A star swallowed by a new type of black holes

Using data from the European Space Agency’s XMM-Newton Observatory, an international team of researchers, including three IRAP researchers, surprised a new type of black hole (an intermediate mass black hole) feasting on the remains of a star passing too close.

Discovery of an intermediate mass black hole, a new class of black holes. An international team has discovered using data from the European XMM-Newton X-ray observatory a very interesting black hole candidate belonging to a new class, intermediate-mass black holes. This black hole with a mass of 50,000 times the mass of our Sun and located at the periphery of a galaxy was detected feasting on the remains of a star that it dislocated, producing a fantastic burst of light observable at the dizzying distance of 760 million light-years from the Earth. The host galaxy is named 6dFGS gJ215022.2-055059 (appearing in yellow/white in the centre of the image) and the X-ray source associated with the black hole is identified as 3XMM J215022.4-055108 (in purple). Credit: ESA/Hubble & NASA/Chandra

Two varieties of black holes have been detected so far: supermassive black holes (about one million to ten billion times the mass of the Sun) at the center of galaxies and lighter stellar black holes (3 to 100 times the mass of the Sun) resulting from the end of life of stars with masses at least 10 times larger than our Sun. Between these two extremes, a class of black holes, known as intermediate mass black holes and potential missing links that could explain the formation of supermassive ogres, has long eluded astronomers. Only a few credible candidates are known, including the HLX-1 source in the galaxy ESO 243-49 discovered at IRAP.

An international research team observed, thanks to the European Space Agency’s XMM-Newton X-ray observatories, NASA’s Chandra & Swift Neil Gehrels and NASA’s Neil Gehrels, a huge burst of light from a source on the periphery of a distant galaxy, marking the feast of an intermediate-mass black hole devouring a star that had come too close.

“This is a very exciting discovery: it’s the first time such a black hole has been seen devouring a star,” says Dacheng Lin of the University of New Hampshire (USA), the first author/coordinator of this study. “A few candidates have been found in the past, but this type of black hole remains particularly difficult to detect. This is one of the most important discoveries of recent years”.

Several scenarios have been invoked to explain the formation of intermediate-mass black holes, including the fusion of several massive stars in the heart of very dense star clusters. These clusters are thus a prime target for the search for such black holes. However, the lack of gas in the core of these clusters in general prevents the black hole from feeding and signalling itself to scientists by the light emitted when this gas is absorbed by the black hole. This then makes their detection virtually impossible with current means.

“An alternative method of detecting them is to wait for a star in the cluster to pass so close to an intermediate-mass black hole that it will be devoured/dislocated. This then generates sudden and huge bursts of light, especially X-rays, which we can then observe,” adds Dacheng Lin. “This type of rare event has so far only been seen at the centre of galaxies and involves a supermassive black hole.

Dacheng Lin and his colleagues have discovered this rare event (aptly named 3XMM J215022.4-055108) from XMM-Newton X-ray observatory archive data collected between 2006 and 2009. They also used data from the Chandra (in 2006 & 2016) and Swift (in 2014) observatories.

“We analyzed images of the host galaxy taken in the visible by several telescopes over several years to study more closely the behaviour of this unique object,” says Jay Strader of Michagan State University (USA), one of the co-authors of the study. “We found that the source had become much brighter in two images taken in 2005. Combining all available data, we concluded that the star was dislocated by the black hole around October 2003 and that this produced a huge burst of light that has been decreasing in intensity for over 10 years, but is still detectable.”

The black hole responsible for the star’s dislocation is thought to weigh about 50,000 times the mass of our Sun and is located in a cluster of stars at the edge of the 6dFGS galaxy gJ215022.2-055059, itself some 760 million light years from Earth.

Apart from the dislocation of a star by a black hole of intermediate mass, the only phenomenon that can explain the observations involves the cooling of a neutron star in our Galaxy after it has been heated by the significant fall on its surface of matter from a companion star. If this had been the case, an even more intense burst of light should have occurred before the one detected. “However, we found no evidence of such a burst in the data, which allows us to invalidate this explanation,” says Strader.

Dislocations of stars by intermediate-mass black holes are rare events. Confirmation of this event suggests that there may be a population of such dormant black holes on the periphery of their host galaxy.

“This intermediate-mass black hole candidate was discovered after a careful search of the XMM-Newton (3XMM) X-ray source catalogue containing more than 500,000 sources spread across the sky. This very good quality data made it possible to weigh this black hole and understand the origin of the observed burst of light,” said Norbert Schartel, the XMM-Newton mission’s Chief Scientist working for the European Space Agency.

“The XMM-Newton source catalogue is produced under our responsibility at IRAP. In the hundreds of thousands of unknown X sources are hidden exotic objects whose nature will be revealed by long-term studies of the type that led to the observation of this new type of black hole,” said Natalie Webb, Chief Scientist at the XMM-Newton Survey Science Center.

The study used data from the European Space Agency’s XMM-Newton X-ray Observatory, the European Space Agency’s XMM-Newton Observatory, NASA’s Chandra & Swift Neil Gehrels and images from the Canada-France-Hawaii Telescope, NASA’s Hubble Telescope, the Subaru Telescope, the Southern Astrophysical Research (SOAR) Telescope, and the Gemini Observatory.

Further Resources

IRAP Contacts

  • Natalie Webb, Olivier Godet & Didier Barret, Institut de Recherche en Astrophysique & Planétologie (IRAP)
  • Emails : nwebb@irap.omp.eu / ogodet@irap.omp.eu / dbarret@irap.omp.eu
  • Tel : 0561557570 / 0561557536 / 0561558561

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