Galaxies in Collision
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Galaxies in Collision European scientists use the Hubble
Space Telescope to catch merging galaxies in the act
July 15, 1999: Exciting new images of
more than a dozen very distant colliding galaxies have been
obtained by a European-led team of astronomers using the
NASA/ESA Hubble Space Telescope. These colliding objects are
part of a large concentration of galaxies, a galaxy cluster.
Though collisions have been observed in other clusters, this
particular cluster displays by far the largest number ever seen.
To astronomers, the finding indicates that, at least in some cases,
big massive galaxies form through collisions between smaller ones.
Right: This galaxy cluster, called MS1054-03, is 8 billion light-years away -- one of the most distant known groups of galaxies. Although hundreds of galaxies appear in this NASA/ESA Hubble Space Telescope image, a European-led team of astronomers has studied in detail 81 galaxies that certainly belong to the cluster, 13 of which are remnants of recent collisions or pairs of colliding galaxies. This is by far the largest number of colliding galaxies ever found in a cluster.
The Hubble Space Telescope studied 81 galaxies in the galaxy cluster MS1054-03, 13 of which are remnants of recent collisions or pairs of colliding galaxies. The 10-meter W.M. Keck Telescope was used to select these 81 cluster galaxies.
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"It has been a real surprise," says team leader Pieter van Dokkum, from Groningen and Leiden universities (The Netherlands). "Collisions had never been observed before at this frequency. Many of the collisions involve very massive galaxies, and the end result will be even more massive galaxies."
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"The Hubble image shows the paired galaxies very close together, with distorted morphologies," explains Marijn Franx, from the University of Leiden. "We can even see streams of stars being pulled out of the galaxies."
These new images from the Hubble Space Telescope will appear in the August 1 issue of Astrophysical Journal Letters. To the authors the data strongly support a Big Bang model prediction that says that large galaxies were formed from smaller ones in many generations of mergers. It contradicts the idea that there was, in the past, a kind of 'galaxy boom' event in which all big massive galaxies were born at the same time.
Right: A gallery of HST images showing distant galaxies in various stages of collision. The merging galaxies have weird, distorted shapes unlike normal spiral or elliptical galaxies. Some show streams of stars apparently being pulled from one galaxy into another. All of the galaxy pairs shown here are located in a larger grouping of galaxies known as MS1054-03.
As Franx states, "the evidence for the theories of galaxy formation through collisions had been strong, but circumstantial. Here we finally see a large number of galaxies caught in the act. If observed in other distant clusters, it would represent a general confirmation for a crucial aspect of our galaxy formation theories."
Collisions are much rarer today than they were in the past, but not impossible. Our own spiral galaxy, the Milky Way, is currently "eating up" several small satellite galaxies. Within 5 to 10 billion years -- some computer simulations show -- the Milky Way may collide with the Andromeda galaxy, and the result would be an elliptical galaxy.
Photo credits: Photo Credits: Pieter van Dokkum (University of Groningen), ESA and NASA Web Links
STScI press release - July 15, 1999
Hubble Space Telescope home page - at STScIRelated Stories:
Through the looking glass -- NASA's Hubble Space Telescope has uncovered exotic rings, arcs and crosses that are optical mirages produced by gigantic gravitational lenses in deep space - May 14, 1999 NASA Science News
Chandra will target the age of the Universe -- Astronomers plan X-ray measurements of galaxy clusters for a new measurement of the Hubble Constant - Feb 22, 1999 NASA Science News
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