After the supernovae, here are the micronovae!

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After the supernovae, here the micronovae!

Artistic illustration of a two-star system where micronovae can occur

A hitherto unknown type of stellar explosion has been detected using the Very Large Telescope (TGT) of the European Southern Observatory (ESO), located in the Atacama Desert , in northern Chile.

We have discovered and identified for the first time what we call a micronova, said in a press release Simone Scaringi, astronomer at the University of Durham , UK, and one of the authors of this work, published in the journal Nature.

Like supernovae, micronovae are extremely powerful explosions that occur on the surface of stars at the end of their lives, called white dwarfs.

In a two-star system, a white dwarf can steal material from its companion star if they are close enough. When this gas falls on the very hot surface of the white dwarf, it triggers the fusion of hydrogen atoms into helium. It's the explosion.

Artistic illustration of what a supernova looks like

In the case of supernovae, these thermonuclear explosions occur all over the surface stellar. Such explosions cause the entire surface of the white dwarf to burn and glow for several weeks, says Nathalie Degenaar, an astronomer at the University of Amsterdam, Netherlands, and co-author of the study.

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Micronovae are similar but smaller-scale (and faster) explosions that occur on certain white dwarfs that have very strong magnetic fields that funnel matter toward the magnetic poles of the star.

“For the first time, we have seen that hydrogen fusion can also occur in a localized way. Hydrogen may be contained at the base of the magnetic poles of some white dwarfs, so fusion only occurs at these magnetic poles.

—Paul Groot, astronomer at Radboud University, Netherlands, and co-author of the study

Artistic illustration showing a two-star system, with a white dwarf (foreground) and a companion star (background), where micronovae can occur. The white dwarf steals material from its companion, which is funneled to its poles. As it falls on the hot surface of the white dwarf, the material triggers a micronova explosion, contained at one of the star's poles.

This leads to the explosion. explosion of microfusion bombs, which have about one millionth the force of a nova explosion, hence the name “micronova”, adds Paul Groot.

It should be noted that the use of the term micro is very relative, since only one of these explosions can burn approximately 20,000,000 billion kilograms of matter, which is equivalent to some 3.5 billion Cheops pyramids of stellar matter. in just a few hours.

The existence of micronovae suggests that stellar explosions would be more abundant than previously thought.

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“It shows how dynamic the Universe is. These events would be fairly common, but because they're so quick, they're hard to capture in action.

— Simone Scaringi

The first three micronovae have been detected in data collected by the US Space Agency's Transiting Exoplanet Survey Satellite (TESS) ( NASA).

We discovered something unusual there: a bright flash of optical light that lasted for a few hours. Looking further, we found several similar signals, explains Nathalie Degenaar.

Scientists then used ESO's TGT to confirm that these three optical flashes were produced by white dwarfs.

“This observation was crucial for the interpretation of our result and for the discovery of micronovae. »

—Simone Scaringi

In the coming months, the team wants to observe more of these stellar events. To achieve this, large-scale soundings and rapid tracking measurements will have to be used.

The following video shows an animation of a micronova explosion. The blue disk swirling around the white dwarf in the center of the image is made of material, mostly hydrogen, stolen from its companion star. Towards the center of the disc, the white dwarf uses its powerful magnetic fields to funnel hydrogen towards its poles. When matter falls on the hot surface of the star, it triggers a micronova explosion, contained by the magnetic fields at one of the poles of the white dwarf.

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