The centre of our galaxy is full of hundreds of strange threads of hot gas, which may have formed due to an outburst from Sagittarius A*, the Milky Way’s resident supermassive black hole.
Farhad Yusef-Zadeh at Northwestern University in Illinois and his colleagues found these filaments using data from the MeerKAT radio telescope in South Africa. In the 1980s, Yusef-Zadeh discovered a set of vertical filaments aligned perpendicular to the disc of the galaxy, but the newfound horizontal filaments were completely unexpected.
“The vertical filaments are aligned with the galaxy’s magnetic field, but the rest should be randomly aligned,” he says. “The pattern that I saw caught me by surprise – at first, I didn’t believe it.”
While the vertical filaments measured up to 150 light years tall, the horizontal ones are only 5 to 10 light years long, all pointing towards Sagittarius A*. These horizontal filaments seem to be made of gas, unlike the vertical filaments, which are most likely made up of high-energy electrons. They also seem to be moving away from Sagittarius A*, towards the outer areas of the galaxy where Earth sits.
The orientations of the filaments and their motion indicate that they may have formed when a jet blasted out of Sagittarius A*, stretching any gas the jet passed through into tendrils. Their positions relatively close to the black hole indicate it is most likely this outburst began about 6 million years ago and may still be going on, albeit with a much lower intensity now.
There have been some hints from studies of the area right next to Sagittarius A* that such an outburst occurred, but they have not been confirmed yet. “We really want to piece together these larger-scale structures with the smaller scale around the black hole and show that there really is this jet coming out along the disc of the galaxy,” says Yusef-Zadeh. “That could have really profound implications on our understanding of the spin axis of the black hole.”
It could mean that Sagittarius A*’s spin axis is perpendicular to that of the galaxy as a whole, which would be an important clue as to how our galaxy formed and how it interacts with its central black hole now.