The night sky is a field of stars. In every direction, stars bright and dim fill the horizon to brimming. Some seem to form distinct patterns, which we recognize as constellations. Yet as beguiling as those patterns may be, most of them are no more than projections of the human mind. The vast majority of stars, in our own galaxy and in others, have no true physical connection to one another.

At least, not anymore. Every star actually begins its life in a group, surrounded by siblings of nearly the same age that only later drift apart. Astronomers know this because some of these stellar nurseries, called star clusters, still exist. The Orion nebula cluster is perhaps the most famous one: in images from the Hubble Space Telescope, its stars wink from within churning clouds of dust and gas. You can see the Pleiades cluster from your backyard: it is the fuzzy patch in the constellation Taurus.

This article was originally published with the title The Inner Life of Star Clusters.

4 Comments

1. 1. Daniel35 06:37 PM 2/20/13

   So how did they get grouped in the first place? Are they all 2nd generations stars, the "children" of a big first generation star? Where are our "siblings" now? Basically, why are there groups, or more basically, why is there something is some place and relatively nothing in others?

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2. 2. chrisstronks 07:49 AM 3/10/13

   Empirical proof for open cluster formation ?
   
   Steven W. Stahler concludes from simulation data that binary stars are the key to the dynamics in static open clusters. He predicts that inclusion of a third star in the system eventually leads to the ejection of the smallest of the trio at high speed. If this were to be the case, the claim of the author that "...open clusters are just too old; ..." (i.e., millions of years) should be an opportunity to put his hypothesis to the test; if binary systems are continuously replaced by successor systems after having been approached by a heavier star, this would mean that older open cluster systems would have binary stars with heavier couples, since the older the open cluster, the more exchange between approaching stars and existing binary stars will have taken place. In addition, when the ejected light stars have high speed, this would increase the chance of light stars in the outer parts of these syatems, since they have been thrown out at high velocity by the heavy binary stars. Hence, old open clusters should contain a core of heavy binary stars surrounded by lighter, non-binary stars, while the distribution should be more random in younger open clusters.
   
   H. Christiaan Stronks, PhD
   Researcher at NICTA, Canberra Research Laboratory, Australia

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3. 3. m allworth 01:02 PM 3/11/13

   There may well be more heavy binary stars in an open cluster if Steven Stahler is correct.
   
   But - why do globular clusters orbit the halos of galaxies?
   
   Are these globular clusters precursors of galaxies? [They do contain the oldest stars]
   
   
   Also there is a correlation between the mass of a SMBH
   and the mass of the globular clusters surrounding a galaxy. So do galaxies maybe need clusters of old stars and, black holes for them to form?
   

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4. 4. wywong 08:28 PM 3/31/13

   Does dark matter play no role in the formation and evolution of star clusters?

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