Mysterious The Great Attractor
If
you’ve been following my article 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 space-time 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?
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 super-clusters, 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 article, the Great Attractor. In an opposite vein from
the supervoids, 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.
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| The Empty Space |
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.
Conclusion
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. Thanks for reading! Have a space related
question? Ask in the comments below! Subscribe so you don’t miss out
on future science article.
This place where everything seems to be moving away from it should be a white hole.
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