What's that large, faint ring in the middle of the image above? It's the remnants of a supernova explosion that took place less than 9,000 years ago.

KEY POINTS CUT AND PASTE Key points Researchers have found 27 new supernova remnants

A radio telescope in remote Western Australia allowed them to find remnants that were bigger, older and fainter than what has been found before

Supernova remnants are like the fossils of dead stars and provide a history of where stars lived and died

Dubbed G0.1-9.7 in reference to its distance from the galactic centre of the Milky Way (0.1 degrees east and 9.7 degrees south), it would have been visible to Indigenous people across Australia at the time.

A supernova is a very rapid explosion from a star that's ended its life, said astrophysicist Natasha Hurley-Walker of Curtin University's node of the International Centre for Radio Astronomy Research, who led the team that discovered this remnant and 26 others.

They published their findings in three separate papers in the Publications of the Astronomical Society of Australia last month.

"When a star runs out of fuel, it starts to collapse downward because the radiation that would be generated from the fusion is no longer keeping it in a big sphere," Dr Hurley-Walker said.

"Then that causes a huge thermonuclear explosion which throws off a massive shell of expanding material, and that moves very quickly, thousands of kilometres per second."

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And because it's moving so fast, it's slamming into the space around it and gathering up all of the material that was lying around the star.

This slows the supernova down, and also makes it glow very brightly, Dr Hurley-Walker said.

"Typically when they explode they're very, very bright for a few days and then they get dimmer and dimmer and dimmer," she said.

"In historical records they're called guest stars, because [one] looked like a very, very, very bright star and it tended to even be visible during the day."

If you could get a front row seat to a supernova explosion, we think it would look like this:

Seen close-up, Dr Hurley-Walker thinks supernova remnants look like soap bubbles or beautiful expanding spheres.

She and her colleagues have been using Western Australia's Murchison Widefield Array (MWA) radio telescope to hunt for them, as part of the Galactic and Extragalactic All-sky MWA survey or GLEAM.

The benefits of looking for supernova remnants in the radio spectrum rather than the visible spectrum is that, while they show up in the visible spectrum for only 1,000 years or so, they can be seen in the radio for tens to hundreds of thousands of years, Dr Hurley-Walker said.

And due to the MWA's wide bandwidth — it maps the sky using radio waves between 72 and 231 megahertz — the researchers were able to see the sky in radio colour.

Dr Hurley-Walker made the lowest frequencies red, the middle frequencies green and the highest frequencies blue.

"The radio colour that we have here, the wide bandwidth, allows us to actually disentangle objects which would otherwise be completely masked by the complexity of the regions if we were looking in black and white," she said.

Use the slider below to see how an optical view of the galactic centre of the Milky Way compares to the view the MWA sees in the radio spectrum.



Optical and radio view of Milky Way Share What the galactic centre of the Milky Way looks like in the visible spectrum. Share What the galactic centre of the Milk Way looks like in the radio spectrum.

While 295 supernova remnants have already been discovered, what's special about these 27 new ones is that the MWA allowed the researchers to pick up remnants that were bigger, older and fainter than what had been found before.

And as you can see in the rogues' gallery below, the "roundish things" the team were looking for are all very different from each other.

Share The 27 newly discovered supernova remnants. G0.1-9.7 is the top left.

Visible in the radio, invisible in the infrared

G0.1-9.7 exploded in a fairly low-density part of space, Dr Hurley-Walker said.

This has meant there wouldn't have been much material around it, so it's quite faint, and it's been able to expand into space without really having very defined edges.

It's also relatively close to us, being only about 3,000 light-years away, Dr Hurley-Walker said, and there's not very much dust in between.

"When it did explode, we probably would have been able to see it.

"There are supernovae that go off in our galaxy, but we can't see them all the time because of the very, very dense dust that obscures the light so it cannot get to us."

Dr Hurley-Walker said supernovae go off in the Milky Way on average about every 200 years.

Radio and infrared view of SNR Share A 9,000-year-old supernova remnant seen in the radio spectrum. Share The same area of sky in the infrared.

And while G0.1-9.7 appears in the radio spectrum, look at the same area of the sky in the infrared and there's nothing like it there.

"That's a good thing for us," said Dr Hurley-Walker, "because it means the emission wasn't from a glowing hot object, such as a region around a bright star, as that would have shown up in both the infrared and the radio."

An archaeological record of when stars lived and died

Share The arch of the Milky Way over the Guilderton Lighthouse. Where the supernova now known as G0.1-9.7 would have been visible in the night sky when it exploded is shown.

Supernova remnants are like the fossils of dead stars, according to astrophysicist Naomi McClure-Griffiths of the Australian National University, who wasn't involved in the research.

"By finding them, we get to go back through the history of where stars lived and died in our own galaxy."

And that's important to know in order to understand why our galaxy is still alive.

But supernova remnants are actually really hard to find, she said, and we haven't yet found as many of them as we think we should.

The MWA is proving to be very good at finding supernova remnants, but its successor, the Square Kilometre Array promises to be thousands of times more sensitive and have much better resolution.

And then the hunt for supernova remnants, even on the opposite side of the Milky Way will be on in earnest.

"They're going to start popping out a lot more," Professor McClure-Griffiths said.

"And this missing-supernova-remnants problem I think will start to disappear."

Editor's note December 2, 2019: An earlier version of this story identified the wrong object in the top image as the supernova remnant. This has been corrected.