"Long before it's in the papers"
July 10, 2015

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Giant black hole “outgrew its galaxy”

July 10, 2015
Courtesy of Yale University 
and World Science staff

As­tro­no­mers say they have spot­ted an ap­par­ent super-sized anom­a­ly: a gi­ant black hole that grew much faster than its host gal­axy.

The find­ing con­flicts with most ob­serva­t­ions about black holes, mas­sive ob­jects with ex­tra­or­di­narily strong gra­vity that can pull in an­y­thing, even light. The more they suck up, the more they grow.

Artist's conception of how CID-947 might look if it were viewed from  rela­tively nearby. (Cour­tesy Mi­chael S. Hel­fen­bein/Yale U.)


Black holes grow as they suck things up, but their growth usu­ally seems to re­spect cer­tain laws. Gi­ant black holes are found to ex­pand at the same rate as the ga­lax­ies to which they be­long, as­tro­no­mers say, be­cause the two pro­cesses in­flu­ence each oth­er. For in­stance, grow­ing black holes give off radia­t­ion that cur­tails star crea­t­ion. 

But the new find­ing chal­lenges this pic­ture. It’s a “gi­gan­ti­c black hole with­in a normal-size gal­axy,” said Ben­ny Trakht­en­brot, a re­search­er at ETH Zu­rich, a uni­vers­ity in Switz­er­land who is the lead au­thor of a re­port on the find­ings.

The ob­ject formed in the early uni­verse, roughly two bil­lion years af­ter the Big Bang that gave birth to eve­ry­thing, the as­tro­no­mers say. They found it dur­ing a proj­ect to map the growth of supermas­sive black holes across cos­mic time.

“Our sur­vey was de­signed to ob­serve the av­er­age ob­jects, not the ex­ot­ic ones,” said Yale Uni­vers­ity re­search­er C. Megan Urry, co-au­thor of the stu­dy, pub­lished in the jour­nal Sci­ence. “This proj­ect spe­cif­ic­ally tar­geted mod­er­ate black holes that in­hab­it typ­i­cal ga­lax­ies to­day. It was quite a shock to see such a gi­nor­mous black hole in such a deep field.”

The so-called deep-field sur­vey was de­signed to point at a small ar­ea of the sky for a long time in or­der to de­tect faint ga­lax­ies. The black hole in ques­tion, lo­cat­ed in a gal­axy des­ig­nat­ed as CID-947, is meas­ured as among the most mas­sive ev­er found, the equiv­a­lent of al­most 7 bil­lion Suns.

Most ga­lax­ies, in­clud­ing our own Milky Way, have a giant black hole at their cen­ter, weigh­ing the equi­valent of mil­lions to bil­lions of Suns. 

Stars were still form­ing in CID-947, the re­search­ers said, and the gal­axy could con­tin­ue to grow. They said CID-947 could be a pre­cur­sor of the most ex­treme, mas­sive sys­tems ob­served in to­day’s lo­cal uni­verse, such as the gal­axy NGC 1277 in the Per­seus con­stella­t­ion, 220 mil­lion light years from the Milky Way. But if so, they said, the growth of the black hole still greatly an­ti­cipated the growth of the sur­round­ing gal­axy, con­tra­ry to what as­tro­no­mers thought.

Urry and her col­leagues cred­ited the W.M. Keck Ob­serv­a­to­ry in Ha­waii and the Chan­dra COS­MOS leg­a­cy sur­vey in aid­ing the team’s work.


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Astronomers say they have spotted an apparent super-sized anomaly: a giant black hole that grew much faster than its host galaxy. The finding conflicts with most observations about black holes, massive objects with extraordinarily strong gravity that can pull in anything, even light. The more they suck up, the more they grow. Black holes grow as they suck things up, but their growth usually seems to respect certain laws. Giant black holes are found to expand at the same rate as the galaxies to which they belong, astronomers say, because the two processes influence each other. For instance, growing black holes give off radiation that curtails star creation. But the new finding challenges this picture. It’s a “gigantic black hole within a normal-size galaxy,” said Benny Trakhtenbrot, a researcher at ETH Zurich, a university in Switzerland who is the lead author of a report on the findings. The object formed in the early universe, roughly two billion years after the Big Bang that gave birth to everything, the astronomers say. They found it during a project to map the growth of supermassive black holes across cosmic time. “Our survey was designed to observe the average objects, not the exotic ones,” said Yale University researcher C. Megan Urry, co-author of the study, published in the journal Science. “This project specifically targeted moderate black holes that inhabit typical galaxies today. It was quite a shock to see such a ginormous black hole in such a deep field.” The so-called deep-field survey was designed to point at a small area of the sky for a long time in order to detect faint galaxies. The black hole in question, located in a galaxy designated as CID-947, is measured as among the most massive ever found, the equivalent of almost 7 billion Suns. Most galaxies, including our own Milky Way, have a black hole at their center, holding millions to billions of solar masses. Stars were still forming in CID-947, the researchers said, and the galaxy could continue to grow. They said CID-947 could be a precursor of the most extreme, massive systems observed in today’s local universe, such as the galaxy NGC 1277 in the Perseus constellation, 220 million light years from the Milky Way. But if so, they said, the growth of the black hole still greatly anticipated the growth of the surrounding galaxy, contrary to what astronomers thought. Urry and her colleagues credited the W.M. Keck Observatory in Hawaii and the Chandra COSMOS legacy survey in aiding the team’s work.