There is a slumbering giant at the heart of our galaxy and occasionally, it wakes up and has an outburst.
Astronomers have found evidence of this activity from the supermassive black hole at the heart of the Milky Way.
The black hole, which is 4 million times the mass of our sun, has the remains of a blowtorch-like jet of material from an outburst that occurred several thousand years ago.
As black holes use their gravitational pull to tug material inward, interstellar gas and dust swirls into something called an accretion disk around the black hole. This swiftly rotating material heats up and blasts away from the black hole in jets that flare out across space at nearly the speed of light, accompanied by radiation.
Although our galaxy’s black hole is often quiet, occasionally it releases activity, like cosmic burps and hiccups, as it gobbles up stars and gas clouds.
Astronomers used data from multiple telescopes to piece together this astronomical blast from the past to find that the jet’s expelled material is still making its mark. A study detailing the findings published last week in the Astrophysical Journal.
In 2013, researchers detected X-rays and radio waves, using NASA’s Chandra X-ray Observatory in space and the Jansky Very Large Array telescope in New Mexico, that suggested a jet was penetrating gas near the black hole.
This caused Gerald Cecil, a professor in the physics and astronomy department at the University of North Carolina in Chapel Hill, to question if there may be another jet radiating from the black hole in another direction.
Data taken from ground and space-based telescopes, including the Hubble Space Telescope, across multiple wavelengths of light essentially allowed Cecil to see an otherwise invisible and glowing hot bubble of gas that lined up about 35 light-years away from the black hole, as well as an expanding knot of gas that is only 15 light-years away.
When the jets strike gas clouds in the galaxy, the clouds react to the heat by expanding. Material within the gas clouds cause the jet to bend and split off into streams.
“The streams percolate out of the Milky Way’s dense gas disk,” said Alex Wagner, study coauthor and assistant professor at Tsukuba University in Japan, in a statement. “The jet diverges from a pencil beam into tendrils, like that of an octopus.”
These streams led to a chain of expanding gas bubbles that extend for at least 500 light-years, a daisy chain that allowed the researchers to reconstruct past events.
“Like in archeology, you dig and dig to find older and older artifacts until you come upon remnants of a grand civilization,” Cecil said.
When Wagner and Cecil ran computer models of the jets within the Milky Way, they were able to reproduce the data from the telescopes.
The black hole at the center of our galaxy is “currently powered down,” Cecil said. But if it becomes active again, the jet will likely fire up again, too, and astronomers could observe how far the jet may reach, he said.
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