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A new type of stellar explosion: there are microns!

As Futura has already explained, especially in the file, it was at the end of the 16th century that astronomers Tycho Brahe and Johaness Kepler introduced the term nova stella, which means “new star” in Latin. In fact, this was necessary after the temporary appearance of new stars in the celestial vault, stars that were not mentioned in any of the star catalogs inherited from Greek science. But it was not until the development of astrophysics in the 20th century that, thanks to the work of Walter Baade and Fritz Zwicky during the 1930s, we began to understand what was behind these strange phenomena and to distinguish between novae and supernovae. then the first now famous supernova subclasses, SN I and SN II of the famous classification proposed by the German astronomer Rudolph Minkowski and Fritz Zwicky, the famous and bubbling Swiss astronomer, were also discovered.

But let’s go back to the initial dichotomy of “nove stellae”.

Sample from Du Big Bang au Vivant (ECP Productions, 2010). Jean-Pierre Luminet talks about the evolution of solar-type stars, their transformation into a red giant and subsequently into a white dwarf. © Jean-Pierre Luminet

Classic novae, recurring explosions in the binary system

So today we know that, unlike supernovae, new ones are explosions that do not (or rarely) destroy the parent star or create a neutron star or black hole. In the case of Nova, it all starts with a white dwarf in a binary system that accretes hydrogen from its companion star until surface pressure and temperature are sufficient to trigger a fusion reaction, an explosive thermonuclear. Recall that the white dwarf is a star corpse, which is the ultimate fate of all stars containing less than 8 solar masses. In this state, our Sun will end up as a hyper-dense star containing its mass in a volume the size of Earth, described by quantum and relativistic effects.

When a nova occurs, the luminosity of the white dwarf then multiplies by 10,000 for several days. The process can be repeated: for example, we know that RS Ophiuchi exploded six times a century. So the novae are recurring because, as we said, the explosion of the white dwarf will not destroy.

Today, the new bestiary has just been expanded following a publication in the journal Nature by a team of astronomers who observed a new type of star with the help of the Very Large Telescope of the European Southern Observatory (ESO’s VLT). an explosion that scientists have called microns. They occur as their relatives with the white dwarfs, who add material from the star to the binary system.

As Nathalie Degenaar, an astronomer at the University of Amsterdam in the Netherlands, explains in an ESO press release, it was thanks to the Transiting Exoplanet Survey Satellite (Tess) that it all started for her and her colleagues. ” something unusual: a bright flash of optical light that lasted several hours. In the next search, we found several similar signals. Tess revealed three more microns, two of which were clearly associated with the white dwarfs, but the X-shooter on the ESO VLT had to be used to determine the origin of the third explosion and confirm that a white dwarf was involved there as well.

Astronomers have discovered a new type of explosion occurring on white dwarfs in two-star systems. This video summarizes the discovery. To get a fairly accurate French translation, click on the white rectangle at the bottom right. Then English subtitles should appear. Then click on the matrix to the right of the rectangle, then on “Subtitles” and finally on “Automatically translate”. Select “French”. © ESO

Misunderstood thermonuclear explosions

In an ESO press release, we also learn that scientists have found that the thermonuclear explosion that occurs on the surface of white dwarfs is less strong than in the classical nova, but converts to “the equivalent of the mass of 3.5 billion Giza Pyramids in energy and in a few hours. Recall that the mass of the Great Pyramid of Cheops on the Giza Plateau in Cairo is approximately 5,900,000,000 kg.

Simone Scaringi, an astronomer at Durham University in the UK who led the team that discovered the microns: We thought we knew, but this discovery offers a whole new way to do it. Nature’s co-author, Nathalie Degenaar, explains that we already know that in the case of microns: “Such explosions will cause the entire surface of the white dwarf to burn and glow for weeks. However, his colleague Paul Groot, an astronomer at Radboud University in the Netherlands, states: “For the first time, we have seen that hydrogen fusion can also occur in a localized manner. Hydrogen may be present at the base of the magnetic poles of some white dwarfs, so fusion occurs only at these magnetic poles. This leads to the explosion of microfusion bombs, which have about one millionth of the power of the Nova explosion, hence the name micron. »

We still have a lot to learn about microns, which are probably more widespread than we think, which should allow for many more observations that concern them. As Simone Scaringi finally explains: “The rapid response of telescopes such as the VLT or ESO’s New Technology Telescope and the set of instruments available will allow us to discover in more detail what these mysterious microns are. »

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