An international group of scientists, including astrophysics from the Polytechnic University of Catalonia (UPC) Gloria Salahas observed, for the first time, a thermonuclear explosion of dead stars which has caused a ‘ball of fire’ with intense X-ray light radiation.
When stars like the Sun use up all their fuel, they shrink to form white dwarfs, and sometimes these dead stars come back to life in a thermonuclear explosion and produce a fireball that emits intense X-ray radiation, Sala explained.
The work, which is published today by the journal ‘Nature’, has been led by the Friedrich-Alexander-Universität Erlangen-Nürnberg in Germany, with the participation of the Max Planck Institute for Extraterrestrial Physics (MPE), the University of Tübingen and the Institute of Astrophysicist of Potsdam, in addition to Glòria Sala, researcher of the Astronomy and Astrophysics Group of the UPC and the Institute of Space Studies of Catalonia (IEEC).
Novas are unpredictable stellar explosions they apparently appear as a ‘new’ star in the sky.
The origin of this phenomenon it is found in the accumulation of material from a star of a similar size to the Sun (such as hydrogen for example) on a companion white dwarf star, a type of star that has a mass similar to that of the Sun but concentrated in a smaller celestial body. little.
The extreme conditions on the surface of the white dwarf cause the material accumulated on the surface to explode and be expelled into outer space in a huge thermonuclear explosion, which expands the material and causes an increase in the visible magnitude of the star, a moment that it can be seen from Earth as a new star in the sky.
Glòria Sala has explained that the initial phases of the explosion of a nova “theoretically they had already been foreseen: The high temperatures of the thermonuclear explosion would cause an intense and brief emission of X-rays. This is what is known as the initial ‘fireball'”.
During the days after the explosion, the expansion of the fireball causes a drop in temperature that causes it to evolve towards a large sphere of cooler gaswhich emits visible light and causes the new star to appear in the sky.
But, according to Sala, “this ‘ball of fire’ phase is very brief and occurs hours before the appearance of the star in the sky”.
Normally, detecting stars with X-ray emissions is done from satellites that are given the order to observe in the direction of the discovered source, but there are some missions that aim to map the sky: this is the case of the German X-ray telescope eROSITAdeveloped at the Max Planck Institute for Extraterrestrial Physics (MPE), traveling aboard the Russian-German Spectrum-X-Gamma mission, launched from Baikonur (Russia) on July 13, 2019.
The goal of the mission is to make a global sky map and for this it scans the entire celestial sphere every six months.
During the second sky mapping, on July 7, 2020, it detected a new extremely bright X-ray source that lasted less than eight hours.
A week later, on July 15, the light from the explosion of Nova Reticuli 2020 (YZ Ret), located at a distance of 2.5 kpc from Earth (2,500 parsecs, astronomical unit of longitude) was discovered from Earth. which corresponds approximately to three light years or 30 billion kilometers).
This made it possible to identify for the first time that the intense X-ray flash detected by eROSITA corresponded to the initial fireball of the nova explosion.
Related news
According to Sala, studying nova explosions allows to fit some of the pieces of the chemical evolution of the Galaxy and how the variety and distribution of chemical elements present in the Solar System have come to be, after the Big Bang, starting with an initial universe with a much simpler composition.
Therefore, the detection of this fireball, initially predicted by models, is a key piece to adjust the stellar explosion theoriesSala has concluded.