Latest / Star Trails: From Backyard Astronomy to Cosmic Wonder / The Birth and Death of Galaxies

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The Birth and Death of Galaxies · Star Trails: From Backyard Astronomy to Cosmic Wonder

0:07
Howdy Star Gazers and welcome to this episode
0:10
of Star Trails. My name is Drew and I'll be your
0:13
guide to the night sky for the week of May the
0:16
24th to the 30th. This week we wrap up our month
0:20
-long exploration of galaxies by examining how
0:24
they form and how they ultimately die. Our journey
0:28
will take us from the hot, early beginnings of
0:30
the universe to the dark end times when even
0:34
black holes begin fading away. Later in the show,
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we'll explore this week's night sky and take
0:40
a trip through one of the iconic constellations
0:43
of summer. Whether you're tuning in from the
0:46
backyard or the balcony, I'm glad you're here.
0:48
So grab a comfortable spot under the night sky
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and let's get started. Just a quick note here
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at the top of the episode, we'll be taking a
0:58
break next week, and I'll likely publish episodes
1:01
every two weeks during the summer months. This
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time of year can be tough for astronomy as we
1:07
have longer days to contend with, and I know
1:10
many of you are spending more time with your
1:13
family or traveling. This shift in the schedule
1:16
will allow me to recharge a bit myself and develop
1:20
some new content for the show before resuming
1:22
our normal weekly schedule. As always, if you
1:26
have any questions or would like to suggest topics
1:29
for coverage, contact me over at our website,
1:32
StarTrails .Show. Over the past several weeks,
1:39
we've talked about galactic collisions, dark
1:42
matter, invisible structure, magnetic fields
1:45
stretching across intergalactic space, and the
1:49
strange realization that galaxies are not isolated
1:52
islands at all, but part of an enormous cosmic
1:56
web spanning the universe. But tonight, I want
1:59
to step back and ask a more fundamental question.
2:03
Where do galaxies actually come from? How does
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something as enormous as the Milky Way come into
2:10
existence in the first place? Why do so many
2:13
galaxies contain supermassive black holes at
2:16
their centers? Did galaxies create those black
2:20
holes or did black holes help create galaxies?
2:24
And why is the James Webb Space Telescope discovering
2:28
ancient galaxies that seem to have formed far
2:31
earlier than they theoretically should have?
2:34
And finally, Do galaxies die? Tonight, we're
2:39
talking about the birth, evolution, and eventual
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fading of galaxies themselves. If you could travel
2:46
back to the earliest moments of the universe,
2:49
you wouldn't see galaxies, stars, or planets.
2:53
The early universe was a hot, expanding sea of
2:56
particles. Mostly hydrogen and helium, forged
3:00
in the aftermath of the Big Bang, nearly 13 .8
3:04
billion years ago. For hundreds of thousands
3:08
of years the cosmos was so hot and dense that
3:11
light itself could barely travel freely. But
3:15
as the universe expanded and cooled, atoms began
3:18
to form. Eventually the first light escaped into
3:22
space. Today we still detect that ancient radiation
3:26
as the cosmic microwave background. the faint
3:30
afterglow of the Big Bang itself. But the universe
3:34
was still dark. No stars yet, no galaxies, just
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enormous clouds of gas spread across expanding
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space. And yet the seeds of galaxies already
3:47
existed. Tiny fluctuations in density, almost
3:52
unimaginably small variations in the distribution
3:55
of matter, were scattered throughout the early
3:58
universe. Some regions contained slightly more
4:01
matter than others. Gravity amplified those differences
4:05
over millions of years. And lurking invisibly
4:09
within all of this was something we still don't
4:12
fully understand. Dark matter. Which we talked
4:15
about extensively in last week's episode. Based
4:20
on everything astronomers can measure, galaxies
4:23
appear to form inside gigantic halos of invisible
4:27
matter. These halos acted like gravitational
4:31
scaffolding in the young universe, helping pull
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ordinary matter into dense regions where stars
4:37
and galaxies could begin to form. In other words,
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galaxies may have been built inside invisible
4:44
structures before the galaxies themselves even
4:47
existed. That idea almost sounds like science
4:51
fiction. Even now, nobody knows exactly what
4:55
dark matter is, but without it, galaxies may
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never have formed at all. Over time, enormous
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clouds of hydrogen collapsed under gravity. The
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first stars ignited. Small proto -galaxies merged
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together into larger galaxies. Gravity built
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structure slowly, patiently over billions of
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years. Galaxies were born not in an instant,
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but through accumulation, collision, and time.
