"Long before it's in the papers"
June 03, 2013

RETURN TO THE WORLD SCIENCE HOME PAGE


Scientists plan to snap picture of black hole

Jan. 18, 2012
Courtesy of the Un­ivers­ity of Ar­i­zo­na
and World Science staff

As­tro­no­mers, phys­i­cists and oth­er sci­en­tists plan to meet in Tuc­son, Ariz. Jan. 18 to 20 to dis­cuss an en­deav­or that a few years ago would have been re­garded as out­ra­geous.

“No­body has ev­er tak­en a pic­ture of a black hole,” said Uni­vers­ity of Ar­i­zo­na as­t­ro­phys­i­cist Dim­itrios Psaltis, who co-organized the event with Dan Mar­rone, an as­tronomer at the uni­vers­ity’s Stew­ard Ob­serv­a­to­ry.

“We are go­ing to do just that.” 

Galaxies such as the one dubb­ed NGC 2841, above—as well as our own Milky Way—are be­lieved to have black holes bur­ied deep within their bright cores. (Cre­dit: NA­SA, ESA, Hub­ble Heri­tage (STScI / AURA) - ESA / Hub­ble Col­la­bor­a­tion)


“E­ven five years ago, such a pro­pos­al would not have seemed cred­i­ble,” said Shep­erd Doele­man, as­sis­tant di­rec­tor of the Hay­stack Ob­serv­a­to­ry at Mas­sa­chu­setts In­sti­tute of Tech­nol­o­gy, who is the prin­ci­pal in­ves­ti­ga­tor of the Event Ho­ri­zon Tel­e­scope, as the proj­ect is dubbed. “Now we have the tech­no­log­i­cal means to take a stab at it.” 

First pos­tu­lat­ed by Al­bert Ein­stein’s Gen­er­al The­o­ry of Rel­a­ti­vity, the ex­ist­ence of black holes has since been sup­ported by dec­ades’ worth of ob­serva­t­ions, mea­sure­ments and ex­pe­ri­ments. But nev­er has it been pos­si­ble to di­rectly ob­serve and im­age one of these mael­stroms whose sheer gra­vity ex­erts such cat­a­clys­mic pow­er that it twists and man­gles the very fab­ric of space and time.

“Black holes are the most ex­treme en­vi­ron­ment you can find in the un­iverse,” Doele­man said.

The field of gra­vity around a black hole is so im­mense that it swal­lows ev­erything in its reach; not even light can es­cape its grip. For that rea­son, black holes are just that; they emit no light whatsoev­er, their “noth­ing­ness” blend­ing in­to the black void of the uni­verse.

So how does one take a pic­ture of some­thing that by def­i­ni­tion is impos­si­ble to see? “As dust and gas swirls around the black hole be­fore it is drawn in­side, a kind of cos­mic traf­fic jam en­sues,” Doele­man ex­plained. “Swirling around the black hole like wa­ter cir­cling the drain in a bath­tub, the mat­ter com­presses and the re­sult­ing fric­tion turns it in­to plas­ma heat­ed to a bil­lion de­grees or more, caus­ing it to ‘glow.’” The re­sult­ing light is what we can see. 

By im­ag­ing the glow of mat­ter swirling around the black hole be­fore it goes over the edge and plunges in­to the abyss of space and time, sci­en­tists can only see the out­line of the black hole, al­so called its shad­ow. Be­cause the laws of phys­ics ei­ther don’t apply to or can­not de­scribe what hap­pens be­yond that point of no re­turn from which not even light can es­cape, that bound­a­ry is called the Event Ho­ri­zon.

“So far, we have indi­rect ev­i­dence that there is a black hole at the cen­ter of the Milky Way,” Psaltis said. “But once we see its shad­ow, there will be no doubt.” Even though the black hole sus­pected to sit at the cen­ter of our gal­axy is a su­per­mas­sive one at four mil­lion times the mass of the Sun, it is ti­ny to the eyes of as­tro­no­mers. Smaller than Mer­cury’s or­bit around the Sun, yet al­most 26,000 light-years away, it ap­pears about the same size as a grape­fruit on the Moon.

“To see some­thing that small and that far away, you need a very big tel­e­scope, and the big­gest tel­e­scope you can make on Earth is to turn the whole plan­et in­to a tel­e­scope,” Mar­rone said.

To that end, the team is con­nect­ing up to 50 ra­di­o tel­e­scopes scat­tered around the globe, in­clud­ing the Sub­mil­lime­ter Tel­e­scope on Mt. Gra­ham in Ar­i­zo­na, tel­e­scopes on Mauna Kea in Ha­waii and the Com­bined Ar­ray for Re­search in Mil­li­me­ter-wave As­tron­o­my in Cal­i­for­nia. The glob­al ar­ray will in­clude sev­eral ra­di­o tel­e­scopes in Eu­rope, a 10-meter dish at the South Pole and po­ten­tially a 15-meter an­ten­na atop a 15,000-foot peak in Mex­i­co.

