Intro To Stars

Question 1

Nebulae

Answer 1

Gigantic clouds of dust and gas (mainly hydrogen)

Question 2

Protostar

Answer 2

A hot, dense sphere of condensing dust and gas that is on the way to becoming a star

Question 3

Fusion

Answer 3

A process in which two smaller nuclei join together to form one larger nucleus

Question 4

Radiation Pressure

Answer 4

Radiation from the photons in the core of a star, which acts outwards to counteract the pressure from the gravitational force pulling the matter in the star inwards

Question 5

Gas Pressure

Answer 5

The pressure of the nuclei in the star’s core pushing outwards and counteracting the gravitational force pulling the matter in the star inwards

Question 6

Main Sequence Star

Answer 6

A protostar that succeeds in hydrogen fusion, becoming a stable main sequence star

Question 7

Planets

Answer 7

An object in orbit around a star

1. Has a mass large enough for its own gravity to give it a round shape
2. Has no fusion reactions
3. Has cleared its orbit of most other objects (asteroids etc.)

Question 8

Planetary Satellites

Answer 8

A body in orbit around a planet, this includes moons and man made satellites

Question 9

Solar Systems

Answer 9

Our Solar System contains the Sun and all objects that orbit it (planets, comets, etc.)

Question 10

Galaxies

Answer 10

A collection of stars, interstellar dust and gas

On average a galaxy will contain 100 billion stars

Question 11

Comets

Answer 11

Small irregular bodies made up of ice, dust, and small pieces of rock

All comets orbit the Sun, many in highly eccentric elliptical orbits. As they approach the Sun, some comets develop spectacular tails

Question 12

Red Giant

Answer 12

An expanding star at the end of its life, with an inert core in which fusion no longer takes place, but in which fusion of lighter elements continues in the shell around the core

Large 10 to 100x radius of Sun

Hydrogen fusion in shells just outside core

No “fusion” in core

Core made of helium

High luminosity, lower temperature

At the end of their life, the star doesn’t have the gravity to hold onto its outer atmosphere, it spreads out into a planetary nebula and it’s core becomes a white dwarf

Question 13

Red Super Giant

Answer 13

A huge star in the last stages of its life before it “explodes” in a supernova

“Onion layers” of shells fuse heavier elements up to iron

When the star has an iron core, no more fusion can be performed

Very high luminosity, very low surface temperature due to large surface

Enormous - 100 to 1000x radius of the Sun

Question 14

White Dwarf

Answer 14

A very dense star formed from the core of a red giant, in which no fusion occurs

Planetary nebulae surround them

About the size of the Earth

Maximum mass of 1.44 Solar Masses (Chandrasekhar limit)

No fusion - core made of electron degenerate matter

Gravitational force inwards is balanced by the electron degenerate pressure outwards

Low luminosity, high temperature

Question 15

Planetary Nebula

Answer 15

The outer layers of a red giant that have drifted off into space, leaving the hot core behind at the centre as a white dwarf

Question 16

Electron Degeneracy Pressure

Answer 16

A quantum mechanical pressure created by the electrons in the core of a collapsing star due to the Pauli exclusion principle

Question 17

Chandrasekhar Limit

Answer 17

The mass of a star’s core beneath which the electron degeneracy pressure is sufficient to prevent gravitational collapse (1.44 solar masses)

Question 18

Supernova

Answer 18

The implosion of a red supergiant at the end of its life, which leads to subsequent ejection of stellar matter into space, leaving an inert remnant core

The star fuses iron - this releases less energy than it takes to

The outward “pressure” drops and gravity pulls the star in

Once this process starts it is unstoppable, even when heavier elements start to fuse

Electrons are forced into protons (electron capture) as it collapses at ~20% speed of light

This creates neutrons and a huge amount of neutrinos, which can be detected before we can see the supernova

This collapsing material bounces off the neutron star at the core of the supernova- the forces involved are gargantuan as are the velocity of the particles

Question 19

Neutron Star

Answer 19

The remnant core of a massive star after the star has gone supernova and (if the mass of the core is greater than the Chandrasekhar limit) the core has collapsed under gravity to an extremely high density (similar to that of an atomic nucleus, ~10^17 kgm^-3), as it is almost entirely made up of neutrons

High density star (made of neutrons)

1.4 Solar Masses < Neutron Star Mass

Question 20

Neutron Degeneracy Pressure

Answer 20

When protons and neutrons push against each other due to gravitational force in a neutron star, creating neutron degeneracy pressure

The gravitation force of a neutron star is balanced by neutron degeneracy pressure

Question 21

Singularity

Answer 21

A point of zero volume and infinite density

Question 22

Black Hole

Answer 22

The remnant core of a massive star after it has gone supernova, and the core has collapsed so far that in order to escape it, an object would need an escape velocity greater than the speed of light, and therefore nothing can escape

Question 23

Hydrostatic Equilibrium

Question 24

Evolution of a low mass star

Question 25

Evolution of a massive star