Artist's
impression of colliding neutron stars. Image Credit: NOIRLab/NSF/AURA/J. da
Silva/Spaceengine |
Whenever you think you know something, Mother Nature
is ready to throw you a curve ball. Take, for example, gamma-ray bursts – brief
flashes of the most powerful light in the universe. The short-duration ones are
created in the kilonova produced by the merging of compact objects such as
neutron stars. The long-duration ones are instead created by supernovae. So,
imagine the surprise of astronomers discovering a kilonova creating a
long-duration gamma-ray burst.
This "oddball" event is known as
GRB 211211A and it originates from 1.3 billion light-years away. Different
teams observed the same events with two telescopes, the Fermi Gamma-ray Space
Telescope and the Neil Gehrels Swift Observatory, and all came to the same
conclusion that the over-50-second-long event was created by a kilonova.
“We surprisingly saw a kilonova. I say surprisingly
because we saw hundreds if not thousands of long gamma-ray bursts, and every
time we saw one there was a supernova following them,” lead author Dr Eleonora
Troja from the Università di Roma Tor Vergata, told IFLScience. “This is a
well-established knowledge. We thought we had figured out the explanation for long-duration
gamma-ray bursts.”
“This time we didn’t find any supernovae. And we
looked with the most powerful telescopes in the world, including the Hubble
Space Telescope; but did not find any sign of a supernova. Instead, we found a
kilonova,” Dr Troja explained.
So instead of the death of a star at least 10 times
the mass of the Sun, the researchers found evidence of a neutron star merging
with either another neutron star or with a stellar-sized black hole. The
catastrophic collision shreds the neutron star apart, releasing an incredible
amount of energy as a kilonova. Something that had not been seen before for
certain.
There has been a previous detection of a
supernova-less long-duration gamma-ray burst, but astronomers did not find a
kilonova behind that one. This latest detection, and the relative vicinity of
the event, has allowed us a more detailed understanding of the process.
However, the researchers remain unsure exactly how kilonovae can produce a
long-duration gamma-ray burst.
“We are still recovering from the shock,” Dr Troja
said laughingly to IFLScience. “What we know is that in most cases, neutron
star collisions can produce a gamma-ray burst of short duration, less than two
seconds long. This event taught us that in some cases they can create gamma-ray
bursts of long duration.”
Kilonovae are also the site of formation for some of
the heaviest elements in the universe, such as gold and platinum, so this
discovery means that long gamma-ray bursts can be used to study those environments
in the case of kilonovae.
The analysis of this discovery was published in four
papers in Nature, here, here, here, and here, and one in Nature Astronomy.
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