What is the Great Attractor, and will it destroy us?

The Great Attractor

Understanding the Supercluster concept:

To understand what's going on with the Great Attractor, we need to look at the bigger picture, and I mean the biggest picture of all. Beyond the Milky Way is our galactic neighbor, the Andromeda Galaxy. A little over 2.5 million light-years away is the Triangulum Galaxy. These galaxies, along with a few dozen others form the Local Group, a gravitationally bound clump about 10 million light-years across. The next big thing down the way is the Virgo Cluster, which has more than 1,300 galaxies packed into a dense clump only 65 million light-years away. The Virgo Cluster is gravitationally bound too; this would mean its member galaxies tend to hang out near each other, tied up by their mutual gravity. 

Going bigger than that gets a little fuzzy, but there are enormous collections of galaxies called 'superclusters'. They got sweet names too, based on what constellation was looked through to map out the structure, or named after old astronomers: Virgo Supercluster, Hydra-Centaurus Supercluster, Shapley Supercluster, etc. 

The Great Attractor:

Our understanding of the Universe has expanded tremendously in the last few decades. But there are still some mysteries out there, and the Great Attractor is one of them. Since the Big Bang, the universe has been spreading out in every direction, and it's picking up speed. The space between galaxies is getting larger every day. Currently, things are drifting apart at a rate of 2.2 million kilometers per hour. Now if you'd think that the galaxies to the left and right of ours would be moving at the same velocity, you'd be wrong. What's slowing us down are enormous clumps of matter. The matter is attracted to matter, which is why we see galaxies form clusters and superclusters. Even so, that's still not enough for the calculations astronomers have been getting. Somewhere out there, in the most heavily veiled area of space, there lies a massive gravitational irregularity that has been dubbed the Great Attractor. Over the course of billions of years, it's been pulling us and all the galaxies near us closer to it. The Great Attractor is thought to be at the gravitational center of the Laniakea supercluster. Our own galaxy is moving towards this anomaly at a whopping 1,342,162 miles per hour. 

One theory is that it's a confluence of dark energy. Another is that it might be caused by over-density, an area of dense mass with an intense gravitational pull. Whatever it is, it's powerful enough to overcome normal dark energy, the force that's believed to push galaxies on and cause them to pick up speed as they move forward. Dark energy is thought to compromise 71% of the universe. Unfortunately, scientists have no idea what it is.

In 1986, a group of astronomers observing the motions of the Milky Way and neighboring galaxies noted that the galaxies were moving towards the Hydra-Centaurus superclusters in the southern sky with velocities significantly different from those predicted by the expansion of the universe in accordance with the Hubble Law. It is estimated that the Great Attractor would have a diameter of about 300 million light-years and that its center would lie about 147 million light-years away from the Earth. 

Part of the reason the Great Attractor is so mysterious is that it happens to lie in a direction of the sky known as the "Zone of Avoidance". This is in the general direction of the center of our galaxy, where there is so much gas and dust that we can't see very far in the visible spectrum. We can see how our galaxy and other nearby galaxies are moving toward the Great Attractor, so something must be causing things to go in that direction. That means either there must be something massive over there, or it's due to something even more strange and fantastic. When evidence of the Great Attractor was first discovered in the 1970s, we had no way to see through the Zone of Avoidance. But while that region blocks much of the visible light from beyond, the gas and dust don't block as much infrared and x-ray light. As X-ray astronomy became more powerful, we could start to see objects within that region. What we found was a large supercluster of galaxies in that area of the Great Attractor, known as the Norma Cluster. It has a mass of about 1,000 trillion Suns. That's thousands of galaxies! While the Norma Cluster is massive, and local galaxies are moving towards it, it doesn't explain the full motion of local galaxies. The mass of the Great Attractor isn't large enough to account for the pull. When we look at an even larger region of galaxies, we find that the local galaxies and the Great Attractor are moving toward something even larger. It's known as the Shapley supercluster. It contains more than 8000 galaxies and has a mass of more than ten million billion suns. The Shapley supercluster is, in fact, the most massive galaxy cluster within a billion light-years, and we along with every other galaxy in our corner of the universe are moving toward it.

Some astronomers don't consider it a threat, while others state that all galaxies and clusters are clumping into greater and greater superclusters and that this may be how the universe ends; as part of what's called the Big Crunch, which could theoretically be followed by another Big Bang.