Hello Space Fans and welcome to another edition
of Space Fan News.
This week a group of astronomers think they’ve
figured out how supermassive black holes billions
of times the mass of our Sun could have formed
in the early universe; dark matter appears
to have less influence on galaxy rotation
in the early universe; and astronomers have
observed a star orbiting a black hole at a
distance of less than three times the distance
of the Earth and the Moon.
Most of you by now know what a supermassive
black hole is, they are black holes that measure
in the hundreds of billions of solar masses
and they are usually nestled at the centers
of most galaxies in the universe.
Now ordinary 100 billion solar mass black
holes that we see in nearby galaxies today
form over a period of a billions of years,
and they grow by merging with other galaxies
supermassive black holes, devouring stars,
gas, dust and anything and everything that
gets too close.
The fact that they take a lot of time makes
intuitive sense, these sorts of mergers and
interactions take a while and as the universe
expands, they slowly become less frequent.
But what’s weird is that if that is how
supermassive black holes are made, then how
come we see them in the early universe too,
when the the cosmos was only around 800 million
years old?
That is not enough time for supermassive black
holes to form through collisions and mergers
alone.
Well this week a new study released in the
journal Nature Astronomy think they have an
answer.
OK stay with me here, it’s gonna get weird.
Running computer simulations this team of
astronomers have found that if an ancient
galaxy has a black hole at its center and
there is a nearby galaxy that is pushing out
enough of its star forming gasses in such
a way that prevent new stars from being born,
in other words, all of the stars have strong
enough stellar winds that pushes out all of
its gas and dust - then the host galaxy (the
one with the black hole) will suck up that
gas and grow enough that it will eventually
collapse forming a black hole that feeds on
the remaining gas, and later, dust, dying
stars, and possibly other black holes, to
become super gigantic million solar mass black
hole.
And get this, the time it takes for that galaxy
to collapse and for the supermassive black
hole form is only 100,000 years.
From there only a few hundred million years
need to pass to create a billion solar
mass black hole.
So how can this happen?
Remember that the stars in the early universe
are not like the stars we see today.
Most of them were formed from molecular hydrogen
and are very large, very hot, very violent
and very short lived stars.
They only hung around for a few hundred million
years at most with the majority lasting less
than 100 million years.
It’s not too far fetched then to have a
galaxy so full of these hot stars with stellar
winds strong enough to stop all star formation
inside that galaxy and kick out its gas to
the black hole galaxy.
Now like most simulations, for this to work
out, conditions need to be just right.
The nearby galaxy can’t be too hot, or too
cold, nor can it be too close or too far.
But there are a lot of galaxies in the sky
and the early universe was full of them too,
so there only needs to be a few situations
laid out like this for a supermassive black
hole to form so early after the Big Bang.
Astronomers haven’t found all that many
so far anyway.
And as usual, we are all waiting for the James
Webb Space Telescope to get to the L2 point
in late 2018 to help us learn more about how
supermassive black holes can exist in the
early universe.
Next, while we on the topic of the early universe,
it turns out that dark matter may have played
less of a part in early galaxies than it does
today.
For those who don’t know, dark matter is
this highly annoying material that no one
has observed directly yet because it won’t
interact with us in any way.
The only way we know it’s there is by looking
at the effect it has on things we can see.
Now it’s easy to get annoyed at dark matter
and say that we’re just making it up but
look at this.
This graph is a perfect example.
On the right is a galaxy rotation curve from
a normal, nearby spiral galaxy.
The outer stars are rotating very fast, too
fast if all that is there were stars, gas,
dust and a supermassive black hole.
The graph on the right is exactly what you’d
expect to see if there were no dark matter
at all.
As you can see, the outer stars are rotating
slowly.
And this is the rotation curves that were
measured in a study that came out this week.
Astronomers using the European Southern Observatory’s
Very Large Telescope measured the rotation
rates of six massive, star-forming galaxies
in the distant Universe, this was a period
when galaxy formation was higher than it’s
ever been, some 10 billion years ago.
