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?