The flash arrived in our skies in May this year, when NASA’s Neil Gehrels Swift Observatory picked up an unexpected source of gamma rays from a distant galaxy. The event quickly caught the attention of the scientific community and telescopes, including Hubble, were pointed at the source of the gamma-ray burst. Initial observations revealed an event that had unleashed more energy in the space of half-a-second than our Sun will ever produce in its 10-billion-year lifespan.
And the astronomers who made the initial observations were baffled – Hubble had detected 10 times more infrared light in the flash than predicted.
Right off the bat, it appeared as though something unexpected has happened far across the Universe.
A theory was put forward to suggest astronomers had witnessed the aftermath of two neutron stars colliding.
And in this case, the head-on collisions may have given birth to a highly magnetised star known as a magnetar.
Study leader Wen-fai Fong of Northwestern University in Evanston, Illinois, said: “These observations do not fit traditional explanations for short gamma-ray bursts.
“Given what we know about the radio and X-rays from this blast, it just doesn’t match up.
“The near-infrared emission that we’re finding with Hubble is way too bright.
“In terms of trying to fit the puzzle pieces of this gamma-ray burst together, one puzzle piece is not fitting correctly.”
Dr Fong added: “It’s amazing to me that after 10 years of studying the same type of phenomenon, we can discover unprecedented behaviour like this.
“It just reveals the diversity of explosions that the Universe is capable of producing.”
Gamma-ray bursts are among the most energetic and explosive events in the Cosmos.
Astronomers divide them into two categories based on their duration: long gamma-ray bursts if they are longer than two seconds and short bursts if they last less than two seconds.
Long gamma-ray bursts are typically associated with the collapse of a massive star and are accompanied by a supernova.
The shorter type is believed to be caused by two neutron stars – the dense, collapsed cores of supergiant stars – colliding.
And although these events are very rare, astronomers speculate neutron stars mergers result in the birth of a black hole.
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This is because these cores are so dense, just a spoonful of their material would weigh billions of tons on Earth.
Astronomers also expect short gamma-ray bursts to be accompanied by kilonovas – the visual and infrared glow from the radioactive decay of heavy elements that is 1,000 times brighter than a regular nova.
In this case, however, Dr Fong and her team speculate an unexpected celestial body may have been born from the merger.
The researchers proposed the neutron stars collided into a magnetar or a star supermassive neutron star with an extremely powerful magnetic field.
Co-investigator Tanmoy Laskar of the University of Bath, UK, said: “You basically have these magnetic field lines that are anchored to the star that are whipping around at about a thousand times a second, and this produces a magnetized wind.
“These spinning field lines extract the rotational energy of the neutron star formed in the merger, and deposit that energy into the ejecta from the blast, causing the material to glow even brighter.”
If a magnetar is to blame for the additional brightness, the theory will be tested in within a few years when astronomers expect light from the event to appear at radio wavelengths.
Dr Fong said: “With its amazing sensitivity at near-infrared wavelengths, Hubble really sealed the deal with this burst.
“Amazingly, Hubble was able to take an image only three days after the burst.”
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