They found that unlike spiral galaxies in
the modern Universe, the outer regions of
these distant galaxies seem to be rotating
more slowly than regions closer to the core
— which as I’ve just told you suggests
there is less dark matter present than expected.
I’m sorry but I just gotta say it.
That is Just Like Downtown.
This result is important because apparently
dark matter didn’t play a big role in galaxy
evolution in the early universe.
What may be going on here is that 3 to 4 billion
years after the Big Bang, the gas in galaxies
had already efficiently condensed into flat,
rotating discs, while the dark matter halos
surrounding them were much larger and more
spread out.
Apparently it took billions of years longer
for dark matter to condense as well, so its
dominating effect is only seen on the rotation
velocities of galaxy discs today.
I feel like I need to come up with a galaxy
rotation dance now…
Finally astronomers using NASA's Chandra X-ray
Observatory as well as NASA's NuSTAR and the
Australia Telescope Compact Array (ATCA) have
found a star that is orbiting really, really
close to a black hole.
The star is part of a binary in the globular
cluster 47 Tucanae, a dense cluster of stars
in our galaxy about 14,800 light years from
Earth.
You may remember that star cluster because
I told you about astronomers finding a IMBH
there in SFN 194.
While astronomers have observed this binary
for many years, it wasn't until 2015 that
radio observations with the ATCA revealed
the pair likely contains a black hole pulling
material from a companion star called a white
dwarf, a low-mass star that has exhausted
most or all of its nuclear fuel.
New Chandra data of this system, known as
X9, show that it changes in X-ray brightness
in the same manner every 28 minutes, which
is likely the length of time it takes the
companion star to make one complete orbit
around the black hole.
This means that this white dwarf is so close
to that black hole that it is going around
twice every hour.
Chandra data also shows evidence for large
amounts of oxygen in the system, which is
a characteristic feature of white dwarfs.
And so a strong case can therefore be made
that the companion star is a white dwarf,
and if that’s true, then it be orbiting
the black hole at only about 2.5 times the
separation between the Earth and the Moon.
That’s close.
Astronomers say this white dwarf is so close
to the black hole that material is being pulled
away from the star and dumped onto a disk
of matter around the black hole before falling
in.
They also say that this star is in a pretty
stable orbit and probably won’t fall in.
However so much matter may be pulled away
from the white dwarf that it ends up only
having the mass of a planet.
If it keeps losing mass, the white dwarf may
completely evaporate.
So how could such a thing come about?
How can a star get so close and not fall in?
One possibility is that the black hole smashed
into a red giant star, and then gas from the
outer regions of the star was ejected from
the binary.
The remaining core of the red giant would
form into a white dwarf, which becomes a binary
companion to the black hole.
The orbit of the binary would then have shrunk
as gravitational waves were emitted, until
the black hole started pulling material from
the white dwarf.
An alternative explanation for the observations
is that the white dwarf is partnered with
a neutron star, rather than a black hole.
In this scenario, the neutron star spins faster
as it pulls material from a companion star
via a disk, a process that can lead to the
neutron star spinning around its axis thousands
of times every second.
A few such objects, called transitional millisecond
pulsars, have been observed near the end of
this spinning up phase.
He astronomers in this study don’t think
this happened though because transitional
millisecond pulsars have properties that aren’t
seen in X9, such as extreme variability at
X-ray and radio wavelengths.
Still, they can’t disprove this explanation
either.
Man, that planet in ‘Interstellar’ has
nothing on this place.
Can you imagine how weird it must be there?
Well that’s it for this week Space Fans.
We had a really great discussion on Wednesday
about the future of SFN so thanks for taking
part, if you couldn’t make it, please leave
comments on that video and I’ll still keep
checking them.
Let’s plan on a follow up LIVE Event in
two weeks to gather what we’ve learned and
make a plan.
Thanks to all Patreon Patrons for making SFN
possible, this is your show and you are crucial
to these episodes.
Thanks to all of you for watching and as always,
Keep Looking Up!
