galaxies. a galaxy is a massive group of stars held together by their mutual gravity
TRANSCRIPT
The milky way is:
• 100,000 LY across• 1000 LY thick• The sun is approximately
28,000 LY from the center
100 000 000 000 stars?
• If you counted one star a second, 24 hours a day, it would take 3171 years to count to 100 billion.
• (this is about 40 human lifetimes)
A billion dollar bills?
• Stacked on top of each other would make a stack 67.7 miles high.
If the stack tipped over, it would reach from Mentor to Canton.
Surrounding the center and arms
Is a “halo” of stars and smaller galaxies (millions of stars, not billions) called “globular clusters)
Gas and Dust clouds
Are the material from which future stars will form, but….
Make it difficult to see into the center of the galaxy.
Thanks to new technologies, however,
new information continues to pour in. The picture that follows was taken by the Hubble space telescope. The circles identify new planets outside of our solar system.
Evidence from radio waves
• Indicates that there is an intense source of radio waves at the center of the galaxy, perhaps 10 AUs in diameter.
(930,000,000 miles)
The object is named
Sagittarius A* (saggitarius a star)(Shown as the red dot in the following photo)
Stars near saggitarius A*
• Appear to be moving 100s of thousands of km per second (the speed of light is 300km/s)
• An object moving this fast should be able to easily break away from the galaxy. Since they don’t there must be something MASSIVE holding them in place.
As is the case with all of the stars in the milky way….
All of the GALAXIES in the LOCAL GROUP orbit a gravitational center.