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Some became spirals, like the Milky Way or the
5:27
Andromeda Galaxy, with elegant rotating arms
5:30
filled with gas, dust, and star formation. Others
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became giant elliptical galaxies, vast football
5:39
-shaped systems dominated by older stars. And
5:43
some remained chaotic, irregular galaxies. Warped
5:47
and distorted by gravitational encounters and
5:50
cosmic turbulence. The universe itself was also
5:54
very different back then. The young cosmos was
5:57
far more violent than the one we inhabit today.
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Galaxies collided more frequently. Quasars blazed
6:05
across intergalactic space. Star formation rates
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were dramatically higher. The universe was crowded,
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chaotic, and energetically alive. In many ways,
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the calmer modern universe we inhabit today is
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the aging aftermath of a much wilder cosmic youth.
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Some galaxies experienced enormous bursts of
6:29
star formation during these chaotic eras. Astronomers
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call these starburst galaxies. One spectacular
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example is the galaxy Messier 82. a galaxy undergoing
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furious star formation likely triggered by gravitational
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interactions with neighboring galaxies. It's
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creating stars at a rate many times faster than
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galaxies like our own. The process is so intense
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that gigantic winds of hot gas are blasting outward
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from the galaxy itself, meaning entire galaxies
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can briefly become cosmic furnaces. And all of
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this stellar activity transforms the galaxy chemically
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over time. Because galaxies aren't merely collections
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of stars, they're recycling systems. Stars forge
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heavier elements through nuclear fusion, oxygen,
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carbon, silicon, iron, and when those stars die,
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they return those materials back into the galaxy
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through stellar winds and supernova explosions.
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Without ancient generations of stars living and
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dying long before our Sun formed, rocky planets
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and life itself could not exist. In a very literal
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sense, galaxies manufacture the raw ingredients
7:51
that make us. And at the center of many galaxies
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lies something even stranger, a supermassive
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black hole. For a long time, astronomers thought
8:02
black holes might simply be exotic oddities,
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rare objects hidden in isolated corners of space.
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Now we know they appear to be almost everywhere.
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The Milky Way contains a supermassive black hole
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known as Sagittarius A -star. Although it contains
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roughly four million times the mass of our Sun,
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it occupies a region of space smaller than our
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solar system. The black hole at the center of
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Messier 87 is vastly larger, containing billions
8:35
of solar masses. In 2019, astronomers working
8:39
with the Event Horizon Telescope produced the
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first direct image of a black hole's shadow using
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observations of M87's central black hole. That
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now famous glowing orange ring became one of
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the defining scientific images of the modern
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era. But supermassive black holes pose one of
9:01
astronomy's greatest mysteries. Where did they
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come from? Astronomers have discovered quasars
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powered by enormous black holes existing less
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than a billion years after the Big Bang. Some
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already contained billions of solar masses astonishingly
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early in cosmic history, and that creates a major
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problem. Black holes grow by consuming matter.
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gas, dust, stars, and anything else unfortunate
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enough to drift too close. But growth takes time.
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In some cases, there simply may not have been
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enough time in the early universe for these black
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holes to become so enormous through ordinary
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feeding alone. So, astronomers have proposed
9:48
several ideas. One possibility is that the first
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generation of stars in the universe, so -called
9:54
population 3 stars, were gigantic compared to
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most modern stars. When those enormous stars
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died, they may have collapsed into relatively
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massive seed black holes that later grew into
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supermassive giants. Another idea is even stranger.
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Some researchers suspect enormous primordial
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gas clouds may have collapsed directly into black
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holes without forming stars first. These hypothetical
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direct collapse black holes may have started
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out already containing tens or thousands or even
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hundreds of thousands of solar masses. In other
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words, some black holes may have just been born
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huge. And then there's an even deeper mystery.
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Did galaxies create black holes, or did black
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holes help create galaxies? For decades, astronomers
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assumed black holes formed inside galaxies as
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kind of a by -product, but observations now suggest
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the relationship may be far more intertwined.
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The mass of a galaxy's central black hole often
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correlates closely with the size and structure
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of the galaxy surrounding it. Bigger galaxies
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tend to host bigger black holes. That correlation
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suggests galaxies and black holes somehow evolve
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together. Some astronomers now suspect supermassive
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black holes may have acted almost like gravitational
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anchors in the young universe, helping organize
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matter around them and influencing how galaxies
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assembled over cosmic time. The galaxy feeds
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the black hole. the black hole regulates the
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galaxy, and a kind of cosmic symbiosis develops.
