Most of the time, the billions of galaxies that make up the universe go about their business without bothering their neighbors. Sometimes, though, like galactic bumper cars, they smash into each other. When they do, the massive black holes at their centers usually behave a certain way. However, a merger of two galaxies observed by some of NASA's space-based tech shows that there's always an exception to the rule.
The galaxies in question have the unusual names of Was 49a and Was 49b. The first galaxy is a large one and the second is a dwarf galaxy that rotates inside the disc of its bigger brother about 26,000 light years from its center.
Typically, when two such galaxies merge, it's the black hole belonging to the one that becomes active and begins to shoot off high-energy x-rays as it devours the gas from the other galaxy. In this case, however, it's 49b's black hole that has kicked into high gear. In fact, the dwarf galaxy's black hole has gotten so active that it is the source of what's known as an active galactic nucleus (AGN), a source of extremely high-energy bursts of radiation.
"We didn't think that dwarf galaxies hosted supermassive black holes this big," said Nathan Secrest, lead author of the study and postdoctoral fellow at the U.S. Naval Research Laboratory in Washington, in a statement. "This black hole could be hundreds of times more massive than what we would expect for a galaxy of this size, depending on how the galaxy evolved in relation to other galaxies."
Secrest told New Atlas that in a typical dwarf galaxy, the mass of the central black hole would be about .01 percent of the overall galaxy mass. In the case of Was 49b though, its black hole is a full two percent of its overall mass. "Now, the correlation between black hole mass and total galaxy stellar mass is not particularly tight, but nonetheless the black hole is around two hundred times larger than what we might expect, given its stellar mass," he told us.
In making the determination of the size of Was 49a and 49b, the researchers relied on X-ray data from the NuSTAR and Chandra space telescopes and the Swift satellite, along with a filtered and enhanced image from the Discovery Channel Telescope in Happy Jack, Arizona. The image, seen above, shows the 39b galaxy in pink, as a result of intense ionizing radiation shooting out of the AGN. The lighter pink region is a group of stars, while the green regions represent normal starlight from the larger Was 39a galaxy.
"This study is important because it may give new insight into how supermassive black holes form and grow in such systems," Secrest said in a statement. "By examining systems like this, we may find clues as to how our own galaxy's supermassive black hole formed."
According to NASA, in a few hundred million years, both black holes will merge "into one enormous beast."
The work of the reaserchers has been published in The Astrophysical Journal.
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