This video is sponsored by Stellarium Mobile Plus. Made by the original creator of the
award-winning Stellarium desktop planetarium, Stellarium mobile puts 1.6 billion stars,
and 2 million nebulae and galaxies at your fingertips. Planets are rendered in high-resolution
textures and the night sky can be viewed in beautiful 3D in real-time from any location
on Earth. I’ll tell you a little more about it at the end of this video.
The black holes we’ve detected so far fall into two categories. Stellar-mass black holes
are often found in binary systems with masses equivalent to 10 Suns. Then there are the
supermassive black holes, which dominate the centers of galaxies and weigh millions to
billions of solar masses.
Somewhere between these extremes must be intermediate-mass black holes with masses ranging from hundreds
to hundreds of thousands of Suns. Models predict they should reside in the centers of dwarf
galaxies and possibly globular clusters, but so far, they’ve avoided detection.
But now after years of investigation, a team of astronomers using the Chandra X-ray, XMM
Newton, and Hubble Space Telescopes made the most convincing detection yet of the missing
link of black hole evolution. A 50,000 solar mass black hole, devouring a star a long time
ago in a galaxy far, far away…
Welcome back to Launch Pad, I’m Christian Ready, your friendly neighborhood astronomer.
Finding black holes is kind of hard to do because they’re…black. Not dark, black.
They greedily consume light, but never radiate so much as a single photon back into space.
The only way we can detect black holes is by detecting the radiation coming from just
outside their event horizons.
For example, we’ve detected stellar mass black holes in binary star systems. If the
two objects are close enough, matter can flow from the companion star into an accretion
disk around the black hole. The disk feeds the black hole but as it does so, it heats
up to millions of degrees, producing X-rays.
Cygnus X-1 was the first black hole discovered. It’s caused by a blue supergiant star losing
mass to a 15 solar mass black hole. We’ve detected several stellar mass black holes
this way, both here in our Galaxy as well as in nearby galaxies.
Then there are the supermassive black holes that live in the centers of galaxies, including
our own. Sagittarius A* holds court in the center of our Milky Way Galaxy. At 4 million
solar masses, it occasionally feeds on clouds of gas, generating X-ray and radio emission
that penetrates the spiral arms that would otherwise block its view.
The black hole at the heart of M87 was initially revealed by a 5000 light-year long jet of
plasma hurtling toward us at nearly the speed of light. Then it was imaged directly by the
Event Horizon Telescope. This black hole is 6.5 billion times the Sun’s mass!
Despite their extreme differences in mass, all black holes follow a simple rule; the
greater their mass, the larger their event horizons. For example, to make a 50 solar
mass black hole, you’d need to squeeze 50 Suns into a ball less than 300 kilometers
across (200 mi). M87’s black hole is the equivalent of 6.5 billion Suns squeezed into
a ball about the size of our solar system.
But if the Universe can have supermassive black holes, then surely there must be intermediate
mass black holes out there, right? Not necessarily. Nature is under no obligation to make sense
to us.
However, it seems that intermediate black holes are needed to solve a problem with supermassive
black holes at the centers of the earliest galaxies.
These black holes consume enormous quantities of gas and their accretion disks shine with
the light of up to a trillion Suns. They’re so bright we can see them from across the
Universe as “quasars”. Because of light’s finite speed, we see quasars when the Universe
was less than a billion years old.
The most distant quasar known is ULAS J1342+0928. The quasar emitted its light when the Universe
was less than 690 million years old, yet its supermassive black hole is estimated to be
800 million solar masses.
So did a nearly billion solar-mass black hole form just a few hundred million years after
the Big Bang?
At first it might seem that it started out as a stellar mass black hole that simply grew
as it fed on the surrounding matter.
But there’s a problem with this hypothesis. Remember that accretion disk we talked about?
It puts out a lot of radiation. So much that it exerts a strong pressure on the surrounding
disk, pushing it outward. Some of it still manages to find its way into the black hole,
but at more of a trickle than a deluge.
Therefore, it might take a stellar mass black hole up to 30 million years to double its
mass through normal accretion. Even 700 million years isn't enough time for a supermassive
black hole to grow from such a small seed.
In order to create supermassive black holes while the Universe was still young, they would
have had to grow from much larger seeds. Black holes in the hundred to hundred-thousand solar
mass range.
Fortunately, the conditions in the very early Universe allowed such black holes to form
pretty quickly.
A couple of hundred million years after the Big Bang, the Universe was a dark cloud of
pure hydrogen and helium gas. With no heavier elements present to arrest its flow, hydrogen
was free to rapidly collapse into ultra-massive stars that weighed as much as a thousand Suns.
These stars would explode as hyper novae after just a couple of million years, producing
violent gamma ray bursts as their cores collapsed into 100 solar mass black holes.
Some of those first stars got so massive, they skipped going supernova altogether and
their entire mass imploded into a several hundred solar mass black hole!
In fact, some of those hydrogen gas clouds may have collapsed so quickly, they may have
collapsed directly into thousand solar mass black holes without ever forming a star!
Such black holes would have been born into a buffet of hydrogen, helium, and nearby stars.
Soon they’d occupy the centers of the first protogalaxies which would quickly merge with
others. Their central black holes would soon find each other and merge into the supermassive
black holes we see today, while entire galaxies grew around them.
But not all of these intermediate black holes would merge. Countless protogalaxies exist
today as dwarf galaxies, presumably with intermediate black holes hiding in their centers.
However, most dwarf galaxies are devoid of gas, so their black holes are less likely
to continuously feed and emit radiation.
But if we’re lucky, we can catch a black hole shredding a passing star.
