A group of scientists led by Simone Scaringi, from the University of Durham, announced on the 20th of this month the discovery of a new astronomical phenomenon: micronovae. The study was published in the journal Nature.
Starbursts are old acquaintances to astronomers. Perhaps supernovas are the most famous; they happen when a very large star, about 10 times the mass of the Sun or more, stops generating energy. Unable to support their own weight, they collapse on themselves, generating an explosion capable of dazzling the light of all the galaxies they inhabit.
Lesser known, but more frequent, are the new ones. In this case, a completely different phenomenon is responsible: white dwarfs, very compact objects, begin to steal gas from another star that is very close, accumulating on the white dwarf’s surface.
This gas then begins to heat up, warmed by the high temperature of the “vampire” star. After some time, this can lead to the hydrogen atoms starting to carry out the fusion process into helium, producing an energetic emission that can last for a few weeks, causing the star to shine 10,000 times brighter during that time.
Now, Scaringi’s team has studied observations from the TESS space telescope and found some objects that have increased in brightness by “only” a factor of 10, and only for a few hours.
According to scientists, the phenomenon can be explained in a similar way to the new ones already known. The difference is that the gas is not distributed around the white dwarf, like a new atmosphere, but along a confined magnetic field.
It’s as if the white dwarf’s magnetism traps the gas in an invisible pipe, a filament along which material is stolen from the companion star.
Thus, the amount of hydrogen that fuses into helium is much less, generating 1 million times less energy than a nova normal. Still, make no mistake: it’s the equivalent of a hundred billion skyscrapers burning down in a few hours.
The great challenge of the work, according to the authors, is to catch the micronova “in the act”. After all, with timescales of a few hours, it is not easy to observe the object during energetic emission. You have to be looking at the right place at the right time, a complicated logistical problem for telescopes.
Still, now that we know that micronovas exist, we can think about observation plans, such as more specific monitoring of white dwarfs.
The group is already thinking about how to find more similar events, making use of rapid responses in telescopes as soon as a new signal is found.