IMAGE PROCESSING: Joseph DePasquale (STScI)
A multi-institutional team led by the University of North Carolina at Chapel Hill traces still active particle beam.
At its center, our Milky Way galaxy has an ancient black hole that over 10 billion years has gobbled millions of suns. Before gas and dust spirals into the hole to vanish, gamma-rays and charged particles emerge at almost light-speed.
The black hole is in a quiet state, but findings published Dec. 6 in Astrophysical Journal by the University of North Carolina at Chapel Hill and collaborators in Japan, Australia, and India provide evidence of powerful bursts within the last million years up to only a thousand years ago.
“The Milky Way’s central black hole powered up tens of millions of times its current luminosity when it ate a stream of gas a few million years ago,” said Gerald Cecil, a professor of physics and astronomy in the UNC-Chapel Hill College of Arts & Sciences.
That event irradiated a gas plume distant from the Milky Way that is still recovering from being hammered by the outburst. In the new paper the team describes finding the particle beam of this event, traced by X-rays, that is still active at a low level.
There’s too much dust along the 26,000-light-year distance to the center of our galaxy for UNC-Chapel Hill’s SOAR telescope in Chile to penetrate.
Instead, the team used the most powerful telescope on Earth, the Atacama Large Millimeter Array (ALMA) of radio telescopes also high in the Chilean Andes, to penetrate dust to trace an organized flow of alcohol and other molecules from the center.
Unlike other radio and X-ray telescopes, ALMA can map gas motions which enabled the team to isolate the flow from unrelated gas.
“Along our line of sight, we found molecular gas being shoved aside by the particle jet that is counter to an elongated X-ray feature,” Cecil said. “The flow is quite feeble today, but in the past, it was fully capable of inflating the huge gamma-ray and X-ray bubbles that loom 50,000 light years above and below the disk of our galaxy.”
The team simulated the impacts of the jet on the Milky Way’s gas using supercomputers at UNC-Chapel Hill and in Australia, obtaining an excellent match.
“We plan to extend our map along the axis of the jet that we’ve found using ALMA and mid-infrared spectra from the soon-to-launch James Webb Space Telescope plus further supercomputer simulations,” Cecil explained. “We want to pin down how often and for how long the jet, hence our black hole powers up.”
Soon, highly magnified images by the Event Horizon Telescope may reveal the base of the jet starting light-hours from the black hole to complement this team’s study on scales of one to 1,000 light years.
“Then we can unravel the history of this exotic but universal phenomenon, and begin to understand how the black hole influenced our Milky Way galaxy,” said study co-author Alex Wagner, an assistant professor at the University of Tsukuba Center for Computational Sciences.