. 24/7 Space News .
Building A Better Guide To The Galaxy

Computer model showing 'tidal tails' of stars being pulled off a satellite galaxy by the Milky Way's gravity.
by Staff Writers
Charlottesville VA (SPX) Feb 23, 2006
It is the job of astronomers to put numbers on the stupefying vastness of space and the objects it holds. That's how they get the universe to spill its secrets. The University of Virginia's Steve Majewski and his team plan to use NASA's SIM PlanetQuest space telescope to make ultra-precise measurements that will reveal more about the nature of our galaxy than ever before.

For now, astronomers know less about the shape and mass of the Milky Way than of many other galaxies. That's because discerning this information is like trying to see a marching band's formation when you're with them on the football field. "We're in the grandstand, looking down on Andromeda and the other galaxies," Majewski said, "whereas in our own galaxy, we're in the marching band."

With SIM PlanetQuest, scheduled to launch within the next decade, Majewski and his team plan to determine the Milky Way's size and shape, the amount and distribution of its mass, and the motions of its stars. En route, they will describe some fascinating tourist attractions, including ... The Galactic Bar

Despite the assertions of the Hitchhiker's Guide, astronomers know of no Restaurant at the End of the Universe. However, there is a very nice Bar at the Center of the Galaxy.

This is not the sort of place where residents of distant solar systems go for Happy Hour (as far as we know). It is instead an odd sort of wave pattern that pulls and pushes large groups of stars into the shape of a candy bar. The wave pattern spins like a propeller about the galactic center, continually adding new stars into its pattern and leaving old ones behind.

Left: Artist's concept of the Milky Way galaxy, with the "galactic bar" visible in the center. (Image by R. Hurt)

Central bars seem to be pretty common, and may help to shovel stars and gas clouds into the supermassive black holes thought to lurk at the core of most galaxies, including our own. By measuring the proper motion (that is, the side-to-side motion as seen from Earth) of about 10,000 stars in the galaxy's central bulge, Majewski's team means to determine the Milky Way bar's shape, mass, rotational speed and history.

The team will also study the dynamics of the disk and halo, measuring how quickly their stars obit the galactic center, how those speeds vary with distance from the center, and how the stars (including our sun) wander about as they orbit, in response to local gravitational influences. This information will help to answer one of the biggest and most puzzling questions astronomers have about the Milky Way: where is the 90 percent of the galaxy that we can't see?

Shedding light on dark matter

If you're the type of traveler who enjoys little-seen places, you're in luck. The vast majority of our galaxy is invisible, at least to existing instruments. How do we know it's there?

Because our galaxy, like many others that astronomers have observed, appears to be spinning much too quickly. The rapid rotation should be tearing it apart unless it is held together by a lot more gravity than can be explained by the stars, gas and dust we can see. More gravity means more mass.

Scientists call this unseen mass "dark matter." The Majewski team plans to sniff it out by observing its gravitational effect on stars within the Milky Way disk and on groups of stars that orbit the disk.

In doing so, they hope also to solve the Missing Satellite Problem. Current models insist that our galaxy should have as many as a thousand dwarf galaxies buzzing around it, each with from 0.01 percent to 10 percent as much mass as the Milky Way. But astronomers can see only a dozen satellite galaxies plus about 150 globular clusters, which are much-smaller collections of stars. As Majewski put it, "They're the sprinkles on the cake."

One hypothesis is that the "missing" satellites are composed entirely of dark matter.

Majewski's team will determine proper motions for most or all of the visible satellites within a million light years of the galactic center (more than 30 times the distance of our solar system from the center), a feat of precision that can be performed only with the SIM PlanetQuest telescope.

This will reveal not only the total amount of mass out to various radii, but also where dark matter is concentrated. And learning where the dark matter is will provide clues to what it is. For example, some hypothetical dark matter candidates would form clumps, while others would be distributed more smoothly.

The tails' tale

Especially revealing will be observations of the "tidal tails" that our galaxy's gravity appears to have been stripping away from the satellites. These are streams of stars drawn out of their parent galaxies and clusters like pulled taffy, marking the trails of those disintegrating satellites as they orbit the Milky Way. Some tails are so long, they encircle the galaxy.

Majewski's team will measure the position and motion of these stream stars very precisely -- again, a unique capability of SIM PlanetQuest. They will plug the findings into computer models, along with various estimates of our galaxy's mass, and run the models backwards. The model with the correct mass distribution will pull all of the stream stars back into their original satellite systems (see animation). It will be like filming a dish shattering, and then running the movie backward to watch the pieces reassemble.

"It seems that almost every halo star is part of one stream or another," Majewski said. "And that suggests that the Milky Way halo actually was formed by accretion, by cannibalization of satellites.

"The Milky Way is lapping up these spaghetti strands from satellites. I call it the Galactic Gourmand."

Maybe there is a Restaurant at the End of the Universe after all.

Related Links
University of Virginia



Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News


Swift Might Have Detected A Supernova Just Beginning
Greenbelt, Md. (SPX) Feb 23, 2006
NASA's Swift satellite has detected a strange cataclysmic event in another galaxy that scientists think could be a supernova just getting started.







  • Radiation 'Safe Zone' Migrates With Solar Cycle
  • NASA Honors A Legendary Astronaut
  • Proton Dangers To Astronauts Underestimated
  • Space Adventures To Build Spaceport In Singapore

  • Martian Gardens
  • Scientists Discover Mars' Atmosphere Altered By Solar Flares
  • Phobos Shadows The Surface of Mars
  • Mars Express Studies Possible Aurorae Above Mars

  • Land Launch Receives Contract Award From Israel Aircraft Industries
  • Arianespace Clears Ariane 5 For Launch
  • Lockheed Martin-Built EchoStar X Satellite Launched Successfully
  • Arianespace And Roscosmos Sign Contract For Soyuz Operations At Guiana Space Center

  • Earth From Space: Copenhagen, Denmark
  • Southern Greenland Glaciers Dumping Ice Faster
  • ALOS Captures First Image of Fujiyama
  • NASA, UNH Scientists Uncover Lost Maya Ruins � From Space

  • New Horizons Set For A Comfortable Cruise Out To Jupiter And Pluto Transfer
  • Questioning Pluto
  • New Outer Planet Is Larger Than Pluto
  • New Horizon On Course For Jupiter Transfer To Pluto And Beyond

  • Building A Better Guide To The Galaxy
  • ESO's VLT Launches Laser Guide Star
  • Swift Might Have Detected A Supernova Just Beginning
  • Milky Way X-Ray Map Reveals Millions Of New Objects

  • X PRIZE Foundation And The $2M Lunar Lander Challenge
  • Lunar Reconnaissance Orbiter Passes Preliminary Design Review
  • The Moon Program The NASA Administrator Is Really Planing For
  • Ancient Impacts Created Man In The Moon

  • Trimble Offers New Modular GPS Solutions For Construction Industry Applications
  • Tetra Tech Wins Federal Aviation Administration Satellite Navigation Assistance Contract
  • Lockheed Martin GPS Updates Enhance System Accuracy Up To 15 Percent
  • Putin And Ivanov Discuss Future Of GLONASS System

  • The content herein, unless otherwise known to be public domain, are Copyright 1995-2006 - SpaceDaily.AFP and UPI Wire Stories are copyright Agence France-Presse and United Press International. ESA PortalReports are copyright European Space Agency. All NASA sourced material is public domain. Additionalcopyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by SpaceDaily on any Web page published or hosted by SpaceDaily. Privacy Statement