South Africa’s 64-dish MeerKAT radio telescope array, which is spread over a diameter of 8 km in the Karoo region of the Northern Cape province, has allowed an international astronomy team to make a major discovery in the centre of our galaxy, the Milky Way. They have discovered gigantic twin structures that resemble balloons which extend for hundreds of light years above and below the centre of our galaxy.

These structures are emitting synchroton radiation, which is generated by electrons moving at speeds close to the speed of light and interacting with powerful magnetic fields. This radiation was detected by the astronomers while using MeerKAT to carry out observations at wavelengths close to 23 cm. Unlike visible light, the radio waves were not blocked by the dense dust clouds that hide the centre of the galaxy from our eyes. The discovery was reported in an article in the renowned science journal Nature earlier this month.

“These enormous bubbles have until now been hidden by the glare of extremely bright radio emission from the centre of the galaxy,” said South African Radio Astronomy Observatory (Sarao) chief scientist and article coauthor Fernando Camilo. “Teasing out the bubbles from the background noise was a technical tour de force, only made possible by MeerKAT’s unique characteristics and ideal location. With this discovery, we’re witnessing in the Milky Way a novel manifestation of galaxy-scale outflows of matter and energy, ultimately governed by the central black hole.”

“The centre of our galaxy is calm when compared to other galaxies with very active central black holes,” pointed out Oxford University astrophysicist and article lead author Ian Heywood. “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.”

“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,” elucidated US National Radio Astronomy Observatory astronomer and paper coauthor William Cotton. “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 centre. In effect, this interstellar gas inflated bubbles in the hot, ionised gas near the galactic centre, energising it and generating radio waves that we eventually detect here on Earth.”

Not only is this discovery important in itself, it suggests an explanation for a mystery that has endured for over three decades. The space around our galaxy’s central black hole contains a unique phenomenon – narrow filaments that are tens of light years long and which emit radio waves. Their origin has been a puzzle ever since they were discovered. “The radio bubbles discovered by MeerKAT now shed light on the origin of the filaments,” affirmed (US) Northwestern University astrophysicist and article coauthor Farhad Yusef-Zadeh. “Almost all of the more than 100 filaments are confined by the radio bubbles.” Because the filaments are so closely associated with the bubbles, the research team suggest, in their paper, that the event which created the bubbles also accelerated electrons along the magnetised filaments, thereby generating the radio waves which led to their discovery 35 years ago.

Sarao MD Dr Rob Adam noted that it was “extremely gratifying” that the first scientific paper based on research conducted using the entire MeerKAT array should have been published in such a prestigious journal as Nature – “the world’s leading science journal”. “Cutting-edge research instruments expand our views in unexpected ways, as this exciting discovery shows,” he highlighted. “MeerKAT’s quality is a testament to the dedicated effort over 15 years by hundreds of people from South African research organisations, industry, universities and government.”