Our galaxy continues to amaze us after an investigation into the filaments surrounding the heart of the Milky Way revealed a mysterious structure that is aligned along the galactic plane and pointing towards the galactic center.
These are most likely the remnants of a stream from the supermassive black hole Sagittarius A* interacting with the surrounding gas several million years ago, according to Northwestern University astrophysicist Farhad Yusef-Zadeh.
Although Sagittarius A* is fairly quiet now, the remnants suggest that the center of our galaxy has been active recently, on cosmic timescales. Their discovery also means that the center of our galaxy, as wild as it was already known to be, has even more fascinating secrets within.
“It was a surprise to suddenly find a new population of structures that seem to be pointing in the direction of the black hole. I was actually blown away when I saw them. We had to work hard to establish that we weren’t fooling ourselves. We found that these filaments are not random, but appear to be related to the outflow of our black hole. By studying them, we could learn more about the rotation of the black hole and the orientation of the accretion disk. It is satisfying when one finds order in the midst of a chaotic field of the core of our galaxy,” says Yusef-Zadeh, quoted by sciencealert.com.
Filaments floating around the galactic center are not a new discovery. In fact, Yusuf-Zadeh and two of his colleagues discovered in the 1980s around 1,000 long, vertical magnetic structures up to about 150 light-years long and hanging in surprisingly orderly arrangements, such as harp strings. They could be the result of wind gusts from an active supermassive black hole or turbulence in the intergalactic medium, stirred up by the motion of galaxies.
The new population was discovered in data collected by the MeerKAT radio telescope in South Africa. Yusuf-Zadeh and his team were cleaning the data, removing the background to make the vertical filaments more visible, when something else appeared. That something was a new population of galactic “harp strings,” arranged horizontally rather than vertically as researchers had previously observed.
The mysteries with which our galaxy continues to surprise us
The new structures are more like dashes than lines: short, hundreds of structures about 5 to 10 light-years long and lying horizontally across the galactic plane, rather than vertically like the other filaments. Although all the structures are magnetized, the vertical ones accelerate particles to near the speed of light, while the recently discovered horizontal ones appear to emit thermal radiation.
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They are also arranged radially only on one side of the galactic centre, pointing back towards Sgr A*, compared to the parallel arrangement of the vertical ones arranged around the galactic centre. This radial arrangement also appears related to the orientation of Sgr A*. It appears to indicate not only the black hole, but also a radial flow driven by the astrophysical jets that erupt from around a black hole when it is actively accreting material.
“Active,” for a supermassive black hole, means that material is falling, or accreting, onto it from a huge disk of material spiraling around it. However, not all material makes it beyond the black hole’s event horizon. A part of them is deflected and accelerated along the magnetic field lines towards the poles of the black hole, where it is launched into space at high speeds in the form of an astrophysical jet.
There are other signs that Sgr A* has fired its jets in the relatively recent past, such as giant bubbles that extend long distances above and below the galactic plane. The radial lines, according to Yusuf-Zadeh and his colleagues, could be the result of pressure produced by a jet outflow from Sgr A*.
Given that new structures seem to emerge as we build and refine the technology to detect them, we are far from knowing the full history and dynamics of our Milky Way’s center. The research was published in The Astrophysical Journal Letters.
