Astronomers discover a black hole orbiting a ‘spinning’ star for the first time

Gabriel Pérez - SMM (IAC)

Binary systems are quite common, but astronomers have just discovered one system that was previously only hypothesized: a black hole orbiting a spinning star, known as a Be star. The research was led by Jorge Casares of Astrofísica de Canarias and was published in Nature.

Black holes were first theorized in the late 18th century and were initially termed “dark stars.” Dark stars were believed to have gravity fields so strong, light was not able to escape. There are believed to be three types of black holes: miniature, supermassive, and stellar. While miniature black holes remain theoretical, supermassive black holes are likely found at the center of all galaxies with a mass millions (potentially billions) times higher than our sun. Stellar black holes are formed by the collapse of an extremely massive star and have a mass 3-100 times our sun. The first definitive proof that stellar black holes exist was provided by Casares in 1992.

There are over 80 known Be stars in our galaxy alone. They are in binary pairs, typically with a high-density neutron star. Their name denotes their spectral wavelength in the B-class, while the lowercase e is added to indicate that it has distinct emissions, whose energy transitions do not act in a way that would be expected according to the main tenets of quantum mechanics. Because Be stars spin incredibly fast, they eject a great deal of material and can form a disk around the central star. 

Casares’ team made the discovery while using the Liverpool and Marcator telescopes on the Canary Islands in Spain. They have been studying the star MWC 656 since 2010. It is located 8,500 light years away in the constellation Lacerta. The team knew it was in a binary pair with another object, but the identity of the object was not immediately clear. It was believed to have a mass up to 6.9 times the sun, making it much too massive to be a neutron star. There was also a lack of radiation that was being picked up by the telescopes, which indicated to the team that it had to be a stellar black hole. 

The black hole is likely consuming the matter kicked out by the Be star, which was determined to be spinning at over 1 million kilometers per hour (621,000 mph). The team also found that it is the black hole that is orbiting the Be star, as the star is more massive at approximately 10 solar masses.

Because there are a seemingly endless amount of stars in the sky, astronomical events that have never before been seen are never believed to be the only occurrence; it is just a matter of locating another one. Future research will seek to find other binary systems like this and will attempt to determine how they were formed.

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