Astronomy

interstellar medium

In astronomy, the interstellar medium (or ISM) is the matter that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, dust, and cosmic rays. It fills interstellar space and blends smoothly into the surrounding intergalactic space.

Summarize the star-gas-star cycle

Molecular clouds - star formation - nuclear fusion in stars - returning gas - hot bubbles - atomic hydrogen clouds. All in cyclical nature.

sun location

The Sun is located in the inner rim of the Orion Arm, which is thought to be an offshoot of the Sagittarius Arm

bulge

The bulge is a round structure made primarily of old stars, gas, and dust. The outer parts of the bulge are difficult to distinguish from the halo. The bulge of the Milky Way is roughly 10,000 light years across.

disk

The disk is a flattened region that surrounds the bulge in a spiral galaxy. The disk is shaped like a pancake. The Milky Way's disk is 100,000 light years across and 1,000 light years thick. It contains mostly young stars, gas and dust, which are concentrated in spiral arms. Some old stars are also present.

halo

The halo primarily contains individual old stars and clusters of old stars ("globular clusters"). The halo also contains "dark matter," which is material that we cannot see but whose gravitational force can be measured. The Milky Way's halo may be over 130,000 light years across.

How do disk stars orbit the center of the galaxy?

They all orbit in roughly the same plane and in the same direction.

spiral galaxy

a galaxy in which the stars and gas clouds are concentrated mainly in one or more spiral arms.

protogalactic cloud

a huge collapsing of inter galactic gas from which an indivisual galaxy formed.

irregular galaxy

appear neither disklike or rounded

100,000 light years

diameter of the milky way

3 types of gravities

elliptical, spiral, and irregular

225 million years

how long it take for the sun to orbit the galaxy

200 billion

how many stars in our milky way

quasars

how we track the evolution of galaxies over time

spiral galaxy

look like white flat disks with yellowish bulges at their centers the disk are filled with cool gasses and dust, interspersed with hotter ionized gas, and usually display beautiful spiral arms.

how do we measure the distance to galaxies

parallax, radar ranging, and standard candles.

elliptical galaxy

redder, rounder, and often longer in one direction then the other. contain very little cool gas and dust, though they often contain very hot ionized gas.

hubble clasification scheme

spiral, ellipictal, barred spirals and irregular

hubble's law

statement of a direct correlation between the distance to a galaxy and its recessional velocity as determined by the red shift.

andromeda

the galaxy nearest to ours

cosmological principle

the idea that matter is distributed uniformly throughout the universe on a very large scale, meaning the universe has neither a center no an edge.

galactic cannibilism

the process by which large galaxies merge with other galaxies in collisions.

active galactic nuclei

the unuasually luminous centers centers of some galaxies throughout to be powered by accretion onto super black holes. Quasars are the brightest form of active galactic nucelei

1000 lightyears

thickness of our milky way

milky way

what is the name of our galaxy

protogalatic spin and protoglatic density

why some galaxies are destined to be elliptical, while others are destined to be spiral