MadSci Network: Astronomy
Query:

Re: What keeps stars from colliding in globular clusters?

Date: Fri Jan 12 00:04:45 2001
Posted By: Irene Little, Faculty, CASA, University of Colorado
Area of science: Astronomy
ID: 979244049.As
Message:

Globular clusters have 100,000 to a million stars in them in a region of 
about 30-100 lightyears. The stars in a globular cluster are crowded a 
thousand times more densely than the stars near the sun. The average 
distance between stars near the sun is about 3-4 lightyears. On the other 
hand the average distance between stars near the center of the cluster is 
only a few lightmonths.  But stars are quite small compared to the 
distance between stars. So even near the center of the cluster, the 
distance between the stars is still tens of thousands times their own 
size. That is like saying that if you have an apple in your hand, the next 
nearest apple is over a mile away. That means the stars are not so tightly 
packed that they get close enough together to explode.  
All the stars in a cluster move around the center of the cluster in their 
own orbits. That means sometimes stars get close enough to each other that 
their orbits get changed; sometimes the change is enough that a star is 
thrown out of the cluster.  But in order to collide with each other, the 2 
stars would have to move exactly towards each other.  It is like saying 
that you want to hit a baseball with another baseball that is over a mile 
away. It is possible, but that happens only very, very rarely.  


Reference: Foundations of Astronomy by M. Seeds,4th ed, p. 256; or any 
other introductory astronomy text book


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