If converted to the iconic Star Wars' opening crawl, this headline would read, "Just a few days ago, we discovered hundreds of galaxies kinda not that far away..." That's because researchers from four countries converged in Australia and used a radio telescope to detect a total of 883 relatively near galaxies heretofore blocked from view by something called the Zone of Avoidance. Their findings, published in the Astronomical Journal, could shed some light on a cosmic force dubbed the Great Attractor...and the nature of our universe.
What's radio telescopy? The Zone of Avoidance? And the Great Attractor?
You might be asking yourself: what exactly is a galaxy? Simply, a galaxy is a hodgepodge of stars, gas and dust, all held together by the inter-gravitational forces of the matter inside it. Astronomers have also noticed that galaxies can be ringed with dark matter that is more or less inert except for exerting a gravitational force.
The Zone of Avoidance is a large swath of the sky so called because it obscures a great many extragalactic (with reference to the Milky Way) stuff that sits behind it. It's made of interstellar dust and dense gases, and so absorbs much of the light coming from these other galaxies and stars. But the use of infrared and radio telescopic devices has allowed astronomers to cut through it like butter.
And just beyond the Zone of Avoidance, there's something even weirder called the Great Attractor ”” which is a loose term, because we really don't know exactly what it is. What we do know is that our galaxy and others that we've seen before are all being pulled and moving in the direction of this Great Attractor. Could it be a very big hoover?
Astronomers noticed that there was a lot of motion of local galaxies in the direction of the Great Attractor ”” more than there should have been. After spending a lot of time looking at it, they noticed that the Great Attractor itself was moving towards something even bigger...the Sharpley Supercluster. It's made up of 8000 galaxies and has a mass of more than, wait for it, ten million...BILLION suns. The mind reels.
You might not know from looking ”” in fact you definitely wouldn't ”” but 80% of what's around you right now is dark matter. That's a rough estimate, and it's believed that parts of the universe has more dark matter, while other evacuated areas have less. Detection of dark matter, like that in the Bullet Cluster, is made possible by a process called weak gravitational lensing ”” how light from other galaxies is distorted by the gravity of a mass. It's believe that most of the universe's dark matter is concentrated in these coronas on top of galaxies, and this new finding should illuminate that further.
But we come around to this belief in dark matter because it seems to be the only solution to why galaxies hold themselves together. Scientists agree that there just doesn't seem to be enough mass to warrant the kind of gravity that would need to keep a collection of stars and dust in tact.
Galaxy clusters are the largest things in our universe (next to, of course, the universe), and can measure ten million lightyears long. Using X-Ray technology, scientists have seen just how these bad boys might form. Most of the matter (baryonic matter they call it) that comprises a galaxy is in a gaseous state, and the dark matter around the galaxy compresses it.
What kind of technology is needed to cut through the Zone of Avoidance and detect galaxies past it? Radio telescopes are useful because they can pick up very weak signals at the longest wavelength of light, ranging from one millimeter to 10 meters in length. Visible lightwaves are only a few hundred nanometers long, but because of their frequencies get absorbed into the Zone of Avoidance rather than coming to Earth.
One hypothesis to detecting dark matter is through dark photons, coming from the sun. A dark photon is believed to be produced when two dark particles come together (like it is believed they do in the sun) and annihilate each other, and then shoot out a resultant dark photon. And although (like regular dark matter) we can't see the dark photon directly, it decays to more standard particles that can be detected.
Part of the reason that dark matter is such a hot topic, beyond its ubiquity in the universe, is that it's believed to contain or be made of supersymmetric particles ”” those that aren't in the Standard Model of particle physics. This would be a huge discovery, and would basically make physics rethink itself.
Another, even cooler theory about dark matter is that it contains a parallel world with very little in common with our own. The "Hidden Valley" theories relate to these low mass planes of existence that might just dip beneath more massive particles and planes that just doesn't act the same way or abide by the same rules. This would be an even huger discovery.
Loeb and Narayan, two astronomers dealing with the Great Attractor, put it succinctly as to why this damn, mystifying thing is so damn important. They stated that "undiscovered mass behind the Milky Way may explain the discrepancy between the cosmic microwave background dipole and what is expected from the gravitational acceleration imparted on the Local Group by matter in the local universe." Oh!
The Cosmic Microwave Background Dipole, you say? Looks like a yin and yang set up going on. The temperature of the CMB is uniform throughout, but the heat wave movement you see is believed to be caused by the Great Attractor's pull, giving it this kind of dichotomy.