Meet micronova, a new type of localized stellar explosion!

New, Supernova, and Micronova: What’s the Difference?

Between nova, supernova and now micronova, it is not difficult to lose your footing and no longer understand anything!

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The term new star that means ” new star » in Latin it was introduced on the 16thi century to characterize the transient and sudden appearance of new stars in the celestial vault. It was only with the advent of astrophysics in the 1920si century that astronomers began to study these stellar phenomena more closely.

A nova, the plural of which is novae, characterizes a star that suddenly becomes very bright for a few days and then regains its initial luminosity. The new ones develop within binary stars and affect the white dwarf of the stellar pair. A white dwarf is an object of very high density as a result of the evolution of a star of medium mass, that is, 3 to 4 solar masses, which collapsed on itself. The term “white na” comes from its extremely high surface temperature.

In this pair of binary stars, the white dwarf attracts hydrogen from its companion star. This hydrogen accumulates on the surface of the white dwarf until a thermonuclear explosion is triggered and all the hydrogen is burned. This short-lived reaction, called new, does not destroy the white dwarf and causes an increase in the brightness of the star that can be multiplied by 10,000 for a few days. A new one can be repeated periodically. Obviously, at some point, the white dwarf may reach a critical mass leading to its destructive supernova explosion.

A supernova is the giant explosion that occurs at the end of a star’s life, leading to its complete destruction and the scattering of its matter into space. There are actually two types of supernovae. The first so-called “thermonuclear supernova” is the result of a white dwarf explosion. The second, called the “core collapse supernova,” corresponds to the expulsion of the outer layers of a massive star (at least 8 solar masses) at the end of its life. The central part of the star contracts to form a neutron star or black hole.

It is with the help of the Very Large Telescope of the European Southern Observatory of ESO that astronomers have just discovered a new type of stellar explosion, never detected before, the micronova.

The micronova, a small but extremely powerful event

Animation of a micronova. The white dwarf steals hydrogen from its companion star, which eventually forms a rotating disk of gas. The white dwarf channels this hydrogen to its poles, which can sometimes trigger a thermonuclear explosion. (Source: ESO / L. Road, M. Kornmesser)

At the astronomical scale, micronoves are small events that may even look ridiculous. However, the energy that emerges from these phenomena is colossal. Just one of these thermonuclear explosions would be enough to destroy our beautiful blue planet. When a single micronova is produced on the surface of a white dwarf, more than 20 billion tons of matter are burned.

When two stars are close enough to each other in a binary system, a white dwarf can attract matter from its companion star. Very often, it is hydrogen that is sucked in and falls to the surface of the white dwarf. When this gas touches the extremely hot surface of the white dwarf, a thermonuclear reaction of explosive fusion of hydrogen into helium occurs. In the case of a new one, this nuclear fusion reaction takes place on the entire surface of the white dwarf. Then the surface of the star begins to glow for sometimes several weeks.

The team of astronomers behind this discovery realized that micronovae are similar phenomena, but located in an area of ​​the white dwarf and that they occur more quickly. Very often these explosive phenomena do not take more than a few hours.

Astronomers have also discovered that these thermonuclear reactions take place in white dwarfs with very powerful magnetic fields so that hydrogen is channeled to the star’s magnetic pole and that the nuclear fusion reactions of hydrogen in the heli only occur there.

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A possible discovery thanks to data analysis from the TESS satellite

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NASA’s TESS satellite is intended for the study of exoplanets. The study of these data allowed to highlight the micronovals.

This amazing discovery allows us to further expand our knowledge of such powerful phenomena that are the explosions of stars within our universe. Astronomers also believe that micronovae are probably much more common than one might think. The problem is being able to capture this phenomenon at the right time, which is ultimately quite fast on an astronomical scale.

The TESS (Transiting Exoplanet Survey Satellite) launched in 2018 by NASA to focus on the search for exoplanets was a great help to the team of astronomers who discovered the micronoves. In fact, it was examining the data collected that they discovered a bright flash of optical light that lasted a few hours. Two were white dwarfs and a third required thorough observations with X-Shooter, a medium-resolution spectrograph that allows the study of gamma rays and is located in the Very Large Telescope (VLT) of ESO. The analysis confirmed that it was indeed a third white dwarf.

Researchers now want to be able to capture other events as quickly as micronoves. To do this, they must carry out rapid monitoring measures using instruments such as the VLT or the New Technology Telescope, also from ESO.

>> Read also: Death of a star: the last moments of a supernova reconstructed in 3D

Source: Scaringi, S., Groot, PJ, Knigge, C. et al.“Localized thermonuclear bursts of accreting magnetic white dwarfs”,Nature, 604, 447–450 (2022), https://doi.org/10.1038/s41586-022-04495-6

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