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Lecture 4

PCS 181 Lecture Notes - Lecture 4: Globular Cluster, Horse Length


Department
Physics
Course Code
PCS 181
Professor
Margaret Buckby
Lecture
4

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Galaxies:
Recall the COBE satellite which was launched to confirm the CMB ~ 3 K (2.728 K).
COBE was LATER asked to seek VERY small temperature variations in the CMB.
COBE found tiny temperature deviations of +/- 0.0003 K.
Galaxy Formation 1:
Pink regions = 2.278 + 0.0003 K.
Blue regions = 2.278 0.0003 K.
Galaxy theorists hypothesize that galaxies “condensed” at the interface between warmer
and cooler volumes of space.
*NOTE: THE HISTORY OF THE UNIVERSE IS ON TEST # 1. E.G. 100 YEARS, 4 S.
Galaxy Formation 2:
The first stars to form after the Big Bang were extremely massive…hundreds of times
the mass of our sun.
These stars only lived a few million years and exploded as supernovae, leaving Black
Holes as remnants.
These massive Black Holes attracted gas/dust into orbit.
Overtime, the system attracted more matter until a galactic mass was present.
Massive Black Holes are found at the centers of most galaxies.
Properties:
A galaxy is a gravitational-bound collection of stars, gas, dust, radiation.
Galaxies range from thousands to hundreds-of-thousands of light years across.
Galaxies contain from thousands to trillions of stars.
Galaxies usually gather into groups.
Many groups = a galaxy Cluster.
Our own galaxy, the Milky Way, is about 100,000 to 120,000 light years across.
Our Milky Way is in the LOCAL GROUP which consists of about 40 member galaxies.
Our sun lies about 8 Kpc ~ 26,000 light years from the center of the Milky Way.
Our sun travels around the Milky Way galaxy at ~ 220 Km/s.
Globular Clusters:
A globular cluster is a spherical distribution of ~105 to 106 stars.
Typically only a few hundred light years across.
Formed early in the life of a galaxy and contain the oldest stars known.
Follow RANDOM paths through their home galaxy = do NOT move ~ circularly in the
plane (disk) of the galaxy as most stars do.
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