| We run simulations using
two general types of stars: main-sequence stars as in a globular cluster,
and neutron stars. Globular clusters are collections of thousands of stars
which are found in galactic halos, the sparse region outside of the disk
of a galaxy. Globular clusters are thought to have formed early in the
evolution of the universe, and for this reason we expect the main sequence
stars within globular clusters to be relatively low mass. We can theoretically
predict that none of the main sequence stars in a globular cluster will
be more massive than some upper-limit mass. This upper limit mass is called
the turn-off mass, and it corresponds to approximately 0.8 times the mass
of the Sun (denoted 0.8Mo). However, when one observes globular clusters,
one finds bright main-sequence stars, called blue stragglers, scattered
throughout the globular cluster. On a Hertzsprung-Russell Diagram, blue
stragglers lie on an extension of the main sequence, beyond the turnoff
point. The blue stragglers appear to 'straggle' behind other main sequence
stars of the same mass in their evolution. Blue stragglers are bluer,
brighter, and more massive than the other main-sequence stars in the cluster.
Thus, we are left with this question: How exactly do blue stragglers form?
The most common belief is that blue stragglers are formed through mergers
of the old, dim main sequence stars in a globular cluster. When two or
more stars collide, the end result is a merger remnant that is brighter
and bluer than its parents. So to summarize, if you smash old, dim stars,
you can end up with a young, bright star - a blue straggler! top |
