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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.”