Download Star Cluster Trivia!

Star Cluster Trivia!
Open Clusters
Hyades
Pleiades
Globular Clusters
Omega Centauri
M15
What are star clusters?
What are star clusters?
Group of stars, bound together by
mutual gravitational pull among all
stars
Describe main differences
between Open and Globular
Clusters
Size
Shape
Describe main differences
between Open and Globular
Clusters
Size
Open clusters have fewer stars than globular
clusters
Open clusters are more sparse, globulars have
higher density or concentration of stars
Shape
globular clusters are very spherical and
symmetric
open clusters are more irregular
How many stars do they
have?
Open Clusters
Globular Clusters
How many stars do they
have?
Open Clusters
hundreds to thousands
~100 - 1000
Globular Clusters
hundreds of thousands to millions
~100,000 to 1,000,000
How many clusters are there in
the Milky Way?
Open:
Globular:
How many clusters are there in
the Milky Way?
Open:
over 1100 known, may be more (up to 10,000)
Globular:
~150, may be more
There may be many more clusters than we know of
so far - they can be hidden by clouds of gas and dust
in the Galaxy!
How old are the clusters in the
Milky Way?
Open:
Globular:
How old are the clusters in the
Milky Way?
Open:
less than a billion years old (typically a few hundred
million years old)
Globular:
10-13 billion years old (much older than open
clusters)
Where do star clusters reside
within the Milky Way?
50
kiloparsecs
Open Clusters:
Globular Clusters:
http://www.atlasoftheuniverse.com/globular.html
Where do star clusters reside
within the Milky Way?
50
kiloparsecs
Open Clusters:
Disk or plane of
the Galaxy
Globular Clusters:
Halo of the Galaxy
Bulge
Galactic
Nucleus
Sun
Halo
Disk
Globular
Clusters
http://www.atlasoftheuniverse.com/globular.html
How dense are clusters?
We can measure the density in terms of
Open Clusters:
Globular Clusters:
How dense are clusters?
We can measure the density in terms of
stars per cubic parsec or stars / parsec3
Open Clusters:
Globular Clusters:
How dense are clusters?
We can measure the density in terms of
stars per cubic parsec or stars / parsec3
Open Clusters:
~ 0.1 - 50 stars / pc3
Globular Clusters:
~ 1 - 100,000 stars / pc3
Much higher densities than open clusters!
How dense are clusters?
We can measure the density in terms of
stars per cubic parsec or stars / parsec3
Open Clusters:
~ 0.1 - 50 stars / pc3
Globular Clusters:
~ 1 - 100,000 stars / pc3
Much higher densities than open clusters!
What did you learn about the density in the cores of
star clusters?
How dense are clusters?
We can measure the density in terms of
stars per cubic parsec or stars / parsec3
Open Clusters:
~ 0.1 - 50 stars / pc3
Globular Clusters:
~ 1 - 100,000 stars / pc3
Much higher densities than open clusters!
What did you learn about the density in the cores of
star clusters?
In the cores, the density is the greatest
In our neck of the woods...
Density
~ 1 star/pc3
4 light years
4 light years
4 light years
4 light years
Density of a globular cluster
compared to density in the Solar
neighborhood?
Density in the Solar neighborhood
The density at the centers of star clusters can be up to...
Density of a globular cluster
compared to density in the Solar
neighborhood?
Density in the Solar neighborhood
3
~ 1 star/pc
The density at the centers of star clusters can be up to
~ 100,000 star/pc3
So, at the center of a globular clusters, the density can
be as much as 100,000 times the density around the
Sun
Density of a globular cluster
compared to density in the Solar
neighborhood?
The Sun will probably never interact with another star,
because …
What about in the cores of globular clusters?
Density of a globular cluster
compared to density in the Solar
neighborhood?
The Sun will probably never interact with another star,
because there are so few nearby (low density of
stars)
What about in the cores of globular clusters? In the
cores of globular clusters, however, the density is so
high that stars have close encounters
- stars can interact with each other, even collide
in globular clusters
How can we determine the
ages of star clusters?
How can we determine the
ages of star clusters?
By creating and analyzing the HR diagram
for the stars in the cluster
We will return to this idea soon!
Why are Globular Clusters
so Interesting?
Why are Globular Clusters
so Interesting?
They are extremely dense!
At the centers of clusters, stars are sometimes as
close together as Pluto is to the Sun!
Because of high density, stars interact with each
other!
- Stars can collide
- Complicated binary interactions help create
cool binary sources, like X-ray binaries
Why are Globular Clusters
so Interesting?
In star clusters, all the stars were born at
approximately the same time, so they are the
same age
Like a laboratory for studying stellar evolution
They are some of the oldest objects in the
Universe
Give clues about what things were like then
Why are open clusters young
but globular clusters are old?
Why are open clusters young
but globular clusters are old?
Star clusters tend to disperse, or evaporate, over time
Open clusters are more loosely bound than globulars
- Lose stars more easily, in shorter amount of time
- Don’t survive more than a few billion years.
Globular clusters - more massive, so more tightly
bound by gravity, so it takes longer for them to
evaporate
- Can live for many billions of years
Why are open clusters young
but
globular
clusters
are
old?
Star clusters tend to disperse, or evaporate, over
time:
Their orbit can take them through the disk of the
galaxy - this rips more stars from the cluster
Why are open clusters young
but globular clusters are old?
So star clusters naturally evaporate over time
Star clusters are in orbit around that can take them
through the plane of the galaxy - this rips more stars
from the cluster
Credit: ESO
Why are open clusters young
but globular clusters are old?
There were many more clusters
earlier, but many of them have
dissolved out of existence.
Credit: ESO