Since the Big Bang, the universe has expanded uniformly in all directions. It spreads out at great speed, making the space between galaxies larger. Cosmic objects are drifting apart at 1.37 million miles (2.2 million kilometers) per hour.
Using this knowledge, it can be assumed that the galaxies near us are moving at the same velocity, but they are not. Somewhere, in the deepest region of the cosmos, far from the safe confines of the Milky Way galaxy, lies a monster. Slowly, it pulls us closer to it over billions of years. This massive gravitational irregularity is known as the Great Attractor.
What is the Great Attractor?
Since the early 1970s, astronomers have noticed something peculiar with the galaxies in our nearby patch of the universe. While there was the general recession of galaxies driven by the overall expansion of the universe, there also seemed to be some vague directionality. It is as if all the galaxies near our own were also heading toward the same focal point.
As scientists continued to map the observable universe, they focused on 400 elliptical galaxies and noticed they were moving toward something we could not see. This region is known as the "Zone of Avoidance" or the area of the sky, which is obscured by the galactic plane of the Milky Way and the cosmic dust within it.
Whatever this force is, it would require a lot of mass to move a large number of galaxies. Experts dubbed it the Great Attractor, a region of the universe that shows gravitational anomaly. It is not a supermassive cosmic object but rather a volume of space that contains the center of attraction for all matter.
This region is thought to be at the heart of the Laniakea supercluster, a massive cluster of galaxies that measures more than 520 million light-years across. It contains over 100,000 galaxies, including our own Milky Way.
Where is the Great Attractor?
Over the past decades, the nature and extent of the Great Attractor has been the subject of much debate. One theory suggests that it is a confluence of dark energy, while another claims that it might have resulted from an area of dense mass with extreme gravitational pull.
Observing the Great Attractor is difficult at optical wavelengths. The plane of the Milky Way both outshines and obscures many of the cosmic objects behind it. One trick to see through this is by infrared or radio observation. However, the region behind the center of the Milky Way galaxy is also the part where the dust is thickest, so it remains an almost complete mystery to scientists.
In the 1990s and early 2000s, the Parkes radio telescope in New South Wales, Australia, examined the universe with high sensitivity. This radio telescope detected thousands of galaxies that used to be invisible to humanity. Using this multibeam receiver, scientists got a good look at the nearby galaxies, as well as the detailed composition of the Milky Way.
Further investigations at the Parkes Observatory in the mid-2000s revealed galaxies in an area that contains the Great Attractor. Although astronomers previously knew that there was some gravitational anomaly, most of the data is now being processed.
Experts can only infer the mass and location of the Great Attractor based on the sparse surveys within the Zone of Avoidance and from the reconstructions of the movements of galaxies. The Great Attractor's possible location contains an immense mass assemblage called the Norma Cluster. Our own Virgo cluster and all its surrounding galaxies are moving toward Norma, the center of the flow of all the galaxies within Laniakea.
Check out more news and information on the Milky Way Galaxy in Science Times.
