"HUBBLE SCIENCE"
"Globular Clusters / Stellar Pockets"
A globular cluster is a big sphere of stars that have collected together they're
orbiting around a Common Center but it's very spherical very organized looks like
a huge basketball contains hundreds of thousands of stars these clusters have
formed early on in the formation of a galaxy when the cluster starts forming
it's a very diffuse and over time things get concentrated more and more toward the center.
Stars are actually moving all around and if they're sort of orbiting around the center
it's not a static cluster even though a single picture makes everything look like it's in place.
One of the more famous ones is Messier 13.
Omega Centauri is a prototypical one in the southern hemisphere
globular clusters are very old there seem to be some of the first stars formed in the Galaxy as
the material that came together in the past one of the pockets of condensed material that occurred
around the center of the Galaxy drew together into the selections of stars so they're mostly very old
stars, 10 or 12 billion years old although we do see a second generation of newer younger stars
in globular clusters still you know relatively old billions of years ago but it's not like it
had one burst of star formation and that was it. It did have a chance to form a second wave later on.
Westerlund 1 still in one is what's called an open cluster it's a very loose collection of stars over a broad
area it's more sort of a cloud of stars as more stars gather in an open cluster like that and more
material comes together it's going to naturally pull things in toward its center. Something like
Westerlund 1 over many millions of years could evolve into something that looks more like a globular
and we do think that most globulars have one or more black holes at the center which is a source
of immense gravity to help hold these clusters together Hubble saw in the globular cluster NGC
6397 the first clear evidence for multiple black holes at the center we had previously assumed that
most globulars would have a single black hole at the center in this case we found a number
of separate black holes they're moving around each other at high speeds around a common center.
If you have a number of black holes in tight orbits around each other at the
center that works as well as a single black hole for holding together the overall cluster
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