C19 Stars

Question 1

Define Nebulae

Answer 1

Nebulae are gigantic clouds of dust and gas (mainly hydrogen), the birthplace of all stars. They are often hundreds of times larger than our solar system.

Question 2

How are nebulae formed?

Answer 2

They are formed over millions of years as the tiny gravitational attraction between particles of dust and gas pulls the particles toward each other, clumping together and eventually forming gas clouds.

Question 3

How do protostars form?

Answer 3

• As dust and gas get closer together within a nebulae, gravitational collapse accelerates.
• Denser regions within the nebulae begin to form, and pull more dust and gas, increasing further in mass and density.
• These regions get very hot, as gravitational energy is transferred into thermal energy, and in one part of the nebulae a protostar forms.

Question 4

Define protostar

Answer 4

A very hot, dense sphere of dust and gas which is not yet a star (it doesn’t shine yet)

Question 5

What conditions are needed for a protostar to turn into a star?

Answer 5

A very high temperature and pressure is required in order to provide hydrogen nuclei with enough kinetic energy to overcome their repulsive electrostatic forces, and begin nuclear fusion.

Question 6

What forces balance a star once it has formed?

Answer 6

• Radiation pressure from the photons emitted during fusion and gas pressure from the nuclei in the core push OUTWARD.
• Gravitational attraction pushes the star INWARD.
• They remain in a stable equilibrium.

Question 7

What is the name of the first phase of a star’s life, after is forms?

Answer 7

Main sequence, the stable part of their life

Question 8

What determined how long a star is in main sequence?

Answer 8

The core of a supermassive core is much hotter than for a small star, releasing more power.
- They convert all the available hydrogen into helium in a much shorter time.
- Therefore, the smaller a star, the longer it can last.

Question 9

Define planet

Answer 9

An object in orbit around a star that:

• Has a mass large enough for its own gravity to give it a round shape.
• Has no fusion reactions.
• Cleared it orbit of most other orbits

Question 10

Define asteroid

Answer 10

A small rocky body that orbits the sun, too small and uneven to be planets.

Question 11

Define planetary satellites

Answer 11

A body in orbit around a planet, including a natural/artificial satellites (moon/satellites).

Question 12

What are comets made of?

Answer 12

Ice, dust, and small pieces of rock

Question 13

Define the universe

Answer 13

The universe can be defined as the combination of all the electromagnetic radiation, energy, matter, and space-time that exists.

Question 14

Define Constellation

Answer 14

A group of stars that form a recognizable pattern that is named after its apparent form/mythological figure.

Question 15

Mass at which stars become a red giant

Answer 15

0.5 to 10 solar masses

Question 16

Explain how a main-sequence star turns into a reed giant

Answer 16

• Once the star runs out of fuel, the rate of nuclear fusion is slowed.
• This reduces the energy released by fusion in the core so the gravitational force is now greater than the reduced force from radiation and gas pressure.
• The core of the star begins to collapse, and the pressure increases enough to start fusion in a shell around the core.

Question 17

What is electron degeneracy pressure?

Answer 17

The outward pressure created by electrons when they are squeezed together under gravity when the core of a star begins to collapse.

Question 18

What is the Chandrasekhar limit?

Answer 18

The limit at which a star will no longer become a white dwarf - 1.44 solar masses.

Question 19

What happens when the remnant core of a star is above the Chandrasekhar limit?

Answer 19

• It will by default from a neutron star, which is about 10km in diameter and typically 2 solar masses.
• Above 3 solar masses the gravitational collapse compressed the core until it becomes a black hole.