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Dark energy, or just dust? Findings raise questions

March 1, 2008
Courtesy Carnegie Institution
and World Science staff

Out­er space may be strewn with ti­ny whiskers of car­bon that dim far­a­way ob­jects, re­search­ers say. They add that this might ex­plain pre­vi­ous find­ings that led to the view, , now widely ac­cept­ed by sci­en­tists, that a mys­te­ri­ous “dark en­er­gy” per­vades the cos­mos.

Ultra­violet im­age of a Type 1a su­per­no­va, des­ig­nat­ed 2005ke, in the spir­al gal­axy NGC 1371. The su­per­no­va is cir­cled. The im­age was tak­en with NA­SA's Swift sat­el­lite.


Sci­en­tists pro­posed the dark en­er­gy hy­poth­e­sis a dec­ade ago in part to ex­plain the un­ex­pected dim­ness of cer­tain stel­lar ex­plo­sions called Type1a su­per­novae. As­tro­no­mers use these bright bursts as “s­tan­dard can­dles” to gauge cos­mic dis­tances. 

Since the explosions are be­lieved to all have about the same in­trin­sic bright­ness, bright­er-look­ing ones are judged clos­er, and dim­mer ones fur­ther.

In the late 1990s re­search­ers no­ticed that some of them seemed too dim—too dis­tan­t—to fit stand­ard the­o­ries. This led to the hy­poth­e­sis that an on­go­ing ex­pan­sion of the uni­ver­se was ac­cel­er­at­ing, pushed by an un­known form of en­er­gy dubbed dark en­er­gy.

In the new stu­dy, An­drew Steele and Marc Fries of the Car­ne­gie In­sti­tu­tion in Wash­ing­ton, D.C. re­port dis­cov­er­ing an un­usu­al new form of car­bon in min­er­als with­in me­te­orites dat­ing from the forma­t­ion of the So­lar Sys­tem. The find­ings ap­pear in the Feb. 29 is­sue of the re­search jour­nal Sci­ence.

The “graph­ite whiskers” were likely pro­duced from hot, car­bon-rich gas and were found in parts of the me­te­orites called cal­cium-alu­min­um in­clu­sions, the in­ves­ti­ga­tors said. At around 4.5 bil­lion years old, these are the old­est known solids in our so­lar sys­tem. “Dur­ing this time when the sun was young, the so­lar wind was very strong,” a cur­rent of par­ti­cles that blow out­ward from the sun, said Fries. “So graph­ite whiskers formed near the sun could have been blown in­to interstel­lar space. The same thing may have hap­pened around oth­er young stars.”

Graph­ite whiskers might al­so be cre­at­ed and dis­persed by su­per­novae, he added. A thin haze of the whisk­ers in space would af­fect how light of dif­fer­ent wave­lengths, or en­er­gies, passes through space. It has been pos­tu­lat­ed, the re­search­ers said, that light of so-called near-infrared wave­lengths would be par­tic­u­larly af­fected—the same wave­lengths whose dim­ming first led to the dark en­er­gy model.

Graph­ite whiskers or si­m­i­lar ma­te­ri­als have been pro­posed to pos­sibly ex­plain those ob­serva­t­ions be­fore, but their pres­ence in space has nev­er been con­firmed pre­vi­ously, said Steele and Fries. With their discovery in the me­te­or­ite, the pair added, re­search­ers can test the whiskers’ prop­er­ties against the­o­ries and ob­serva­t­ions.

“We can­not com­ment fur­ther” on the im­pli­ca­tions for dark en­er­gy, Steele said, but “it is im­por­tant to study the char­ac­ter­is­tics of this form of car­bon care­fully so we can un­der­stand its im­pact on dark en­er­gy mod­els. We’ll then feed this da­ta for­ward to the up­com­ing NASA and ESA (Eu­ro­pe­an Space Agen­cy) mis­sions that will look for the ef­fects of dark en­er­gy.”


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Outer space may be strewn with tiny whiskers of carbon that dim faraway objects, researchers say. They add that this might explain previous findings that led to the view that a mysterious “dark energy” permeates the cosmos, now widely accepted among scientists. Scientists proposed the dark energy hypothesis a decade ago in part to explain the unexpected dimness of certain stellar explosions called Type1a supernovae. Astronomers use these bright bursts as “standard candles” to gauge cosmic distances. Since they’re believed to all have about the same instrinsic brightness, brighter-looking supernovae are thought to be closer, dimmer ones further. In the late 1990s researchers noticed that some of these objects seemed too dim—too distant—to fit standard theories. This led to the hypothesis that an ongoing expansion of the universe was accelerating, pushed by an unknown form of energy dubbed dark energy. In the new study, Andrew Steele and Marc Fries of the Carnegie Institution in Washington, D.C. report discovering an unusual new form of carbon in minerals within meteorites dating from the formation of the Solar System. The findings appear in the February 29 issue of the research journal Science. The “graphite whiskers” were likely produced from hot, carbon-rich gas and were found in parts of the meteorites called calcium-aluminum inclusions, the investigators said. At around 4.5 billion years old, these inclusions are the oldest known solids in our Solar System. “During this time when the Sun was young, the solar wind was very strong,” said Fries. “So graphite whiskers formed near the sun could have been blown into interstellar space. The same thing may have happened around other young stars.” Graphite whiskers might also be created and dispersed by supernovae, he added. A thin interstellar haze of the whiskers would affect how light of different wavelengths, or energies, passes through space. It has been postulated, the researchers said, that light of so-called near-infrared wavelengths would be particularly affected—the same wavelengths whose dimming first led to the dark energy hypothesis. Graphite whiskers or similar materials have been proposed to possibly explain those observations before, but their presence in space has never been confirmed previously, said Steele and Fries. With their discovery in the meteorite, the pair added, researchers can test the whiskers’ properties against theories and observations. “We cannot comment further on the effects of whiskers on the dark energy hypothesis,” Steele said, but “it is important to study the characteristics of this form of carbon carefully so we can understand its impact on dark energy models. We’ll then feed this data forward to the upcoming NASA and ESA (European Space Agency) missions that will look for the effects of dark energy.”