there's a supermassive black hole at the center of almost every galaxy in the
universe how did they get there what's the relationship between these monster
black holes and the galaxies that surround them every time astronomers
look further out in the universe they discover new mysteries these mysteries
require all new tools and techniques to understand these mysteries lead to more
mysteries what I'm saying is that it's mystery Turtles all the way down and one
of the most fascinating is the discovery of quasars understanding what they are
and the unveiling of an even deeper mystery where do they come from now as
always I'm getting ahead of myself so let's go back and talk about the
discovery of quasars back in the 1950s astronomers scanned the skies using
radio telescopes and found a class of bizarre objects in the distant universe
they were very bright an incredibly far away hundreds of millions or even
billions of light-years away the first ones were discovered in the radio
spectrum but over time astronomers found even more blazing in the visible
spectrum the astronomer Hanyu Chu coined the term quasar which stood for quasi
stellar objects they were like stars shining from a single point source but
they clearly weren't stars blazing with more radiation than an entire galaxy
over the decades astronomers puzzled out the nature of quasars learning that they
were actually black holes actively feeding and blasting out radiation
visible billions of light years away but they weren't the stellar-mass black
holes which were known to be from the death of giant stars
these were supermassive black holes with millions or even billions of times the
mass of the Sun as far back in the 1970s astronomers considered the possibility
that there might be these supermassive black holes at the heart of many other
galaxies even the Milky Way and in 1974 astronomers discovered a radio source at
the center of the Milky Way emitting radiation and it was titled Sagittarius
a star with an asterisk that stands for exciting well in the excited atoms
perspective this would match the emissions of a supermassive black hole
that wasn't actively feeding on material our own galaxy could have been a quasar
in the past or in the future but right now the black hole was mostly silent
apart from this saddle radiation astronomers needed to be certain so they
performed a detailed survey of the very center of the Milky Way in the infrared
spectrum which allowed them to see through the gas and dust that obscures
the core invisible light and they discovered a group of stars orbiting
Sagittarius a star like comets orbiting the Sun only a black hole with millions
of times the mass of the Sun could provide the kind of gravitational anchor
to whip these stars around in such bizarre orbits further surveys found a
supermassive black hole at the heart of the Andromeda galaxy in fact it appears
these monsters are at the center of almost every galaxy in the universe but
where did they come from how did they form did the galaxies form first and
cause the black hole to form in the middle or did the black hole form and
build up the galaxies around them until recently this was actually still one of
the big unsolved mysteries in astronomy that said runners have done plenty of
research using more and more sensitive observatories worked out their theories
and now they're gathering evidence to help us get to the bottom of this
mystery astronomers have developed two models to how the large-scale structure
of the universe came together top-down and bottom-up in the top-down model an
entire galactic super cluster formed all at once out of a huge cloud of
primordial hydrogen left over from the Big Bang a super clusters worth of stars
as the cloud came together its spun up kicking out smaller spirals and dwarf
galaxies these could have combined later on to form the more complex structure we
see today the supermassive black holes would have formed as the dense cores of
these galaxies as they came together if one wrap your mind around
this think of the stellar nursery that formed our Sun and a bunch of the stars
imagine a single cloud of gas and dust forming multiple star systems within it
over time the Stars matured and drifted away from each other
that's top down one big event that leads to the structure we see today in the
bottom up model pockets of gas and dust collected together into larger and
larger masses eventually forming dwarf galaxies and even the clusters and
superclusters that we see today the supermassive black holes at the heart of
galaxies were grown from collisions and mergers between black holes over eons in
fact this is actually how astronomers think that the planets in the solar
system formed by pieces of dust attracting one another into larger and
larger grains until the planet sized objects formed over millions of years
bottom up small parts coming together so which is it astronomers think they know
the answer now and we'll get to it in a second but first I'd like to thank Pablo
patty Nathan Dana Baskin and the rest of our 773
patrons for the generous support if you love what we're doing and you want to
get it on the action head over to patreon.com/scishow stood a shortly
after the Big Bang the entire universe was incredibly dense but it wasn't the
same density everywhere tiny quantum fluctuations in the density at the
beginning evolved over billions of years of expansion into the Galactic super
clusters we see today now I want to stop and let this sink into your brain for a
second there were microscopic variations in density in the early universe and
these variations became the structures hundreds of millions of light-years
across that we see today imagine the two forces at play as the expansion of the
universe happened on the one hand you've got the mutual gravity of the particles
pulling one another together and then on the other hand you've got the expansion
of the universe separating the particles from
one another the size of the galaxies clusters and superclusters were decided
by the balance point of those opposing forces if small pieces came together
then you get that bottom-up formation if large pieces came together then you get
that top-down formation when astronomers look out into the universe at the
largest scales they observe clusters and superclusters as far as they can see
which supports the top-down model on the other hand observations show that the
first stars formed just a few hundred million years after the Big Bang which
supports bottom-up so the answer is both no the most modern observations give the
edge to the bottom-up process the key is that gravity moves at the speed of light
which means that the gravitational interactions between particles spreading
away from each other needed to catch up going the speed of light in other words
you wouldn't get a super clusters worth of material coming together only as
stars worth of material but those first stars were made of pure hydrogen helium
and could grow much more massive than the stars we have today they would live
fast and die in supernova explosions creating much more massive black holes
than we get today the first protocol exes came together collecting together
these first monster black holes and the massive stars surrounding them into
dwarf galaxies and then over millions and billions of years these black holes
merged again and again accumulating millions and even billions of times the
mass of the Sun and this is how we got the modern galaxies that we see today
there was a recent observation that supports this conclusion
earlier this year astronomers announced the discovery of supermassive black
holes at the center of relatively tiny galaxies in our own Milky Way the
supermassive black hole is 4.1 million times the mass of the Sun but accounts
for only point zero one percent of the galaxy's total mass
but astronomers from the University of Utah found to ultra-compact galaxies
with black holes of 4.4 million and 5.8 million times the mass of the Sun
respectively and yet the black holes account for 13 and 18 percent of the
mass of their host galaxies and the thinking is that these galaxies were
once normal but collided with other galaxies early on in the history of the
universe were stripped of their stars and then they were spat out to roam the
cosmos they're the victims of those early merging events evidence of the
carnage that happened in the early universe when the mergers were happening
we always talked about the unsolved mysteries in the universe but this is
one that astronomers are starting to puzzle out it seems most likely that the
structure of the universe we see today formed bottom-up the first stars came
together into proto galaxies dying as supernovae to form the first black holes
the structure of the universe we see today is the end result of billions of
years of formation and destruction with the supermassive black holes coming
together over time once telescopes like James Webb get to work we should be able
to see these pieces coming together at the very edge of the observable universe
this was a fun episode and I know you're fascinated by black holes were there any
other topics that you'd like me to dig into lemonade your thoughts in the
comments in our next episode we look at the deep-space gateway NASA's plans to
put a Space Station out of the moon which will serve as a stepping stone to
the rest of the solar system it's time for a playlist all about supermassive
black holes first I'd like to direct you to an interview I did with dr. Andrea
guess who found the supermassive black hole at the heart of the Milky Way
followed by TED talk she gave a response from Michio Kaku about the puzzling
mystery scishow space video about the black holes
finally a public lecture about supermassive black holes and that starts
right now yeah you're like sweating profusely and
you're in the Sun oh really
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