Super black hole a “headache” for astronomers

World Science staff

As­tro­no­mers have found a mam­moth ob­ject that they say smashes records for dis­tance and bright­ness and could shed light on a never-probed early stage of cos­mic his­tory.

The ob­ject is al­so, to some ex­tent, un­want­ed.

Cur­rent phys­i­cal the­o­ries don’t ac­count for such huge ob­jects ap­pear­ing as early in the his­to­ry of the un­iverse as this one is. The time of its ap­pear­ance can be es­ti­mat­ed by its dis­tance.

The ob­ject dubbed ULAS J1120+0641 is not the bright­est spot in this im­age. It is the tiny red dot to the left of it, near the mid­dle—its faint­ness due on­ly to its in­cred­i­ble dis­tance. (Cred­it: ES­O/UKIDSS/S­DSS)

“This gives as­tro­no­mers a head­ache,” said Dan­iel Mort­lock of Im­pe­ri­al Col­lege Lon­don, one of the dis­cov­er­ers and lead au­thor of a pa­per re­port­ing the find in the June 30 is­sue of the re­search jour­nal Na­ture.

“It’s dif­fi­cult to un­der­stand,” he ex­plained, how some­thing “a bil­lion times more mas­sive than the Sun can have grown so early in the his­to­ry of the un­iverse. It’s like roll­ing a snow­ball down the hill and sud­denly you find that it’s 20 feet across.”

This is­n’t the first time that prob­lem has come up; as­tro­no­mers have been work­ing on the­o­ries to ad­dress it. But the new ob­ject, the bright­est known by far so early in the his­tory of the uni­verse,  is per­haps the most dra­mat­ic ex­am­ple of the prob­lem.

The thing in ques­tion is be­lieved to be the most dis­tant known su­per­mas­sive black hole, a type of ob­ject so com­pact and heavy that its gra­vity over­whelms and drags in an­y­thing that strays too close, even light rays. Black holes aren’t di­rectly vis­i­ble, but can be seen when in­falling ob­jects heat up and be­come bright. In this case, riv­ers of gas are plung­ing in­to the black hole, re­search­ers say.

The dis­cov­ery came to light thanks to an on­go­ing sky sur­vey be­ing con­ducted at the U.K. In­fra­red Tel­e­scope and fol­low-up ob­serva­t­ions with the Gem­i­ni North tel­e­scope, both on Mauna Kea in Ha­waii. The black hole is al­so re­ferred to as a qua­sar, a type of black hole that sits and the cen­ter of a gal­axy guz­zling ma­te­ri­al, light­ing up the whole re­gion. To be pre­cise, “qua­sar” ac­tu­ally refers to the en­tire gal­axy, not just the black hole.

The light from this qua­sar started head­ing to­ward us when the un­iverse was only 6 per­cent of its pre­s­ent age, 770 mil­lion years af­ter the un­iverse was born, sci­en­tists say. The next most-dis­tant known qua­sar is seen as it was 870 mil­lion years af­ter that event. Be­cause of the dis­tance of these ob­jects, they ap­pear to us some­what as they would have back in their time.

“This qua­sar is a vi­tal probe of the early uni­verse. It is a very rare ob­ject that will help us to un­der­stand how su­per­mas­sive black holes grew,” said Ste­phen War­ren, the stu­dy’s team lead­er. Quasars are in ef­fect very bright, dis­tant ga­lax­ies thought to be pow­ered by “supermas­sive” black holes. Their bril­liance makes them pow­er­ful bea­cons that may help to probe the era when the first stars and ga­lax­ies were form­ing.

The new­found qua­sar, es­ti­mat­ed to weigh the equiv­a­lent of two bil­lion Suns, is so dis­tant that its light is be­lieved to probe the last part of an age called the reion­iz­a­tion era.

Some 300,000 years af­ter the Big Bang, an explosion-like event that sci­en­tists say cre­at­ed our uni­verse, the uni­verse had cooled down enough to al­low charged par­t­i­cles called elec­trons and pro­tons to com­bine in­to atoms of hy­dro­gen, a gas with no elec­tric charge. This cool dark gas would have per­me­at­ed the uni­verse un­til the first stars started form­ing about 100 to 150 mil­lion years lat­er. In­tense radia­t­ion from these stars slowly split the hy­dro­gen atoms back in­to pro­tons and elec­trons, a pro­cess called reion­iz­a­tion, mak­ing the uni­verse more trans­par­ent to ul­tra­vi­o­let light. It is be­lieve that this pro­cess, a mile­stone in cos­mic his­to­ry, oc­curred be­tween about 150 mil­lion to 800 mil­lion years af­ter the Big Bang.

An artist’s im­pres­sion shows how ULAS J1120+0641 may have looked from clos­er up. (ES­O/M. Ko­rn­messer).

Cos­mol­o­gists are keen to meas­ure the state of gas in the early un­iverse, and to un­der­stand how stars and ga­lax­ies formed. Most of the gas in the un­iverse is hy­dro­gen, and most of it is ion­ized to­day, mean­ing the elec­trons and pro­tons are sep­a­rat­ed.

The qua­sar is an op­por­tun­ity as well as a head­ache, be­cause it lets sci­en­tists meas­ure the con­di­tions in the gas that the qua­sar’s light passes through on its way to us, Mort­lock said. “What is par­tic­u­larly im­por­tant… is how bright it is,” he ex­plained. “It’s hun­dreds of times brighter than an­y­thing else yet dis­cov­ered at such a great dis­tance. This means that we can use it to tell us for the first time what con­di­tions were like in the early uni­verse.”

“It took us five years to find this ob­ject,” added Bram Ven­e­mans of the Eu­ro­pe­an South­ern Ob­serv­a­to­ry in Garch­ing, Ger­ma­ny, one of the au­thors of the stu­dy.

As one looks fur­ther away and thus fur­ther back in time, sci­en­tists rea­son that we should eventually reach the time when the hy­dro­gen was neu­tral, with the elec­trons and pro­tons com­bined as atoms. The light from the new qua­sar dis­plays the char­ac­ter­is­tic sig­na­ture of neu­tral gas, the in­ves­ti­ga­tors said. This sig­na­ture, show­ing the qua­sar pre­cedes the ep­och of reion­iz­a­tion, was pre­dicted in 1998 but has nev­er been ob­served be­fore.

“Be­ing able to an­a­lyze mat­ter at this crit­i­cal junc­ture in the his­to­ry of the uni­verse is some­thing we’ve been long striv­ing for but nev­er quite achieved. Now it looks like we have crossed the bar­ri­er,” said Steve War­ren of Im­pe­ri­al Col­lege, lead­er of the qua­sar team. “It’s like dis­cov­er­ing a new con­ti­nent which we can now ex­plore.” The qua­sar, named ULAS J1120+0641, was dis­cov­ered in the UKIRT In­fra­red Deep Sky Sur­vey, a new map of the sky as it ap­pears in in­fra­red light.