Spanish Researchers Discover the First Black Hole Orbiting a Fast-spinning Star
Spanish scientists have discovered the first binary system ever known to consist of a black hole and a fast-spinning star known as a Be-type star. Although predicted by theory, none had previously been found. The observations that led to the discovery were performed with the Liverpool and Mercator telescopes at the Observatorio del Roque de los Muchachos in the Canary Islands.
Be-type stars are quite common across the Universe. In our Galaxy alone more than 80 of them are known in binary systems together with neutron stars. "Their distinctive property is their strong centrifugal force. They rotate very fast, close to their break-up speed. It is like they were cosmic spinning tops" says Jorge Casares from the Instituto de Astrofisica de Canarias (IAC) and La Laguna University (ULL). Casares is an expert in stellar-mass black holes. He presented the first solid proof of their existence back in 1992.
The newly discovered black hole orbits the Be-type star known as MWC 656, located in the constellation Lacerta (the Lizard), 8,500 light years from Earth. The Be-type star rotates so fast that its surface speed exceeds 1 million kilometers per hour. "We started studying this star back in 2010, when space telescopes detected transient gamma-ray emission coming from its direction," explains Marc Ribo, from the Institute for Sciences of the Cosmos of the University of Barcelona (ICCUB). "No more gamma-ray emissions have subsequently been detected, but we found that the star was part of a binary system," he adds.
A detailed analysis of its spectrum allowed scientists to infer the characteristics of its companion. "It turned out to be an object with a mass between 3.8 and 6.9 solar masses. An object like that, invisible to telescopes and with such large mass, can only be a black hole, because no neutron star with more than three solar masses can exist," states Ignasi Ribas, researcher at the Institute of Space Sciences.
The black hole orbits the Be-type star and is fed by matter ejected from the latter. "The high rotation speed of the Be-type star causes matter to be ejected into an equatorial disc. This matter is attracted by the black hole and falls on to it, forming another disc called an accretion disc. By studying the emission from the accretion disc we can analyze the motion of the black hole and measure its mass," comments Ignacio Negueruela, researcher at the University of Alicante.
Scientists believe this object to be a nearby member of a hidden population of Be-type stars paired with black holes. "We think these systems are much more common than previously thought, but they are difficult to detect because their black holes are fed from gas ejected by Be-type stars without producing much radiation, in a silent way," Casares adds. Experts hope to detect other similar binary systems in the Milky Way and other nearby galaxies by using bigger telescopes, such as the Gran Telescopio Canarias (GTC).
Also participating in the study with Jorge Casares, Ignacio Negueruela, Marc Ribo and Ignasi Ribas are Jose M. Paredes, from the Institute for Scinces of the Cosmos of the University of Barcelona, and Artemio Herrero and Sergio Simon, both from IAC and ULL. ICCUB and ICE researchers are also members of the Institute for Space Studies of Catalonia.
Animation of the system MWC 656. The Be-type star spins at an extremely high speed, ejecting matter through an equatorial disc. Part of this matter falls on to the black hole forming an accretion disc. (Animation Credit: Gabriel Perez - SMM, IAC).
The detection of black holes has been a challenge since their existence was first surmised by John Michell and Pierre Laplace in the 18th century. Given that they are invisible, since their enormous gravitational force prevents light from escaping, telescopes cannot detect them. However, black holes can occasionally trigger high energy radiation from the environment surrounding them and can thus be traced by X-ray satellites. This is the case with active black holes that are fed by matter transferred from a nearby star. If violent X-ray emission is detected from a place where nothing but a normal star is seen, a black hole might be hiding there.
Thanks to this method, researchers have discovered fifty-five potential black holes over the last fifty years. Seventeen of them have what astronomers call a "dynamic confirmation," that is, the feeding star has been localized, allowing for the mass of its invisible companion to be measured. If it is above three solar masses, then it is considered to be a black hole.
The biggest problem is put forth by dormant black holes, such as the one found by the Spanish researchers. "Their X-ray emission is almost absent, so it is very unlikely that our attention would be drawn to them," Casares explains. Researchers believe there are thousands of black hole binary systems across the Milky Way, some of them also with Be-type stellar companions.
