Distant dead star shows ‘signs of life’ and sends out repeated flares, scientists say

A distant star died – and then went on to send out “signs of life” in the form of repeated, energetic flares, scientists have said.

Nothing of the kind has ever been seen before and researchers are still unsure about the mechanisms that would allow such a zombie star to continue to send out bright, brief flashes of light.

The flares continued over the course of several months, each lasting for just a few minutes but staying as bright as the star’s original explosion even 100 days later, the researchers say. Those scientists had been by looking for a particular kind of stellar explosion – known as a luminous fast blue optical transient, or LFBOT – but found something else in its wake.

Now scientists believe that the activity after death must be the explanation of those mysterious, extreme explosions. Researchers believe that they emerge from the corpse of the star itself, after it has died off and left behind a corpse as a black hole or neutron star.

“We don’t think anything else can make these kinds of flares,” said Anna YQ Ho, assistant professor of astronomy in the College of Arts and Sciences. “This settles years of debate about what powers this type of explosion, and reveals an unusually direct method of studying the activity of stellar corpses.”

Professor Ho wrote the software that first spotted the event in September 2022, picking it out of data taken from a facility in California. Later, in December, scientists including Professor Ho were studying the star and noticed that the star appeared to have erupted in an intensely bright spike that quickly died away.

“No one really knew what to say,” Professor Ho said. “We had never seen anything like that before – something so fast, and the brightness as strong as the original explosion months later – in any supernova or FBOT. We’d never seen that, period, in astronomy.”

Researchers then attempted to better understand the dead star by gathering colleagues, in an effort that would eventually take up more than 70 co-authors and 15 telescopes. They looked through data to make sure that the brightening had not been a mistake.

But they found that the light was coming from the star, and that it had pulsed at least 14 times in 120 days, and probably much more than that.

“Amazingly, instead of fading steadily as one would expect, the source briefly brightened again – and again, and again,” Professor Ho said. “LFBOTs are already a kind of weird, exotic event, so this was even weirder.”

In effect, the star allows scientists to look at a star as it turns into its corpse, and so could provide a way of watching that process that is usually only seen at specific times.

“Because the corpse is not just sitting there, it’s active and doing things that we can detect,” Ho said. “We think these flares could be coming from one of these newly formed corpses, which gives us a way to study their properties when they’ve just been formed.”

Scientists are still attempting to work out the processes that would cause the dead star to behave in such a way. They hope that by doing so they will not only understand the mysterious flashes but gain a better picture of how stars die and what might happen to them afterwards.

The research is described in a new paper, ‘Minutes-duration Optical Flares with Supernova Luminosities’, published in Nature.