A team of international astronomers has recently discovered one of the largest features ever observed in the center of the Milky Way. This hourglass-like feature appears like a pair of enormous radio-emitting bubbles that tower hundreds of light-years above and beneath the central region of the galaxy.
According to astronomers, this feature dwarfs all other radio structures in the galactic center and is likely the result of an amazingly energetic burst that ejected close to the Milky Way’s supermassive black hole a couple of million years ago.
Astronomers used the South African Radio Astronomy Observatory (SARAO) MeerKAT telescope and mapped out broad regions in the center of the galaxy, conducting observations at wavelengths near 23 centimeters.
Radio emission of this kind is produced in a procedure known as synchrotron radiation, in which electrons moving at near the speed of light interact with powerful magnetic fields. This creates a characteristic radio signal that can follow energetic regions in space. This radio light effectively penetrates the dense clouds of dust that block visible light from the center point of the galaxy.
Ian Heywood of the University of Oxford said, “The center of our galaxy is relatively calm compared to other galaxies with very active central black holes. 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.”
Scientists examined the nearly identical size and shape of the twin bubbles and thought they had 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 strongly suggest that a staggeringly powerful event happened a few million years ago very near our galaxy’s central black hole.
William Cotton, an astronomer with the National Radio Astronomy Observatory in Charlottesville, Virginia, said, “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.”
Farhad Yusef-Zadeh at Northwestern University in Evanston, Illinois, said, “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. Almost all of the more than one hundred filaments are confined by the radio bubbles.”
“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 magnetized filaments.”
Fernando Camilo of SARAO in Cape Town, a co-author of the paper, said, “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 ideal location. With this unexpected 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 is published in the journal Nature.