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Galaxies
- 8. 90% of a Spiral Galaxy is Dark Matter!
- 9. SPIRALS
- 10. BARRED SPIRALS
- 12. Type E0 Type E3 Type E6 ELLIPTICALS
- 13. IRREGULAR
- 20. Looks like a star….but it is 4 billion light years away!
- 21. What are Quasars? Quasars get their energy from swallowing up matter in the accretion disk
- 23. • • • • • • • •
Editor's Notes
- There are billions of galaxies in the Universe. Everything in this photograph is a galaxy, except for one thing. The star near the middle is the ONLY star in the picture. We do not find stars outside of galaxies! So what galaxy do you think that star is in? All of the stars we see in the sky are in our Milky Way galaxy. In fact everything we can see with the naked eye is in our Milky Way galaxy, except the Andromeda galaxy. This I just a tiny, tiny piece of sky!!!! So there are billions and billions of galaxies out there.
- Remember that galaxies tend to hang out in clusters or groups. This is the Seyfert galaxy group. It is particularly compact. A galaxy group, remember, is a gravitationally bound system.
- This is a galaxy. It is a spiral galaxy, which we will learn more about later. A galaxy is a massive, gravitationally bound system with stars and stellar remnants, an interstellar medium of gas and dust, and dark matter. The word galaxy is derived from the Greek galaxias, literally "milky", a reference to the Milky Way galaxy.
- Here is a picture of the Milky Way from Earth. Remember that we are looking at the center of the plate in this picture. Somewhere in there is a super-massive black hole!
- How do we know there is dark matter if we can’t see it? Two main ways. The first is related to Kepler’s laws. Remember that one of Kepler’s laws said that the distance from the center of the orbit dictates how fast a body moves?The second is using Einstein and the blanket we talked about last week. When gravity bends spacetime, not only does matter fall toward very massive things, but light does too. This does something interesting we call gravitational lensing.
- If you want to take part in REAL research, the best way to do that is through the Galaxy Zoo project, where you get to classify galaxies that go into a database. Astronomers tried to use computers to classify the galaxies, but it turns our humans are much better at it than computers. And there are billions out there, so astronomers need help classifying them all.http://www.galaxyzoo.org/how_to_take_part
- When we are looking at the side of a galaxy, like this one, it makes it hard to classify. A lot of other things make galaxies hard to classify as well. The differences are enormous, and there are some weird looking galaxies out there. Let’s try out. Here is a worksheet we are going to do individually.
- SbSBaE6-7
- SBbSb/cI
- IrregularSaE0-3
- This is called the antennae galaxy. Can anyone guess what is going on here? This is actually 2 galaxies merging!!!! What did you guys classify this as? I would take either spiral, or irregular, since it is technically two spirals merging.
- This is what spiral galaxies like ours look like today. There is still a super-massive black hole at the center, but it is not ACTIVE anymore. Our galaxy, the Milky Way, is about 100,000 light years acrosss. Remember that 1 light year is 6 trillion (6,000,000,000,000,000) miles, so we are talking enormous distances. At the center is the nuclear bulge, around the galactic nucleus, where the BH is. We are about 28,000 light years from this center. Most stars and gas are concentrated in the disk of the galaxy, but there are a lot of old globular clusters in what we call the galactic halo, out here.