15.4 Star Systems &Galaxies

1. 15.4 Star Systems &Galaxies • Our sun is a loner, but most stars are parts of star systems of 2 or more stars.

2. Binary and Triple Stars • Groups of 2 or three stars locked together by gravity. • These are NOT moons. • Moons don’t carry out nuclear fusion.

3. Detecting Star Systems • Often, one star in a system is brighter than the others, so how do we know it’s a system and not just one star? • Wobble- Imagine a dancer with an invisible partner. You could tell from their movements that a partner must be present • Eclipses- If a dim star passes between a brighter partner star and earth, we will se an eclipse.

4. Star Clusters • A cluster is a group of stars that all formed from the same nebula • Open Clusters – contain up to a few thousand randomly placed stars • Globular Clusters – are large groups of up to a million densely packed stars Pleiades or Seven Sisters

5. Galaxies • Lone stars and star systems are grouped in to larger collections of stars called galaxies. • Galaxies are held together by gravity. • Many galaxies, like our Milky Way, have a black hole at the center.

6. The Milky Way Galaxy • Our home!

7. Other Galaxy Shapes • Spiral – has “arms” • Eliptical – no “arms” and tend to have older stars • Irregular – not spiral or eliptical

8. Clusters of Galaxies • Galaxies tend to appear in clusters as well. • The Milky way is part of a galaxy cluster called the Local Group. • The Local Group is then part of a larger system, the Virgo Supercluster

9. Scale of the Universe • http://scaleofuniverse.com

10. 15.5 The Expanding Universe • The Big Bang is the most widely accepted explanation for how the universe began. • It states that around 15 billion years ago, there was a huge explosion in whichthe entire universe was born and it has been expanding ever since.

11. How do we know this? • We look at the positions of galaxies. • Edwin Hubble discovered that galaxies are moving away from us (like the dots on your balloon in the warm up). • Hubble’s Law – the further away a galaxy is, the faster it is moving away from us.

12. Cosmic Background Radiation • This type of electromagnetic radiation was detected by a radio telescope in the 1960’s and was determined to be energy leftover from the Big Bang.

13. What does the future hold? • One idea is that universe will continue to expand and get colder foreverin a “Big Chill” • Or, it may expand to a point and then remain the same. • Another idea is that gravity will eventually pull everything back together in a “Big Crunch”.

14. Dark Matter & Dark Energy • Dark Matter is matter that does not give electromagnetic radiation. So we cannot “see” or detect it. • Dark Energy is an undetectable source of gravity used to explain the fact that the universe appears to expand faster and faster.