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Discovery of a bright quasar without a massive host galaxy

2005; Nature Portfolio; Volume: 437; Issue: 7057 Linguagem: Inglês

10.1038/nature04013

1476-4687

Pierre Magain, G. Letawe, F. Courbin, P. Jablonka, K. Jahnkę, Georges Meylan, L. Wisotzki,

Astronomy and Astrophysical Research

Astrophysicists may be forgiven a bout of déjà vu following the discovery of a quasar that is not at the centre of a massive host galaxy. The claim that 'naked quasars' had been observed caused a flurry of excitement in the mid-1990s. Quasars are among the most powerful energy sources in the Universe, and their energy is thought to derive from the infall of matter into a black hole at the centre of a massive galaxy. Quasars with no galaxy to power them seemed an anachronism and on inspection 'naked quasars' were nothing of the sort: the host galaxies were just hidden by the extreme luminosity of the quasars. The 'new' quasar is not naked, but it is not wearing much. HE0450–2958 is at the edge of a large gas cloud; if it has a host galaxy it is too small to drive the quasar, which might be feeding on mass from a nearby ultraluminous infrared galaxy with which it may be interacting. This discovery could change our ideas about how these objects form and suggests that isolated supermassive black holes may exist in the Universe. A quasar is thought to be powered by the infall of matter onto a supermassive black hole at the centre of a massive galaxy1,2. Because the optical luminosity of quasars exceeds that of their host galaxy, disentangling the two components can be difficult. This led in the 1990s to the controversial claim of the discovery of 'naked' quasars3,4,5,6,7. Since then, the connection between quasars and galaxies has been well established8. Here we report the discovery of a quasar lying at the edge of a gas cloud, whose size is comparable to that of a small galaxy, but whose spectrum shows no evidence for stars. The gas in the cloud is excited by the quasar itself. If a host galaxy is present, it is at least six times fainter than would normally be expected8,9 for such a bright quasar. The quasar is interacting dynamically with a neighbouring galaxy, whose gas might be feeding the black hole.