galaxies astronomy 100. what is a “star cluster”? stars formed together at same time stars may...
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Galaxies
Astronomy 100
What is a “star cluster”?What is a “star cluster”?
• stars formed together at same time
• stars may be gravitationally bound together
• two types: open (galactic) and globular
Image at http://hubblesite.org/newscenter/archive/releases/star%20cluster/globular/2007/18/image/a/format/web/results/50/
Open ClustersOpen Clusters• dozens to
thousands of stars• young stars! only
a few million years old
• may still be surrounded by nebula from which they formed
• located in the spiral arms of a galaxy
• example: Pleiades
Image at http://hubblesite.org/newscenter/archive/releases/star%20cluster/open/2004/20/image/a/results/50/
More open star clusters
Globular ClustersGlobular Clusters
• millions to hundreds of millions of stars
• old! 6 to 13 billion years• mostly red giants and dwarfs• stars are clumped closely together,
especially near the center of the cluster (densely)
• surround our disk as a halo
Image at http://hubblesite.org/newscenter/archive/releases/star%20cluster/globular/1999/26/image/a/results/50/
What is a “nebula”?What is a “nebula”?
• A cloud in space• Made of gas and dust
– Can have stars inside
• Most of the ones we see are inside our Milky Way Galaxy
• Different types
Large, massive, bright nebulae
Emission NebulaEmission Nebula•The hot gas is emitting lightThe hot gas is emitting light
Colder, darker nebulaeDark dust blocking Dark dust blocking the hot gas behind the hot gas behind itit
Leftovers from an Explosion
Supernova remnantSupernova remnant (smaller, less gas) (smaller, less gas)
What is a “galaxy”?What is a “galaxy”?
• A large group of stars outside of our own Milky Way• Made of billions to trillions of stars– Also may have gas and dust
• Spiral, or elliptical, or irregular shaped
Spiral galaxy--Andromeda
NOAO/AURA/NSF Images at http://www.noao.edu/image_gallery/html/im0606.html and http://www.noao.edu/image_gallery/html/im0685.html
Elliptical Galaxies
Irregular Galaxies
NASA and NOAO/AURA/NSF Images at http://hubblesite.org/newscenter/archive/releases/galaxy/irregular/2005/09/results/50/ , http://www.noao.edu/image_gallery/html/im0560.html , and http://www.noao.edu/image_gallery/html/im0993.html
Our Galaxy: the Milky WayOur Galaxy: the Milky Way
• has about 200 billion stars, and lots of gas and dust
• is a barred-spiral (we think)• about 100,000 light-years wide• our Sun is halfway to the edge, revolving at
half a million miles per hour around the center of the Galaxy
• takes our Solar System about 200 million years to revolve once around our galaxy
The Milky WayThe Milky Way
Mapping the Milky Way
We can see: • Stars and star clusters• Nebulae• Galaxies
How do we know what our Galaxy How do we know what our Galaxy looks like?looks like?