Bursts of radio from across the universe
Now for a slightly different type of signal. We've mostly focused on single stars or planetary systems so far, but Fast Radio Bursts (FRBs) are coming from all across the sky – and we don't know what's causing them.
FRBs are short but intense bursts of radio energy, lasting for thousandths of a second. They seem to be coming from outside the Milky Way, and we have found a few dozen. One has been seen to repeat, while others disappear as quickly as they appear. They are incredibly powerful too, with some appearing to travel billions of lightyears to reach us.
At the moment, our best ideas are that these may be the result of neutron stars or black holes merging. We are now in a new era of gravitational wave astronomy, where we are actually able to detect such events. Maybe one will yield an accompanying FRB. Alternatively, they may be caused by a neutron star collapsing into a black hole, releasing a burst of gravity.
Of course, there is one other option: aliens. In 2017, astronomers Manasvi Lingam and Avi Loeb suggested these bursts could be the result of extraterrestrial beams powering alien space ships, firing powerful lasers into sails to propel forwards. This theory is anything but accepted – Lingam and Loeb say it is just a thought experiment.
Their calculations, however, suggest it is at least hypothetically possible. So while we await a true answer to what FRBs really are, this one can't be completely ruled out.