Astronomers discover a black hole using LT observations

Artists impression
Artists impression
Image credit: Gabriel Perez - SMM (IAC)

A group of Spanish astronomers using the Liverpool and Mercator Telescopes in La Palma have recently reported the discovery of a binary star system comprising a Be-type star and, remarkably, a black hole.

Jorge Casares of the Instituto de Astrofisica de Canarias (IAC) and La Laguna University (ULL) is lead author on a paper, recently published in the science journal Nature, in which he and his colleagues present their exciting results.

Be-type stars are known to be fast rotators, and many find themselves to be one-half of an interacting binary system. However, their companions are usually neutron stars. This is the first time that the object orbiting the Be star has been identified as a black hole.

The newly-discovered system is located in the constellation Lacerta (the Lizard), at a distance of about 8,500 light years from the Earth. Known as MWC 656, the Be star rotates with an angular velocity of more than 1 million kilometres per hour. At this speed the star is close to being ripped apart by centrifugal forces, and is ejecting matter through an equatorial disk towards its mysterious companion. Casares' new spectroscopic observations indicate that this companion is a black hole.

In all likelihood, binary systems comprising Be-type stars and black holes are far more common than previously thought. Even so, it is notable that such a discovery was made using two relatively modest-sized telescopes, the 2.0 metre LT and the 1.2 metre Mercator telescope.

1Casares J., Negueruela I., Ribo M., Ribas I., Paredes J.M., Herrero A., Simon-Diaz S., 2014, Nature, 505, 378 [links: Nature | Astro-ph].