Classification of Stars

Question 1

Under what conditions will a supernova occur?

Answer 1

• Star must be a red supergiant
• Iron core of supergiant must be greater than 1.4 solar masses

Question 2

What happens when a supernova occurs?

Answer 2

• core collapses and its density increases to that of atomic nuclei : 1 x 10^17 kgm-3
• core become rigid
• collapsing surrounding matter hits and rebounds as a shock wave propelling matter outwards into space
• elements heavier than iron are fused and flung out into space

Question 3

State the absolute magnitude range of a supernova?

Answer 3

-15 to -20

Question 4

What does the existence on Earth of elements with an atomic number greater than iron tell us?

Answer 4

Some parts of the Earth are are made from remnants of supernovae

Question 5

What is a standard candle?

Answer 5

A type Ia supernova which is the consequence of a white dwarf exploding

Question 6

Why are standard candles useful to astronomers?

Answer 6

They have a known peak luminosity which can be used to work out distances to galaxies

• they always reach about the same maximum absolute magnitude (-19.3)

Question 7

What is a neutron star?

Answer 7

An incredibly dense star that is formed when the core of a large star collapses

• Protons and electrons are forced together under gravity to form neutrons

Question 8

Describe how a Ia supernova occurs

Answer 8

In a binary system, where one star has collapsed to a white dwarf, the companion star runs out of hydrogen and expands

• This allows the white dwarf to begin accumulating matter from the companion star collapses
• white dwarf explodes after reaching a critical mass

Question 9

What is the defining characteristic of a supernova?

Answer 9

It’s rapidly increasing absolute magnitude

Question 10

State the temperature range for class O

Answer 10

25000 - 50000K

Question 11

State the temperature range for class B

Answer 11

11000 - 25000K

Question 12

State the temperature range for class A

Answer 12

7500 - 11000K

Question 13

State the temperature range for class F

Answer 13

6000 - 7500K

Question 14

State the temperature range for class G

Answer 14

5000 - 6000K

Question 15

State the temperature range for class K

Answer 15

3500 - 5000K

Question 16

State the temperature range for class G

Answer 16

<3500K

Question 17

State the colour of class O stars

Answer 17

blue

Question 18

State the colour of class B stars

Answer 18

blue

Question 19

State the colour of class A stars

Answer 19

blue-white

Question 20

State the colour of class F stars

Answer 20

white

Question 21

State the colour of class G stars

Answer 21

yellow-white

Question 22

State the colour of class M stars

Answer 22

red

Question 23

State the colour of class K stars

Answer 23

orange

Question 24

Which classes of stars produce Balmer Absorption lines?

Answer 24

OBA

Question 25

Explain what is meant by a black body spectrum

Answer 25

The variation of intensity against wavelength of radiation emitted from a heated object

Question 26

State Wein’s Law

Answer 26

peak wavelength x surface temperature = 2.9 x 10-3

Question 27

Define what meant by a standard candle

Answer 27

An object whose absolute magnitude is known

Question 28

Define a parsec

Answer 28

The distance at which 1 AU subtends a parallax angle of one arc second (1/3600 degree)

Question 29

Define a supernova

Answer 29

An object which exhibits a rapid and enormous increase in absolute magnitude

Question 30

State two types of supernova and when they occur

Answer 30

Type II - supergiant collapses and then explodes Type 1a - a white dwarf accumulates matter and explodes

Question 31

Define a gamma-ray burst

Answer 31

A short, extremely high energy burst of gamma radiation emitted by a collapsing supergiant star

Question 32

In which class of stars are hydrogen balmer lines strongest?

Answer 32

Class A