1.4 Stability of Spiral Arms

Question 1

Under what condition can spiral arms not be stable?

Answer 1

When they are traced by the same stars and gas i.e if they are material

Question 2

What is the winding problem?

Answer 2

That the angle calculated for spirals is approximately 2.3 degrees

• Compatible with Sa/SBa spirals, but not late spirals
• Late material spirals should not exist

Question 3

Why do spiral arms arise?

Answer 3

Due to density waves

Question 4

What causes stars to have a non circular orbit?

Answer 4

Due to their gravitational potential not being perfectly central

Question 5

What is a kinematic spiral?

Answer 5

When we get an intersection of orbits, creating a higher density of material shapes like a spiral

Question 6

What happens to the blue stars on the spiral arms, and why?

Answer 6

They die before they can leave, with new ones forming continuously

Question 7

Why do we get star formation on spiral arms?

Answer 7

Due to the overdensity of material

- It compresses the gas entering a spiral wave triggering star formation

Question 8

What causes the stability of the spiral structure?

Answer 8

The self gravity of the spiral reinforces and stabilises the structure