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And sometimes when enormous amounts of matter
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fall toward these black holes, the result becomes
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one of the brightest phenomena in the universe,
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an active galactic nucleus. As matter spirals
12:00
inward, it forms a superheated accretion disk
12:03
glowing with extraordinary energy. Magnetic fields
12:07
twist and intensify. Jets of particles erupt
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outward at nearly the speed of light, blasting
12:14
radiation across intergalactic space. These active
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galaxies can become so luminous that they outshine
12:22
all the stars in the galaxy combined. Quasars,
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the brightest active galactic nuclei, are visible
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across billions of light years of space. which
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means some of the brightest objects in the universe
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are powered not by creation, but by matter falling
12:39
into darkness. These black holes may dramatically
12:43
influence the fate of the galaxies around them.
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As matter falls inward and energy blasts outward,
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gas inside the galaxy can become heated or blown
12:54
away entirely, and that suppresses future star
12:58
formation. And now we arrive at one of the biggest
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astronomical surprises of the modern era, the
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ancient galaxies discovered by the James Webb
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Space Telescope. Astronomy is really an act of
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looking backward in time. Light travels at a
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finite speed, so the farther away an object is,
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the older the light we receive from it becomes.
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The Andromeda galaxy appears to us as it existed
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more than two million years ago. more distant
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galaxies appear as they existed billions of years
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ago. As the universe expands, the light from
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extremely distant galaxies becomes stretched
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into longer wavelengths, a phenomenon known as
13:44
redshift. You can think of it almost like sound
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from a receding siren lowering in pitch as it
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moves away from you. except instead of sound
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waves stretching, it's light itself being stretched
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by the expansion of space. Visible light from
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some of the earliest galaxies becomes shifted
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so dramatically that by the time it reaches Earth,
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it arrives as infrared light. And that's one
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reason Webb is so powerful. It was specifically
14:13
designed to observe the ancient infrared glow
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of the early universe. And what Webb found surprised
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astronomers almost immediately. Researchers expected
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to find small primitive galaxies slowly assembling
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themselves shortly after the Big Bang. The early
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universe was supposed to contain messy galactic
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building blocks, not mature giant systems. Instead,
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Webb started finding galaxies that appeared far
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brighter, more massive, and more chemically evolved
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than expected. astonishingly early in cosmic
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history. One example is a galaxy known as Jade's
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GSZ140, observed at a time when the universe
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was less than 300 million years old, so extraordinarily
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early. And yet this galaxy already appeared luminous
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and developed. Some early Webb observations hinted
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at galaxies containing unexpectedly large numbers
15:15
of stars. only a few hundred million years after
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the Big Bang, as though galaxies had evolved
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too quickly. In some cases, Webb even detected
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evidence of heavier elements already existing
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inside these early galaxies. That matters because
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the Big Bang primarily produced hydrogen and
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helium. Heavier elements like oxygen, carbon,
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and iron must be forged inside stars and distributed
15:42
through supernova explosions. And that means
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some stars in these ancient galaxies may have
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already lived and died astonishingly quickly.
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Webb is clearly forcing astronomers to rethink
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parts of the timeline of galaxy formation. Maybe
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early star formation was dramatically more efficient
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than expected. Maybe dark matter structures formed
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faster. Maybe black holes played a role much
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earlier than anticipated. Or maybe the young
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universe was simply stranger than our models
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predicted. Galaxies are not permanent things.
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They evolve, collide, eat other galaxies, and
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eventually they die. The Milky Way itself may
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be on a collision course with the Andromeda Galaxy.
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In roughly four to five billion years, there's
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a chance the two galaxies will experience a long
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gravitational interaction that will eventually
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reshape both galaxies. Their spiral arms will
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distort and unravel. Vast streams of stars will
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arc through intergalactic space. Giant clouds
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of gas may collapse and trigger enormous waves
16:59
of star formation before settling into a giant
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elliptical galaxy. And after that, things begin
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to quiet down. Galaxies slowly consume the gas
17:10
needed to create new stars. The bright blue stars
17:14
die first, leaving older red stars behind. Star
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formation slows, spiral structure fades. Astronomers
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refer to old inactive galaxies as red and dead.
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These galaxies might be full of material, but
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their great era of creation has largely ended.
