Image Shows a Staggeringly Powerful Event Occurred Near Center of the Milky Way

Radio image of the center of the Milky Way with a portion of the MeerKAT telescope array in the foreground. The plane of the galaxy is marked by a series of bright features, exploded stars and regions where new stars are being born, and runs diagonally across the image from lower right to top center. The black hole at the center of the Milky Way is hidden in the brightest of these extended regions. The radio bubbles extend from between the two nearest antennas to the upper right corner. Many magnetized filaments can be seen running parallel to the bubbles. In this composite view, the sky to the left of the second nearest antenna is the night sky visible to the unaided eye, and the radio image to the right has been enlarged to highlight its fine features.
Credit: Oxford, SARAO

An international team of astronomers has discovered one of the largest features ever observed in the center of the Milky Way – a pair of enormous radio-emitting bubbles that tower hundreds of light-years above and below the central region of our galaxy.

This hourglass-like feature, which dwarfs all other radio structures in the galactic center, is likely the result of a phenomenally energetic burst that erupted near the Milky Way’s supermassive black hole a few million years ago.

“The center of our galaxy is relatively calm when compared to other galaxies with very active central black holes,” said Ian Heywood of the University of Oxford and lead author of an article appearing in the journal Nature. “Even so, the Milky Way’s central black hole can – from time to time – become uncharacteristically active, flaring up as it periodically devours massive clumps of dust and gas. It’s possible that one such feeding frenzy triggered powerful outbursts that inflated this previously unseen feature.”

Using the South African Radio Astronomy Observatory (SARAO) MeerKAT telescope, Heywood and his colleagues mapped out broad regions in the center of the galaxy, conducting observations at wavelengths near 23 centimeters. Radio emission of this kind is generated in a process known as synchrotron radiation, in which electrons moving at close to the speed of light interact with powerful magnetic fields. This produces a characteristic radio signal that can be used to trace energetic regions in space. This radio light easily penetrates the dense clouds of dust that block visible light from the center of the galaxy.

By examining the nearly identical size and shape of the twin bubbles, the researchers think they have found convincing evidence that these features were formed from a violent eruption that over a short period of time punched through the interstellar medium in opposite directions.

“The shape and symmetry of what we have observed strongly suggests that a staggeringly powerful event happened a few million years ago very near our galaxy’s central black hole,” said William Cotton, an astronomer with the National Radio Astronomy Observatory in Charlottesville, Virginia, and co-author on the paper. “This eruption was possibly triggered by vast amounts of interstellar gas falling in on the black hole, or a massive burst of star formation which sent shockwaves careening through the galactic center. In effect, this inflated bubbles in the hot, ionized gas near the galactic center, energizing it and generating radio waves that we could eventually detect here on Earth.”

The environment surrounding the black hole at the center of our galaxy is vastly different than the environment elsewhere in the Milky Way, and is a region of many mysteries. Among those are very long and narrow filaments found nowhere else, the origin of which has remained an unsolved puzzle since their discovery 35 years ago. The filaments appear as radio structures tens of light-years long and approximately a light-year wide.

“The radio bubbles discovered by MeerKAT now shed light on the origin of the filaments,” said Farhad Yusef-Zadeh at Northwestern University in Evanston, Illinois, and a co-author on the paper. “Almost all of the more than one hundred filaments are confined by the radio bubbles.”

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