What’s a micronova? Astronomers discover a powerful new type of cosmic explosion!

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DURHAM, United Kingdom — Many astronomy fans probably know what a supernova is, but a new study is now revealing a new kind of stellar explosion — a micronova. Don’t let the name fool you, researchers say this cosmic eruption still burns through enough stellar dust to fill 3.5 billion Great Pyramids of Giza!

Astronomers spotted the phenomenon on the surface of three white dwarfs as they fed on hydrogen and other materials from their companion stars. White dwarfs are the remnants of dead stars which have exhausted all of their fuel.

The explosions last for just a few hours, rapidly burning through huge amounts of stellar material. These events could be commonplace throughout the universe but are extremely difficult to observe. An international team stumbled on them after noticing a brief, bright, flash of light while analyzing data from NASA’s Transiting Exoplanet Survey Satellite (TESS).

Two of the explosions took place on the surface of known white dwarfs. The third required more observations using an instrument on the European Southern Observatory’s (ESO) Very Large Telescope (VLT).

“We have discovered and identified for the first time what we are calling a micronova,” explains Simone Scaringi, an astronomer at Durham University, in a media release. “The phenomenon challenges our understanding of how thermonuclear explosions in stars occur. We thought we knew this, but this discovery proposes a totally new way to achieve them.”

“It just goes to show how dynamic the Universe is. These events may actually be quite common, but because they are so fast they are difficult to catch in action,” Scaringi adds.

What’s the difference between a micro and supernova?

Despite their immense force, micronovae are small on an astronomical scale in comparison to novae and supernovae — which are extremely bright and visible to astronomers for centuries. There are numerous accounts across history of “new stars” appearing in the sky, which scientists now call novae.

In novae, this thermonuclear explosion occurs over the entire surface. The intensely bright light is visible for weeks. A supernova, on the other hand, is so energetic that they burn the entire white dwarf. Both types occur on white dwarfs with a mass similar to that of our Sun, even though the actual star is as small as the Earth in size.

White dwarfs can steal material, mostly hydrogen, from their companion stars if they are close enough. As the hydrogen falls towards the very hot surface of the dwarf star, its atoms fuse into helium in very explosive fashion.

This artist’s impression shows a two-star system, with a white dwarf (in the foreground) and a companion star (in the background), where micronovae may occur. The white dwarf steals materials from its companion, which is funneled towards its poles. As the material falls on the hot surface of the white dwarf, it triggers a micronova explosion, contained at one of the star’s poles. (Credit: Mark Garlick)

‘One millionth of the strength of a nova’

Researchers say micronovae occur on some white dwarfs with strong magnetic fields which funnel material towards the star’s magnetic poles.

“For the first time, we have now seen that hydrogen fusion can also happen in a localized way. The hydrogen fuel can be contained at the base of the magnetic poles of some white dwarfs, so that fusion only happens at these magnetic poles,” says co-study author Paul Groot, an astronomer at Radboud University in the Netherlands.

“This leads to micro-fusion bombs going off, which have about one millionth of the strength of a nova explosion, hence the name micronova,” Groot continues.

The researchers now want to capture more of these elusive events. This will require large-scale surveys and quick follow-up measurements.

“Rapid response from telescopes such as the VLT or ESO’s New Technology Telescope and the suite of available instruments will allow us to unravel in more detail what these mysterious micronovae are,” Scaringi concludes.

The findings are published in the journal Nature.

South West News Service writer Mark Waghorn contributed to this report.

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