Astronomers discover flashes of micronovae

With the help of the Very Large Telescope of the European Southern Observatory (VLT ESO), astronomers observed a new type of stellar explosions — a micronova flashes. In the course of each such event occurring on the surface of some stars, an amount of matter equivalent to about 3.5 billion of the Great Pyramids of Giza is burned in just a few hours.

What is a micronova

By human standards, micronovae are very powerful explosive events, but on an astronomical scale, they are still not very noticeable. Their flashes lead to the release of a much smaller amount of energy compared to the explosions of micronovae familiar to astronomers. Both processes are united by the fact that they occur in white dwarfs — dead stars with masses about the same as the Sun, but comparable in size to the Earth.

Micronova in the artist’s image. Source: ESO/M. Kornmesser, L. Calçada

A white dwarf in a binary system can take away matter (mainly hydrogen) from its companion star, if both objects are located close enough to each other. When the gas falls on the very hot surface of a white dwarf, the hydrogen nuclei merge into helium, which is accompanied by the release of explosive energy. When a nova flashes, these thermonuclear explosions cover the entire surface of the star, causing it to glow brightly for several weeks.

Similar explosions occur in the case of micronovae, but on a smaller scale and faster – in just a few hours. They are observed on some white dwarfs that have a strong magnetic field that directs the flows of matter to the magnetic poles of the star. It is there that the nuclear burning of hydrogen takes place. The power of these explosions is approximately one millionth of the energy of the nova flash. Hence, the name micronova.

At the same time, although the prefix “micro” indicates a small scale of events, it should be borne in mind that with each of these flashed, about 20,000,000 trillion kilograms of matter are burned. This is equivalent to about 3.5 billion of the Great Pyramids of Giza.

Discovery of Micronovae

Astronomers first noticed micro-explosions lasting several hours while analyzing data obtained by the TESS (Transiting Exoplanet Survey Satellite), which was launched by NASA to search for exoplanets. In total, the researchers found three micronovae. Two flashes occurred on known white dwarfs, but in order to confirm the status of a white dwarf for the star on which the third flash occurred, additional observations had to be made with the X-shooter receiver mounted on the VLT. Subsequently, they were able to confirm that all the events were generated by white dwarfs.

Micronova in the artist’s image. Source: Mark Garlick

The discovery of micronovae is an important addition to the “gallery” of explosive events associated with stars. Now astronomers plan to “catch” other equally elusive phenomena, which will require large-scale surveys of the sky and rapid measurements of detected flashes.

According to