By examining the nearly identical extent and morphology 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 suggest 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 US National Radio Astronomy Observatory and a 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 centre. In effect, this inflated bubbles in the hot, ionised gas near the galactic centre, energising it and generating radio waves that we eventually detect here on Earth.”
The environment surrounding the central black hole is vastly different than elsewhere in the Milky Way, and is a region of many mysteries. Among those are very long (tens of light-years) and narrow radio filaments found nowhere else, the origin of which has remained an unsolved puzzle since their discovery 35 years ago.
“The radio bubbles discovered by MeerKAT now shed light on the origin of the filaments,” said Farhad Yusef-Zadeh at Northwestern University in the USA, and a co-author of the paper. “Almost all of the more than 100 filaments are confined by the radio bubbles.”
The authors suggest that the close association of the filaments with the bubbles implies that the energetic event that created the radio bubbles is also responsible for accelerating the electrons required to produce the radio emission from the magnetised filaments.
“These enormous bubbles have until now been hidden by the glare of extremely bright radio emission from the centre of the galaxy,” said Fernando Camilo of SARAO in Cape Town, and a co-author on the paper. “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,” according to Camilo. “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 discovery of the MeerKAT bubbles relatively nearby in the centre of our home galaxy brings astronomers one step closer to understanding spectacular activities that occur in more distant cousins of the Milky Way throughout the universe.
“It’s extremely gratifying that the first paper based on the full MeerKAT array is being published in the world’s leading science journal,” said Rob Adam, SARAO Managing Director. “Cutting-edge research instruments expand our views in unexpected ways, as this exciting discovery shows.”
“MeerKAT’s quality,” added Adam, “is a testament to the dedicated effort over 15 years by hundreds of people from South African research organisations, industry, universities, and government.”