GALAXIES By Christopher Wrobleski & Patrick Bradford Poole

What are Galaxies? A component of our universe made up of gas and a large number of stars held together by gravity.

Types of Galaxies Spiral Lenticular Elliptical Irregular

Spiral Forms distinct spiral patterns. Two major components: 1.) A flat large disk 2.) Young Star Clusters

The Milky Way The Milky Way is our galaxy. ~ 200,000,000,000 make up the M.W. –Our sun is one of them. –The sun is 2/3 away from the center. Like other spiral galaxies, it has several parts; disk, bulge, and halo.

Milky Way (cont.) It would take 100,000 light years to cross the MW. Using visible light, we cannot see the center of the galaxy. Therefore, astronomers have to use other wavelengths to make observations. This picture was taken with light from the infrared region of the electromagnetic spectrum.

Lenticular The lenticular galaxies are disk galaxies without any conspicuous structure in their disks.

Elliptical Football shaped Little or no global angular momentum

Irregular Do not fit any of the other categories. Chaotic in appearance. Make up about 25% of the galaxies.

Active Galaxies Active galaxies are intensely studied at all wavelengths. They can change their behavior on short timescales. A diagram of an active galaxy, showing the primary components.

Seyfert Galaxies Unusually bright, compact nuclei.

Radio Galaxies Extensive double radio sources, shining by synchrotron radiation as electrons spiral through magnetic fields at relativistic speeds.

Quasars z = (Observed wavelength - Rest wavelength)/(Rest wavelength) The only interesting thing about quasars is their spectrum.

Mass of Our Galaxy Estimate the total mass of our Galaxy using the orbital data of the Sun (including our solar system) about the center of the Galaxy. Assume that most of the mass of the Galaxy can be approximated as a uniform sphere of mass (the center bulge). The Milky Way EXAMPLE 33-1, pg. 1001

The Dark Matter It’s a lot of different stuff, from tiny subatomic particles to black holes. Massive Astrophysical Compact Halo Objects Weakly Interacting Massive Particles

MACHOs Strong dark matter objects ranging in size from small stars to super massive black holes. Made of baryonic matter. Make up the halos around galaxies.

Brown Dwarfs Vs. Black Holes Made out of hydrogen--the same as our sun but they are typically much smaller. Stars like our sun form when a mass of hydrogen collapses under its own gravity and the intense pressure initiates a nuclear reaction, emitting light and energy. Brown dwarfs are different from normal stars, because of their relatively low mass, Brown dwarfs do not have enough gravity to ignite when they form. Brown dwarfs give off some heat and a small amount of light. Have an over-abundance of matter. All that matter "collapses" under its own enormous gravity into a relatively small area. Extremely strong gravitational field. Stars at safe distance will circle around the black hole. Black holes emit no light; they are truly black.

References Our text book