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Supermassive Black Holes: Rare Keys To The Universe

First Posted: Sep 22, 2015 10:46 AM EDT

Massive galaxies are centered by supermassive black holes that have millions of times more mass than our Sun, and when these galaxies collide, these black holes often begin to orbit one another, resulting in their eventual combination.

This process is expected to be the strongest source of gravitational waves, or ripples in space-time, the ever-elusive and long-sought keys to understanding more of the Universe. These waves, first predicted by Albert Einstein's theory of general relativity in 1916, have yet to be directly detected by astronomers.

"Gravitational waves represent the next great frontier in astrophysics, and their detection will lead to new insights on the Universe," said David Roberts, of Brandeis University. "It's important to have as much information as possible about the sources of these waves," he added.  

The only problem is that these mergers don't actually happen that often.

Scientists previously thought that this was the usual procedure for colliding galaxies with supermassive black holes, but a study led by Roberts has revealed that fewer than 1.3 percent of galaxies experience these mergers, a rate five times lower than what was previously thought.

"This could significantly lower the level of very-long-wave gravitational waves coming from X-shaped radio galaxies, compared to earlier estimates," Roberts said. "It will be very important to relate gravitational waves to objects we see through electromagnetic radiation, such as radio waves, in order to advance our understanding of fundamental physics."  

The team used the National Science Foundation's Karl G. Jansky Very Large Array, and studied a group of galaxies known as "X-shaped radio galaxies," which are known for their particular structures. They emit jets of superfast particles that have been dished out by disks of material spinning around the black holes in the center of them, an indicator that these radio galaxies have changed direction. Astronomers suggest that change in direction is a sign that the galaxy has merged with another at some point in the past.

Researchers conducted their study with only 11 legitimate candidate galaxies, narrowed down from an original list with as many as 100 potential subjects.

Gravitational waves were first evidenced by observations of a pulsar orbiting another star, a system discovered in 1974 by Joseph Taylor and Russell Hulse. Pulsars are spinning, superdense neutron stars that emit lighthouse-like beams of light and radio waves that allow precise measurement of their rotation rates, according to Universe Today.

Taylor and Husle's observations showed that the orbits of the stars decayed at exactly the rate predicted by Einstein's equations that indicate gravitational waves carrying energy away from the system, according to the release. They would receive the Nobel Prize for this observation in 1993.

The study's findings may help scientists to have a better understanding of when and how to detect gravitational waves, although they now know how much more difficult that will be.

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