groups of stars 26.4
TRANSCRIPT
Groups of Stars 26.4
Star Systems
Star Clusters
Galaxies
Star Systems
• Star System is two or more stars held together by gravity.
• More than half of all stars are part of a star system
• A two star system = binary star• Eclipsing binary = One star may pass
around another
Star Cluster
• Why study star clusters?
• All stars formed together in the same nebula (space cloud) so can find ages of stars and clusters.
• 3 kind of clusters
• Open, Associations, Globular cluster
3 kind of clusters• Open cluster = has a disorganized,
loose appearance contains a few thousand stars spread out
• Associations cluster = are temporary groupings of bright young stars –
• Get pulled apart by gravity –
• Larger than open clusters
Globular Clusters
• A large group of old stars• Lack dust and gas to form new stars• Contain more than 1 million stars• No short lived blue stars—they died• Oldest 12 billion years old• Therefore the universe is that OLD
Galaxies• Classified into 4 categories:• Spiral, Barred-spiral, Elliptical, and
Irregular• Spiral & Barred-Spiral = • Have a bulge of stars at the center• With arms extending outward like a
pinwheel • If Barred has a bar on either side of arms
Elliptical Galaxies
• Spherical or Oval• Has wide range of sizes• Have little dust and gas between
stars• No new stars forming in older EG• Contain only old stars
Irregular Galaxies
• Small fraction of all galaxies• Have a disorganized appearance• Have many shapes• Typically smaller than other types of
galaxies• Often located near large galaxies with
strong gravity = gives shape