Astrophysics - Stellar evolution

Question 1

What colour are the coolest stars?

Answer 1

red - M

Question 2

What colour are the hottest stars?

Answer 2

blue - O

Question 3

What is the luminosity of a star?

Answer 3

this measures how much energy is given out by a star and will depend on the size and temperature of the star

Question 4

What is the brightness of a star?

Answer 4

how bright a star appears from earth, depends on the luminosity of the star and the distance

Question 5

What is absolute magnitude?

Answer 5

This is the brightness of the star if it was at a standard distance from earth. It allows us to make better comparisons between stars.

Question 6

Spectral Class types for Stars

Answer 6

O - blue
B - blue/white
A - white
F - yellow/white
G - yellow
K - yellow/orange
M - red

Question 7

Different stages in the evolution of stars

Answer 7

• nebula
• protostar
• average star
• red giant
• planetary
• white dwarf
• massive star
• red supergiant
• supernova
• neutron statr
• black hole

Question 8

stellar nebular

Answer 8

mostly hydrogen, forms from clouds of gas and dust in the galaxy

Question 9

Protostar

Answer 9

• as the mass falls together it gets hot
• a star is formed when it is hot enough for the hydrogen nuclei to fuse together to make helium
• this is known as nuclear fusion
• the fusion process releases energy, which keeps the core of the star hot

Question 10

main sequence star

Answer 10

• the force of gravity holding the star together is balanced by higher pressure due to the high temperatures
• this phase in a star’s life usually lasts for around 10 billion years

Question 11

red giant star

Answer 11

when the hydrogen has been completely used up in the fusion process, larger nuclei begin to form and the star may even expand to become a red giant

Question 12

white dwarf

Answer 12

• average mass star will throw off the outer layers, but the centre will cool and contract into a white dwarf
• as the light then fades it will become a black dwarf

Question 13

planetary nebula

Answer 13

• cloudy remnants of smaller stars that have shed their outer layers of gas, but haven’t exploded into supernovas

Question 14

red supergiant

Answer 14

• eventually the hydrogen at the core of the star will run out as it has all been used up in nuclear fusion
• the star will then expand into a red supergiant

Question 15

supernova

Answer 15

• the red supergiant will eventually explode, causing a supernova, which throws out gas and dust into space
• this type of explosion is so strong that it would be too dangerous to stimulate on earth

Question 16

neutron star/black hole

Answer 16

• the force of the supernova will cause the star’s core to collapse
• this then either forms a neutron star, a small star with a diameter of a few km made solely of neutrons, or a black hole, a region of space with a gravitational field so strong that not even light can escape it

Question 17

What is the Hertzsprung-Russel diagram?

Answer 17

A graph relating to the surface temperatures and absolute brightness of stars

Question 18

What are the four key components of the hertz sprung-russel diagram group?

Answer 18

• supergiants (top right)
• giants (below supergiants, off to the right)
• main sequence (central, diagonal S shape)
• white dwarf (bottom left)