Astronomers unexpectedly discover a completely new phenomenon in outer space

A newly discovered type of stellar explosion could help us better understand thermonuclear explosions in dead stars.

This new phenomenon is called a micronova , and they occur on the surfaces of white dwarf stars that are actively shedding material from a close binary "companion ." The accumulation of material on the white dwarf leads to a localized thermonuclear explosion: a micronova.

" This is the first time we have discovered and identified what we call a micronova," said astrophysicist Simone Scaringi of Durham University in the UK .

Astronomers say these explosions burned tens to hundreds of kilograms of stellar material over several hours. Micronovae are a type of phenomenon that scientists have not really understood until now.

"This phenomenon challenges our understanding of how thermonuclear explosions in stars occur. We thought we knew a lot about thermonuclear explosions in stars, but this discovery suggests a completely new way of looking at things than we have traditionally understood . "

White dwarfs in close binary systems can act as thermonuclear explosives. White dwarfs are known as 'dead' stars—the collapsed cores of main-sequence stars that have run out of fuel and shed their outer material. Other stars of this type are typically in different mass classes, including neutron stars and black holes.

This collapsed core is very dense. White dwarfs have masses 1.4 times that of the Sun, packed into a sphere the size of Earth. Many of them can be found in binary systems.

In space, even the smallest explosions are incredibly powerful. A newly discovered phenomenon, the Micronova, may sound like a small explosion, but it is actually as powerful as a nuclear bomb larger than any ever created by humans.

In rare cases—about 10 have been identified in the Milky Way—binaries are close enough for the white dwarf to separate material from its companion.

As the two stars orbit each other, material — mostly hydrogen — is sucked away from the companion by the smaller, denser, more massive white dwarf. This hydrogen accumulates on the white dwarf's surface, where it heats up.

Periodically, the mass becomes so large that the pressure and temperature at the bottom of the layer are enough to trigger a thermonuclear explosion, violently expelling the excess matter into space. And micronovae are exactly the unique phenomenon that Scaringi and his team found.

Researchers have first identified a white dwarf star emitting a micronova in data from the TESS exoplanet-hunting telescope. TESS is optimized to look for tiny brightness variations in stars with exoplanets; planets passing in front of the star cause a very small dimming.

A micronova is a type of thermonuclear explosion on the surface of a white dwarf star that is much smaller than a nova; it has a power of about 1 × 10³⁹, about one millionth that of a typical nova. The phenomenon was first described in April 2022.

In the TESS data, the team detected a micronova when they saw a flash of light from a white dwarf, rather than a dim flare. This prompted a search for similar events at other white dwarfs. In total, they found three explosions — the third, after follow-up observations, led to the discovery of a previously unknown white dwarf.

So the team set out to find a scenario that could explain the observations. They found that the most likely explanation was a micronova.

When a white dwarf star has a strong magnetic field in a binary, it can pull material from its companion. The magnetic field guides this material to the poles of the white dwarf, where it accumulates, eventually causing an explosion.

Hydrogen fuel may be stored at the magnetic poles of some white dwarfs.

"For the first time, we have seen that hydrogen fusion can also occur locally," said astronomer Paul Groot of Radboud University in the Netherlands.

"Hydrogen fuel can be stored at the magnetic poles of some white dwarfs, so that fusion only occurs at these poles. This results in tiny thermonuclear bombs exploding, with about a millionth the power of the supernova explosions we know, hence the name micronova."

The discovery could solve a decades-long mystery. One of the white dwarfs, in the TV Columbae binary system, has been observed to have similar flashes for more than 40 years. The discovery suggests that the bursts may be fairly common, but astronomers will need to collect more observations to understand them better.

'It just shows how dynamic the universe is ,' Scaringi said. 'These events may actually be quite common, but because they happen so quickly, they are very difficult to observe . '