Astronomers might have seen a star disappear. Turning proper in direction of a black gap with out supernova

The massive stars have violent deaths. Whereas they lack hydrogen to fuse, the burden of the star squeezes its coronary heart to make it an increasing number of scorching and dense. The star fuses heavier components in a single final effort to keep away from collapsing. From carbon to silicon to iron, every step producing warmth and strain. However quickly that is now not sufficient. The fusion of even heavier components doesn’t give extra vitality to the star and the nucleus collapses rapidly. The protons and neutrons of the nuclei collide so violently that the ensuing shock wave tears the star aside. The outer layers of the star are projected outward, turning into a brilliant supernova. For a short while, the star shines greater than all of its galaxy and its core collapses right into a neutron star or a black gap. It was thought that every one massive stars resulted in a supernova, however new analysis reveals that this might not be the case.

A multi-wavelength association of the crab nebula. Credit score: (Credit score: X-ray: NASA / CXC / SAO; Optics: NASA / STScI; Infrared: NASA / JPL / Caltech; Radio: NSF / NRAO / VLA; Ultraviolet: ESA / XMM-Newton).
The proof comes from a 75 million light-year galaxy often known as the Kinman dwarf galaxy. Between 2001 and 2011, a number of teams of astronomers studied the spectra of this galaxy as a result of its metallicity is especially low. As a result of the galaxy is small and distant, astronomers can’t see the entire particular person stars, however the galactic spectra enable them to determine a few of the brilliant stars by specific emission traces. One in all them was a brilliant blue variable star.

The brilliant blue variables (LBV) are very massive stars of their time. They’ve lively, calm intervals and may shine 2.5 million occasions brighter than the solar. The sunshine traces of LBV are uncommon for a large blue star, so they’re simple to determine. Since astronomers noticed these traces within the specters of the Kinman dwarf galaxy, they knew that the galaxy contained such a star.

Line spectra of a brilliant blue variable star. Credit score: Campagnolo et al., 2017
However when new spectral measurements of the Kinman dwarf galaxy have been taken in 2019, the spectral traces of the LBV disappeared. They merely disappeared as if the star was not there. It appeared just like the star was gone. However the large blue stars don't simply disappear. They need to explode in supernova earlier than disappearing. This specific star has not change into a supernova, so one thing unusual is going on.

Picture of the Kinman dwarf galaxy, often known as PHL 293B. Credit score: NASA, ESA / Hubble, J. Andrews (U. Arizona)

Since astronomers didn’t observe the star immediately, it’s potential that the star grew to become a supernova and that we missed it. However it’s extremely unlikely. The Kinman dwarf galaxy is repeatedly noticed, and a supernova can be troublesome to overlook. It’s extra doubtless that the star will fade, and the authors of this newest analysis have some concepts why.

One thought is that the star has entered a very calm part concurrently it’s obscured by mud within the galaxy. However a second thought is extra attention-grabbing. Maybe the star suffered an uncommon core collapse, forming a black gap with out present process a supernova. There was a debate over whether or not that is potential, and this new work may very well be proof to help the thought.

However it was solely a star and never even one which was immediately imaged. It’ll take much more work to find out what actually occurred.

Reference: Allan, Andrew P., et al. "The potential disappearance of a large star within the low-metallicity galaxy PHL 293B." Royal Astronomical Society month-to-month notices 496.2 (2020): 1902-1908.

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