Featured Research

from universities, journals, and other organizations

'Zombie' stars key to measuring dark energy

Date:
June 30, 2011
Source:
University of California - Santa Barbara
Summary:
"Zombie" stars that explode like bombs as they die, only to revive by sucking matter out of other stars. According to an astrophysicist, this isn't the plot for the latest 3-D blockbuster movie. Instead, it's something that happens every day in the universe -- something that can be used to measure dark energy.

This is a Chandra X-ray image of Tycho's supernova remnant. This Type Ia sueprnova was observed by Tycho Brahe in 1572, and today is just an expanding ball of gas. Astronomers used to have to wait years for a close, bright supernova to learn about them. Today big surveys are discovering supernovae by the thousands.
Credit: NASA/Chandra X-ray Observatory

"Zombie" stars that explode like bombs as they die, only to revive by sucking matter out of other stars. According to an astrophysicist at UC Santa Barbara, this isn't the plot for the latest 3D blockbuster movie. Instead, it's something that happens every day in the universe -- something that can be used to measure dark energy.

This special category of stars, known as Type Ia supernovae, help to probe the mystery of dark energy, which scientists believe is related to the expansion of the universe.

Andy Howell, adjunct professor of physics at UCSB and staff scientist at Las Cumbres Observatory Global Telescope (LCOGT), wrote a review article about this topic, published recently in Nature Communications. LCOGT, a privately funded global network of telescopes, works closely with UCSB.

Supernovae are stars that have been observed since 1054 A.D., when an exploding star formed the crab nebula, a supernova remnant.

More recently, the discovery of dark energy is one of the most profound findings of the last half-century, according to Howell. Invisible dark energy makes up about three-fourths of the universe. "We only discovered this about 20 years ago by using Type Ia supernovae, thermonuclear supernovae, as standard or 'calibrated' candles," said Howell. "These stars are tools for measuring dark energy. They're all about the same brightness, so we can use them to figure out distances in the universe."

These supernovae are so bright that they shine with the approximate power of a billion suns, noted Howell.

He calls Type Ia supernovae "zombie" stars because they're dead, with a core of ash, but they come back to life by sucking matter from a companion star. Over the past 50 years, astrophysicists have discovered that Type Ia supernovae are part of binary systems -- two stars orbiting each other. The one that explodes is a white dwarf star. "That's what our sun will be at the end of its life," he said. "It will have the mass of the sun crammed into the size of the Earth."

The white dwarf stars that tend to explode as Type Ia supernovae have approximately the same mass. This was considered a fundamental limit of physics, according to Howell. However, in an article in Nature about five years ago, Howell reported his discovery of stars that go beyond this limit. These previously unknown Type Ia supernovae have more than typical mass before they explode -- a fact that confounds scientists.

Howell presented a hypothesis to understand this new class of objects. "One idea is that two white dwarfs could have merged together; the binary system could be two white dwarf stars," he said. "Then, over time, they spiral into each other and merge. When they merge, they blow up. This may be one way to explain what is going on."

Astrophysicists are using Type Ia supernovae to build a map of the history of the universe's expansion. "What we've found is that the universe hasn't been expanding at the same rate," said Howell. "And it hasn't been slowing down as everyone thought it would be, due to gravity. Instead, it has been speeding up. There's a force that counteracts gravity and we don't know what it is. We call it dark energy."

The new findings relate to Einstein's concept of the cosmological constant. This is a term he added into his equations to make them valid. However, Einstein did it because he thought the universe was static; he didn't know the universe was expanding. When it was revealed that the universe is expanding, Einstein believed this concept was his biggest blunder. "It turns out that this cosmological constant was actually one of his greatest successes," said Howell. "This is because it's what we need now to explain the data."

He said that dark energy is probably a property of space. "Space itself has some energy associated with it," said Howell. "That's what the results seem to indicate, that dark energy is distributed everywhere in space. It looks like it's a property of the vacuum, but we're not completely sure. We're trying to figure out how sure are we of that -- and if we can improve Type Ia supernovae as standard candles we can make our measurements better."

Throughout history, people have noticed a few supernovae so bright they could be seen with the naked eye. With telescopes, astronomers have discovered supernovae farther away. "Now we have huge digital cameras on our telescopes, and really big telescopes," said Howell, "We've been able to survey large parts of the sky, regularly. We find supernovae daily." Astronomers have discovered thousands of supernovae in recent years.

During his career, Howell has used these powerful telescopes to study supernovae. Currently, besides teaching at UCSB, he is involved in LCOGT's detailed study of supernovae that is aimed at helping to understand dark energy. With this extensive network of observatories, it will be possible to study the night sky continuously.

"The next decade holds real promise of making serious progress in the understanding of nearly every aspect of supernovae Ia, from their explosion physics, to their progenitors, to their use as standard candles," writes Howell in Nature Communications. "And with this knowledge may come the key to unlocking the darkest secrets of dark energy."


Story Source:

The above story is based on materials provided by University of California - Santa Barbara. Note: Materials may be edited for content and length.


Journal Reference:

  1. D. Andrew Howell. Type Ia supernovae as stellar endpoints and cosmological tools. Nature Communications, 2011; 2: 350 DOI: 10.1038/ncomms1344

Cite This Page:

University of California - Santa Barbara. "'Zombie' stars key to measuring dark energy." ScienceDaily. ScienceDaily, 30 June 2011. <www.sciencedaily.com/releases/2011/06/110630131836.htm>.
University of California - Santa Barbara. (2011, June 30). 'Zombie' stars key to measuring dark energy. ScienceDaily. Retrieved July 29, 2014 from www.sciencedaily.com/releases/2011/06/110630131836.htm
University of California - Santa Barbara. "'Zombie' stars key to measuring dark energy." ScienceDaily. www.sciencedaily.com/releases/2011/06/110630131836.htm (accessed July 29, 2014).

Share This




More Space & Time News

Tuesday, July 29, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Russia Saves Gecko Sex Satellite, Media Has Some Fun With It

Russia Saves Gecko Sex Satellite, Media Has Some Fun With It

Newsy (July 27, 2014) The satellite is back under ground control after a tense few days, but with a gecko sex experiment on board, the media just couldn't help themselves. Video provided by Newsy
Powered by NewsLook.com
NASA EDGE: OCO-2 Launch

NASA EDGE: OCO-2 Launch

NASA (July 25, 2014) NASA EDGE webcasts live from Vandenberg AFB for the launch of the Oribiting Carbon Observatory-2 (OCO) launch. Video provided by NASA
Powered by NewsLook.com
This Week @ NASA, July 25, 2014

This Week @ NASA, July 25, 2014

NASA (July 25, 2014) Apollo 11 celebration, Next Giant Leap anticipation, ISS astronauts appear in the House and more... Video provided by NASA
Powered by NewsLook.com
Space to Ground: Coming and Going

Space to Ground: Coming and Going

NASA (July 25, 2014) One station cargo ship leaves, another arrives, aquatic research and commercial spinoffs. Questions or comments? Use #spacetoground to talk to us. Video provided by NASA
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:
from the past week

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