For more information:
http://www.ub.edu/web/ub/en/menu_eines/noticies/2014/01/015.html
http://web.ua.es/en/actualidad-universitaria/2014/enero2014/enero2014-13-19/spanish-researchers-discover-the-first-black-hole-orbiting-a-star.html
http://www.astromart.com/news/news.asp?news_id=638
http://www.astromart.com/news/news.asp?news_id=432
http://www.astromart.com/news/news.asp?news_id=1251
http://www.astromart.com/news/news.asp?news_id=1124
http://www.astromart.com/news/news.asp?news_id=955
AstroMart News Archive:
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Be-type stars are quite common across the Universe. In our Galaxy alone more than 80 of them are known in binary systems together with neutron stars. "Their distinctive property is their strong centrifugal force. They rotate very fast, close to their break-up speed. It is like they were cosmic spinning tops" says Jorge Casares from the Instituto de Astrofisica de Canarias (IAC) and La Laguna University (ULL). Casares is an expert in stellar-mass black holes. He presented the first solid proof of their existence back in 1992.
The newly discovered black hole orbits the Be-type star known as MWC 656, located in the constellation Lacerta (the Lizard), 8,500 light years from Earth. The Be-type star rotates so fast that its surface speed exceeds 1 million kilometers per hour. "We started studying this star back in 2010, when space telescopes detected transient gamma-ray emission coming from its direction," explains Marc Ribo, from the Institute for Sciences of the Cosmos of the University of Barcelona (ICCUB). "No more gamma-ray emissions have subsequently been detected, but we found that the star was part of a binary system," he adds.
A detailed analysis of its spectrum allowed scientists to infer the characteristics of its companion. "It turned out to be an object with a mass between 3.8 and 6.9 solar masses. An object like that, invisible to telescopes and with such large mass, can only be a black hole, because no neutron star with more than three solar masses can exist," states Ignasi Ribas, researcher at the Institute of Space Sciences.
The black hole orbits the Be-type star and is fed by matter ejected from the latter. "The high rotation speed of the Be-type star causes matter to be ejected into an equatorial disc. This matter is attracted by the black hole and falls on to it, forming another disc called an accretion disc. By studying the emission from the accretion disc we can analyze the motion of the black hole and measure its mass," comments Ignacio Negueruela, researcher at the University of Alicante.
Scientists believe this object to be a nearby member of a hidden population of Be-type stars paired with black holes. "We think these systems are much more common than previously thought, but they are difficult to detect because their black holes are fed from gas ejected by Be-type stars without producing much radiation, in a silent way," Casares adds. Experts hope to detect other similar binary systems in the Milky Way and other nearby galaxies by using bigger telescopes, such as the Gran Telescopio Canarias (GTC).
Also participating in the study with Jorge Casares, Ignacio Negueruela, Marc Ribo and Ignasi Ribas are Jose M. Paredes, from the Institute for Scinces of the Cosmos of the University of Barcelona, and Artemio Herrero and Sergio Simon, both from IAC and ULL. ICCUB and ICE researchers are also members of the Institute for Space Studies of Catalonia.
Animation of the system MWC 656. The Be-type star spins at an extremely high speed, ejecting matter through an equatorial disc. Part of this matter falls on to the black hole forming an accretion disc. (Animation Credit: Gabriel Perez - SMM, IAC).
The detection of black holes has been a challenge since their existence was first surmised by John Michell and Pierre Laplace in the 18th century. Given that they are invisible, since their enormous gravitational force prevents light from escaping, telescopes cannot detect them. However, black holes can occasionally trigger high energy radiation from the environment surrounding them and can thus be traced by X-ray satellites. This is the case with active black holes that are fed by matter transferred from a nearby star. If violent X-ray emission is detected from a place where nothing but a normal star is seen, a black hole might be hiding there.
Thanks to this method, researchers have discovered fifty-five potential black holes over the last fifty years. Seventeen of them have what astronomers call a "dynamic confirmation," that is, the feeding star has been localized, allowing for the mass of its invisible companion to be measured. If it is above three solar masses, then it is considered to be a black hole.
The biggest problem is put forth by dormant black holes, such as the one found by the Spanish researchers. "Their X-ray emission is almost absent, so it is very unlikely that our attention would be drawn to them," Casares explains. Researchers believe there are thousands of black hole binary systems across the Milky Way, some of them also with Be-type stellar companions.
For more information:
http://www.ub.edu/web/ub/en/menu_eines/noticies/2014/01/015.html
http://web.ua.es/en/actualidad-universitaria/2014/enero2014/enero2014-13-19/spanish-researchers-discover-the-first-black-hole-orbiting-a-star.html
http://www.astromart.com/news/news.asp?news_id=638
http://www.astromart.com/news/news.asp?news_id=432
http://www.astromart.com/news/news.asp?news_id=1251
http://www.astromart.com/news/news.asp?news_id=1124
http://www.astromart.com/news/news.asp?news_id=955
AstroMart News Archive:
http://www.astromart.com/news/search.asp?search=.+
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