TitleAuthorsAbstractBlack holes in the formation of red ellipticalsBlack holes in galaxy clustersBlack holes in galaxy evolutionRemaining issuesReferencesFigure 1 The galaxy bimodality.Figure 2 A computer simulation of the formation of an elliptical galaxy.Figure 3 The entropy of the intracluster medium in spherical shells of radius r.Figure 4 Optical, radio and X-ray images of the Perseus cluster.Figure 5 Cooling, heating, and black hole accretion rates.REVIEWSThe role of black holes in galaxy formationand evolutionA. Cattaneo1,2, S. M. Faber3, J. Binney4, A. Dekel5, J. Kormendy6, R. Mushotzky7, A. Babul8, P. N. Best9, M. Bru¨ggen10,A. C. Fabian11, C. S. Frenk12, A. Khalatyan13, H. Netzer14, A. Mahdavi15, J. Silk4, M. Steinmetz1& L. Wisotzki1Virtually all massive galaxies, including our own, host central black holes ranging in mass from millions to billions of solarmasses. The growth of these black holes releases vast amounts of energy that powers quasars and other weaker activegalactic nuclei. A tiny fraction of this energy, if absorbed by the host galaxy, could halt star formation by heating and ejectingambient gas. A central question in galaxy evolut ion is the degree to which this process has caused the decline of starformation in large elliptical galaxies, which typically have little cold gas and few young stars, unlike spiral galaxies.Galaxies come in two basic types: ‘football-shaped’ ellipti-cals and ‘disk-shaped’ spirals (Fig. 1). Spirals containplenty of cold gas, which forms stars, whereas the gas inellipticals is too hot to form stars. Thus, ellipticals lack theyoung blue stars that are usually seen in spirals, and are generallyquite red. Spirals also have central bulges structurally resemblingminiature ellipticals. Owing to this similarity, we use the term‘bulges’ for bulges within spirals and for ellipticals indiscriminately.Each bulge contains a central black hole, whose mass is propor-tional to the bulge stellar mass1–5, MBH< 0.001Mbulge. Black holesand bulges also formed at about the same epoch in the lifetime of theUniverse6,7. These observations imply that the formation of blackholes and the formation of bulges are closely linked. Matter fallingonto a black hole releases a huge amount of energy8, of the order of10% of the rest mass energy, E 5 mc2, mainly in the form of photonsbut also in the form of radio-luminous jets of charged particles9,10.Even a tiny fraction (,1%) of the energy released within each bulgecould heat and blow away its entire gas content, thus explaining thelack of star formation in bulges.The theorist’s goal is to understand these observations in a cosmo-logical context. In the standard picture11–13, most of the Universe iscomposed of dark matter, whose nature is unknown. Protons, elec-trons and neutrons, which compose gas and stars, make up the rest.They interact with dark matter purely through gravity, which deter-mines the evolution of the Universe on large scales. The Universeemerged from the Big Bang with small inhomogeneities. These even-tually grew into lumps, called haloes, by attracting surrounding mattergravitationally (Fig. 2). The competition between radiative coolingand gravitational heatingdetermines the fate of gas in these haloes14–16.In low-mass haloes, cooling dominates. Galaxies grow through theaccretion of gas that falls to the centre in cold flows17,18, settles intodisks19(but see refs 20, 21), and forms stars. However, when the halomass grows above a critical value of about 1012solar masses18, heatingdominates, and the gas no longer accretes onto galaxies. Halo mergersform large haloes that contain tens or even hundreds of galaxies,called groups or clusters, respectively. Galaxy mergers within haloes1Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany.2Observatoire de Lyon, Universite´de Lyon 1, 9 avenue Charles Andre´, 69561 Saint Genis Lavalcedex, France.3University of California Observatories/Lick Observatory, University of California, Santa Cruz, California 95064, USA.4Department of Physics, University of Oxford,Keble Road, Oxford OX1 3RH, UK.5Racah Institute of Physics, The Hebrew University, Jerusalem 91904, Israel.6Department of Astronomy, University of Texas, Austin, Texas 78712,USA.7Goddard Space Flight Center, NASA, Greenbelt, Maryland 20771, USA.8Department of Physics and Astronomy, University of Victoria, Elliot Building, 3800 Finnerty Road,Victoria, British Columbia V8P 1A1, Canada.9Institute for Astronomy, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK.10Jacobs University Bremen, Campus Ring 1, 28759Bremen, Germany.11Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK.12Institute for Computational Cosmology, University of Durham,South Road, Durham DH1 3LE, UK.13Observatoire Astronomique Marseille-Provence, 38 rue Fre´de´ric Joliot-Curie, 13388 Marseille cedex 13, France.14Wise Observatory, University ofTel Aviv, 69978 Tel Aviv, Israel.15Department of Physics and Astronomy, San Francisco State University, 1600 Holloway Avenue, San Francisco, California 94132, USA.2.52.09.5 10 10.5 11 11.51.5u – rLog(Mgal /M . )Figure 1|The galaxy bimodality. The contours show the galaxy distributionon a stellar mass (Mgal)–colourdiagram92. The difference between ultravioletluminosity and red luminosity, quantified by the magnitude difference u 2 r,isa colour indicator; larger values of u 2 r correspond to redder galaxies. Thecolour bar has been inserted to convey this notion visually and has noquantitative meaning. Galaxies are classified into two main types: spirals thatmainly grew through gas accretion (‘S’, shown in blue) and ellipticals thatmainly grew through mergers with other galaxies (‘E’, shown in red). ‘S0’galaxiesareanintermediatetype,butweassimilatethemtoellipticals.Spiralshave central bulges, shown in red, that resemble miniature ellipticals. Allellipticals and bulges within spirals contain a central black hole, shown with ablack dot. Moreover, ellipticals and bulges within spirals have the same black-holemasstostellarmassratio,oftheorderof0.1%.Thisiswhywecallthem‘bulges’ indiscriminately. In contrast, there is no connection between masses ofblack holes and masses of disks (the galactic component shown in blue). Spiralsandellipticalsareseparatedbyacolourwatershedatu 2 r < 2andamasswatershed at Mgal<M* < 1010.5M[(ref. 92). M* is of the order of fbMcrit,where Mcrit<1012M[is the critical