Download Astronomy 360 Physics/Geology 360

Astronomy 360
Physics/Geology 360
Measuring the Age of Star Clusters
A star only uses
hydrogen in its core
(available fuel is 0.1
times the star’s mass.
t = 1010 M/L years
Where M is in solar
masses and L is in
solar luminosities
where t is the main
sequence
lifetime(see page
381)
In a star cluster all stars form at approximately the same
time and at their birth all a burning hydrogen in their
core. All stars at their birth lie on the main sequence.
Calculate the main sequence
lifetime of a star of 2 M and 20L
How about 1 M
and 1 L?
The shortness of massive stars lives implies that those
we see must be relatively young.
The point at which the line bends away from the main sequence straight line is
the turnoff point. The star’s age is just a tiny bit less than the main sequence
lifetime. To get the cluster’s age we therefore measure the age of the star at the
turnoff point by calculating its main sequence lifetime from its mass and
luminosity.
Old clusters have few if any stars on the upper part of the main sequence in
contrast to young clusters on the other hand have stars on the upper main
sequence.
In astronomy, the Pleiades, or Seven Sisters (Messier object 45), is an open star cluster
containing middle-aged hot B-type stars located in the constellation of Taurus. It is among the
nearest star clusters to Earth and is the cluster most obvious to the naked eye in the night sky.
Pleiades has several meanings in different cultures and traditions.
The cluster is dominated by hot blue and extremely luminous stars that have formed within the
last 100 million years. Dust that forms a faint reflection nebulosity around the brightest stars
was thought at first to be left over from the formation of the cluster (hence the alternate name
Maia Nebula after the star Maia), but is now known to be an unrelated dust cloud in the
interstellar medium that the stars are currently passing through. Astronomers estimate that the
cluster will survive for about another 250 million years, after which it will disperse due to
gravitational interactions with its galactic neighborhood.
The fate of a star like our sun
The fate of a one solar mass one Luminosity Star