Astrophysics 11 - Supernovae, Neutron Stars and Black Holes

What happens when the core of a red supergiant star has fused up to iron?

The core begins to contract. As it does so, the outer layers fall in also, and rebound off the core causing a supernovae explosion.

What happens to the core of a red supergiant after a supernovae?

If it is between 1.4 - 3 solar masses, then it forms a neutron star.

If it is more than 3 solar masses, then it forms a black hole.

What happens to the brightness of the star during a supernova?

It experiences a brief and rapid increase in absolute magnitude, briefly outshining an entire galaxy, befor fading over a few days or months.

What makes a type I supernova different from a type II supernova?

Type II contain Hydrogen Balmer lines, whereas type I do not.

What makes a type Ia supernova different from a type I.

Type Ia are only formed when a white-dwarf core absorbs enough matter from a binary partner to reach 1.4 solar masses. After this, it will immediately supernova.

As they all have a similar mass, they have identical light curves, with the same peak in absolute magnitude, so they can be used as standard candles.

What is the typical density of a neutron star.

4 ×10¹⁷ kg m^-3

The density is the same as nuclear material.

What do neutron stars emit?

Radio waves from their poles.

What is a pulsar?

A neutron star emitting radio waves such that they appear as pulses of radio waves on earth.

What is the difference between the formations of black holes and neutron stars?

Mass.

A black hole is massive enough that the gravitational force on the core is so great that it collapses into an infinitely dense point at the centre.

Define the event horizon of a black hole.

The area of space around a black hole at which the escape velocity of the black hole’s gravitational field is exactly equal to the speed of light.

Inside the event horizon, not even light can escape a black hole.

Define the Schwarzschild radius.

The radius of the event horizon from the centre of a black hole.

What do astronomers lies at the centre of every galaxy?

Supermassive black holes (10⁶ solar masses).

Give the equation for the Schwarzschild radius.

Radius = 2 x Newton’s gravitational constant x mass of the black hole / speed of light squared

R_s = 2GM / c²