Mysterious The Great Attractor | Unknown force in space

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.

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.

Sources 

The Powerful and Mysterious Great Attractor

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