Astronomers have discovered that supermassive black holes in galaxies are firing out beams into space, and that the direction of these beams has changed over time.
This could be a result of cosmic material falling onto the black hole and altering the direction of the black hole's rotation axis.
A team of astronomers have dubbed these objects 'Death Star' black holes, because they are destructive behemoths that are rotating and firing their beams at new targets, like the Imperial space station in the Star Wars franchise.
The observations were made using NASA’s Chandra X-ray Observatory and the NSF’s Very Large Array.
X-ray data shows cavities in hot gas that mark where the black hole beams used to point, while radio data shows where they currently point.
Astronomers examined 16 galaxies with central supermassive black holes and charted the directions of the black hole beams both today and in the distant past.
It seems around a third of the black hole beams - also known as jets - have changed direction over the course of 10 million years.
The study
Images above show hot gas in the middle of galaxy cluster Abell 478 (left) and galaxy group NGC 5044 (right).
The centre of each image shows one of the 16 black holes studied, which are firing beams outwards into space.
Each black hole is in the centre of a galaxy embedded in hot gas.
The oval shapes mark cavities in the hot gas around Abell 478 and NGC 5044, which were carved out by the beams shooting out from the black holes, leaving a tell-tale sign as to the direction of those beams in the past.
The 'X' shows the location of each supermassive black hole.
Comparison of the Chandra and VLBA images shows the Abell 478 beams have changed direction by about 35° and the NGC 5044 beams have changed direction by about 70°.
In fact, across the study, the astronomers found that one third of the 16 galaxies are pointing in different directions, and some have changed direction by nearly 90°.
This has occurred over timescales between one million years and a few tens of millions of years.
Given the black holes are as old at 10 billion years, these changes are happening in the blink of a cosmic eye.
The mystery of black hole jets
Black hole jets are a well-observed phenomenon, and are caused when cosmic material gets pulled inwards by a black hole's inescapable gravity.
This material forms a spinning disc of matter, and the enormous energy involved in the process can cause black holes and their surrounding region to glow in brilliant light.
Another effect of this process is that some of the matter gets fired outwards, producing incredible jets.
The direction of the beams from each of the black holes in this study aligns with the rotation axis of the black hole.
This means the beams point along a line connecting the poles and are perpendicular to the black hole's disk.
And if material falls towards the black hole at an awkward angle, it could upset the direction of the black hole’s rotation, changing the direction of the beams.
Black hole beams and star formation
As is seen in the above images, the beams from black hole jets carve out cavities into surrounding hot gas.
This can prevent galaxies from cooling down enough to form large numbers of new stars.
So if black hole jets can change direction this quickly, it could have a huge effect on star formation within the host galaxy.
"We found that about a third of the beams are now pointing in completely different directions than before,” says Francesco Ubertosi of the University of Bologna in Italy, who led the study.
"These Death Star black holes are swivelling around and pointing at new targets, like the fictional space station in Star Wars."
The paper describing these results was published in the 20 January 2024 issue of The Astrophysical Journal.
