[meteorite-list] Graphite Whiskers, Rather Than Dark Energy, Could Explain Dimness Of Stellar Explosions

[Darren Garrison]

http://www.sciencedaily.com/releases/2008/02/080228143538.htm

Graphite Whiskers, Rather Than Dark Energy, Could Explain Dimness Of Stellar
Explosions
ScienceDaily (Feb. 29, 2008) — Interstellar space may be strewn with tiny
whiskers of carbon, dimming the light of far-away objects. This discovery by
scientists at the Carnegie Institution may have implications for the "dark
energy" hypothesis, proposed a decade ago in part to explain the unexpected
dimness of certain stellar explosions called Type1a supernovae.

Type1a supernovae are among the brightest objects in the universe. Astronomers
use them as "standard candles" to gauge cosmological distances:
brighter-appearing supernovae are closer, dimmer ones are farther away. In the
late 1990s some astronomers noticed that some seemed too dim--too far away--to
be explained by conventional theories of the universe's expansion. This led to
the hypothesis that the expansion was accelerating, pushed along by an unknown
form of energy -- dark energy.

In the current study, published in the February 29 issue of Science, Andrew
Steele and Marc Fries of the Carnegie Institution's Geophysical Laboratory
report the discovery of an unusual new form of carbon in minerals within
meteorites dating from the formation of the solar system. These "graphite
whiskers" were likely produced from carbon-rich gas at high temperatures and
were found within features called calcium-aluminum inclusions, which at around
4.5 billion years old are the oldest known solids in our solar system.

"During this time when the sun was young, the solar wind was very strong," says
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 as
well."

Graphite whiskers might also be produced and dispersed into space by supernovae
explosions.

A thin interstellar haze of graphite whiskers spewed from stars and supernovae
would affect how different wavelengths of light pass through space. It has been
postulated that wavelengths in the near infrared would be particularly affected.
It is the dimming of light from Type 1a supernovae at these wavelengths that
first led researchers to think that the universe's expansion was accelerating
and that therefore a hitherto unknown force "dark energy"must exist. However,
since the 1970s it has been postulated that graphite or other whisker-like
materials could explain the observations. The presence of graphite whiskers in
space has never been confirmed until this study.

With the discovery of graphite whiskers in the meteorite, researchers can test
their properties against the cosmological models and astronomical observations.

"If graphite whiskers in space are absorbing supernovae's light," says Steele,
"then this could affect measurements of the rate of the universe's expansion.
While we cannot comment further on the effects of whiskers on the dark energy
hypothesis 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."

Adapted from materials provided by Carnegie Institution, via EurekAlert!, a
service of AAAS.