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Super Star Clusters Linked To Intergalactic Violence

M82, a small nearby galaxy, long ago slammed into its larger neighbor, M81. Now new infrared and visible-light pictures from NASA's Hubble Space Telescope reveal for the first time important details about large clusters of stars which arose from the interaction.

Hubble's sharp eye spied more than 100 young, bright, compact star clusters, known as "super star clusters," in M82's central region. Each cluster contains about 100,000 stars.

The ages of these stars tell astronomers when the wreck occurred. Sampling clusters of stars in an older "fossil starburst" region, astronomers concluded that the galactic violence between M82 and M81 began some 600 million years ago and lasted about 100 million years.

The results are published in the February 2001 issue of the Astronomical Journal.

This discovery provides evidence linking the birth of super star clusters to violent interactions between galaxies. The clusters themselves provide insight into the rough-and-tumble universe of long ago, when galaxies bumped into each other more frequently.

"The last tidal encounter between M82 and M81 about 600 million years ago had a major impact on what was probably an otherwise normal, quiescent disk galaxy," says Richard de Grijs of the University of Cambridge, UK, who is leading an international team of astronomers in the M82 study. "It caused a concentrated burst of star formation in the fossil starburst region. The active starburst taking place today is probably related to debris from M82 itself that has slowly 'rained' back on the galaxy since the interaction with M81."

"It is possible that a large fraction of the star formation in starbursts takes place in such concentrated clusters," de Grijs explains. "And we argue that these clusters are in fact very young globular clusters (spherically shaped clusters of up to one million stars)."

So far, astronomers have observed only very old globular clusters in our Milky Way. Astronomers once thought that this type of cluster only formed during the early stages of galaxy evolution many billions of years ago.

"Our results support other observations, mostly made with Hubble, that the formation of globular clusters does indeed continue today," de Grijs says. "This is, in our opinion, one of Hubble's main contributions to astrophysics to date."

Astronomers using ground-based telescopes have provided circumstantial evidence supporting the galactic encounter 600 million years ago. Radio observations have shown a cocoon of hydrogen enclosing the two galaxies and about a dozen smaller galaxies belonging to the M81/M82 group.

M82 is a bright (eighth magnitude), nearby (12 million light-years from Earth) galaxy in the constellation Ursa Major (the Great Bear).

The Space Telescope Science Institute (STScI) is operated by the Association of Universities for Research in Astronomy, Inc. (AURA), for NASA, under contract with the Goddard Space Flight Center, Greenbelt, MD. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency (ESA).

Related websites:

Electronic images, animation and additional information are available at these URLs:

http://oposite.stsci.edu/pubinfo/pr/2001/08

http://oposite.stsci.edu/pubinfo/latest.html

http://oposite.stsci.edu/pubinfo/pictures.html

http://hubble.stsci.edu/go/news

http://hubble.esa.int

[Contact: Richard de Grijs, Lars Lindberg Christensen, Ray Villard]

08-Mar-2001

 

 

 

 

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