Featured Research

from universities, journals, and other organizations

Astrophysicist: White dwarfs could be fertile ground for other Earths

Date:
March 31, 2011
Source:
University of Washington
Summary:
Hundreds of planets have been discovered outside the solar system in the last decade. Now an astrophysicist is suggesting that the best place to look for planets that could support life is around dying stars called white dwarfs.

This Hubble Space Telescope image shows the "last hurrah" of a star like our sun, the outer layers of gas being cast off and leaving behind the burned out white dwarf, the white dot in the center.
Credit: NASA/European Space Agency

Planet hunters have found hundreds of planets outside the solar system in the last decade, though it is unclear whether even one might be habitable. But it could be that the best place to look for planets that can support life is around dim, dying stars called white dwarfs.

In a new paper published online March 29 in The Astrophysical Journal Letters, 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. They are much 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 nearest white dwarf to Earth is Sirius B at a distance of about 8.5 light years (a light year is about 6 trillion miles). It is believed to once have been five times more massive than the sun, but now it has about the same mass as the sun packed into the same volume as Earth.

Agol is proposing a survey of the 20,000 white dwarfs closest to Earth. Using a 1-meter ground telescope, he said, one star could be surveyed in 32 hours of observation. If there is no telltale dimming of light from the star in that time, it means no planet orbiting closely enough to be habitable is passing in front of the star so that it is easily observable from Earth. Ideally, the work could be carried out by a network of telescopes that would make successive observations of a white dwarf as it progresses through the sky.

"This could take a huge amount of time, even with such a network," he said.

The same work could be accomplished by larger specialty telescopes, such as the Large Synoptic Survey Telescope that is planned for operations later this decade in Chile, of which the UW is a founding partner. If it turns out that the number of white dwarfs with potential Earthlike planets is very small -- say one in 1,000 -- that telescope still would be able to track them down efficiently.

Finding an Earthlike planet around a white dwarf could provide a meaningful place to look for life, Agol said. But it also would be a potential lifeboat for humanity if Earth, for some reason, becomes uninhabitable.

"Those are the reasons I find this project interesting," he said. "And there's also the question of, 'Just how special is Earth?'"


Story Source:

The above story is based on materials provided by University of Washington. The original article was written by Vince Stricherz. Note: Materials may be edited for content and length.


Journal Reference:

  1. Eric Agol. Transit Surveys for Earths in the Habitable Zones of White Dwarfs. The Astrophysical Journal, 2011; 731 (2): L31 DOI: 10.1088/2041-8205/731/2/L31

Cite This Page:

University of Washington. "Astrophysicist: White dwarfs could be fertile ground for other Earths." ScienceDaily. ScienceDaily, 31 March 2011. <www.sciencedaily.com/releases/2011/03/110330150854.htm>.
University of Washington. (2011, March 31). Astrophysicist: White dwarfs could be fertile ground for other Earths. ScienceDaily. Retrieved October 2, 2014 from www.sciencedaily.com/releases/2011/03/110330150854.htm
University of Washington. "Astrophysicist: White dwarfs could be fertile ground for other Earths." ScienceDaily. www.sciencedaily.com/releases/2011/03/110330150854.htm (accessed October 2, 2014).

Share This



More Space & Time News

Thursday, October 2, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Astronomers Spot Largest, Brightest Solar Flare Ever

Astronomers Spot Largest, Brightest Solar Flare Ever

Newsy (Oct. 1, 2014) — The initial blast from the record-setting explosion would have appeared more than 10,000 times more powerful than any flare ever recorded. Video provided by Newsy
Powered by NewsLook.com
French Apple Fans Discover the Apple Watch

French Apple Fans Discover the Apple Watch

AFP (Sep. 30, 2014) — Apple fans in France discover the latest toy, the Apple Watch. The watch comes in two sizes and an array of interchangeable, fashionable wrist straps. Duration: 00:42 Video provided by AFP
Powered by NewsLook.com
The Water You Drink Might Be Older Than The Sun

The Water You Drink Might Be Older Than The Sun

Newsy (Sep. 27, 2014) — Researchers at the University of Michigan simulated the birth of planets and our sun to determine whether water in the solar system predates the sun. Video provided by Newsy
Powered by NewsLook.com
First Woman Cosmonaut in 17 Years Blasts Off for ISS

First Woman Cosmonaut in 17 Years Blasts Off for ISS

AFP (Sep. 26, 2014) — A Russian Soyuz spacecraft carrying an American astronaut and two Russian cosmonauts, including the first woman cosmonaut in 17 years, blasted off on schedule Friday. Duration: 00:35 Video provided by AFP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

Strange & Offbeat Stories

 

Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins