Chapter 19- Galaxies Flashcards
Galaxies and how do we know how many there are
- large collection of stars, gas, dust, blackholes, dark matter, all gravitationally bound together
- 100 Billion stars
- we can estimate the number of stars by counting stars in smaller region OR take mass of stars and divide by average mass
what is special about the milky way
- we have never seen the Milky Way our selves
- all photos are artists renditions
what DO we know about the MW
- it is some sort of flat structure and were inside it
- we know because we don’t see many stars above and below is
were is the sun relation to center
-we are actually 27,000 light years from the bulge
spiral galaxy
- flattened disk shape
- gas and stars in disk all orbit in the same direction
orbit in galaxy
- we orbit around galaxy at speed of 790,000 km/h
- it takes about 230 million years to complete one orbit
Halo stars
- 0.2% heavy elements
- only old stars (aka formed first)
- where we find the globular clusters
- population II stars
- stars orbit in all different directions
Disk stars
- 2% heavy elements
- stars of all ages
- still producing stars
- population I stars
our galaxy formed from what
- a cloud of intergalactic gas
- halo stars formed first as gravity caused gas to contract
- remaining fas settled into. spinning disk
where will gas be in 1 trillion years
locked into WD and low mass stars
how long does it take the sun to orbit MW
-230 million years
we can only find mass of the
thing we orbit aka the bilge and part of the disk
bulge
- ball of stars in center of galaxy
- bright
- stars in it orbit randomly
- old population II stars
- old and dull but theres a lot of stars so it appears super bright
spiral arms
- bright bands of newly formed stars
- contains large concentration of O and B stars/ emission nebula/ molecular clouds
- 4 major arms
4 major spiral arms
- cygnus
- perseus
- sagittarius
- centaurus
density wave theory
- explains why theres so much dust and gas in arms
1) gas clouds get squeezed as they move into spiral arms
2) squeeze of clouds triggers star formation
3) young star flows out of spiral arms
whats at the center of the galaxy
- a black hole called Sagittarius A*
- 4 million x the size of the sun
- we know because stars orbit something invisible