From across the Universe, 5.5 billion light-years away, a spread of telescopes has captured the intense flash of a brief gamma-ray burst. It's harking back to the kilonova explosion related to the star collision we detected in a very historic first back in 2017, prompting astronomers to wonder if that is what we've witnessed now.
That 2017 detection, referred to as GW 170817, was an excellent gift: a wealth of information across multiple signals to assist us to understand these events, and recognise what we're watching if one shows up again.
But there's something within the kilonova accompanying the new gamma-ray burst, called GRB 200522A, very unlike that star collision. The flash captured in near-infrared wavelengths by the Hubble Space Telescope was incredibly bright - 10 times brighter than predicted by models of star collisions.
"These observations don't fit traditional explanations for brief gamma-ray bursts," said astronomer Wen-fai Fong of Northwestern University.
"Given what we all 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 much too bright."
The light was first detected by NASA's Neil Gehrels Swift Observatory, an area telescope designed to detect gamma-ray bursts as early as possible with its Burst Alert Telescope. Once the alert came in, other space and terrestrial telescopes homed in on the burst's location.
The Very Large Array, the W.M. Keck Observatory, and therefore the Las Cumbres Observatory Global Telescope network all worked to get an electromagnetic profile of the event from radio wavelengths to X-rays. They showed that the event was a brief gamma-ray burst - a kind of blast but two seconds in duration related to merging neutron stars.
But the Hubble Space Telescope, observing in near-infrared, threw a spanner within the works.
"As the info was coming in, we were forming an image of the mechanism that was producing the sunshine we were seeing," said astronomer Tanmoy Laskar of the University of Bath within the UK.
"We had to completely change our thought process because the data that Hubble added made us realise that we had to discard our conventional thinking which there was a brand new phenomenon happening. Then we had to work out about what that meant for the physics behind these extremely energetic explosions."
The collision of two neutron stars - the collapsed cores of dead stars - may be a momentous event. Neutron stars are tiny and dense, about 1.1 to 2.5 times the mass of the Sun, but packed into a sphere just 20 kilometres (12 miles) across.
When they collide, they release an incredible amount of energy in an exceeding kilonova explosion, 1,000 times brighter than a daily nova. this is often in the middle of a burst of high-energy gamma-rays from jets of expelled material travelling at near the speed of sunshine.
The kilonova itself could be a glow in optical and infrared wavelengths produced by the nuclear reaction of heavy elements. Astronomers believe that the 2 neutron stars in GW 170817 merged to make a part. The near-infrared brightness of the GRB 200522A kilonova, the researchers believe, indicates that these two neutron stars merged to make something else: a magnetar.
Magnetars are a sort of star, but they're super weirdos, with insanely powerful magnetic fields - around 1,000 times more powerful than the common star.
"You basically have these field of force lines that are anchored to the star that is whipping around at about 1,000 times a second, and this produces a magnetised wind," Laskar said.
"These spinning field lines extract the rotational energy of the star formed within the merger, and deposit that energy into the ejecta from the blast, causing the fabric to glow even brighter."
Magnetars also are rare; only 24 are confirmed to this point within the Milky Way Galaxy. that creates it pretty tricky for us to work out how they got that way. If the 2 neutron stars related to GRB 200522A formed a magnetar, that offers us a replacement mechanism whereby these extreme stars can get being.
"We know that magnetars exist because we see them in our galaxy," Fong said.
"We think most of them are formed within the explosive deaths of massive stars, leaving these highly magnetised neutron stars behind. However, it's possible that a little fraction form in star mergers. we've got never seen evidence of that before, not to mention in infrared, making this discovery special."
It's a little early to understand obviously. only 1 kilonova up to now has been confirmed and well characterised; that, of course, is that the kilonova related to GW 170817.
But the new detection, with its near-infrared weirdness, maybe a step towards cataloguing the range possible in kilonovae and understanding the range of outcomes when two neutron stars collide.
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