A team of astronomers from the Massachusetts Institute of Technology and the Kavli Institute for Astrophysics and Space Research reported the disappearance of a huge star in the Andromeda Galaxy. It could directly turn into a black hole, bypassing the supernova explosion stage. The study is published on the arXiv preprint server.
How big stars die
Giant stars, whose mass is eight or more times that of the sun, usually end their lives with a dazzling fireworks show called a supernova explosion. During such an event, more energy is released than the Sun produces in its entire lifetime. Supernovae are so bright that they can outshine the galaxies in which they are located.
As for the dying star itself, a part of its enriched heavy element envelope is dispersed throughout the galaxy and subsequently becomes part of other luminaries and planets. The core, on the other hand, collapses to form an extremely dense object — a neutron star or a black hole.
Disappearance of star in the Andromeda Galaxy
This is the usual scenario for the death of a giant star. However, as recently clarified, in some cases they can “skip” the supernova stage and directly collapse into a supernova. This may have happened to a red giant located in the Fireworks Galaxy. In 2009, it suddenly stopped being observed in the optical range.
Now astronomers have another candidate for a failed supernova, which is much closer to us — in the Andromeda Galaxy. We are talking about a star known by the designation M31-2014-DS1. In 2014, astronomers noticed an increase in its brightness in the mid-infrared range. For the next thousand days, the luminosity of M31-2014-DS1 remained constant. Then, for another thousand days between 2016 and 2019, it dimmed dramatically. In 2023, astronomers were no longer able to find M31-2014-DS1 in either the visible or near-infrared range.
Such a profile of luminosity change is uncharacteristic for variable stars and is not consistent with ordinary supernovae, which led to the conclusion of a “failed” supernova. Based on available data, astronomers have determined that the initial mass of M31-2014-DS1 was 20 times the solar mass. By the time it disappeared, it had decreased to 6.7 solar masses. A dust shell was found around the star, corresponding to an ejection of material like a supernova, but without an apparent bright flash. According to the researchers, this means that about 98 percent of the mass of M31-2014-DS1 collapsed to form a black hole with a mass of about 6.5 solar masses.
Mechanism of a failed supernova
But why did M31-2014-DS1 never become a supernova? A possible explanation has to do with neutrinos. The density of matter inside the collapsing stellar core is so great that electrons are forced to combine with protons to create neutrons and neutrinos. This process is called neutronization, and it creates a powerful neutrino burst that carries about 10% of the rest mass energy of the star. Such a burst is called a neutrino shock.
Neutrinos got their name because they are electrically neutral and rarely interact with ordinary matter. Every second, about 400 billion neutrinos from our Sun pass right through every person on Earth.
But in a dense stellar core, the density of neutrinos is so great that some of them release their energy to the matter surrounding the star. This material heats up, causing a shock wave to form, which then ejects the outer shell of the star, generating a supernova. But if, for some reason, this shock wave “stops”, the star collapses directly, forming a black hole.
Provided by Phys.org