“In es­sence, we are mak­ing a vir­tu­al tel­e­scope with a mir­ror that is as big as the Earth,” Doele­man said. “Each ra­di­o tel­e­scope we use can be thought of as a small sil­vered por­tion of a large mir­ror. With enough such sil­vered spots, one can start to make an im­age.” 

“The Event Ho­ri­zon Tel­e­scope is not a first-light proj­ect, where we flip a switch and go from no da­ta to a lot of da­ta,” he added. “Every year, we in­crease its ca­pa­bil­i­ties by adding more tel­e­scopes, grad­u­ally sharp­en­ing the im­age we see of the black hole.” 

One cru­cial and ea­gerly ex­pected key el­e­ment about to join Event Ho­ri­zon’s glob­al net­work of ra­di­o tel­e­scopes is the At­a­cama Large Mil­li­me­ter Ar­ray in Chil­e. Com­pris­ing 50 ra­di­o an­ten­nas it­self, the ar­ray is to func­tion as the equiv­a­lent of a light-collecting dish that is 90 me­ters (yards) wide. 

“We will be able to ac­tu­ally see what hap­pens very close to the ho­ri­zon of a black hole, which is the strongest gravita­t­ional field you can find in the un­iverse,” Psaltis said. “No one has ev­er tested Ein­stein’s Gen­er­al The­o­ry of Rel­a­ti­vity at such strong fields.” The theory pre­dicts that the bright out­line de­fin­ing the black hole’s shad­ow must be a per­fect cir­cle.

“If we find the black hole’s shad­ow to be ob­late [a flat­tened cir­cle] in­stead of cir­cu­lar, it means Ein­stein’s Gen­er­al The­o­ry of Rel­a­ti­vity must be flawed,” he said. “But even if we find no de­via­t­ion from gen­er­al rel­a­ti­vity, all these pro­cesses will help us un­der­stand the fun­da­men­tal as­pects of the the­o­ry much bet­ter.” Black holes re­main among the least un­der­stood phe­nom­e­na in the un­iverse. Rang­ing in mass from a few times the mass of the Sun to bil­lions, they ap­pear to co­a­lesce like drops of oil in wa­ter. Most if not all ga­lax­ies are now be­lieved to har­bor a su­per­mas­sive black hole at their cen­ter, and smaller ones are scat­tered through­out. Our Milky Way is al­so be­lieved to house about 25 small­ish black holes rang­ing from 5 to 10 times the Sun’s mass.

“What is great about the one in the cen­ter of the Milky Way is that it is big enough and close enough,” Mar­rone said. “There are big­ger ones in oth­er ga­lax­ies, and there are clos­er ones, but they’re smaller. Ours is just the right com­bina­t­ion of size and dis­tance.” 

The rea­son as­tro­no­mers rely on ra­di­o waves rath­er than vis­i­ble light to spy on the black hole is two-fold: For one, ob­serving the cen­ter of the Milky Way from the Earth re­quires peer­ing through vast oceans of stars, gas and dust that ob­struct the view, but ra­di­o waves can pass through such block­ages. Sec­ond­ly, only ra­di­o waves lend them­selves to com­bining many tel­e­scopes in­to a vir­tu­al super-tel­e­scope. But only very re­cent tech­no­log­i­cal ad­vanc­es have made it pos­si­ble to work out the de­tails of this proj­ect, re­search­ers said.

Each tel­e­scope will rec­ord its da­ta on­to hard drives, which is to be be col­lect­ed and shipped to a cen­tral da­ta pro­cess­ing cen­ter at MIT’s Hay­stack Ob­serv­a­to­ry. “This is not only the usu­al in­terna­t­ional con­fer­ence where peo­ple come from all over the world be­cause they are in­ter­est­ed in shar­ing their re­search,” Psaltis said. “For the Event Ho­ri­zon Tel­e­scope, we need the en­tire world to come to­geth­er to build this in­stru­ment be­cause it is as big as the plan­et. Peo­ple are com­ing from all over the world be­cause they have to work on it.”


* * *

Send us a comment on this story, or send it to a friend

Homepage image: Artist's conception of a black hole






 

Sign up for
e-newsletter
   
 
subscribe
 
cancel

On Home Page         

LATEST

  • Meet­ing on­line may lead to hap­pier mar­riages

  • Pov­erty re­duction, environ­mental safe­guards go hand in hand: UN re­port

EXCLUSIVES

  • Was black­mail essen­tial for marr­iage to evolve?

  • Plu­to has even cold­er “twin” of sim­ilar size, studies find

  • Could simple an­ger have taught people to coop­erate?

