Black holes ‘eat’ stars and gas. We all know that. Turns out, black holes can “also burp after their meal,” says Eric Schlegel from the University of Texas in San Antonio. Schlegel led a study that took a closer look at NGC 5195, a small companion galaxy merging with “The Whirlpool” galaxy (also known as NGC 5194).
Using NASA’s Chandra X-ray Observatory, astronomers detected two arcs of X-ray emission they believe were created by a supermassive black hole.
“We think these arcs represent fossils from two enormous blasts when the black hole expelled material outward into the galaxy,” says co-author Christine Jones from the Harvard-Smithsonian Center for Astrophysics (CfA). “This activity is likely to have had a big effect on the galactic landscape.”
An optical image of NGC 5195 from the Kitt Peak National Observatory also points to powerful blasts produced by a massive black hole. In the image, Schlegel and his colleagues noticed a thin region of emission of relatively cool hydrogen gas. These emissions suggest the X-ray emitting gas snatched hydrogen gas from the center of the galaxy. When a black hole affects its host galaxy in this way, astronomers call it ‘feedback.’
Marie Machacek, who also co-authored the study, explains feedback and how it affects galaxies. “We think that feedback keeps galaxies from becoming too large,” says Machacek. “But at the same time, it can be responsible for how stars form. This shows that black holes can create, not just destroy.”
Ok, so what’s causing the explosive outbursts? As you can see in the image above, NGC 5195 and NGC 5194 are merging. Astronomers believe this merger could be what is triggering the outbursts. As the two interact, extra gas is funneled towards the black hole. And the energy generated from this matter could be producing the outbursts.
What’s interesting about these two outbursts is their locations. The study authors estimate the inner arc took somewhere between 1-3 million years to reach its current position. And 3-6 million years for the outer arc. The two arcs are outside the area where rapid outflow has been detected from active supermassive black holes in other galaxies. But, they are inside the large cavities seen in the hot gas around other massive galaxies. Astronomers could be getting a rare glimpse at the middle stage of the feedback process.
“Our observation is important because this behavior would likely happen very often in the early universe, altering the evolution of galaxies. It is common for big black holes to expel gas outward, but rare to have such a close, resolved view of these events,” Schlegel said.
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