Astronomers discover a new type of star explosion: a micronova

ENGINEERINGNET.BE – A micronova is less powerful than regular novas, the starbursts that astronomers have known about for centuries. Micronovas are smaller in size and only last a few hours. Such a micronova also consumes about a millionth of the amount of ordinary supernova fuel.

Researchers have discovered micronovas in three white dwarfs. These are exhausted stars that have about the same mass as the Sun, but are as small as the Earth.

All three white dwarfs have a companion star from which they extract hydrogen. In addition, they have a strong magnetic field. Researchers believe that hydrogen gas collects at the poles due to the magnetic field. The idea is that the temperature and pressure at the poles will slowly rise until hydrogen fuses into helium, resulting in a thermonuclear explosion.

“We thought we knew how explosions happen on stars, but this finding suggests they could also start in a very different way,” said study leader Simon Scaringi, from Durham University in the UK.

The team first encountered the mysterious micro-eruptions when analyzing data from NASA’s Transiting Exoplanet Survey Satellite (TESS). “When reviewing this data, we discovered something unusual: a bright flash of light that lasted for a few hours,” said co-author Nathalie Degenar from the University of Amsterdam. “As we searched further, we found more of these signals.”

The third flash of light was also observed using TESS, but it was not yet certain whether it was a white dwarf. Follow-up observations with the X-shooter, a high-speed spectrometer jointly developed in the Netherlands for the European Very Large Telescope in Chile, confirmed the white dwarf’s condition.

“The fact that we are only now detecting such extreme events is in part because they last so short,” says co-author Paul Groot, an astronomer at Radboud University. Similar to Type I explosions in neutron star systems, but only now have we been able to establish a correlation with the TESS data.”

The team aims to capture more micronovas in the near future using a combination of long-term monitoring campaigns and rapid follow-up measurements.