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Some galaxies die even more dramatically. Astronomers
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have discovered so -called jellyfish galaxies,
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systems moving through dense galaxy clusters
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so rapidly that enormous streams of gas are literally
17:49
stripped away behind them. leaving tendrils stretching
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across intergalactic space like cosmic jellyfish
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drifting through dark water. One famous example
18:00
is ESO 137001, discovered in 2005. As this galaxy
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plunges through the hot gas filling galaxy clusters,
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pressure strips away the raw material needed
18:13
for future star formation. In a sense, the galaxy
18:17
is being suffocated, leaving a 260 ,000 light
18:22
-year -long tail behind in the process. Astronomers
18:26
sometimes describe galaxies transitioning between
18:29
active blue star -forming systems and older red
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dormant systems as green valley galaxies, a kind
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of galactic middle -age where star formation
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begins fading away. Galaxies age. Trillions of
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years from now, galaxies may become darker and
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quieter still. White dwarves will cool. Neutron
18:53
stars will drift through darkness. Black holes
18:56
may become some of the final surviving structures
18:59
in the cosmos. Basically, a galaxy doesn't die
19:04
in fire. It dies in silence. Right now we live
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during one of the few eras in cosmic history
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when galaxies are still actively forming stars,
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colliding, evolving, and illuminating the darkness
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between them. We exist at a moment when the universe
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is still bright enough for us to witness it.
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And perhaps most remarkable of all, the universe
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became conscious enough to observe itself. Not
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bad for a species living on a small rocky planet.
19:36
inside one ordinary spiral galaxy. After a quick
20:00
break we'll be back with this week's night sky.
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Stay with us. Welcome back! We're heading toward
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the end of May now and the sky is beginning to
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shift from the familiar constellations of spring
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toward the richer star fields of summer. If you
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head outside after sunset this week, you'll notice
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the evenings growing warmer, the twilight lingering
20:35
a little longer, and the Milky Way beginning
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to rise higher in the overnight hours. And fortunately
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for backyard astronomers, the moon will cooperate
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fairly nicely for much of the week. The moon
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reached first quarter on May the 23rd, so early
20:51
in the week we'll be dealing with a waxing gibbous
20:53
moon hanging in the evening sky. That means the
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moon will grow brighter night after night as
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we approach the second full moon of May on the
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31st, a so -called blue moon. Despite the name,
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the moon will not actually appear blue. Traditionally,
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the phrase blue moon referred to the third full
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moon occurring within a season containing four
21:17
full moons instead of the usual three. But today,
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most people use the term to describe the second
21:23
full moon occurring within a single calendar
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month. That's where the expression once in a
21:29
blue moon comes from. It's something relatively
21:32
uncommon. Actual blue -colored moons can occur
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under very rare atmospheric conditions, usually
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after major volcanic eruptions or large wildfires
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when tiny particles in Earth's atmosphere scatter
21:48
red light and allow bluish wavelengths to dominate.
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But this month's blue moon is purely a matter
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of calendar timing, not color. Even though brighter
21:59
moonlight will gradually begin washing out faint
22:02
deep sky objects later in the week, the first
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half of the week still offers excellent opportunities
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for binocular observing and casual telescopic
22:11
viewing. First quarter and waxing gibbous phases
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are wonderful times to study the moon itself.
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Along the lunar terminator, the dividing line
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between lunar night and day, craters and mountain
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ranges cast long, dramatic shadows across the
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surface. Even a modest telescope can reveal astonishing
22:32
detail. Rugged crater walls, lava plains, overlapping
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impacts, and wrinkle ridges stretching across
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ancient basalt seas. As darkness falls this week,
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look toward the western sky after sunset and
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you'll find brilliant Venus shining brightly
22:50
in twilight. Nearby, you should also be able
22:54
to spot Jupiter glowing above the western horizon.
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The two planets have been putting on an excellent
23:00
evening show throughout May and continue drawing
23:03
closer together in the sunset sky. With a modest
23:06
scope, or even a pair of high -magnification
23:09
binoculars, you can catch a glimpse of Jupiter's
23:12
four large Galilean moons lined up beside the
23:15
planet like tiny stars. Meanwhile, early risers
23:20
can still find Saturn low in the eastern sky
23:23
before dawn, with reddish Mars nearby. The morning
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planets remain fairly low right now for northern
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hemisphere observers, but they hint at richer
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pre -dawn skies still to come as summer approaches.
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This week, let's spend some time with the constellation
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Leo, now drifting gradually toward the western
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sky during the evening hours. Leo is one of the
23:48
easiest constellations to recognize because it
23:50
actually resembles what it's supposed to be.
