Chapter 21

CHAPTER 2121.4 Star Systems and Galaxies

Double and Triple Stars Most solar systems have more than one

star. Solar systems with 2 stars are called

binary systems. Solar systems with 3 stars are called triple stars

The stars orbit each other, and when one star passes in front of another star it is called an eclipsing binary system

The effects of gravity often clue astronomers to the presence of the 2nd star by a distinct wobble the star has when it orbits.

Extrasolar planets The pull of gravity is one of the ways that

astronomers have used to discover planets orbiting other stars. A different more subtle wobble indicates the presence of planets.

More than 400 planets have been found orbiting other stars.

Technology is not good enough to detect Earth like planets yet, but it is getting better all the time.

Galaxies A galaxy is a collection of stars,

dust, and gas that usually orbits a supermassive black hole and contains billions of stars.

There are 3 kinds of galaxies:SpiralEllipticalIrregular

Spiral Galaxies Have a pinwheel shape. Our galaxy, the

Milky Way, is a spiral galaxy

Elliptical Galaxies They are older galaxies that lack a lot of

dust and gas. Star formation has virtually ceased as a

result.

Irregular Galaxies Galaxies that have odd shapes are called

irregular galaxies. The odd shapes come from collisions with

other galaxies.