Far out cosmology: very active Milky Way center (Introduction)

by David Turell , Friday, June 02, 2023, 18:39 (541 days ago) @ David Turell

New discoveries:

https://www.sciencealert.com/hundreds-of-mystery-structures-found-at-the-heart-of-the-m...

"An investigation into the mystery filaments hanging in space around the heart of the Milky Way has turned up an entirely new population of them, aligned along the galactic plane and pointing in the direction of the galactic center.

"The magnetized strands are likely the remnants of an outflow from the supermassive black hole Sagittarius A* interacting with the surrounding gas a few million years ago, says astrophysicist Farhad Yusef-Zadeh of Northwestern University.

"Although Sgr A* is pretty quiet now, these remnants suggest that our galaxy's center has been active recently – on cosmic timescales, that is. And their discovery also means that our galaxy's center, as wild and wooly as we already knew it to be, has more fascinating secrets lurking within.

***

"Filaments floating about the galactic center aren't a novel finding. In fact, Yusuf-Zadeh with two of his colleagues discovered them in the 1980s – around 1,000 long, vertical, magnetic structures up to around 150 light-years in length, and hanging in surprisingly orderly arrangements, like harp strings. These could be the result of winds gusting from an active supermassive black hole, or turbulence in the intergalactic medium, stirred 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 up the data, removing the background to make the vertical filaments more visible, when something else emerged.

"That something was a new population of galactic 'harp strings'.

***

"Although all of the structures are magnetized, the vertical ones accelerate particles to near light speed, while the newly discovered horizontal ones appear to emit thermal radiation.

"They're also radially arranged just on one side of the galactic center, pointing back towards Sgr A*, compared to the parallel arrangement of the vertical ones, arrayed all around the galactic center. This radial arrangement also seems linked to the orientation of Sgr A*. It seems to point, not just at the black hole, but at a radial outflow driven by the astrophysical jets that erupt from around a black hole when it is actively accreting material.

"'One of the most important implications of radial outflow that we have detected is the orientation of the accretion disk and the jet-driven outflow from Sagittarius A* along the galactic plane," Yusuf-Zadeh says.

***

"There are other signs Sgr A* fired up its jets in the relatively recent past, such as giant bubbles that extend vast distances above and below the galactic plane. The radial dashes, according to Yusuf-Zadeh and his colleagues, could be the result of ram-pressure produced by a jet-driven outflow from Sgr A*. And analysis of their extent and position suggest that this took place around 6 million years ago.

"'We think they must have originated with some kind of outflow from an activity that happened a few million years ago," Yusef-Zadeh says. "It seems to be the result of an interaction of that outflowing material with objects near it."

"Given new structures seem to be emerging as we build and refine the technology to detect them, we're far from knowing the complete history and dynamics of the center our our Milky Way."

Comment: the Milky Way is vast, very old, but its center is still acting very young