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Black holes may scatter “seeds of life” through cosmos

April 22, 2007
Courtesy Harvard-Smithsonian Center for Astrophysics
and World Science staff

Black holes aren’t the all-consuming mon­sters they’re of­ten por­trayed as, new re­search has found: in­stead, warm gas es­cap­ing from the clutches of gi­ant black holes could be one source of the chem­i­cal el­e­ments used for life.

NGC 4051 (Courtesy CfA)


Black holes are cos­mic ob­jects con­sist­ing of tre­men­dous amounts of ma­te­rial packed in­to a ti­ny space. The huge quan­ti­ty of mat­ter ex­erts a grav­i­ta­tion­al pull so strong that it sucks in eve­ry­thing near­by, in­clud­ing light. 

Im­me­di­ate­ly af­ter the Big Bang ex­plo­sion that as­tro­no­mers be­lieve gave birth to the uni­verse, the cos­mos is thought to have con­tained on­ly hy­dro­gen and he­li­um, the light­est chem­i­cal el­e­ments. 

Heav­i­er el­e­ments had to be cooked up in stars, then scat­tered to be in­cor­po­rat­ed in oth­er stars and their plan­ets. Black holes may have helped spread those el­e­ments across the cos­mos, sci­en­tists now say.

Black holes tend to suck in clouds of gas that sur­round them, but not all gas falls in. Un­til the gas crosses a bound­a­ry known as the event ho­ri­zon, it can still es­cape if it is heat­ed, that is en­er­gized, enough. 

“One of the big ques­tions in cos­mol­o­gy is how much in­flu­ence mas­sive black holes ex­ert on their sur­roundings,” said Mar­tin El­vis of the Har­vard-Smith­son­ian Cen­ter for As­t­ro­phys­ics in Cam­bridge, Mass. “This re­search helps an­swer that ques­tion.” A group of as­tro­no­mers in­clud­ing El­vis found that hot winds from gi­ant black holes in the cen­ters of ga­lax­ies may b­low heavy el­e­ments like car­bon and ox­y­gen in­to the vast space be­tween ga­lax­ies. 

Most ga­lax­ies are thought to con­tain a “supe­rmas­sive” black hole at their cen­ter. The re­search team, led by Yair Kro­n­gold of the Uni­ver­si­dad Na­cional Au­tonoma de Mex­i­co, stud­ied such an ob­ject at the cen­ter of a gal­axy called NGC 4051. They found that gas was es­cap­ing from much clos­er to the black hole than pre­vi­ously thought. 

The out­flow source was about 2,000 times fur­ther from the black hole cen­ter than the dis­tance from there to its event ho­ri­zon—a length called the Schwarz­sc­hild ra­di­us that is about four mil­lion miles for this black hole. The team al­so es­ti­mat­ed the frac­tion of gas that avoided be­ing swal­lowed; this turned out to be smaller than ear­li­er stud­ies sug­gested. “We cal­cu­late that be­tween two to five pe­r­cent of the ac­cret­ing ma­te­ri­al is flow­ing back out,” said team mem­ber Fab­rizio Nicas­tro of the Cen­ter for As­t­ro­phys­ics.

Winds from black holes have been clocked at speeds of up to four mil­lion miles per hour, re­search­ers said. So over thou­sands of years, el­e­ments such as car­bon and ox­y­gen in those winds can trav­el huge dis­tances; they eventually be­come part of great clouds of gas and dust, called neb­u­lae, that form new stars and plan­ets. The re­search, which used da­ta from the Eu­ro­pe­an Space Agen­cy’s XMM-Newton sat­el­lite, is re­ported in the April 20 is­sue of the re­search pub­li­ca­tion As­t­ro­phys­i­cal Jour­nal.


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Black holes aren’t the all-consuming monsters they’re often portrayed as, new research has found: instead, warm gas escaping from the clutches of giant black holes could be one source of the chemical elements used for life. Black holes are cosmic objects in which a tremendous amount of matter is packed into a tiny space. The huge quantity of matter exerts a gravitational pull so strong that it sucks in everything nearby, including light. Immediately after the Big Bang explosion that astronomers believe gave birth to the universe, the cosmos is thought to have contained only hydrogen and helium, the lightest chemical elements. Heavier elements had to be cooked up in stars, then scattered to be incorporated in other stars and their planets. Black holes may have helped spread those elements across the cosmos, scientists now say. Black holes tend to suck in clouds of gas that surround them, but not all gas falls in. Until it crosses a boundary known as the event horizon, it can still escape if it is heated, that is energized, enough.”One of the big questions in cosmology is how much influence massive black holes exert on their surroundings,” said Martin Elvis of the Harvard-Smithsonian Center for Astro physics in Cambridge, Mass. “This research helps answer that question.” A group of astronomers including Elvis found that hot winds from giant black holes in the centers of galaxies may blow heavy elements like carbon and oxygen into the vast space between galaxies. Most galaxies are thought to contain a “supermassive” black hole at their center. The research team, led by Yair Krongold of the Universidad Nacional Autonoma de Mexico, studied such an object at the center of a galaxy called NGC 4051. They found that gas was escaping from much closer to the black hole than previously thought. The outflow source was about 2,000 times further from the black hole center than the distance to its event horizon—a length called the Schwarzschild radius, which is about four million miles for this black hole. The team also estimated the fraction of gas that avoided being swallowed; this turned out to be smaller than earlier studies suggested. “We calculate that between 2 to 5 percent of the accreting material is flowing back out,” said team member Fabrizio Nicastro of the Center for Astro physics. Winds from black holes have been clocked at speeds of up to four million miles per hour, researchers said. So over thousands of years, elements such as carbon and oxygen in those winds can travel huge distances; they eventually become part of great clouds of gas and dust, called nebulae, that form new stars and planets. The research, which used data from the European Space Agency’s XMM-Newton satellite, is reported in the April 20 issue of the research publication Astro physical Journal.