Dying white dwarf stars could be fertile ground for other EarthsMarch 31st, 2011 - 2:06 pm ICT by ANI
Washington, Mar 31 (ANI): The best place to look for planets that can support life is around dim, dying stars called white dwarfs.
Eric Agol, a University of Washington associate professor of astronomy, suggests that potentially habitable planets orbiting white dwarfs could be much easier to find — if they exist — than other exoplanets located so far.
White dwarfs, cooling stars believed to be in the final stage of life, typically have about 60 percent of the mass of the Sun, but by volume they are only about the size of Earth. Though born hot, they eventually become cooler than the Sun and emit just a fraction of its energy, so the habitable zones for their planets are significantly closer than Earth is to the Sun.
“If a planet is close enough to the star, it could have a stable temperature long enough to have liquid water at the surface — if it has water at all — and that’s a big factor for habitability,” Agol said.
A planet so close to its star could be observed using an Earth-based telescope as small as 1 meter across, as the planet passes in front of, and dims the light from, the white dwarf, he said.
White dwarfs evolve from stars like the Sun. When such a star’s core can no longer produce nuclear reactions that convert hydrogen to helium, it starts burning hydrogen outside the core.
That begins the transformation to a red giant, with a greatly expanded outer atmosphere that typically envelops — and destroys — any planets as close as Earth.
Finally the star sheds its outer atmosphere, leaving the glowing, gradually cooling, core as a white dwarf, with a surface temperature around 5,000 degrees Celsius (about 9,000 degrees Fahrenheit). At that point, the star produces heat and light in the same way as a dying fireplace ember, though the star’s ember could last for 3 billion years.
Once the red giant sheds its outer atmosphere, more distant planets that were beyond the reach of that atmosphere could begin to migrate closer to the white dwarf, Agol said. New planets also possibly could form from a ring of debris left behind by the star’s transformation.
In either case, a planet would have to move very close to the white dwarf to be habitable, perhaps 500,000 to 2 million miles from the star. That’s less than 1 percent of the distance from Earth to the Sun (93 million miles) and substantially closer than Mercury is to the Sun.
“From the planet, the star would appear slightly larger than our Sun, because it is so close, and slightly more orange, but it would look very, very similar to our Sun,” Agol said.
The planet also would be tidally locked, so the same side would always face the star and the opposite side would always be in darkness. The likely areas for habitation, he said, might be toward the edges of the light zone, nearer the dark side of the planet.
The study has been published online in The Astrophysical Journal Letters. (ANI)
- Earth-sized planets found beyond solar system - Dec 21, 2011
- NASA's Spitzer detects light of alien 'Super-Earth' - May 09, 2012
- New planet 22 light years away may host water - Feb 03, 2012
- First multi-planet solar system spotted - Aug 29, 2012
- Astronomers discover 'Rosetta Stone' for T-Dwarf stars - Nov 23, 2010
- Scientists discover first Earth-Size planets outside the Milky Way - Dec 21, 2011
- Scientists ferret out planet-hunting targets with NASA telescope - Apr 08, 2011
- Hubble observes star eating a planet - May 21, 2010
- Astronomers spot merging star systems that might explode - Nov 17, 2010
- Exoplanets with two suns sprout black plants: Study - Apr 21, 2011
- Exoplanet neighbour smaller than Earth discovered - Jul 19, 2012
- Kepler 10b planet discovered - Jan 12, 2011
- New 'super-earth' 40 light years away might have water - Dec 03, 2010
- 'Watery, rocky planets are commonplace in the Milky Way' - Apr 13, 2010
- New addition to solar system may be bigger than Jupiter - Feb 14, 2011
Tags: degrees celsius, distant planets, ember, eric agol, exoplanets, fertile ground, habitable planets, habitable zones, heat and light, helium, hydrogen, liquid water, mass of the sun, nuclear reactions, outer atmosphere, red giant, stable temperature, stage of life, surface temperature, white dwarf stars