Royal Astronomical Society | 2015 Apr 24
[c][img3="A radio image highlighting the shock wave (seen here as the bright arc running from bottom left to top right) in the ‘Sausage’ merging cluster, made using the Giant Metrewave Radio Telescope. The shock wave was generated 1 billion years ago, when the two original clusters collided, and is moving at a very high speed of 9 million kilometres per hour. (Credit: Andra Stroe)"]https://www.ras.org.uk/images/stories/p ... _image.png[/img3]Galaxies are often found in clusters, with many 'red and dead' neighbours that stopped forming stars in the distant past. Now an international team of astronomers, led by Andra Stroe of Leiden Observatory and David Sobral of Leiden and the University of Lisbon, have discovered that these comatose galaxies can sometimes come back to life. If clusters of galaxies merge, a huge shock wave can drive the birth of a new generation of stars – the sleeping galaxies get a new lease of life. The scientists publish their work in the journal Monthly Notices of the Royal Astronomical Society.
A composite image of the ‘Sausage’ merging cluster CIZA J2242.8+5310, made using
data from the Subaru and Canada France Hawaii Telescopes (CFHT). The white circles
indicate galaxies outside of the cluster, while yellow circles are cluster galaxies, where
accelerated star formation is taking place. Green marks regions of radio emission,
tracing out shock waves and purple marks the hot gas between the galaxies that emits
X-rays. The cluster is one of the most massive in the Universe. (Credit: Andra Stroe)[hr][/hr][/c]
Galaxy clusters are like cities, where thousands of galaxies can be packed together, at least in comparison to the sparsely-populated space around them. Over billions of years, they build up structure in the universe - merging with adjacent clusters, like growing cities absorb nearby towns. When this happens, there is a huge release of energy as the clusters collide. The resulting shock wave travels through the cluster like a tsunami, but until now there was no evidence that the galaxies themselves were affected very much.
Stroe and Sobral observed the merging galaxy cluster CIZA J2242.8+5301, nicknamed the 'Sausage', located 2.3 billion light years away in the direction of the constellation of Lacerta, in the northern hemisphere of the sky. They used the Isaac Newton and William Herschel Telescopes on La Palma, and the Subaru, CFHT and Keck Telescopes on Hawaii, and found that far from ‘watching from the back’ the cluster galaxies were transformed by the shock wave, triggering a new wave of star formation.
Stroe comments: "We assumed that the galaxies would be on the sidelines for this act, but it turns out they have a leading role. The comatose galaxies in the Sausage cluster are coming back to life, with stars forming at a tremendous rate. When we first saw this in the data, we simply couldn’t believe what it was telling us."
The new work implies that the merger of galaxy clusters has a major impact on the formation of stars. "Much like a teaspoon stirring a mug of coffee, the shocks lead to turbulence in the galactic gas. These then trigger an avalanche-like collapse, which eventually leads to the formation of very dense, cold gas clouds, which are vital for the formation of new stars", says Stroe. ...
The rise and fall of star-formation in z∼0.2 merging galaxy clusters - Andra Stroe et al
- Monthly Notices of the RAS 450(1) 646 (2015 June 11) DOI: 10.1093/mnras/stu2519
arXiv.org > astro-ph > arXiv:1410.2891 > 10 Oct 2014 (v1), 28 Nov 2014 (v2)
- Monthly Notices of the RAS 450(1) 630 (2015 June 11) DOI: 10.1093/mnras/stv521
arXiv.org > astro-ph > arXiv:1503.02076 > 06 Mar 2015