  • Diff­erent cul­tures’ mu­sic matches their spe­ech styles, study finds

MORE NEWS

  • F­rog said to de­scribe its home through song

  • Even r­ats will lend a help­ing paw: study

  • D­rug may undo aging-assoc­iated brain changes in ani­mals

Astronomers, physicists and other scientists plan to meet in Tucson, Ariz. Jan. 18 to 20 to discuss an endeavor that a few years ago would have been regarded as outrageous. “Nobody has ever taken a picture of a black hole,” said University of Arizona astrophysicist Dimitrios Psaltis, who co-organized the event with Dan Marrone, an astronomer at the university’s Steward Observatory. “We are going to do just that.” “Even five years ago, such a proposal would not have seemed credible,” said Sheperd Doeleman, assistant director of the Haystack Observatory at Massachusetts Institute of Technology, who is the principal investigator of the Event Horizon Telescope, as the project is dubbed. “Now we have the technological means to take a stab at it.” First postulated by Albert Einstein’s General Theory of Relativity, the existence of black holes has since been supported by decades’ worth of observations, measurements and experiments. But never has it been possible to directly observe and image one of these maelstroms whose sheer gravity exerts such cataclysmic power that it twists and mangles the very fabric of space and time. “Black holes are the most extreme environment you can find in the universe,” Doeleman said. The field of gravity around a black hole is so immense that it swallows everything in its reach; not even light can escape its grip. For that reason, black holes are just that; they emit no light whatsoever, their “nothingness” blending into the black void of the universe. So how does one take a picture of something that by definition is impossible to see? “As dust and gas swirls around the black hole before it is drawn inside, a kind of cosmic traffic jam ensues,” Doeleman explained. “Swirling around the black hole like water circling the drain in a bathtub, the matter compresses and the resulting friction turns it into plasma heated to a billion degrees or more, causing it to ‘glow.’” The resulting light is what we can see. By imaging the glow of matter swirling around the black hole before it goes over the edge and plunges into the abyss of space and time, scientists can only see the outline of the black hole, also called its shadow. Because the laws of physics either don’t apply to or cannot describe what happens beyond that point of no return from which not even light can escape, that boundary is called the Event Horizon. “So far, we have indirect evidence that there is a black hole at the center of the Milky Way,” Psaltis said. “But once we see its shadow, there will be no doubt.” Even though the black hole suspected to sit at the center of our galaxy is a supermassive one at four million times the mass of the Sun, it is tiny to the eyes of astronomers. Smaller than Mercury’s orbit around the Sun, yet almost 26,000 light-years away, it appears about the same size as a grapefruit on the Moon. “To see something that small and that far away, you need a very big telescope, and the biggest telescope you can make on Earth is to turn the whole planet into a telescope,” Marrone said. To that end, the team is connecting up to 50 radio telescopes scattered around the globe, including the Submillimeter Telescope on Mt. Graham in Arizona, telescopes on Mauna Kea in Hawaii and the Combined Array for Research in Millimeter-wave Astronomy in California. The global array will include several radio telescopes in Europe, a 10-meter dish at the South Pole and potentially a 15-meter antenna atop a 15,000-foot peak in Mexico. “In essence, we are making a virtual telescope with a mirror that is as big as the Earth,” Doeleman said. “Each radio telescope we use can be thought of as a small silvered portion of a large mirror. With enough such silvered spots, one can start to make an image.” “The Event Horizon Telescope is not a first-light project, where we flip a switch and go from no data to a lot of data,” he added. “Every year, we increase its capabilities by adding more telescopes, gradually sharpening the image we see of the black hole.” One crucial and eagerly expected key element about to join Event Horizon’s global network of radio telescopes is the Atacama Large Millimeter Array in Chile. Comprising 50 radio antennas itself, the array is to function as the equivalent of a light-collecting dish that is 90 meters (yards) wide. “We will be able to actually see what happens very close to the horizon of a black hole, which is the strongest gravitational field you can find in the universe,” Psaltis said. “No one has ever tested Einstein’s General Theory of Relativity at such strong fields.” General relativity predicts that the bright outline defining the black hole’s shadow must be a perfect circle. According to Psaltis, whose research group specializes in relativity theory, this provides an important test. “If we find the black hole’s shadow to be oblate [a flattened circle] instead of circular, it means Einstein’s General Theory of Relativity must be flawed,” he said. “But even if we find no deviation from general relativity, all these processes will help us understand the fundamental aspects of the theory much better.” Black holes remain among the least understood phenomena in the universe. Ranging in mass from a few times the mass of the Sun to billions, they appear to coalesce like drops of oil in water. Most if not all galaxies are now believed to harbor a supermassive black hole at their center, and smaller ones are scattered throughout. Our Milky Way is also believed to house about 25 smallish black holes ranging from 5 to 10 times the Sun’s mass. “What is great about the one in the center of the Milky Way is that it is big enough and close enough,” Marrone said. “There are bigger ones in other galaxies, and there are closer ones, but they’re smaller. Ours is just the right combination of size and distance.” The reason astronomers rely on radio waves rather than visible light to spy on the black hole is two-fold: For one, observing the center of the Milky Way from the Earth requires peering through vast oceans of stars, gas and dust that obstruct the view, but radio waves can pass through such blockages. Secondly, only radio waves lend themselves to combining many telescopes into a virtual super-telescope. But only very recent technological advances have made it possible to work out the details of this project, researchers said. Each telescope will record its data onto hard drives, which is to be be collected and shipped to a central data processing center at MIT’s Haystack Observatory. “This is not only the usual international conference where people come from all over the world because they are interested in sharing their research,” Psaltis said. “For the Event Horizon Telescope, we need the entire world to come together to build this instrument because it is as big as the planet. People are coming from all over the world because they have to work on it.”