Supernovae, neutron stars and black holes (A-level only) Flashcards – AQA A-level Physics (7408)

What is a neutron star?

A compact stellar remnant composed predominantly of neutrons.

How does a neutron star's mass compare with its size?

A mass comparable to that of a star is concentrated in an object only tens of kilometres across.

How can a neutron star form?

Through the collapse of the core of a massive star.

What is a black hole?

A region bounded by an event horizon, from within which light cannot escape to a distant observer.

In the escape-velocity model, how does escape velocity compare with the speed of light at and inside a black hole’s event horizon?

At the horizon it equals the speed of light; inside it exceeds the speed of light.

What is the Schwarzschild radius of a non-rotating black hole of mass $M$?

$R_s \approx \frac{2GM}{c^2}$ Here $G$ is the gravitational constant and $c$ is the speed of light in a vacuum.

How does the Schwarzschild radius depend on a black hole’s mass?

It is proportional to the mass.

Where are supermassive black holes found?

At the centres of galaxies.

What is a gamma-ray burst?

A brief, intense emission of gamma radiation.

How can the collapse of a supergiant star produce a gamma-ray burst?

Its core collapses to form a neutron star or black hole, releasing energy in a short time.

How can the inferred energy of a powerful gamma-ray burst compare with the Sun’s lifetime energy output?

It can be comparable to the Sun’s total energy output over its lifetime.

Why can assuming equal emission in all directions overestimate a gamma-ray burst’s total energy?

The radiation may instead be concentrated into a jet.

What can comparing type Ia supernova distances with their redshifts reveal?

How the expansion of the Universe has changed.

How do distant type Ia supernovae provide evidence for accelerated expansion?

They appear fainter and therefore farther away than expected in a comparable model without accelerating expansion.

What is dark energy’s proposed connection to cosmic acceleration?

Dark energy is a proposed explanation for the acceleration, but its physical nature is not established.

What does the inference and interpretation of cosmic acceleration from supernovae depend on?

The cosmological model and the control of uncertainties in supernova observations and their calibration.