4: SUPERNOVAE

Question 1

How are SN classified?

Answer 1

By the spectra around their peak output

Question 2

What is different between Type I and Type II SN?

Answer 2

Type 1 - Don’t have H lines
Type 2 - Do have H lines

Question 3

Define Type Ia, Ib, and Ic

Answer 3

Ia - Have silicon lines
Ib - Don’t have silicon lines, but do have helium
Ic - No silicon or helium

Question 4

Type IIs are the result of the collapse of a massive star called a core-collapse supernova. Describe this process.

Answer 4

1. Fe core grows too massive for degenerate e- pressure support (Chandrasekhar limit)
2. Core collapses and further nuclear reactions produce large amounts of neutrinos which carry away a significant amount of total energy
3. Collapse stops when repulsive part of the nuclear force prevents further collapse. Outer layers bounce back causing shock wave and further fusion

Question 5

What do Type II SN usually leave behind?

Answer 5

A compact object such as a neutron star (NS) or a black hole (BH) of a few solar masses

Question 6

Type Ib and Ic are also supernovae. What is their difference?

Answer 6

In type Ib, the star has already shed its outer layer of H before the core collapses, while for type Ic, the outer layers of H and He have been shed before collapse. Absence of elements in their spectra.

Question 7

Define white dwarf

Answer 7

Remnants of less massive stars that have shed their outer layers leaving beghind a core supported by degenerate electron pressure

Question 8

What are the two main models for how a WD gains the mass needed to ignite fusion?

Answer 8

1. Single-degenerate - WD accretes material from a companion star in a binary system until it has enough mass for SN to ignite
2. Double-degenerate - The majority of type 1as could be caused by the merger of two WDs in a binary system. In this case, the resulting object exceeds the Chandrasekhar limit and collapses to ignite the SN

Question 9

Why are Type 1as good standard candles?

Answer 9

They have similar peak luminosities

Question 10

How can Type 1as be used to measure the expansion history of the universe?

Answer 10

If their redshifts are measured they ccan be used to construct a Hubble diagram

Question 11

1. Are all the peak luminosities of type 1as the same and why?
2. How does this help us infer peak luminosity?
3. How does this make it more accurate?

Answer 11

1. No, brighter SN has a slower decline in brightness than the fainter ones.
2. By measuring the change in brightness over a period
3. Removing the uncertainty that arises from assuming a fixed value

Question 12

Define SN remnant

Answer 12

1. After the explosions of a SN, the ejected material from the star expands into the ISM.
2. This causes shocks that heat and sweep up the ISM in a roughly spherical region around the SN, that is visible from radio to x-rays.

Question 13

What are the two categories of SNR?

Answer 13

1. Crab-like or plerions - Make up < 10% of SNR. They are filled with synchrotron emission from radio to X-rays and have a central radio source (pulsar)
2. Shell-like: Radio, optical, and x-ray emission are seen from the outer shell, but no emission from inside the shell

Question 14

For filled, crab-like SNR the observed synchrotron is from e-. What is this accelerated by?

Answer 14

Supernova shock

Question 15

What is associated with type II SN?

Answer 15

A left behind pulsar

Question 16

What is seen from the shell-like SNR and why? What leads to a shell like SNR?

Answer 16

1. Emission
2. No central source to replenish electrons
3. Type 1a SN