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The front half of the lion forms a backward question
23:56
mark shape known as the sickle, with the bright
23:59
star Regulus marking the lion's heart. Leo is
24:03
traditionally associated with the Nemean lion
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from Greek mythology, a nearly invulnerable beast
24:10
defeated by Hercules during the first of his
24:13
twelve labors. According to legend, the lion's
24:16
hide could not be pierced by ordinary weapons,
24:20
forcing Hercules to strangle it with his bare
24:22
hands. Afterward, the lion was supposedly placed
24:26
into the sky by the gods, becoming the constellation
24:29
we still recognize thousands of years later.
24:33
Leo is also one of the constellations of the
24:36
zodiac. Long before astrology became newspaper
24:39
entertainment, the zodiac simply referred to
24:42
the band of sky through which the sun, moon,
24:45
and planets appear to move over the course of
24:47
the year. Because the Earth orbits within a relatively
24:51
flat plane, the planets tend to trace similar
24:54
paths across the sky, drifting through the familiar
24:57
constellations including Leo, Virgo, Gemini,
25:01
and Scorpio. This week the waxing moon passes
25:05
near Regulus early in the observing period, making
25:08
it easier to locate the constellation if you're
25:11
still learning the spring sky. But Leo also serves
25:15
as a doorway into one of the richest galaxy regions
25:18
visible from Earth. Between Leo and Virgo lies
25:22
the famous Virgo Coma Galaxy region, a sprawling
25:26
collection of distant galaxies scattered across
25:29
tens of millions of light years of space. With
25:33
a moderate telescope under dark skies, observers
25:36
can begin hunting faint smudges of light that
25:39
are actually entire galaxies unto themselves.
25:42
And that feels particularly fitting after this
25:45
month's theme. You're literally looking out into
25:48
an ocean of galaxies. For a deep sky object this
25:53
week, I'd recommend trying from Messier 87 in
25:56
the constellation Virgo. At first glance, M87
26:00
may not look especially dramatic through a small
26:03
telescope. Unlike grand spiral galaxies, it appears
26:07
mostly as a soft oval glow suspended in darkness
26:11
roughly 53 million light years away. But what
26:15
you're actually looking at is extraordinary.
26:19
M87 is a gigantic elliptical galaxy containing
26:23
trillions of stars and dominating part of the
26:25
nearby Virgo cluster. And at its center lies
26:29
one of the most famous black holes in astronomy,
26:33
the supermassive black hole imaged by the Event
26:36
Horizon Telescope in 2019. That now iconic glowing
26:41
orange ring, the first direct image of a black
26:44
hole's shadow, came from this galaxy. And hidden
26:49
within that faint smudge of light is something
26:51
even more astonishing. M87's central black hole
26:56
is actively launching an enormous jet of particles
26:59
across space, extending thousands of light years
27:02
beyond the galaxy itself. In other words, when
27:05
you observe M87, you're looking at a galaxy whose
27:09
central black hole is literally reshaping its
27:12
cosmic environment. And, perhaps even more hauntingly,
27:16
galaxies like M87 may represent a part of the
27:20
future of the universe itself. Old, massive,
27:24
and quiet. The remnants of countless galactic
27:27
mergers stretched across cosmic time. And finally,
27:32
if you can stay up late or head out before dawn,
27:34
there's another region hiding a black hole. The
27:37
core of our Milky Way is beginning to return
27:40
to the sky. From dark locations away from city
27:44
lights, you may notice a faint, cloudy river
27:47
of light stretching upward from the southeastern
27:49
horizon. That glow is the combined light of countless
27:54
unresolved stars concentrated toward the center
27:57
of our galaxy. It's an amazing view made even
28:01
more amazing when you remember we're seeing the
28:03
internal structure of the galaxy that we call
28:06
home. That's going to do it for this week. If
28:13
tonight's episode sparked your curiosity or maybe
28:17
gave you something new to think about the next
28:19
time you look up, I'd be honored if you shared
28:22
Star Trails with someone who might also enjoy
28:25
the journey. You can always find the latest episodes,
28:29
show notes, and extras at startrails .show. And
28:34
if you'd like to help support the show, there's
28:36
also a little buy me a coffee link on the site.
28:39
It genuinely helps keep these stories coming.
28:43
Be sure to follow Star Trails on Blue Sky and
28:46
YouTube. Links are in the show notes. Until we
28:49
meet again beneath the stars. Clear skies everyone.