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Astronomers using the MeerKAT telescope at the South African Radio Astronomy Observatory have spotted a pair of huge radio-emitting bubbles in the central region of our Milky Way galaxy. The structure of the bipolar bubble has a width of about 457 light-years per 1,403 light-years and is probably the result of a phenomenal explosion of energy that erupted near Sagittarius A * – the supermassive black hole of the Milky Way – a few million years ago.
Radio image of the central parts of the Milky Way. The galactic plane is characterized by a series of luminous features, exploded stars and regions where new stars are being born, and horizontally crosses the image. The black hole in the center of the Milky Way is hidden in the brightest of these extensive areas. The radio bubbles discovered by MeerKAT extend vertically above and below the plane of the galaxy. Many magnetized filaments can be seen parallel to the bubbles. Image credit: University of Oxford / SARAO.
"The center of the Milky Way is relatively quiet compared to other galaxies with very active central black holes," said co-lead author Dr. Ian Heywood, an astronomer at Oxford University.
"Even so, the central black hole of the Milky Way can – from time to time – become unusually active, ignite by periodically devouring huge masses of dust and gas."
"It is possible that such binge eating triggered terrible explosions that inflated this unique feature."
Using the MeerKAT telescope, Dr. Heywood and his colleagues mapped large areas in the center of the galaxy, making observations at wavelengths close to 23 centimeters.
Radio broadcasts of this type are generated by a process called synchrotron radiation, in which electrons traveling at a speed close to the speed of light interact with strong magnetic fields.
This produces a characteristic radio signal that can be used to draw energy regions in space.
This radio light easily penetrates dust clouds that block visible light from the center of our galaxy.
"The shape and symmetry of what we have observed strongly suggests that an event of incredible power occurred a few million years ago very close to Sagittarius A *" , said co-author Dr. William Cotton, astronomer of the National Observatory of Radioastronomy.
"This eruption was probably triggered by large amounts of interstellar gas falling into the black hole, or by a massive explosion of star formation that sent a shockwave through the galactic center."
"In fact, these swollen bubbles in the hot ionized gas near the Galactic center feed it and generate radio waves that we can eventually detect here on Earth."
The environment surrounding Sagittarius A * is very different from that found elsewhere in the Milky Way and is a region full of mysteries.
Among them are large-scale and highly organized magnetic filaments, not found anywhere else, whose origin has remained an unresolved puzzle since their discovery 35 years ago.
The filaments appear as radio structures of several tens of light years and about a light year.
"The radio bubbles discovered by MeerKAT now shed some light on the origin of the filaments. Almost all the more than one hundred filaments are confined by radio bubbles, "said co-author Dr. Farhad Yusef-Zadeh, a researcher at Northwestern University, who discovered the filaments in the early 1980s.
The close association of filaments with bubbles implies that the energy event that created the radio bubbles is also responsible for the acceleration of the electrons needed to produce the radio emission of the magnetized filaments .
"Until now, these huge bubbles were masked by the extremely bright radiation emitted by the center of the galaxy," said the co-author, Dr. Fernando Camilo, astronomer at SARAO.
"With this unexpected discovery, we are witnessing the Milky Way to a new manifestation of flow of matter and energy on the scale of the galaxy, ruled by Sagittarius A *."
The results were published in the journal Nature.
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I. Heywood et al. 2019. Inflation of bipolar radio waves of 430 parsecs in the galactic center by an energy event. Nature 573: 235-237; doi: 10.1038 / s41586-019-1532-5
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