Astronomers Spot Massive Radio-Emitting Structures in the Milky Way

"The shape and symmetry of what we have observed strongly suggest that a staggeringly powerful event happened a few million years ago very near our galaxy's central black hole..."

Astronomers have discovered supermassive radio-emitting structures at the center of the Milky Way.

A pair of huge radio-emitting bubbles have been observed rising hundreds of light-years above and below the central region of our galaxy, in an unprecedented discovery.

This awkward characteristic – one of the largest ever observed in that region of the Milky Way – is similar to an hourglass and outshines all other radio structures in the galactic center.

It is probably the result of a phenomenally energetic burst near the supermassive black hole of the Milky Way which occurred a few million years ago.

“The center of our galaxy is relatively calm when compared to other galaxies with very active central black holes,” explained Ian Heywood of the University of Oxford, first author of the study.

“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.”

This is a radio image of the central part of the Milky Way Galaxy. Image Credit: Oxford / SARAO.
This is a radio image of the central part of the Milky Way Galaxy. Image Credit: Oxford / SARAO.

MeerKAT: Unparalleled capabilities

Using the MeerKAT telescope of the South African Radio Astronomy Observatory (SARAO), Heywood and his colleagues mapped large regions in the center of the galaxy, making observations at wavelengths close to 23 centimeters.

MeerKAT has unparalleled sensitivity and imaging capacities which, linked with its unique geographic vantage point for observing the Galactic center, result in the sharpest ever image of the radio waves originating from the heart of the Milky Way, a part of the sky that is particularly challenging to image at such wavelengths.

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“These enormous bubbles have until now been hidden by the glare of extremely bright radio emission from the center of the galaxy. Teasing out the bubbles from the background ‘noise’ was a technical tour de force, only made possible by MeerKAT’s unique characteristics and propitious location in the Southern hemisphere,” explained co-author Fernando Camilo of SARAO in Cape Town.

And precisely these unique observational capabilities have allowed experts to peer into a “fossil record” that allows astronomers to piece together a puzzle of the history of our Galactic center, as well as the supermassive black hole that lurks there.

Radio emission of this type are generated in a process known as synchrotron radiation, in which electrons that move near the speed of light interact with powerful magnetic fields. This, in turn, produces a characteristic radio signal that can be used to track energy regions in space.

This radio light easily penetrates the dense clouds of dust that block visible light from the center of the galaxy.

By studying the almost identical size and shape of the twin bubbles, the researchers think they have found compelling evidence that these characteristics formed from a violent eruption that for a short period of time crossed the interstellar medium in opposite directions.

“The shape and symmetry of what we have observed strongly suggest that a staggeringly powerful event happened a few million years ago very near our galaxy’s central black hole. 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,” explained co-author of the study, William Cotton, from the National Radio Astronomy Observatory in Charlottesville, Virginia.

“In effect, this inflated energetic bubbles in the hot, ionized gas near the galactic center, energizing it and generating radio waves which we could eventually detect here on Earth,” Cotton added.

The new discovery is detailed in a paper published in Nature.