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Supernova Remnant That Takes Up More Of The Sky Than Most Constellations Revealed

author

Stephen Luntz

author

Stephen Luntz

Freelance Writer

Stephen has a science degree with a major in physics, an arts degree with majors in English Literature and History and Philosophy of Science and a Graduate Diploma in Science Communication.

Freelance Writer

Hoinga SNR

The supernova remnant known as Hoinga is the largest ever found through X-Ray telescopes first, and radio telescopes later. It is just one of three giant supernova remnants announced nearly simultaneously found far from the plane of the galaxy. Image Credit: SRG /eROSITA

Astronomers have, almost simultaneously, announced the largest supernova remnant (SNR) ever found, as seen from Earth, and the largest one ever detected by X-ray source. Besides being their immense size, both were discovered outside the places we have previously searched for the remains of stellar explosions, suggesting we've been looking in the wrong places.

Earlier this week astronomers announced the discovery of a supernova remnant they called Hoinga using the eROSITA X-ray telescope. Despite being 1,500-4,000 light-years away, it takes up an area 90 times the size of the full Moon in the sky being approximately 4º across. “If you could see it in the skies people would freak out,” Dr Natasha Hurley-Walker of Curtin University told IFLScience. “But fortunately it's only visible in X-rays and radio waves.”

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A handful of supernova remnants discovered by radio astronomy were already known to be larger, but even these are dwarfed by the Antlia nebula. At 20º by 26º this giant takes up around 2,000 times as much of the sky as the Moon, making it larger than most constellations, including the one it is named after. Antlia was discovered in 2002 by Dr Peter McCullough of the Space Telescope Science Institute, who suspected it was a supernova remnant but couldn't prove it. Now Professor Robert Fesen and co-authors have submitted what they claim is the missing proof in a preprint paper accepted to The Astrophysical Journal. The same paper also provides evidence the 11º × 14º G354-33 nebula is another SNR.

“They’ve done good work,” McCullough told ScienceNews. “This is a case where it looks like a duck, quacks like a duck, walks like a duck, and now someone else 20 years later comes along and says, `Not only that, it has feathers.’”

To achieve such apparent sizes SNRs need to be relatively close, and also quite old, since they expand with time, seeding large portions of the galaxy with the elements formed in the initial explosion. How far this expansion gets before the SNR becomes too cool to detect depends on the density of the interstellar medium its gasses have to push through.

The fact all three of these SNRs were located more than 10º away from the plane as seen from Earth, 24.5º for Hoinga, probably contributes to their size, and may resolve a mystery that has been increasingly bothering astronomers.

Both the Antlia and G354-33 supernova remnants lie well above and below the galactic plane. Areas in black have been surveyed by the Galaxy Evolution Explorer. Fesen et al/The Astrophysical Journal

Based on the number of supernovae a galaxy the size of the Milky Way should produce each century, and the period SNRs last before fading away, 1,200 remnants should be visible in the galaxy, but only 300 have been found. Almost all SNR searches have been conducted in the galactic plane, where most stars large enough to end their lives as supernovas lie.

If many SNRs are far enough off the plane to evade these searchers it would explain the previous undercount, but raise questions about how they got there. The announcement of three so close together suggests there are plenty more, and Hurley-Walker told IFLScience she knows of a third team with another recent high galactic latitude discovery.

Hurley-Walker added young SNRs look different depending on the type of supernova that made them. However, after 500 years (0.5 percent of an SNR’s lifespan) the gas bubble produced by a collapsing giant star looks the same as the one resulting from a white dwarf pulling enough material off a companion to explode. Only the presence of a neutron star or black hole can distinguish the two events, and these can be very hard to find.


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