When two astrophysical objects
go up against each other, one usually comes out on top. Red giant stars incinerate
planetary systems, but neutron stars cannibalize
their red giant neighbors. And stellar mass black holes
rip neutron stars to shreds. But supermassive black holes
eat all of the above breakfast. So what happens when two
gigantic black holes tango? We may be about to find out,
because astronomers report spotting a pair of them in a
close binary orbit for the very first time. [THEME MUSIC] Today on Space
Time Journal Club, we're going to dig
into a paper that reports the detection of a pair
of supermassive black holes orbiting only one light-year
apart from each other. We've never seen
such a binary system this close together before. This is extremely cool,
because we knew for a long time that such tight
binaries must exist. But it's taken until
now to spot one. Studying the dance
of these giants should tell us a ton about
how black holes grow. Now, this paper was just
published in "Nature Astronomy" by Preeti Kharb
and Dharam Vir Lal from India's National Center
for Radio Astrophysics, and David Merritt
from the Rochester Institute of Technology. Before we get to
this new result, let's talk about
supermassive black holes-- SMBHs. These things live in the
dead centers of pretty much every decent-size galaxy. Now, we've he talked about
the black hole that form in the deaths of massive stars. They start with masses
of up to 10 or so Suns. The ones in the
course of galaxies contain the mass of a
million two billion Suns. The largest have event
horizons that would envelop most of our solar system. We're still figuring out
how supermassive black holes got so big. Did they get most of their
mass from eating gas and stars from their surrounding galaxy? Or do they mostly grow when
smaller SMBHs find each other and merge during
galaxy collisions? We know a lot more
about the first process because we've been watching
SMBHs munching on their host galaxies for half a century now. This is what causes
the quasar phenomenon. On the other hand, we know very
little about emerging SMBHs. In fact, this new
observation may turn out to be a pair of supermassive
black holes as close to merger as we've ever witnessed. If so, it's incredibly
important for understanding that whole aspect of
black hole growth. Actually, let me say a
bit more about quasars. We talk about them in more
detail here, but the TLDR. When gas from the
surrounding galaxy falls into and feeds the
central supermassive black hole, you get an active
galactic nucleus-- AGN. Quasar is the term for
the most powerful AGNs, and they contain SMBHs with up
to billions of Suns in mass. But lower down the
power scale, we have Seyfert galaxies,
which typically contain a single SMBH weighing
in at millions of solar masses. Now, the purported binary
black holes in this new study were found in a
known Seyfert galaxy. That means they're feeding
on their surrounding galaxy, and they're approaching merger. So we get to see everything
happening at once. Let's talk a bit about how these
binary black holes were found, because it wasn't easy. The Seyfert galaxy
in question is Markarian 533, which is around
400 million light-years away. The black holes are around
one light-year apart in the center of the galaxy. In order to measure
such a small separation at such a large distance,
we need resolution around 100 times better than
the Hubble Space Telescope. Kharb and collaborators
achieve this using a technique called
very-long-baseline interferometry. In, short the target is
observed with radio telescopes on opposite sides of the
planet, and phase differences in the incoming
radio waves are used to find the origin of each
wave with incredible accuracy. In fact, the spatial
resolution is equivalent to what you would get
with a telescope equal in size to the separation of
the radio antenna. Now, in this case, the
very-long-baseline array, VLBA, was used, and its antenna span
Hawaii to the US Virgin Islands and through the
continental United States to give an effective antenna
size of over 8,000 kilometers. Here's the radio map at
15 gigahertz frequency. Those two hot spots
are the locations of the possible black holes. Now, black holes
themselves are invisible. So what we're
actually seeing here is radio emission from jets. Let's talk about AGN
jets for a minute. When a black hole feeds, the
vortex of infalling plasma-- the accretion disk-- can produce
a powerful magnetic field. That field can
accelerate narrow streams of high-energy particles
away from the black hole. Those jets can blast through the
surrounding galaxy and beyond, carrying their magnetic
fields with them. The radio light seen
here is from electrons spiraling in those magnetic
fields, so-called synchrotron radiation. Now, this map alone
doesn't tell us that there are two black holes. We frequently see separate
knots of radio light in AGN jets, which can splatter
as their fuel supply changes or as the jets smash into denser
regions of the surrounding galaxy. In fact, we see such hot
spots in Markarian 533 when we look at a
much larger map. Here, we can see two bright
spots far from the black holes, presumably from a burst of
jet activity some time ago. So how do we know that
the hot spots in the core are from two unique black holes
instead of a lumpy jet from one black hole? Well, the researchers
tested this by looking at
multiple frequencies to get a crude radio spectrum. Typically, knots
and lumps in a jet have a pretty even
energy distribution. Spiraling electrons
produce radio waves a lots of frequencies all the
way down to very low energies. But right down near the black
hole where the jet begins, we think the matter
should be so dense that the lowest
energy radio waves have trouble escaping the jet. Now, this is a process called
synchrotron self-absorbtion, and it causes the
base of AGN jets to be much fainter
at long wavelengths. That is exactly
what's seen here. Both knots have the
classic energy distribution of a completely independent
jet launching point. The extreme energy
densities observed are also what you'd expect from
the bases of two distinct jets. The only way this is possible is
with two separate black holes, each one powering
its own mini quasar. OK, let's assume the
