By Olivia Johnson
The birth of a black hole is marked by not just one massive explosion but by a series of energetic blasts, according to data from the Swift space telescope.
Impression: Gamma-ray bursts are the most energetic events in the Universe
Swift has detected many huge bursts of high-energy light associated with black holes just seconds old, surprising astronomers expecting a single flare.
The data suggest new black holes may begin devouring nearby material within minutes of their formation.
The findings will be published in the journal Science in September.
Swift was designed to study fleeting but extremely intense flares of high-energy radiation called gamma-ray bursts.
These bursts appear without warning and emit millions of times more energy than anything else in the Universe, though they are typically only a few seconds to a few minutes in duration.
Astronomers believe the shorter bursts result from collisions among black holes and neutron stars. Longer, more energetic bursts accompany the creation of new black holes at the cores of dying stars.
The latter process occurs in massive stars which have exhausted their supply of nuclear fuel. Suddenly unsupported by nuclear power, the central region rapidly collapses under the force of gravity to form a black hole.
It is this collapse which generates the extremely energetic gamma-ray burst explosions. Afterward, the stellar death throes continue as the outer layers of the star are blown away in a spectacular supernova explosion.
Because the gamma-ray burst provides the earliest indication of which star will play host to this incredible 'fireworks' show, Swift's ability to quickly train its cameras on bursts ensure astronomers get a front-row seat.
"This star has everything going on at once: it forms a black hole, has a gamma-ray burst, and then a supernova," explains Professor Paul O'Brien, of the University of Leicester, UK, who is a member of the research team. "For astronomers it's the most interesting place in the Universe," he told the BBC News website.
The new data make it all the more interesting because they show for the first time that subsequent blasts of high-energy X-ray light follow rapidly after the initial burst.
"What we had seen primarily in the past was we'd have a bright flash of high-energy radiation and then it would just fade away gradually," says Professor David Burrows, of Pennsylvania State University, US, who leads the team.
"What we're seeing with Swift is a lot of cases where they brighten up again, sometimes three or four times."
The Swift space telescope takes aim at newborn black holes
Most surprisingly, the energy in these "late-time" flares is extremely significant, the scientists report; in one case matching that released in the original gamma-ray burst.
"None of this was realised before simply because we couldn't get to the scene of the explosion fast enough," said Dr Neil Gehrels of the US space agency's (Nasa) Goddard Space Flight Center, who is the principle investigator on the Swift observatory.
Baby's first meal?
Though detailed understanding of the new data will take time, researchers believe they indicate early activity on the part of the newborn black hole.
"The newly formed black hole immediately gets to work," says Professor Pete Meszaros, of Penn State, who heads the Swift theory team. "We aren't clear of the details yet, but it appears to be messy."
One explanation, say the scientists, is that the black hole begins consuming material around it in fits and starts within minutes of its creation.
"The black hole is unable to eat all of the available fuel in one go, so instead it digests it over a few minutes," says Professor O'Brien, explaining the model. "It's a bit like feeding a baby - sometimes it takes big mouthfuls and sometimes little ones."
Another theory is the material shooting away from the dead star starts to fall back on to itself - in the process heating up enough to produce X-ray light.