How light travels through various media can tell us volumes. Take the phenomenon called ‘extinction,’ which describes what happens to light as it encounters dust and gas between the original object and our position on Earth. Studying this effect led to our earliest understanding of interstellar dust as a factor to be taken into account of when discussing the space between the stars. And because we have much to learn about what is in that space, a new observation proves useful indeed, adding to our options for the study of ‘dark energy,’ the mysterious repulsive force that seems to account for the accelerating expansion of the universe.
Examining what they describe as a new form of carbon found within minerals in meteorites, Andrew Steele and Marc Fries (Carnegie Institution) examine the question of how these so-called ‘graphite whiskers’ might affect astronomical observations. The going theory is that the whiskers may have formed near the Sun early in our Solar System’s life, being pushed into interstellar space through the action of the solar wind. Supernovae may also be a factor in their production.
We’re early in the game on this, but a haze of this material would clearly have effects on the way light passes through space. Type 1a supernovae have been considered to be ‘standard candles,’ their brightness offering a useful gauge of their distance. It was observations of particular Type 1a supernovae whose light was believed to be dimmer than it ought to have been at near infrared wavelengths that in the 1990’s helped to shape the accelerated expansion theory.
But if these supernovae are dimmer than expected, accelerated expansion is but one explanation. An alternative in the form of some kind of intervening material has long been suggested as a solution, but evidence for graphite whiskers has never been confirmed until now. Which leads us to Andrew Steele’s interesting comment:
“If graphite whiskers in space are absorbing supernovae’s light, 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.”
The researchers note that graphite whiskers ought to form close to the Sun in the condensation period as protoplanetary disk materials coalesce. The inference, then, is that any young star system may expel such whiskers, accounting for what could be a factor to be reckoned with in near infrared dimming. The paper is Fries and Steele, “Graphite Whiskers in CV3 Meteorites,” Science Express February 28, 2008 (abstract). More in this Carnegie Institution news release.