SCE205 Lecture16 Week8 Essay

Submitted By negsummer2015
Words: 750
Pages: 3

 Galaxy

= immense collection of stars and interstellar matter. Larger than a star cluster.

 We

have an edge on view from the inside of our galaxy

 See


our galaxy as a band around the

 Disk


~ 100,000 ly in diameter and 10,000 ly

 Disk

has a high concentration of interstellar gas and dust

 Galactic

center surrounded by a large distribution of stars  Central Bulge
 Bulge not perfectly symmetrical, may have a bar or

peanut shape

 Disk

surrounded by spherical distribution of globular clusters and old stars  Galactic Halo

 ~200

billion stars in the Galaxy’s disk, central bulge and halo!


– lies within the galactic disk

 30,000 ly from the center of the galaxy
 Orbits around the center of the galaxy at

a speed of ~790,000 km/hr
 The Sun takes ~ 200 million years to complete one orbit around the galaxy!

 We

have a Black Hole at the center of our galaxy!!

 Called

Sagittarius A star (Sag A*)


 How

would you classify galaxies?  A)

 B) Size
 C) Shape
 D)Other

 How
 A)

would you classify galaxies?


Classified Galaxies

 B) Size
 C) Shape
 D)Other

How Hubble

 Largest telescope
 Used cepheid variable stars to

measure distance to nebula

 Hubble discovered universe is

billions of galaxies

Cosmology – study of the universe, how it formed, how is today and how it will end.  Spiral
 Elliptical
 Irregular & Dwarf
 Active galaxies
 quasars

Arched lanes of stars like the Milky Way
Spiral Arms – young, hot, blue stars, HII regions  on going star formation
 Central Bulges – Yellow/Red color, old stars, with low metal content. Little star formation. 

 Spiral

arm structure originating at end of a bar-shaped region in the center of the galaxy

 No spiral
 Round


to Flat ellipse
 Devoid of interstellar gas and dust
 Old, red, stars with small amounts of

 Giant Ellipticals – rare
 Dwarfs Ellipticals – very common

 Don’t

fit into the other type
 Rich in interstellar gas and dust
 Have both old and young stars, but mainly younger stars
 10% of known galaxies
 Examples: Large and Small Magellanic
Clouds  Southern Hemisphere

 Which

galaxy type has the oldest stellar population?

 A)

 B) Barred Spiral
 C) Elliptical
 D) Irregular

 Which

galaxy type has the oldest stellar population?

 A) Spiral
 B) Barred Spiral
 C) Elliptical
 D) Irregular

 Look

like stars but emit large amounts of energy as radio waves
 Have a large redshift, therefore they are very far away!
 Believed to originate from a Black Hole
 Since they are so far away, it is essentially like looking back in time:
Quasars are the Oldest objects we have observed in the universe…they were formed when the universe was young!

Quasars emit in an large range: Radio to X-ray!
 Extreme amounts of radiations
 Extremely luminous
 More than
“just starlight”

 Do

galaxies exist independently or are they parts of groups of galaxies?
Yes – Galaxies are independent
No – Galaxies exist in groups