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Too-big black hole flummoxes scientists

Nov. 28, 2012
Courtesy of the University of Texas at Austin
and World Science staff

As­tro­no­mers have found what they say may be the most mas­sive black hole known—one weigh­ing the equiv­a­lent of 17 bil­lion Suns. And they don’t quite know what to make of it.

Dwarf­ing our whole so­lar sys­tem in size, the black hole up­sets con­ven­tion­al mod­els of gal­axy ev­o­lu­tion, they say. These mod­els as­sume a fairly pre­dict­a­ble rela­t­ion­ship be­tween the mass (weight) of ga­lax­ies, and that of their cen­tral black holes. But the new find­ing in­volves a gal­axy that’s “al­most all black hole,” said re­search tem mem­ber Karl Geb­hardt of the Uni­vers­ity of Tex­as at Aus­tin.

Gal­axy NGC 1277 as seen through the Hub­ble Space Tel­e­scope. This small, flat­tened gal­axy is said to con­tain one of the most mas­sive cen­tral black holes ev­er found. (Cred­it: NA­SA/E­SA/An­drew C. Fa­bi­an )


Sci­en­tists used the uni­vers­ity’s Hobby-Eberly Tel­e­scope to study the ob­ject, in a gal­axy dubbed NGC 1277. 

A black hole is an ob­ject so com­pact that its gra­vity over­pow­ers and draws in an­y­thing that strays too close, even light. Most ga­lax­ies have black holes at their cores.

The new­found black hole makes up 14 per­cent of its gal­ax­y’s mass, rath­er than the usu­al 0.1 per­cent, re­search­ers re­ported. The gal­axy and sev­er­al more in the same stu­dy, they added, could change the­o­ries of how black holes and ga­lax­ies form and evolve. The find­ings ap­pear in the Nov. 29 is­sue of the re­search jour­nal Na­ture.

NGC 1277 lies 220 mil­lion light-years away in the di­rec­tion of the con­stella­t­ion Per­seus. (A light-year is the dis­tance light trav­els in a year.) The gal­axy is only one-tenth the size and mass of our own, yet the black hole at its heart is more than 11 times as wide as Nep­tune’s or­bit around the Sun.

“This is a really odd­ball gal­axy,” said Gebardt. “This could be the first ob­ject in a new class of gal­ax­y-black hole sys­tems.” Fur­ther­more, the most mas­sive black holes have been seen in gi­ant blobby ga­lax­ies called “el­lip­ti­cals,” but this one in­hab­its a lens-shaped or “len­tic­u­lar” gal­axy.

The study aims at bet­ter un­der­stand­ing how black holes and ga­lax­ies form and grow to­geth­er.

“At the mo­ment there are three com­pletely dif­fer­ent mech­a­nisms that all claim to ex­plain the link be­tween black hole mass and host ga­lax­ies’ prop­er­ties. We do not un­der­stand yet which of these the­o­ries is best,” said study lead au­thor Remco van den Bosch, who be­gan the work while a post­doc­tor­al fel­low at The Uni­vers­ity of Tex­as at Aus­tin. He is now at the Max Planck In­sti­tute for As­tron­o­my in Hei­del­berg, Ger­ma­ny.

The prob­lem is lack of da­ta, he ex­plained. As­tro­no­mers know the mass­es of few­er than 100 black holes in ga­lax­ies. But meas­ur­ing black hole mass­es is tough and time-con­sum­ing. So the team de­vel­oped a proj­ect called the HET Mas­sive Gal­axy Sur­vey to win­now down the num­ber of ga­lax­ies that would be in­ter­est­ing to fol­low up on. (HET stands for Hobby-Eberly Tel­e­scope.)

“When try­ing to un­der­stand an­y­thing, you al­ways look at the ex­tremes: the most mas­sive and the least mas­sive,” Geb­hardt said. “We chose a very large sam­ple of the most mas­sive ga­lax­ies in the near­by uni­verse,” to learn more about the rela­t­ion­ship be­tween black holes and their host ga­lax­ies.

