In 2013, scientists attempted to recreate the evolution of the universe from shortly
after the Big Bang until today.
This simulation, which took 19 million CPU hours to produce, started with a predicted
amount of matter, dark matter and dark energy that should have existed shortly after the
Big Bang.
The simulation was allowed to run to see if these parameters that were set at the beginning
can produce the galaxies and the universe’s structure we see today.
What you are looking at here is limited to a 32 million light year cube of the simulation,
the expansion of the universe considered, with simply gas density and temperature visible.
This is the intergalactic medium.
Even though space is a vacuum, there are still a few particles in every cubic centimetre
of space.
Blues are the coldest regions here; whites are the hottest.
As gas particles are drawn together by their own gravity and that of dark matter, the gas
clumps and over the course of millions of years, coalesces into galaxies, which increases
the gas’s temperature drastically.
What you’ll immediately notice is that there appear to be explosions coming from the densest
clumps.
But galaxies exploding?
That can’t be right, I surely would have heard of that before.
Remember, this is just the intergalactic gas temperature we are seeing, and each second
passing in the video is a few million real time years.
Quasars, or extremely active blackholes, are the brightest objects in the universe, emitting
more electromagnetic radiation than entire galaxies combined.
When a Quasar lights up, its rapid increase in radiation blasts into space ionises the
intergalatic gas as it expands out, heating it up to extreme temperatures.
This is known as quasar-mode, or Active Galactic Nuclei feedback.
Blackholes don’t remain as quasars for lengthy periods of time, rather quasars are the result
of a large amount of mass falling into them, lighting them up and causing them to eject
huge amounts of mass and energy.
They’ll remain quasars as long as there is matter being fed into them.
Although, you may wonder, how can a black hole emit anything?
Don’t they absorb it all?
And the answer is yes.
It is in fact the accretion disk around the quasar that is so energetic and luminous.
A black hole’s accretion disk is the result of matter passing by being ripped apart and
sucked into orbit.
These supermassive black holes often have billions of solar masses, the gravity around
them is immense.
As the material in the accretion disk orbits and falls inwards, the friction from the material
in the disk rubbing together creates energy so intense that a quasar can be thousands
of times brighter than our Milky Way.
In fact, a quasar’s host galaxy is often too dim to detect next to the bright quasar,
although techniques with the Hubble Space Telescope have allowed a few of these host
galaxies to be seen too.
Quasars could light up from collisions of galaxies, when suddenly an abundance of matter
falls into a supermassive black hole, although this doesn’t always happen.
You’ll also notice these jets coming from the quasar’s poles, these extend well beyond
the galactic disk, and can even be seen illuminating other galaxies and dust clouds like a spotlight.
Quasars themselves are bright, but when these jets are pointed towards us, they are known
as Blazars.
The jets are believed to be powered by the black hole’s magnetic structure, and they
can carry high energy plasma away from the black hole at almost the speed of light.
The days of Quasars and Blazars are thought to be over, the closest Quasar to us is 600
million light years away, and thus was going on 600 million years ago.
However, you’ll notice that the explosions in the simulation don’t let up in this video
as time passes.
This comes from the last in the Active Galactic Nuclei family of black holes, radio galaxies.
Typical Quasars and Blazars are so bright that they light up in all frequencies of the
electromagnetic spectrum uniformly, radio galaxies originate from black holes that,
unsurprisingly, are brighter in radio wavelengths.
These explosions now come from radio galaxies, and this is known as radio mode feedback.
The simulation stops at the present day.
Now, while impressive, the simulation isn’t perfect.
For instance, it could only simulate a trillion particles compared to the countless number
of particles in the equivalent section of space.
Also, we don’t have a perfect knowledge of the parameters of the universe, and so
there were certain mistakes evident in the model like the overprediction of star formation.
There are plans to try this again at some point with an updated understanding.
Being able to model how the universe evolved can give us a confirmation about how we believe
it formed, and this is of great interest to scientists.
Let’s see what future results will bring!
So, can galaxies explode?
Not in the conventional sense, but if you are talking about exploding with electromagnetic
radiation, then absolutely. Thanks for watching!
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