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If you’ve been following the Astrum Answers series recently, you’ll notice that we’ve
talked a lot about how the universe is structured, filament structures of galaxies being pulled
apart by the universe’s expansion, with bubbles or voids forming in the gaps.
Because of the universe’s expansion, everything is moving away from everything.
But of course, this isn’t totally true in practice, due to a mysterious force called
gravity.
Gravity is a pulling force, or technically it is the curvature of spacetime caused by
uneven distribution of mass.
On very small scales, gravity is hardly relevant at all.
I don’t feel any pull towards objects around me, only towards the Earth because it is so
massive.
Celestial objects close enough to the Sun are most influenced by its gravity, and all
stars in the galaxy orbit around a supermassive black hole at the galaxies core.
But it doesn’t stop there.
You’ve probably heard that the Andromeda galaxy is hurtling towards us.
How can that be when everything is moving apart?
Gravity.
Objects that are close enough together with a large enough mass are pulled towards each
other by gravity faster than the universe can expand.
This is why we have galaxy superclusters, and in fact we are part of one.
Gravity is keeping these galaxy clusters bound together, meaning over extremely large time
scales, collisions aren’t totally unusual.
In fact, a new theory has just recently been proposed that the Milky Way may have recently
experienced such a collision with a ‘Large Magellanic Cloud-sized’ diffuse galaxy called
Antlia 2.
Scientists have discovered that the Milky Way has ripples consistent with it having
had a collision in the past, but we couldn’t pinpoint what it collided with, until Gaia
discovered the Antlia 2 galaxy hidden behind our galactic disk.
This makes it very hard to spot as although it is massive, it is very spread out due to
the collision, and being behind our galactic disk makes it hard to see due to the stars
and dust in the way.
But that brings us onto the main topic of this episode, the Great Attractor.
In an opposite vein from the supervoids video, where there are regions of space where there
is an almost total absence of mass for hundreds of millions of light years in any direction,
the Great Attractor is the biggest concentration of mass for hundreds of millions of light
years.
It is so massive, that even though our galaxy is between 150-250 million light years away,
we, and all galaxies around it, are currently moving towards it.
Estimates put its mass at roughly 1,000 trillion Suns, which is enough for many thousands of
galaxies.
But what could possibly be there that is that massive?
Well for the longest time, it was a total mystery, because like Antlia 2, the region
where the Great Attractor is located is hidden behind our galaxy’s disk.
However, X-ray telescopes can see through the disk, and recent technological improvements
and advances in x-ray teleoscopes have meant we have been able to detect thousands of galaxies
in the region where the Great Attractor is supposed to be.
But the mass detected didn’t add up.
There wasn’t enough present to create such a pull.
Further analysis has revealed something very interesting: that while we are being pulled
towards the Great Attractor, there is something even more massive behind it, located 650 million
light years away called the Shapley Attractor, or the Shapley Supercluster.
Located there are many thousands of galaxies densely packed together, with a mass of 10,000
trillion Suns and everything within 1 billion light years is being pulled towards it.
On the other hand, looking the opposite direction from the Shapley supercluster, we see an underdense
region, where everything seems to be moving away from it called the Dipole Repeller.
It isn’t actually repelling mass, but due to all the mass around it being pulled towards
more dense regions by gravity, it creates the illusion that it is repelling that mass,
although there are some scientists that do claim that an unknown repelling force is at
work there.
Simply put, we are still in very early days when it comes to understanding the universe.
We observe certain things, like the motion of galaxies, dense galaxy groups, and absences
of galaxies in large voids or “repelling regions”.
We observe the expansion of the universe, and observe the filamentary structures.
But the universe is an impossibly large place, and we can only see so far, only live so long.
Plus, our technology is still limited.
We have theories which try and explain what we see, but I really wouldn’t be surprised
to see these theories change as more data becomes accessible.
Some may ask, what’s the point then?
However, I for one am hugely grateful to the bright minds working on this, as discovering
our place in the universe is so fascinating!
I’m glad humans have an insatiable need to explore and understand everything around
them.
This innate sense of wonder and curiosity is what drives the evolution of mankind.
And I am excited to witness it.
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Thanks for watching!
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