If a star comes too close to a black hole, tidal forces increase until the star can no
longer hold itself together. The star shreds and encircles the star, heating up to hundreds
of millions of degrees and unleashing a torrent of X-ray radiation.
This is a Tidal Disruption Event or TDE. TDE’s have been detected in our own Galaxy, allowing
astronomers to discover new black holes.
These events are rare, occurring only once every 10,000-100,000 years in our Galaxy.
But they create Hyper-Luminous X-ray events that can emit up to a billion times more X-ray
energy than the Sun. That’s bright enough to be detected in distant galaxies. If we
can catch one of those events, we may be able to determine if a black hole was involved,
and weigh it.
TDEs have a characteristic light curve of an almost immediate outburst that holds steady
for a couple of years, followed by a long, gradual decline in X-rays over time.
Several intermediate black hole candidates have been detected in dwarf galaxies and even
in some globular clusters from X-ray events that were thought to be due to TDEs. But as
we’ll see, the X-ray light curve produced by a TDE can also be produced by a cooling
neutron star.
In 2006, an HLX event called 3XMM J215022.4−055108 was detected by the XMM-Newton x-ray observatory.
The name’s a mouthful so I’m gonna call it “J2150”. Anyway, it seemed to originate
in the vicinity of a galaxy approximately 800 million light-years distant. A team of
astronomers led by Dacheng Lin at the University of New Hampshire discovered the event in archival
data from the XMM-Newton and Chandra X-Ray observatories.
Now, a previous image of the galaxy made by the Hubble Space Telescope in 2003 revealed
an optical counterpart to the source, which appeared to be just slightly off-center from
the X-ray source.
Lin’s team made follow-up observations with Swift in 2014 and Chandra in 2016. These observations
showed the X-ray flux had decreased at a rate that was consistent with a tidal disruption
event involving a black hole weighing 50,000 to a hundred-thousand solar masses.
That’s an encouraging result, but the same X-ray cooling curve could also be mimicked
by a neutron star in a low-mass binary system. If its crust were heated in a large accretion
outburst, it would create an X-ray flare similar to the J2150 event and cool off in the same
manner.
Still, Lin and his team had good reason to believe this wasn’t due to a nearby neutron
star flare-up. For one thing, the apparent source seemed to be right next to a large,
lenticular galaxy, dubbed "Gal 1". Several smaller galaxies appear to surround it, including
a slightly larger dwarf dubbed “Gal 2”. The two galaxies appear to be connected by
a stream of gas and stars that were stripped from Gal 2 as it was tidally disrupted by
Gal 1.
But proximity in the sky to a galaxy isn’t proof it can’t be a nearby neutron star.
Images of galaxies are photobombed by nearby stars in our galaxy all the time.
If the source of the J2150 event were a star, it would appear as a point source. But a small
galaxy or cluster would appear as an extended object. Unfortunately, the 2003 Hubble observation
was designed to resolve the Gal 1 galaxy, not the J2150 source. So there wasn’t any
way to determine if the source was a dwarf galaxy, a globular cluster, or just a fuzzy
image of a foreground star.
To settle the question, the Hubble Space Telescope observed the galaxy once again in 2018. The
difference from 2003 and 2018 may not seem like much at first, but it was it was a huge
improvement, allowing the team to resolve the source as a compact, but extended object.
J2150 was extragalactic in origin!
Accounting for its apparent brightness and distance, Lin’s team determined the source
object is roughly 176 light-years in diameter with a mass of about 10 million suns. It’s
likely the remnant nucleus of a tidally stripped dwarf galaxy rather than a massive globular
cluster.
The new Hubble observations allowed the team to refine their measurements of the X-ray
spectrum of the flare. They found it was caused by a 50,000 solar-mass black hole shredding
a passing star.
This makes J2150 the strongest Intermediate Black Hole candidate to date. We may have
finally have found the missing link the evolution of supermassive black holes.
That in turn will help us to answer questions like ‘what came first, the galaxy or the
black hole’? Did the black hole build the galaxy? Did the galaxy build the black hole?
Or did they build each other?
Our best chance of answering these questions will come when the James Webb Space Telescope
launches sometime in…well who knows now. But even though some science has been delayed,
it hasn’t stopped. And neither should you. The night sky still calls to us, which is
why I invite you to step out every now and then and see what the Universe is doing.
In fact, it's super easy to navigate the sky with Stellarium Mobile Plus. I’ve been using
Stellarium desktop to depict the night sky here on Launch Pad Astronomy and in my classroom
for a number of years, so I was very happy to learn that I can now take it with me when
I’m gazing at the night sky.
To that end, you can switch to a night-vision mode, zoom in on planets, moons, galaxies,
and nebulae, track the planets and even satellites as they pass overhead, all while experiencing
the most realistic depiction of the night sky.
And if you have a motorized telescope, you can control it with Stellarium’s built-in
Telescope Server Protocol. You don’t even have to have an internet connection.
Stellarium Mobile Plus puts Stellarium’s elegant combination of power and simplicity
into the palm of your hand. It’s available now on Apple's App Store and on Google Play,
and I invite you to download it today. I’ll have a link in the description below.
My thanks to my Patreon supporters for keeping this channel going and I’d like to welcome
my newest patrons:
* Lucas B * Tom Carlson
* Douglas D. Farren * Simon Hallman
* And RJ Johnson
And I’d like to thank my Cosmological supporters Michael Dowling and Steven J. Morgan.
If you’d like to help out for the price of a cup of coffee every month, head on over
to my Patreon page.
And if you’d like to join me on this journey through this incredible universe of ours,
well please be sure to subscribe and ring that notification bell so that you don't miss
out on any new videos. Until next time, stay home, stay healthy, and stay curious, my friends.