Scientific Method —

Applying shellsort to stars

The Hubble space telescope provided the first direct evidence of stars sorting …

It has long been suspected that stars in globular clusters will undergo
a "mass segregation" and separate themselves based on their
mass.  Heavier stars will slow down and fall into the center
of a cluster where lighter, faster stars find their way to the
periphery of the grouping.  Today the results of a seven year
long survey using the Hubble Space Telescope are released
and they provided the first direct observation of this phenomena.

Globular clusters are home to hundreds of thousands of stars, and are
typically very densely packed in the center, but have a very low
stellar density on the edges.  The density near the center
reaches the cosmological equivalent of stars being packed
nuts-to-butts, with densities reaching 10,000 times higher than the
local density we enjoy in our neck of the galaxy each day.  If
our local region of space was to match this stellar density, than there
would need to be 10,000 stars in the area between the sun and it's
nearest neighbor Alpha Centauri, a mere 4.3 light-years away.
 This high packing of stars leads to a game of gravitational
billiards, with many pushes and jostles among the stars, which was
thought to lead to this mass segregation effect.

47 Tucanae, Credit:
the ultra-high resolution provided by the Hubble Space Telescope,
astronomers looked at the center of the nearby globular cluster 47
Tucanae (pictured at right, full size here ).  Over the course of the study they
took snap shots of the center of this cluster, each snapshot containing
over 130,000 separate stars. By looking at these images over time the
researchers, using advanced computer algorithms and measurement
techniques, were able to examine the velocity of approximately 15,000
distinct stars.  What they found was a collection of rare
"blue straggler" stars: very hot, very heavy stars that are thought to
be the remnants of a stellar collision.  By measuring the
motion of these relative to other, lighter stars they found that the
heavy blue stragglers did move slower; this confirms the theory that
massive stars do move slower than their less massive

This study never would have been possible with out the ultra-high
precision gained by using the Hubble telescope.  The motion of
the stars that was measured was less than 1x10-7 of a degree—that
is the equivalent change of an object moving the width of a dime at a
distance of about 7,000 km! With detailed values of the velocities of
such a high number of stars the researchers also looked to see if they
could find evidence of a large black hole at the center of 47 Tucanae,
but the data does not support the theory that one exists there.

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