Space Fan News #79: Missing Baryons Found?; Supercolliding Supermassive Black Holes

Uploaded by tdarnell on 12.10.2012

Hello Space Fans and welcome to another edition of Space Fan News.
This week, astronomers using the Chandra X-Ray space telescope have found evidence that our
Milky Way Galaxy is embedded in an enormous halo of hot gas that extends for hundreds
of thousands of light years. The estimated mass of the halo is comparable to the mass
of all the stars in the galaxy.
Now I know what you're thinking, you thinking, YAY, we don't need dark matter anymore. We
found the missing mass of the galaxy that invoked the need for it, now we can throw
it out the window.
Yay. WoooHooooo! no Dark Matter! Yay!
Sorry, I get a little carried away...
Nope. Sorry it doesn't work that way, we still need dark matter to explain the rotation curves
of galaxies and large scale structure in the universe.
But, it does help solve another problem astronomers have with matter in the universe: the "missing
baryon" problem.
If the size and mass of this gas halo is confirmed, it could be an explanation for the "missing
baryon" problem for the galaxy.
OK, so what's the missing baryon problem?
Well, first of all, baryon is a fancy term for ordinary matter, stuff like protons, neutrons,
electrons, atoms, all that stuff is called baryonic matter.
And, apparently there's not enough of it.
We know this because measurements of extremely distant galaxies and their gas halos have
shown us the baryonic matter present when the universe was only a few billion years
old and at that time represented about one-sixth the mass and density all matter available,
with the rest being dark matter.
In the current epoch, about 10 billion years later, another measurement of the baryons
present now in stars and gas in our galaxy and nearby galaxies shows at least half the
baryons are unaccounted for.
So, we see even less baryons in the galaxies of today than we saw in those in the early
universe, so where are they?
Forget dark matter, it seems like ordinary matter is elusive in its own right.
Well this discovery from a team of five astronomers using Chandra may have found some of it.
Chandra observed eight bright X-ray sources located far beyond the galaxy at distances
of hundreds of millions of light-years. The data revealed that X-rays from these distant
sources are absorbed selectively by oxygen ions in the vicinity of the galaxy, which
allowed scientists to determine that the temperature of the absorbing halo is between 1 million
and 2.5 million kelvins, or a few hundred times hotter than the surface of the sun.
But it is extremely diffuse, it's not like if you held your hand up you would go …. ooooh,
that's hot.
Now other studies have also shown that the Milky Way and other galaxies are embedded
in warm gas, but with temperatures between only 100,000 and 1 million kelvins. This new
research provides evidence the gas halo enveloping the Milky Way is much more hot and massive
than the warm gas halo previously thought to exist.
So how massive is it?
Well, the authors supplemented the Chandra data with XMM-Newton and Suzaku data on the
X-rays emitted by the gas halo to get a handle on the amount of absorption produced by the
oxygen ions. They concluded that the mass of the gas is equivalent to the mass in more
than 10 billion stars, and maybe as large as 60 billion stars.
This study provides the best evidence yet that the galaxy's missing baryons have been
hiding in a halo of million-kelvin gas that envelopes the galaxy. The estimated density
of this halo is so low that similar halos around other galaxies would have escaped detection.
So there you go, missing baryons found (maybe). So that's one less thing.
Next, ever wonder what happens when supermassive black hole collide?
Come on, you know you have.
Because you're Space Fans, I know you already know what a supermassive black hole is, so
I'm not gonna waste time telling you that, but when you put these bad boys together,
they make a big splash.
In space-time that is.
What I'm very nerd-ily referring to here is that it's pretty intuitive to most of us that
when two of these objects interact, it makes sense to say they gobble each other up and
make a bigger black hole.
A super-super massive black hole if you will.
Here is a simulation created with supercomputers at the University of Colorado that shows the
interaction of two supermassive black holes and their associated magnetic fields. Including
the magnetic fields are important as we'll see in a minute.
The black holes orbit each other and lose orbital energy by emitting strong gravitational
waves, and this causes their orbits to shrink. The black holes spiral toward each other and
eventually merge.
When they begin to come together they make a huge splash in the fabric of space-time,
sending out huge ripples that permeate throughout the cosmos.
It is through these gravitational waves in space-time that we will be able to detect
these mergers, and while those waves can tell us a lot, the one thing they can't tell us
where it happened.
For that, we need electromagnetic information in addition to the gravitational signal - a
flash of light from radio to x-rays - that will let our telescopes pinpoint the location.
Understanding the electromagnetic counterparts that may accompany a merger involves the daunting
task of tracking the complex interactions between the black holes, which can be moving
at more than half the speed of light in the last few orbits, and the disks of hot, magnetized
gas that surround them.
Since 2010, lots of studies have found that mergers could produce a burst of light, but
no one knew how common this was or whether the emission would be strong enough for us
to detect it on Earth.
So using the latest models, researchers made this simulation which show the complex interaction.
The most important aspect of the study is the brightness of the merger's flash. The
team finds that the magnetic model produces beamed emission that is some 10,000 times
brighter than those seen in previous studies.
So it looks like if we can detect the occurrence of a supermassive black hole collision from
the gravity waves they produce, then we can pinpoint the location of it from the elecromagnetic
beam using our telescopes.
And that, is just like downtown.
Well, that's it for this week Space Fans, thank you for watching, and as always, Keep
Looking Up!