Confirming the nature of an intermediate mass black hole thanks to its radio emission.

In 2009, an international team of researchers discovered the best candidate intermediate mass black hole to date. In a follow-up studypublished in Science Express on the 5th July 2012 and conducted by asimilar research team led at the IRAP (CNRS/Université Toulouse III -Paul Sabatier) and which also included scientists from the CEA in Saclay, the intermediate mass black hole hypothesis has been confirmedand further light shed on this rare type of object. Thanks to new observations, the researchers demonstrated that this black hole alsoshows sporadic ejections of matter (jets), in a similar way to stellar and supermassive black holes. Such jets have never been detected froman intermediate mass black hole. Thanks to the emission, the scientists have estimated the mass of the black hole to be between9000 and 90000 times the mass of our Sun. These pioneering results have allowed analogies between all types of black hole to be made.

Image of the host galaxy ESO 243-49 and the study source (white circle) HLX-1, the intermediate-mass black hole, taken with the Hubble Space Telescope.

Astronomers class black holes into several categories, from stellar mass black holes with masses larger than that of our Sun to supermassive black holes situated in the centre of galaxies, with masses that are millions to billions that of our Sun. Between these two extremes are the intermediate mass black holes, but proof of their existence has been elusive. In 2009, a team of scientists led by members of the IRAP, Toulouse, discovered the best intermediate mass black hole candidate which they named HLX-1 (for Hyper-Luminous X-raysource 1) and which lies in the galaxy ESO 243-49 at about 300 million light years from the Earth.

Stellar mass and supermassive black holes are known to eject jets of matter as material falls into them. These jets can be seen in radiolight. In 2003, Merloni, Heinz and di Matteo showed that there was a link between the matter that falls onto the black hole (seen usingX-rays), the mass of the black hole and power in the jets (seen using radio light). If this correlation is correct, then intermediate massblack holes should also show these radio jets. To verify this theory, the team instigated an international project to observe HLX-1 inX-rays with the X-ray Satellite Swift (NASA) and the radio emission using the array of radio telescopes, ATCA, in Australia. They showedthat there was indeed radio light detected when the X-ray light from HLX-1 increased. These observations indicate that a jet was ejected,in a similar way to the stellar mass and supermassive black holes. This study also allowed constraints on the mass of the intermediatemass black hole to be made, which shows that it is between 9000 and 90000 solar masses. This result therefore reinforces the ideathat HLX-1 is indeed an intermediate mass black hole.

The detection of intermediate mass black holes is essential as they may play a central role in the formation of galaxies and in thecentral supermassive black hole of the galaxy, but without theiridentification, such theories were difficult to ratify.

IRAP Contact:

  • Natalie Webb, Institut de Recherche en Astrophysique et Planétologie (IRAP – CNRS/UPS), Email :

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