Sunday, January 14, 2007

Cosmic Collisions


Scientists plan to pin down the date of a galactic collision billions of years in our future by first reaching back to the Big Bang, a feat that will be made possible by the extreme precision of NASA's planned SIM PlanetQuest mission.

By recreating some of the earliest moments of our portion of the universe, a team led by the University of Maryland's Ed Shaya will establish for the first time the masses and orbits of galaxies ranging from one million to 15 million light years from Earth. The study will reveal when the Andromeda galaxy will collide with our galaxy, the Milky Way, and will also strip away some of the mystery surrounding dark matter, the unknown substance whose gravity is thought to hold galaxies together.

The portion of each galaxy's motion that moves it closer to or further away from Earth, which is called its "radial motion," has already been well-established using the Doppler-shift technique. That's the observation of how light shifts toward the blue end of the spectrum for approaching galaxies, and toward the red for receding galaxies. But proper motion has been elusive because of the exceedingly slow rate at which galaxies millions of light-years away appear to move across the sky, even if they're actually traveling at very high speeds.

Proper motion, combined with the values established for radial motion and distance, will enable Shaya and his colleagues to calculate the three-dimensional velocity and direction of motion for each galaxy in the study. Then, after the observation phase of the study is completed, they will run a series of computer models to calculate masses and orbits for each galaxy.

The successful model will also produce an orbital path taking each galaxy from the Big Bang to its present location. Running the model forward into the future will enable Shaya to determine, among other things, when the Milky Way is destined to collide with the Andromeda galaxy.

Read more SIM PlanetQuest to predict date of cosmic collision

Arp 82 is an interacting pair of galaxies with a strong bridge and a long tail. NGC 2535 is the big galaxy and NGC 2536 is its smaller companion. The disk of the main galaxy looks like an eye, with a bright “pupil” in the center and oval-shaped “eyelids.” Dramatic “beads on a string” features are visible as chains of evenly spaced star-formation complexes along the eyelids. These are presumably the result of large-scale gaseous shocks from a grazing encounter.

The pair first burst with new star formation about 2 billion years ago after swinging by each other. A second close passage more recently resulted in yet another batch of star formation.

The new observations are from NASA's Galaxy Evolution Explorer, NASA's Spitzer Space Telescope and the Southeastern Association for Research in Astronomy Observatory at Kitt Peak, Ariz.

PHOTO CREDIT: NASA/JPL-Caltech/M. Hancock, B.J. Smith,
C. Struck, M.L. Giroux, P.N. Appleton, V. Charmandaris and W.T. Reach.
Graphics and additional information about
the Galaxy Evolution Explorer @ .
More information about Spitzer @ .
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