Featured Research

from universities, journals, and other organizations

Milky Way Galaxy Wears Two Halos Of Stars

Date:
December 22, 2007
Source:
Texas Tech University
Summary:
Though it's devoured and destroyed countless smaller galaxies in its nearly 14-billion-year history, the Milky Way has earned itself two halos of stars, according to astronomers. Though our galaxy is shaped like a flat disk of up to 400 billion stars rotating clockwise, it also wears two crowns of stars that make up a spherical haze and envelops the galaxy's disk. Though others have suggested that the galaxy wears two halos of stars before, this is the first definitive proof of two different halos, he said.

The Milky Way Galaxy is shaped like a disk with a bulge in the center and is made up of hundreds of billions of stars and huge clouds of dust and gas.
Credit: Serge Brunier

After studying more than 20,000 stars, researchers conclude that our disk-shaped galaxy wears two spherical halos of stars left behind when their original galaxy was either assimilated or dissolved into our own.

Related Articles


Though it’s devoured and destroyed countless smaller galaxies in its nearly 14-billion-year history, the Milky Way has earned itself two halos of stars, according to a Texas Tech researcher.

Ronald Wilhelm, an assistant professor of physics and co-author of the report, Two Stellar Components in the Halo of the Milky Way, said that though our galaxy is shaped like a flat disk of up to 400 billion stars rotating clockwise, it also wears two crowns of stars that make up a spherical haze and envelops the galaxy’s disk. Though others have suggested that the galaxy wears two halos of stars before, this is the first definitive proof of two different halos, he said.

The report will be published in the Dec. 13 issue of the journal, Nature. It was produced with 11 other researchers working through the Sloan Digital Sky Survey and the Sloan Extension for Galactic Understanding and Exploration.

“These stars in the halos are really, really ancient,” Wilhelm said. “They’re some of the oldest stars in the universe. Probably, this outer halo of stars came about through the cannibalization of smaller galaxies that ran retrograde to our galaxy’s rotation.

“The big deal is that people have suggested for some time this outer halo existed, but they only had small samples of stars in their studies. We’ve created a much larger sample and can see that there is definitely a second halo orbiting retrograde, or backward, to the direction which the disk of the galaxy is rotating. If it was a part of the original formation of our galaxy, that halo should orbit the same direction.”

From a sampling of 20,000 stars, Wilhelm and collaborators determined that the inner halo of stars is more flattened, and orbit slowly but in the same direction as the disk. It remains unclear whether the inner halo arose from mergers of small satellite galaxies or as part of the overall formation of the galactic disk.

The outer halo, however, seems to be composed of a population of stars which were stripped from smaller galaxies that orbited counter to the rotation of the disk. While small galaxies which orbit with our galaxy’s rotation tend to rapidly fall into our galaxy, the retrograde orbiting satellite galaxies dissolve and their stars are spread throughout the outer halo.

By probing the chemical composition of the stars in the second halo, Wilhelm and collaborators were able to determine that these stars came from early protogalaxies or small satellite galaxies that had fewer processed elements such as calcium and iron, when compared to the inner halo.

This change in chemical composition, and orbital characteristics, confirms that two separate populations of stars exist in the halo of the Milky Way. Furthermore, the most likely explanation for the origin of the outer halo stars is that of small, disrupted, satellite galaxies which did not share the chemical history of the Milky Way Galaxy.


Story Source:

The above story is based on materials provided by Texas Tech University. Note: Materials may be edited for content and length.


Cite This Page:

Texas Tech University. "Milky Way Galaxy Wears Two Halos Of Stars." ScienceDaily. ScienceDaily, 22 December 2007. <www.sciencedaily.com/releases/2007/12/071215210517.htm>.
Texas Tech University. (2007, December 22). Milky Way Galaxy Wears Two Halos Of Stars. ScienceDaily. Retrieved January 28, 2015 from www.sciencedaily.com/releases/2007/12/071215210517.htm
Texas Tech University. "Milky Way Galaxy Wears Two Halos Of Stars." ScienceDaily. www.sciencedaily.com/releases/2007/12/071215210517.htm (accessed January 28, 2015).

Share This


More From ScienceDaily



More Space & Time News

Wednesday, January 28, 2015

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Asteroid's Moon Spotted During Earth Flyby

Asteroid's Moon Spotted During Earth Flyby

Rumble (Jan. 27, 2015) Scientists working with NASA&apos;s Deep Space Network antenna at Goldstone, California discovered an unexpected moon while observing asteroid 2004 BL86 during its recent flyby past Earth. Credit to &apos;NASA JPL&apos;. Video provided by Rumble
Powered by NewsLook.com
Water Fleas Prepare for Space Voyage

Water Fleas Prepare for Space Voyage

Reuters - Innovations Video Online (Jan. 26, 2015) Scientists are preparing a group of water fleas for a unique voyage into space. The aquatic crustaceans, known as Daphnia, can be used as a miniature model for biomedical research, and their reproductive and swimming behaviour will be tested for signs of stress while on board the International Space Station. Jim Drury went to meet the team. Video provided by Reuters
Powered by NewsLook.com
Mars Rover Opportunity Celebrates 11-Year Anniversary

Mars Rover Opportunity Celebrates 11-Year Anniversary

Rumble (Jan. 26, 2015) Eleven years ago NASA&apos;s Opportunity rover touched down on Mars for what was only supposed to be a 90-day mission. Since then it has traveled 25.9 miles (41.7 kilometers), further than any other off-Earth surface vehicle has ever driven. Credit to &apos;NASA&apos;. Video provided by Rumble
Powered by NewsLook.com
NASA's On Course To Take Pluto's Best Photo Ever

NASA's On Course To Take Pluto's Best Photo Ever

Newsy (Jan. 25, 2015) NASA&apos;s New Horizons probe is en route to snap a picture of Pluto this summer, but making sure it doesn&apos;t miss its one chance to do so starts now. Video provided by Newsy
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