Two Hubble images from a sample of 20 nearby quasars

Black hole without a home

14 September 2005

The detection of a super-massive black hole without a massive 'host' galaxy is the surprising result from a large Hubble and VLT study of quasars.

This is the first convincing discovery of such an object. One intriguing explanation is that the host galaxy may be made almost exclusively of 'dark matter'.



Quasar HE0450-2958, after advanced image processing


The astronomers suggest that this may indicate a rare case of a collision between a seemingly normal spiral galaxy and an 'exotic' object harbouring a very massive black hole.


The best fed of these objects shine as 'quasars' (standing for 'quasi-stellar object' because they had initially been thought of as stars).


To overcome this problem, the astronomers devised a new and highly efficient strategy. Combining Hubble’s ultra-sharp images and spectroscopy from ESO’s VLT, they observed their sample of 20 quasars at the same time as a reference star. The star served as a reference pinpoint light source that was used to disentangle the quasar light from any possible light from an underlying galaxy.


We must therefore conclude that, contrary to our expectations, this bright quasar is not surrounded by a massive galaxy.

"With the powerful combination of Hubble and the VLT we are confident that we would have been able to detect a normal host galaxy," said Pierre Magain of the Université de Liège, Belgium.

The astronomers did however detect an interesting smaller cloud of gas about 2500 light-years wide near the quasar, which they call 'the blob'. VLT observations show this cloud to be glowing because it is bathed in the intense radiation coming from the quasar, and not from stars inside the cloud. Most likely, it is the gas from this cloud that feeds the super-massive black hole, thereby allowing it to become a quasar.

The left image above shows a strongly disturbed galaxy, with all the signs of a recent collision, near the quasar. The VLT observations show it to be forming stars at a great rate.

"The absence of a massive host galaxy, combined with the existence of the blob and the star-forming galaxy, lead us to believe that we have uncovered a really exotic quasar," said Frédéric Courbin of the Ecole Polytechnique Federale de Lausanne, Switzerland.



Another intriguing hypothesis is that the galaxy harbouring the black hole was almost exclusively made of 'dark matter'. It may be that what is observed is a normal phase in the formation of a massive galaxy, which in this case has taken place several 1000 million years later than in most others.

For more information:

The paper on HE0450-2958 is published in the 15 September 2005 issue of the journal Nature.

Frédéric Courbin/Pascale Jablonka
Laboratoire d'Astrophysique, Ecole Polytechnique Federale de Lausanne, Switzerland
Tel: +41 22 379 2418 / +41 22 379 2469
E-mail: frederic.courbin @ / pascale.jablonka @

Pierre Magain
Institut d'Astrophysique de Geophysique, Universite de Liege, Belgium
Tel: +32 4366 97 53
E-mail: Pierre.Magain @

Lutz Wisotzki
Astrophysikalisches Institut Potsdam, Germany
Tel: +49 331 7499532
E-mail: lwisotzki @

Lars Lindberg Christensen
Hubble European Space Agency Information Centre, Garching, Germany
Tel: +49 89 3200 6306
Mobile +49 173 3872 621
E-mail: lars @

Henri Boffin European Southern Observatory
Tel: +49 89 3200 6222
E-mail: hboffin @

Ray Villard Space Telescope Science Institute, Baltimore, USA
Tel: +1 410 338 4514
E-mail: villard @

The full team is: Pierre Magain, Géraldine Letawe (Univ. Liege, Belgium), Frederic Courbin, Georges Meylan (Ecole Polytechnique Federale de Lausanne (EPFL), Switzerland), Pascale Jablonka (EPFL; also affiliated to Univ. Geneve), Knud Jahnke and Lutz Wisotzki (Astrophysikalisches Institut Potsdam, Germany).