researchers are right, and we've spotted supermassive
black holes in a tight binary dance. How did this happen, and
when will they merge? Like I said earlier, we
already knew this sort of thing must happen when galaxies grow
by merging with each other. And the SMBHs of these
galaxies must eventually fall towards the new
merged galactic core. This happens through a process
called dynamical friction. Basically, the black
holes slingshot stars outwards through
gravitational interactions. Each time they do that they
lose a bit of orbital energy or angular momentum,
causing them to fall deeper into the gravitational well. You can think of it as a sort
of gravitational friction dragging the black
holes downwards and towards each other. However, by the
time the black holes are only a few
light-years apart, there shouldn't be any
stars left in between them. That means they stall and fall
into a stable binary orbits around each other. In fact, we still don't know how
supermassive black holes merge once they're within one
parsec, or a few light-years, of each other. And this is called the
central parsec problem. We know they must merge,
we just don't know how. One possibility is that gas
can provide the needed friction beyond that point. The newly discovered
binary definitely has a reservoir of gas. After all, that's
how it passes jets. So perhaps it'll
give us the answer. A lot of you are
probably thinking, what about gravitational waves? Can't gravitational radiation
cause supermassive black holes to merge, just like it does
with regular stellar mass black holes? And can LIGO see those waves? The answer is no. And no. Oh, this system is definitely
producing gravitational waves, but it's going to take
many billions of years to lose enough angular
momentum to merge that wave. And while those waves
may be powerful, they have an incredibly
low frequency-- something like 1 ten
trillionth of a hertz. LIGO is sensitive to
gravitational waves from 10 to 10,000 hertz. This binary is just too huge
and slow to register with LIGO. There may be ways to
detect the actual merger of a supermassive
black hole binary with a galaxy-sized
gravitational wave observatory called a pulsar timing array. But more on that another time. For Markarian 533,
we're going to have to stick to traditional
observing methods. Longer exposure
radio observations will pin down the
energy distribution to confirm whether
these really are jets produced by two black holes. And this galaxy is
so dusty that it's hard to peer into the core at
other wavelengths of light. However, careful observations
of the stars in the galaxy can help us figure out the
masses of the black holes and look for signs
of galaxy mergers. And if this binary
SMBH is the real thing, then it's certainly
not the only one. This finding will
inspire astronomers to search for more of
these dazzling giants, leading us closer
to understanding the incredible growth of the
largest black holes in all of spacetime. As always, a huge
thanks to everyone supporting us on Patreon. Every little bit really helps. And today, an extra
shout-out to Justin Lloyd. Justin, your contributions
at the quasar level have been an amazing help. As such, we're renaming your
personal Patreon contribution the Markarian 533 Binary
Active Galactic Nucleus Fund. We will spend it exclusively
on animating black holes and quasars, and also pizza. Thanks, Justin. Last week, we talked about
the intriguing possibility that the fundamental constants
of nature are changing. You guys had a lot to say. Nevermind asks whether
the fundamental constants are connected to each other. Well, the answer is
we just don't know. The standard model
of particle physics contains 26
independent parameters, things like the
coupling constants and the masses of
each particle type. Now, these can't be predicted. They need to be measured. These are like the tunable
knobs of the theory. However, we don't know how
they ended up with the values that they have. And presumably a deeper
theory explains this, and may connect to them. In this theory, the
value of some constants may prove to be tied to the
values of other constants. A few of you took issue with
my suggestion that changing fundamental constants help
with the fine--tuning problem. Either that the fine-tuning
problem isn't actually a mystery, or that the anthropic
principle solves the problem without even changing the
fundamental constants. To answer, I would ask
you to imagine that the entirety of our universe-- or even the multiverse-- has the same laws of
physics, including the same fundamental constants. Assuming then that the universe
wasn't set up specifically to be able to produce life,
then is it not just too lucky that the only
universe that exists is a life-supporting one? The alternative is that
many universes or patches of universe exist that
encompassed an extremely wide range of physical states. Then only a small fraction would
be capable of supporting life. And, of course, we're
in one of those. WispXLegend asks where
a 15-year-old Australian should start to pursue
a career as a physicist. Well, it sounds
like you're already studying the right stuff
in secondary/high school. Keep that up. Take whatever math and
physics they offer. To become a working physicist,
you're going to need a PhD. So that means
university/college. Start a Bachelor of
Science degree someone with a decent physics program. Major in physics, and
work your butt off. Get good grades,
and you should be able to win a scholarship
for a PhD program. Keep working your
butt off, and you'll be making real contributions
to physics before you even finish your doctorate. You should also talk
to teachers and even contact university
physics departments to get more career mentorship. Rubbergnome suggests that
the three-component SU2 boson field in the
electroweak Lagrangian should have had mu as
a superscript instead of a subscript. Wait, we're summing
over the superscript mu in gamma as per the Einstein
summation convention. Is-- is Einstein
out the window now? Is there some new Rubbergnome
summation convention that we should talk about?
Only posting this for the sake of posterity and locking the post to keep things organized. Head on over to this thread to discuss the contents of this video and the paper that was mentioned.