At https://phys.org/news/2022-03-massive-center-milky-supermassive-black.html … the supermassive black hole thought to reside at the centre of the Milky Way galaxy is said to have started spewing out material around 2.6 million years ago. Note, million as opposed to billion in the earlier post. Therefore, fairly recently on the geological column. A study in Nature Astronomy claims Fermi Bubbles, discovered in 2010, and a haze of microwaves, otherwise described as a fog of charged particles, were formed by a jet of energy emitted by the black hole.
There are currently two explanations for the Fermi Bubbles. One is a nuclear starburst event – a star exploding in a supernova. The second one is an outpouring of material that was drived by energy thrown out by the black hole. Further, to get around the idea black holes condense material it catches, and is unable therefore to subsequently escape out of the black hole, a new theory has been devised. Outflows from black holes occur when material travels towards the black hole but does not breach the event horizon. This is the hypothetical ring around the black hole. This must not be traversed as that material would become trapped forever and ever. Some of this travelling material is said to stay outside the event horizon, and is thrown back into space. An ingenious way around the problem. In the process it creates the Fermi Bubbles.
The new study rules out the first explanation. It also claims to have fine tuned the second explanation. What is inside the Fermi Bubbles? Gamma rays, it would seem. See https://doi.org/10.1038/s41550-022-01618-x