It is generally believed that stars much more massive than the Sun explode in a “supernova” (Type II supernova) at the end of their lives. However, in reality, the star collapses into a black hole without causing a supernova explosion at all.Complete collapseIt is believed that some stars may undergo a complete collapse.
A research team led by Alejandro Vigna-Gomez of the Max Planck Institute for Astrophysics has discovered a binary star system, in which one star may have reached complete collapse.Fifties 243By comparing observational records and model calculations, we validated the hypothesis of a complete collapse. Results,The black hole of VFTS 243 was not affected by the supernova explosion, meaning it underwent a complete collapse.We obtained results that are reasonable.
The results of this study show that VFTS 243 can be useful as a model case for exploring the interior of supernova explosions, where the actual situation is not well understood.
■Complete collapse of the star without a supernova explosion
Massive stars with a mass more than eight times the mass of the Sun are thought to come to an end through a very dramatic energy release phenomenon called a “supernova explosion.” At this time, it leaves behind a “neutron star” or “black hole” at the center of the explosion, and sometimes a neutron star or black hole is created that moves at enormous speeds ranging from 100 to 1000 kilometers per second. . It is thought that the reason a celestial body with a mass several times the mass of the Sun moves at such a high speed is that it obtains kinetic energy by being expelled through an asymmetric, biased explosion. This phenomenon is described as “Birth kick(Birth kick).
On the other hand, there is a hypothesis that not all massive stars necessarily explode as supernovas, and that some stars may collapse directly without causing an explosion. “Complete collapse」(※)In this scenario, the star collapses into a black hole with a simple explosion. In this case, birth kicks are unlikely to occur.
*…This type of phenomenon is sometimes referred to as a “direct collapse” or a “failed supernova.” However, these terms may mean different phenomena, so be careful of the context.
Whether or not stars actually undergo complete collapse is one of the major debates in astronomy. There are several candidates for black holes that are born from complete collapse, but one that is attracting particular interest is a binary star system called VFTS 243 that was discovered in 2022. This binary star system, located in the Large Magellanic Cloud at a distance of about 160,000 light-years from Earth, from one star with a mass of about 25.0 times the mass of the Sun and the other a black hole with a mass of about 10.1 times the mass of the Sun. The sun is believed to be composed of.
From the observation results, the black hole's orbit is almost circular (orbital eccentricity 0.017±0.012), and the radius of the orbit has also been measured to be very small, leading to the theory that the black hole VFTS 243 was born through complete collapse. If a supernova explosion occurred in a binary star system, not only would the black hole be expelled by the birth kick, but the star would also move due to the impact of the explosion. In other words, if a black hole was born in an ordinary supernova explosion, the probability that it would have a nearly circular orbit with a radius as small as the one observed would be very low.
Related item
・Newly discovered black hole that may have formed directly from a collapsed star (July 21, 2022)
■ The black hole of VFTS 243 was created by complete collapse
The Vigna-Gómez research team ran simulations to confirm whether the black hole in VFTS 243 was indeed born through complete collapse. The research team assumed different values for the parameters of the binary star's orbit before the explosion, the force of the birth kick resulting from the explosion, the mass lost when it is converted into energy, and calculated the expected orbit after the explosion. We looked for scenarios in which the actual observed values were closest.
Results,The most plausible scenario to explain the orbit of VFTS 243 is that there was almost no supernova explosion or birth kick.The simulation result is obtained. In this study, the black hole of VFTS 243 is thought to receive a birth kick at most 4 km/s, which is several orders of magnitude slower than a normal birth kick.
In the case of VFTS 243, all the energy from the supernova explosion is thought to have escaped in the form of elementary particles called “neutrinos.” If there were matter other than neutrinos (ordinary matter like protons and neutrons) the birth kick would be very large. On the other hand, neutrinos, also known as “ghost particles,” are elementary particles that barely interact with other matter, so they can explain their extremely small birth kicks.
■ Clues to solve the mystery of supernova explosions in general
While this research strongly supports the idea that the black hole in VFTS 243 could have been created by complete collapse without a supernova explosion, it only sheds light on one aspect of the final stages of a massive star.
It is known that the neutrinos emitted immediately before the explosion represent most of the energy released in the supernova explosion. Neutrinos, which are “ghost particles,” often collide with matter in very dense environments such as the center of a star just before the explosion, and the shock waves generated at that time may also increase the energy of the explosion. However, there is no suitable environment to simulate such an extreme environment, and there are many mysteries regarding the amount of neutrinos generated and their collisions with matter.
However, this study shows that the black hole of VFTS 243 was born through complete collapse, and that a star with a mass of about 10 times the mass of the Sun is capable of complete collapse. This can be said to be a major achievement in astrophysical research. If further research narrows down the circumstances, we may be able to find clues to solve the mystery of supernova explosions in general, not just complete collapse.
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Text / Riri Ayaka Editing / sorae editorial department
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