Butcher-Oemler effect
The Butcher-Oemler effect is the term used to describe the excess of blue galaxies in galaxy clusters that are far away compared to those at closer distances. He was founded in 1978 by Harvey Butcher and Augustus Oemler, Jr. discovered.
Because of the finite speed of light, galaxy clusters at great distances are observed at a time when the universe was younger than it is today. The increasing proportion of blue galaxies with distance (or redshift ) corresponds to a temporal development of the composition of galaxy clusters in the sense of a decreasing proportion of blue galaxies.
The blue color of galaxies is an indicator of active star formation; these are predominantly spiral or irregular galaxies . The majority of galaxies in galaxy clusters are elliptical galaxies , which contain little gas and do not form new stars, while blue, actively star-forming galaxies predominate in the field. If a galaxy from the surrounding field falls into a cluster, it interacts in various ways with the intergalactic medium and the gravitational field of the cluster and other galaxies in the cluster. This leads to the loss of the interstellar gas and thus to the suppression of star formation. The exact physical mechanisms that cause this transformation are the subject of active research. The observation of the Butcher-Oemler effect plays an important role in this.
Individual evidence
- ↑ Harvey Butcher and Augustus Oemler, Jr .: The evolution of galaxies in clusters. I - ISIT photometry of Cl 0024 + 1654 and 3C 295 . In: Astrophysical Journal . tape 219 , 1978, pp. 18–30 , doi : 10.1086 / 155751 , bibcode : 1978ApJ ... 219 ... 18B .