Chapter 19- Galaxies

Question 1

Galaxies and how do we know how many there are

Answer 1

• 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

Question 2

what is special about the milky way

Answer 2

• we have never seen the Milky Way our selves

- all photos are artists renditions

Question 3

what DO we know about the MW

Answer 3

• it is some sort of flat structure and were inside it

- we know because we don’t see many stars above and below is

Question 4

were is the sun relation to center

Answer 4

-we are actually 27,000 light years from the bulge

Question 5

spiral galaxy

Answer 5

• flattened disk shape

- gas and stars in disk all orbit in the same direction

Question 6

orbit in galaxy

Answer 6

• we orbit around galaxy at speed of 790,000 km/h

- it takes about 230 million years to complete one orbit

Question 7

Halo stars

Answer 7

• 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

Question 8

Disk stars

Answer 8

• 2% heavy elements
• stars of all ages
• still producing stars
• population I stars

Question 9

our galaxy formed from what

Answer 9

• a cloud of intergalactic gas
• halo stars formed first as gravity caused gas to contract
• remaining fas settled into. spinning disk

Question 10

where will gas be in 1 trillion years

Answer 10

locked into WD and low mass stars

Question 11

how long does it take the sun to orbit MW

Answer 11

-230 million years

Question 12

we can only find mass of the

Answer 12

thing we orbit aka the bilge and part of the disk

Question 13

bulge

Answer 13

• 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

Question 14

spiral arms

Answer 14

• bright bands of newly formed stars
• contains large concentration of O and B stars/ emission nebula/ molecular clouds
• 4 major arms

Question 15

4 major spiral arms

Answer 15

• cygnus
• perseus
• sagittarius
• centaurus

Question 16

density wave theory

Answer 16

• 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

Question 17

whats at the center of the galaxy

Answer 17

• a black hole called Sagittarius A*
• 4 million x the size of the sun
• we know because stars orbit something invisible