Though still on­go­ing, the team has stud­ied 700 of their 800 ga­lax­ies with the tel­e­scope. “This study is only pos­si­ble with” that in­stru­ment, Geb­hardt said. It “works best when the ga­lax­ies are spread all across the sky. This is ex­actly what HET was de­signed for.”

The team ze­roed in on the six big­gest ga­lax­ies. They found that one of those, NGC 1277, had al­ready been pho­tographed by Hub­ble Space Tel­e­scope. This pro­vid­ed mea­sure­ments of the gal­ax­y’s bright­ness at dif­fer­ent dis­tances from its cen­ter. When com­bined with Hobby-Eberly da­ta and var­i­ous mod­els run via su­per­com­puter, the re­sult was a mass for the black hole of 17 bil­lion Suns, give or take three bil­lion. “It leads us to think that very mas­sive ga­lax­ies have a dif­fer­ent phys­i­cal pro­cess in how their black holes grow,” Geb­hardt said.


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Astronomers have measured what they say may be the most massive black hole known—one weighing the equivalent of 17 billion Suns. And they don’t quite know what to make of it. Dwarfing our whole solar system in size, the black hole upsets conventional models of galaxy evolution, they say. These models assume a fairly predictable relationship between the mass (weight) of galaxies, and that of their central black holes. But the new finding involves a galaxy that’s “almost all black hole,” said research tem member Karl Gebhardt of the University of Texas at Austin. Scientists used the university’s Hobby-Eberly Telescope to study the object, in a galaxy dubbed NGC 1277. A black hole is an object so compact that its gravity overpowers and draws in anything that strays too close, even light. Most galaxies have black holes at their cores. The newfound black hole makes up 14 percent of its galaxy’s mass, rather than the usual 0.1 percent, researchers reported. The galaxy and several more in the same study, they added, could change theories of how black holes and galaxies form and evolve. The findings appear in the Nov. 29 issue of the research journal Nature. NGC 1277 lies 220 million light-years away in the direction of the constellation Perseus. (A light-year is the distance light travels in a year.) The galaxy is only one-tenth the size and mass of our own Milky Way. Despite that relatively small size, the black hole at its heart is more than 11 times as wide as Neptune’s orbit around the Sun. “This is a really oddball galaxy,” said Gebardt. “This could be the first object in a new class of galaxy-black hole systems.” Furthermore, the most massive black holes have been seen in giant blobby galaxies called “ellipticals,” but this one is seen in a relatively small lens-shaped or “lenticular” galaxy. The study aims at better understanding how black holes and galaxies form and grow together. “At the moment there are three completely different mechanisms that all claim to explain the link between black hole mass and host galaxies’ properties. We do not understand yet which of these theories is best,” said study lead author Remco van den Bosch, who began the work while a postdoctoral fellow at The University of Texas at Austin. He is now at the Max Planck Institute for Astronomy in Heidelberg, Germany. The problem is lack of data, he explained. Astronomers know the masses of fewer than 100 black holes in galaxies. But measuring black hole masses is tough and time-consuming. So the team developed a project called the HET Massive Galaxy Survey to winnow down the number of galaxies that would be interesting to follow up on. (HET stands for Hobby-Eberly Telescope.) “When trying to understand anything, you always look at the extremes: the most massive and the least massive,” Gebhardt said. “We chose a very large sample of the most massive galaxies in the nearby universe,” to learn more about the relationship between black holes and their host galaxies. Though still ongoing, the team has studied 700 of their 800 galaxies with the telescope. “This study is only possible with” that telescope, Gebhardt said. It “works best when the galaxies are spread all across the sky. This is exactly what HET was designed for.” The team zeroed in on the six biggest galaxies. They found that one of those, NGC 1277, had already been photographed by Hubble Space Telescope. This provided measurements of the galaxy’s brightness at different distances from its center. When combined with Hobby-Eberly data and various models run via supercomputer, the result was a mass for the black hole of 17 billion Suns, give or take 3 billion. “It leads us to think that very massive galaxies have a different physical process in how their black holes grow,” Gebhardt said.