Featured Research

from universities, journals, and other organizations

Puzzle Of Galactic Evolution Solved

Date:
November 25, 1999
Source:
University Of Wisconsin-Madison
Summary:
Massive clouds of gas, discovered long ago but only recently identified as being within the margins of the Milky Way, play a key role in the ability of the galaxy to churn out new stars by raining gas onto the plane of the galaxy, a new report suggests.

MADISON - Massive clouds of gas, discovered long ago but only recently identified as being within the margins of the Milky Way, play a key role in the ability of the galaxy to churn out new stars by raining gas onto the plane of the galaxy, a new report suggests.

Writing this week in the scientific journal Nature, Bart P. Wakker, a University of Wisconsin-Madison astronomer, and colleagues have chipped away at a three-decade-old mystery about the nature and role of what astronomers call high-velocity clouds. In the process, they've discovered a mechanism by which the galaxy is seeded with the stuff of stars and solved a long-standing question of galactic evolution.

Discovered 35 years ago, the clouds were an enigma because they behave differently than most galactic objects -- coursing through space at high speeds and not neatly rotating along with the rest of the galaxy. Moreover, scientists could never pinpoint their exact location, with distance estimates ranging from a few hundred light years to 10 million light years, an estimate that would place them well beyond the pale of the Milky Way.

But improved instrumentation, such as new large ground-based telescopes and the orbiting Hubble Space Telescope, recently allowed astronomers to determine that one such cloud lies about 20,000 light years from Earth in the halo of the Milky Way, a region high above the star-studded plane of the galaxy. And now, with the help of Hubble, Wakker and his colleagues have provided astronomers with measurements that reveal an inventory of some of the heavy elements in another high-velocity cloud which, they suggest, lies between 10,000 and 40,000 light years above the plane of the galaxy.

The new evidence, said Wakker, strongly suggests that some of the clouds play a key role in the chemical evolution of the galaxy by showering it with metal-poor gas that counteracts a buildup of heavy elements within the stars and gas found in the disk of the Milky Way.

Every star in the Milky Way was born of gas millions or billions of years ago, and they constantly turn hydrogen into helium or heavier elements like metals. They shed these metals back into interstellar space, a scenario that suggests recently-formed stars should be richer in metals than old stars. Yet astronomers observe that most stars in the disk of the galaxy have similar heavy element concentrations no matter how old or young they are.

"This rain of gas," Wakker said, "is material that has never been in the Milky Way before, suggesting, then, that metal production by stars is offset by this influx of metal-poor gas."

The new Hubble observations conform to a popular theory that there is a continual inflow of material into the galaxy to account for the continuing formation of stars, as well as their chemical composition. Competing theories -- ranging from the idea that, in the past, stars may have been more efficient at producing heavy elements to the notion of unknown processes at work -- can now be discarded, Wakker said.

"You don't need any other explanations anymore," he said, "because we now know that this gas is raining down onto the plane of the galaxy."

The finding also explains how the Milky Way can create, on average, a new star each year without running out of its supply of gas after a tenth of its lifetime.

The cloud observed by Wakker is estimated to contribute about one-fifth of a solar mass per year. But there are other such high-velocity clouds, Wakker noted, that can provide the balance of new gas needed for the galaxy to form a new star each year.

The origin of this accreting, low-metal gas remains a mystery. It could be gas left over from the formation of the so-called Local Group of galaxies that includes the Andromeda Nebula. Alternatively, it may be that the Milky Way is still forming, continuously gathering gas from near the edge of its sphere of influence. Or, said Wakker, the clouds might have been stripped away from passing dwarf galaxies.

###

NOTE TO PHOTO EDITORS: A high-resolution image is available for downloading at: http://www.news.wisc.edu/newsphotos/wakker.html


Story Source:

The above story is based on materials provided by University Of Wisconsin-Madison. Note: Materials may be edited for content and length.


Cite This Page:

University Of Wisconsin-Madison. "Puzzle Of Galactic Evolution Solved." ScienceDaily. ScienceDaily, 25 November 1999. <www.sciencedaily.com/releases/1999/11/991125091204.htm>.
University Of Wisconsin-Madison. (1999, November 25). Puzzle Of Galactic Evolution Solved. ScienceDaily. Retrieved August 29, 2014 from www.sciencedaily.com/releases/1999/11/991125091204.htm
University Of Wisconsin-Madison. "Puzzle Of Galactic Evolution Solved." ScienceDaily. www.sciencedaily.com/releases/1999/11/991125091204.htm (accessed August 29, 2014).

Share This




More Space & Time News

Friday, August 29, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Experiment Tests Whether Universe Is Actually A Hologram

Experiment Tests Whether Universe Is Actually A Hologram

Newsy (Aug. 27, 2014) Researchers at Fermilab are using a device called "The Holometer" to test whether our universe is actually a 2-D hologram that just seems 3-D. Video provided by Newsy
Powered by NewsLook.com
SpaceX’s Falcon 9 Rocket Explodes After Liftoff

SpaceX’s Falcon 9 Rocket Explodes After Liftoff

Newsy (Aug. 23, 2014) The private spaceflight company says it is preparing a thorough investigation into Friday's mishap. Video provided by Newsy
Powered by NewsLook.com
Did Russia Really Find Plankton On The ISS? NASA Not So Sure

Did Russia Really Find Plankton On The ISS? NASA Not So Sure

Newsy (Aug. 21, 2014) Russian cosmonauts say they've found evidence of sea plankton on the International Space Station's windows. NASA is a little more skeptical. Video provided by Newsy
Powered by NewsLook.com
Space to Ground: Hello Georges

Space to Ground: Hello Georges

NASA (Aug. 18, 2014) Europe's ATV-5 delivers new science and the crew tests smart SPHERES. 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