Thursday, February 28, 2013

White Dwarfs and life beside them

Scientists widen their perspective hunting planets that harbor life. According to a new theoretical study of Earth-like planets orbiting white dwarf stars, oxygen in such planets could be more easily detected than in planets orbiting a Sun-like star (where oxygen would indicate life). Best part: we might be able to detect such a planet within the next decade, thanks to NASA’s James Webb Telescope (JWST).

A white dwarf is what remains after a star like our Sun dies. It puffs of its outer layers leaving a hot core that can be about the size of the Earth. It is much smaller and fainter than the Sun, but it can give enough heat to a nearby world for billions of years. Before becoming a white dwarf though, a star swells into a red giant, destroying any nearby planets. Thus, any planet would either have to arrive in the habitable zone afterwards or form from the disks of dust that reportedly surround white dwarfs.

How does life relate? Well, certain biomarkers in a planet’s atmosphere (like oxygen, or methane) indicate the presence of life. Such biomarkers are elements that regenerate with the help of biological processes. For example, oxygen in our atmosphere is constantly replenished by plant and algae. Should all life suddenly vanish, oxygen would decline as it would oxidize rocks and dissolve in the oceans. So, large quantities of oxygen in a distant planet would likely mean life there.

Scientists use photometry to determine the consistency of a planet’s atmosphere. Light coming from the parent star of that planet passes though the atmosphere and is absorbed by certain elements that exist there. Thus, more light than normal will be blocked at particular wavelengths, and using that signature, scientists can determine the elements present.

As the new study shows, white dwarfs are a lot better to observe than Sun-like stars. Problems would arise observing planets around normal stars, as the extreme faintness of the biomarker signals would “hide” in the glare of the parent star. In white dwarfs though, the dim light will greatly enhance our ability to see the O2 biomarker in particular. JWST could perform those observations.

Problem is exoplanets have yet to be found around white dwarfs. However, several evidence suggest they exist, like dust disks around them. Still, scientists must first find one before observing it.

Looking forward to the JWST launch.

The paper:

Image: Artist’s impression of a planet orbiting a white dwarf. Hydrogen gas ejected from the star as it evolved from a red giant to a white dwarf, is seen as a blue ring (Credit: David A. Aguilar(CfA))

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