Media Releases

Where have all the quasars gone?

December 5, 2011

Record-breaking black holes discovered, U of T astronomer on international team

TORONTO, ON ‑An inter­na­tion­al team of astronomers has dis­cov­ered two gigan­tic black holes with mass­es about 10 bil­lion times the mass of our sun. These black holes have a mass more than 50 per cent greater than any oth­er pre­vi­ous­ly mea­sured.

“They may be the dor­mant remains of quasars that were extreme­ly lumi­nous bil­lions of years ago,” says Pro­fes­sor James Gra­ham, direc­tor of the Dun­lap Insti­tute for Astron­o­my and Astro­physics at the Uni­ver­si­ty of Toron­to and found­ing mem­ber of the team behind the dis­cov­ery.

A black hole is a region of space that has so much mass con­cen­trat­ed in it that there is no way for a near­by object to escape its grav­i­ta­tion­al pull. The mass­es of black holes are mea­sured by fig­ur­ing out how strong their grav­i­ty is. More mass means more grav­i­ty and a stronger effect on stars that orbit in the galax­ies that they inhab­it.

Using sev­er­al tele­scopes − the Gem­i­ni Obser­va­to­ry, the Mac­Don­ald Obser­va­to­ry and the Keck Obser­va­to­ry – the sci­en­tists mea­sured the speed of stars orbit­ing in these galax­ies, there­by mea­sur­ing the strength of the grav­i­ta­tion­al field of the black hole.

“Black holes inhab­it the cen­tres of near­ly all galax­ies − the cen­tre of our very own Milky Way galaxy har­bours a black hole four mil­lion times the mass of the sun − rel­a­tive­ly speak­ing, a baby! But only a few dozens of these black holes have been ‘weighed’ care­ful­ly,” says Gra­ham.

“We believe that 10-bil­lion solar mass black holes like these are the ulti­mate pow­er sources for the dis­tant quasars observed in the ear­ly uni­verse, one to three bil­lion years after the Big Bang,” he says. Quasars are among the bright­est phe­nom­e­na in the   uni­verse, emit­ted by mate­r­i­al whirling around and falling into the black hole at the cen­tre of a galaxy. The more mas­sive the black hole, the more pow­er­ful the quasar can be.

More recent­ly, quasars have toned it down: the ones clos­er to home are not near­ly as lumi­nous as those of 10 bil­lion years ago. The light com­ing from the two galax­ies the team observed shows them as they were less than half a bil­lion years ago. No quasar there, but black holes mas­sive enough to have pow­ered extreme­ly bright quasars sev­er­al bil­lions of years ear­li­er.

“Our mea­sure­ments of black holes with 10-bil­lion solar mass­es in near­by galax­ies show that these types of galax­ies orig­i­nal­ly host­ed very lumi­nous quasars,” says Gra­ham. “For the last 10 bil­lion years, these enor­mous black holes have been dor­mant.”

To look for such mas­sive black holes, the team turned their tele­scopes toward giant galax­ies since there appears to be a tight cor­re­la­tion between prop­er­ties of the host galaxy and the mass of its black hole. This key piece of evi­dence helps sci­en­tists piece togeth­er how galax­ies and their cen­tral black holes form and grow. The cor­re­la­tion sug­gests there is a sort of feed­back between the growth of the cen­tral black hole and the for­ma­tion of the stars that even­tu­al­ly com­prise the cen­tral region of the galaxy.

“But these new­ly mea­sured black hole mass­es are a sur­prise,” says Gra­ham. “They are sig­nif­i­cant­ly more mas­sive than pre­dict­ed using the pre­vi­ous­ly known cor­re­la­tions.  Some­thing that we had not antic­i­pat­ed for the most mas­sive black holes must be at play here.”

Graham’s research career includes an impres­sive list of astron­o­my firsts. He dis­cov­ered the first disk of aster­oidal debris orbit­ing a white dwarf star. He made the first images of the bina­ry black holes in the ultra-lumi­nous galaxy Arp 220. In 1994, he was a mem­ber of a team which made one of the first defin­i­tive iden­ti­fi­ca­tions of a brown dwarf in the Pleiades open clus­ter, an accom­plish­ment that was also one of the first impor­tant dis­cov­er­ies made using the Keck tele­scope. In 2008, he and his Berke­ley col­league Paul Kalas dis­cov­ered Foma­l­haut b, the first exo­plan­et seen with vis­i­ble light.  Cap­tured by the Hub­ble Space Tele­scope, the image was named one of the 10 biggest sci­en­tif­ic break­throughs of all time by Time mag­a­zine. Cur­rent­ly, Gra­ham is work­ing to detect many more plan­ets by direct imag­ing. He is the project sci­en­tist for the Gem­i­ni Plan­et Imager, a high­ly advanced adap­tive optics instru­ment at the Gem­i­ni Obser­va­to­ry in Chile.

The research will be pub­lished in Nature on Decem­ber 8.  Oth­er mem­bers of the inter­na­tion­al team are lead authors Chung-Pei Ma, Nicholas McConnell, a for­mer stu­dent of Graham’s, and Shel­ley Wright, all of UC Berke­ley (Wright will join U of T in Jan­u­ary 2012); Karl Geb­hardt and Jere­my Mur­phy of Uni­ver­si­ty of Texas, Austin; Todd Lauer of the Nation­al Opti­cal Obser­va­to­ry in Tuc­son, Ari­zona and Dou­glas Rich­stone of Uni­ver­si­ty of Michi­gan, Ann Arbor.  Research was sup­port­ed by the Nation­al Sci­ence Foun­da­tion, the Hub­ble Fel­low­ship, NASA, and the Miller Insti­tute for Basic Research in Sci­ence at UC Berke­ley.  The Gem­i­ni Obser­va­to­ry is oper­at­ed by the Asso­ci­a­tion of Uni­ver­si­ties for Research in Astron­o­my, Inc. under a coop­er­a­tive agree­ment with Nation­al Sci­ence Foun­da­tion on behalf of the Gem­i­ni part­ner­ship.

Illus­tra­tion and Nature paper at

Video at

For more infor­ma­tion, please con­tact:

Pro­fes­sor James Gra­ham
Dun­lap Insti­tute for Astron­o­my and Astro­physics
Uni­ver­si­ty of Toron­to

Johannes Hirn
Com­mu­ni­ca­tions, Dun­lap Insti­tute for Astron­o­my and Astro­physics
Uni­ver­si­ty of Toron­to

Kim Luke
Com­mu­ni­ca­tions, Fac­ul­ty of Arts & Sci­ence|
Uni­ver­si­ty of Toron­to