The remains of a star that exploded in intergalactic space, outside the realms of any galaxy, may have been spotted by astronomers for the first time.
Many exploding stars, or supernovae, have been seen across the universe. While most reside inside galaxies, some have been seen These are known as intergalactic supernovae, and may have ended up there after the stars were thrown from their host galaxies. We have seen intergalactic supernova explosions, but never in our galactic neighbourhood, so we haven’t observed the remnant of one as it expands into the sparse gas between galaxies.
at Western Sydney University in Australia and his colleagues think they have now seen one between our Milky Way and a neighbouring galaxy called the Large Magellanic Cloud (LMC). If confirmed, this would be the “first and only intergalactic supernova remnant” known, says Filipović.
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The object, called J0624–6948, appears ring-like in shape, which is consistent with a supernova remnant, and is estimated to be about 150 light years across. Other possibilities include a superflare from a passing star inside our Milky Way, but the team favours the supernova idea. It was initially detected in 2019 using the Australian Square Kilometre Array Pathfinder while the team was hunting for other mysterious phenomena known as odd radio circles, which may result from black holes merging.
The team thinks the star that caused the supernova would have exited the LMC about 40 million years ago, before exploding between 2000 and 7000 years ago. The type of supernova would likely have been a Type 1a, where a small white dwarf star is overfed with material by a companion star.
“The circularity of this object is extraordinary,” which points to a supernova expanding unhindered into sparse intergalactic space, says Filipović. “There are no dense clouds or objects it would interact with.” He estimates up to a dozen other intergalactic supernova remnants may be discoverable in our galactic neighbourhood.
at the Netherlands Institute for Radio Astronomy, however, isn’t completely convinced that this supernova is intergalactic just yet. While the team estimates the object is 160,000 light years from our galaxy – about 10,000 light years outside the LMC – the exact distance is unknown, with its position in the sky possibly placing it in the outskirts of the LMC. “We don’t know where it is,” says Oosterloo. “It could be associated with the LMC.”
Further observations in the coming months could help resolve the matter, while continued observations in the coming years could confirm its supernova status. “If we detect a small expansion, that means we’re on the money,” says Filipović. “If it does not expand over the next 10 to 15 years, then I have no idea what this could be.”
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