Transcript Goal: To understand clusters of stars

Goal: To understand clusters
of stars
Objectives:
1) To explore Some nearby clusters
2) To understand How clusters in our
galaxy form
3) To understand Globular clusters
4) To learn about What we can
determine from clusters
5) To explore the Local region
Nearby clusters
• Here are the Hyades
and Pleiades
clusters.
• These are two of the
closest star clusters
to us.
• Which one do you
think is closer?
• Top group is
Pleiades, bottom is
Hyades.
Nearby clusters
• These are called
open clusters
(because they are not
tightly bound and will
eventually drift apart).
• Open clusters are
young (usually < 1
billion years old).
Another cluster
• This is the Urza
Major moving cluster.
• Moving clusters are
sets of stars that all
move in the same
direction.
• This means they all
came from the same
place.
• Age ~ 800 million
years
Another cluster
• This cluster is
passing us
currently.
• We are just on its
outskirts.
• However we are
definitely NOT a
member of this
cluster.
• How can we tell?
Another cluster
• How can we tell?
• Well, our sun is
4.5 billion years
old.
• And the cluster is
moving by us at
46 km/s.
• 46 km/s = 1 light
year per 6000
years
A bit further out…
• Beehive
Cluster (M44)
• 577 light
years
• Also about
800 million
years old
So, basically…
• Open clusters are YOUNG clusters that
drift apart in about a billion years.
• As viewed from Earth you tend to see the
blue high mass stars.
• Those are always young stars as they
don’t last long.
• These are clusters with stars of equal age,
distance, and composition, but range in
mass.
In our galaxy alone
• We know of over 1000 of these types of
clusters.
• However, there are probably far more –
maybe even 100,000.
• What happens to the lower mass stars of
the cluster after a billion years?
Globular Clusters
• What is
different
about
this
cluster?
Omega Centauri
• Brightest
globular
cluster.
• Millions of
stars
closely
packed.
• This is a
closed
group.
• Close or
far away?
Omega Centauri
• The
diameter is
only 150
light years.
• Brightest
globular
cluster.
• It is 15000
light years
away!
Globular Cluster 47 Tucanae
• 2nd brightest. There are about 150 known
globular clusters for our galaxy.
• I say for not in because they all are on the
outskirts of our galaxy (sort of like
suburbs).
• Notice the cluster looks very red – what
does that tell you about this cluster?
NGC 6723
• Where is it on this image?
• NGC 6723 is 30,000 light years away vs
500 light years for the dark spots.
M15 – from HW4
Why are clusters important?
• What can we learn by studying a cluster?
Why are clusters important?
•
•
•
•
•
•
•
•
What can we learn by studying a cluster?
Age of cluster
Distance to cluster
A key step in finding distances to other galaxies.
How stars evolve
How clusters evolve
How our galaxy evolves
How the composition of our galaxy changes with
time
• How stars and clusters are formed
400
light
years
1500
Light
Years
Conclusion
• Clusters are very useful and important.
• All stars star in clusters.
• Open clusters are young clusters in the
disk of our galaxy which only stay for
about a billion years.
• Globular clusters are old and lie on the
outskirts of our galaxy.