Chapter 21, Section 4Star Systems and Galaxies

Based on Prentice Hall

Textbook by Rusty Sturken

May, 2009

Background imaghttp://mayda.com/astro/Img/M31_LRGB-03C-1k.jpge from http://mayda.com/astro/Img/M31_LRGB-03C-1k.jpg

Star Systems• More than half of all stars are

members of groups of two or more stars. Our sun is not.

• Star systems with two stars are called double stars or binary stars.

• Star systems with three stars are called triple stars.

Binary Systems• Often astronomers can detect the

presence of a star in a binary system without seeing it, they can tell it is there by observing the effect of its gravity on the second star

• Sometimes with binary stars, one star blocks the light from the other star and the system is called an eclipsing binary

Eclipsing Binary

http://calgary.rasc.ca/images/Algol_Eclipsing.gif

Planets around other stars

• Scientists have discovered planets around stars by observing how a star “wobbles” very slightly back and forth

• Over 300 “extrasolar” planets have been found according to Space.com

• Most of the extrasolar planets found so far are massive gas giants with large influence on their star’s gravity.

Saturday, April 2nd, 2005Astronomers Photograph Extrasolar

Planet

http://www.utahskies.org/image_library/deepsky/misc/top.extrasolar.planet.photo.jpg

“First ever photo of an extrasolar planet, a Jupiter-sized gas giant.”

Where to look for Earthlike planets

• The so-called "habitable zone" around a star is a belt in which liquid water could exist on the surface in lakes, rivers or oceans. Too close to its stellar parent and a planet would be too hot, while an orbit too far out would yield only a frozen world, NASA scientists have said.

Quote from http://www.space.com/scienceastronomy/090416-kepler-first-images.html

Galaxies• Galaxies are giant structures that

contain hundreds of billions of stars, Oh, by the way…There are billions of galaxies in the universe

• Galaxies contain single stars, double stars, star systems and lots of gas and dust between the stars.

• Astronomers classify most galaxies into three main categories: – spiral galaxies, – elliptical galaxies, – irregular galaxies

Spiral Galaxies• Spiral galaxies have arms that

spiral outward, like pinwheels

http://zoo1.galaxyzoo.org/images/tutorial/example_face_on_spiral.jpg

http://www.spacetoday.org/images/Hubble/HubbleBeauty/NGC1512BarredSpiralGalaxy.jpg

The Milky Way• Our solar system exists in the Milky

Way galaxy, and is about 25,000 light-years away from the center of the Milky Way

• Our solar system is about two-thirds of the way out on one of the spiral arms of the Milky Way

• We can’t see the center of the Milky Way due to the massive cloud of gas and dust between the sun and the center

The Milky Way

http://abyss.uoregon.edu/%7Ejs/images/milky_way_large.jpg

The Milky Way

http://www.crystalinks.com/galaxymilkyway.jpg

Elliptical Galaxies• Elliptical galaxies look like

flattened balls

• Have little gas and dust between the stars so new stars can not form– Ellliptical galaxies only contain old

stars

http://photojournal.jpl.nasa.gov/jpegMod/PIA08696_modest.jpg

Elliptical Galaxy

http://zuserver2.star.ucl.ac.uk/%7Eidh/apod/image/0406/m87_cfht.jpg

Irregular Galaxies

• Some galaxies don’t have a regular shape, they are called irregular galaxies

• The Large Magellanic Cloud is an irregular galaxy

http://www.nasa.gov/images/content/159426main_image_feature_666_ys_4.jpg

Irregular Galaxy

http://starchild.gsfc.nasa.gov/Images/StarChild/universe_level2/ngc6822.gif

Irregular Galaxy

http://www.astro.utu.fi/news/img/RGB_bird_idl600.jpeg