we bootstrap our way up. We figured that out,
• 43:57
  Speaker 1: and then we come up with other ways. And so
• 43:59
  Speaker 1: it's just an opportunity for creativity. I mean, somebody needs
• 44:02
  Speaker 1: to figure out more ways to see these things, because
• 44:05
  Speaker 1: there are a lot more planets out there to look at. Yeah,
• 44:07
  Speaker 1: there's room for improvement or new technology, or room for
• 44:12
  Speaker 1: us actually going to these other galaxies and looking. Yeah,
• 44:16
  Speaker 1: of course the direct observation would be fascinating, but that
• 44:19
  Speaker 1: would take millions of years, we think, unless, of course,
• 44:21
  Speaker 1: you know, we could just build that worm whole highway
• 44:23
  Speaker 1: and then we can get to those other galaxies pretty quickly.
• 44:26
  Speaker 1: But yeah, there are opportunities out there. This is a
• 44:28
  Speaker 1: young field. We only recently saw the first observation of
• 44:32
  Speaker 1: a planet around any other star, and so studying planets
• 44:36
  Speaker 1: around stars and other galaxies is a whole open field
• 44:38
  Speaker 1: out there. So for you enthusiast thinking about school and
• 44:42
  Speaker 1: becoming a physicist, this could be your big discovery. There's
• 44:45
  Speaker 1: lots of exciting stuff left to do. This could be
• 44:47
  Speaker 1: your PhD. That might take millions of years, but you know,
• 44:51
  Speaker 1: get a hang in there. Yeah, Unfortunately you can't get
• 44:54
  Speaker 1: the posthumous Nobel Prize. So well, I'm gonna wait for
• 44:56
  Speaker 1: a new film starting called The Exo Universe Galactic Planets.
• 45:01
  Speaker 1: We need for us to be able to type things
• 45:03
  Speaker 1: in other universes, and then we'll zoom in on those
• 45:06
  Speaker 1: planets will see people snowboarding down weird slopes filled with
• 45:09
  Speaker 1: weird kinds of chemical snow. Yeah. All right, Well, I
• 45:12
  Speaker 1: guess it's kind of interesting to think about planets and
• 45:14
  Speaker 1: other galaxies because it doesn't seem likely that will ever
• 45:19
  Speaker 1: visit them, do you know what I mean? Like in
• 45:21
  Speaker 1: our galaxy when we see a planet now it's like,
• 45:23
  Speaker 1: you know, twenty thousand or twenty seven light years away,
• 45:27
  Speaker 1: that's sort of doable for a human colony. But you know,
• 45:30
  Speaker 1: other gasy that is really far away, like we may
• 45:33
  Speaker 1: never get to those other galgs. No, you're right, and
• 45:35
  Speaker 1: it's more about like asking these questions about whether our
• 45:37
  Speaker 1: galaxy is typical and whether it's usual. Like when we're
• 45:40
  Speaker 1: studying our galaxy, are we getting misled about how the
• 45:43
  Speaker 1: universe works? Or is our galaxy like a pretty good
• 45:46
  Speaker 1: test case for understanding the whole universe. So it's more
• 45:49
  Speaker 1: about like understanding the broader context than actually like finding
• 45:53
  Speaker 1: other homes for humanity. Yeah, I guess it would be
• 45:55
  Speaker 1: pretty cool to know what those plants are like and
• 45:59
  Speaker 1: how many they are are and if we can pretty
• 46:01
  Speaker 1: much expect all galaxies to have as many planets as
• 46:04
  Speaker 1: we have, because that would be pretty mind blowing. That's
• 46:07
  Speaker 1: a big number to hold in your head. But it
• 46:09
  Speaker 1: makes a lot more sense than thinking that there are
• 46:11
  Speaker 1: no planets in other galaxies or fewer planets in other galaxies.
• 46:15
  Speaker 1: Most likely the Milky Way is pretty typical. It's also
• 46:17
  Speaker 1: cool to think about maybe there are civilizations in those
• 46:20
  Speaker 1: other planets in other galaxies and they're trying to look
• 46:23
  Speaker 1: at us. Yeah, I hope. So. Unfortunately, there's nothing really
• 46:26
  Speaker 1: weird enough about our start to make it extra visible
• 46:29
  Speaker 1: from other galaxies. Right, We're not like eclipsing and X
• 46:33
  Speaker 1: ray source or whatever. But maybe physics students in those
• 46:36
  Speaker 1: other galaxies have come up with a crazy clever way
• 46:39
  Speaker 1: to discover planets in our galaxy. Yeah, stay tuned, let's
• 46:43
  Speaker 1: just listen to their podcasts. Yeah, wait, wait, a few
• 46:46
  Speaker 1: million years, or maybe it's arriving now like the Star
• 46:50
  Speaker 1: Wars movie. Al Right, well, hopefully that gives you something
• 46:54
  Speaker 1: to think about when you look at the night sky
• 46:56
  Speaker 1: and wonder how many planets there are. Now many people
• 47:00
  Speaker 1: are in the Thanks for joining us you hope you
• 47:02
  Speaker 1: enjoyed that, and stay safe on the slopes. See you
• 47:04
  Speaker 1: next time. Thanks for listening, and remember that Daniel and
• 47:15
  Speaker 1: Jorge Explain the Universe is a production of I Heart Radio.
• 47:18
  Speaker 1: Or more podcast from my Heart Radio visit the I
• 47:21
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• 47:25
  Speaker 1: your favorite shows.