Classification of Stars Flashcards

Question

Explain the general shape of black-body curves

Answer 1

Wein’s law shows that the peak wavelength of a black body decreases as it gets hotter meaning the frequency increases so the energy of the wave increases

Answer 2

* The absorption lines are dependent on the temperature of the star * This is because the energy of the particles which make up the star is dependent on its temperature

Answer 3

* Hydrogen Balmer lines are caused by the excitment of hydrogen atoms from the n = 2 state to higher/lower energy levels * If the temperature of a star is too high, the majority of hydrogen atoms will become excited to higher levels than n = 2 or electrons might even become ionised, so hydrogen balmer lines will not be present * If the temperature of a star is too low, the hydrogen atoms are unlikely to become excited, or may not be present at all, so hydrogen balmer lines will not be present

Answer 4

The sun is a main sequence star, its spectral class is G and its absolute magnitude is about 5

Answer 5

1. Protostar - clouds of gas and dust get clump together under gravity, eventually the protostar gets dense and hot enough so it begins to fuse elements 2. Main Sequence Star - the inward force of gravity and the outward force due to fusion are in equilibrium – the star is stable, hydrogen nuclei are fused into helium 3. Red Giant - once the hydrogen runs out, the temperature of the core increases and begins fusing helium nuclei into heavier elements (e.g Carbon and Oxygen) The outer layers of the star expand and cool 4. White Dwarf - when a red giant has used up all its fuel, fusion stops and the core contracts as gravity is now greater than the outward force. The outer layers are thrown off. The core becomes very dense 5. Black Dwarf - a white dwarf will eventually cool to a black dwarf

Answer 6

1. Protostar - clouds of gas and dust get clump together under gravity, eventually the protostar gets dense and hot enough so it begins to fuse elements 2. Main Sequence Star - the inward force of gravity and the outward force due to fusion are in equilibrium – the star is stable, hydrogen nuclei are fused into helium 3. Red Supergiant - when the core runs out of hydrogen, the temperature of the core increases fusing helium nuclei into heavier elements (e.g Carbon, Oxygen and Iron) 4. Supernova - when all fuel runs out, fusion stops and the core collapses inwards very suddenly. This causes gamma ray bursts and the outer layers of the star fall inwards and rebound off of the core, launching them out into space in a shockwave 5. Neutron Star - when the core of a large star collapses, gravity is so strong that it forces protons and electrons together to form neutrons, this is incredibly dense 6. Black Hole - when the core of a giant star collapses, the neutrons are unable to withstand gravity forcing them together., the gravitational pull of a black hole is so strong that not even light can escape

Answer 7

Spinning neutron stars that emit beams of radiation from the magnetic poles as they spin

Answer 8

* Gravity is so strong that it forces protons and electrons together to form neutrons * A neutron star is incredibly dense – about 10¹⁷kg m- 3 (the density of nuclear matter)

Answer 9

* The gravitational pull of a black hole is so strong that not even light can escape * Escape velocity \> speed of light

Answer 10

The point at which the escape velocity becomes greater than the speed of light

Answer 11

The radius of the event horizon R_s = 2GM / c² Schwarzchild Radius = 2 x Gravitational Constant x Mass of Black Hole / Speed of Light²

Answer 12

Supernovae may release around 10⁴⁴ J of energy, which is the same amount of energy as the sun outputs in its 10 billion year lifetime

Answer 13

A system where two stars orbit a common centre of mass

Answer 14

* Type I - when a star accumulates matter from its companion star in a binary system and explodes after reaching a critical mass * Type II - the death of a high-mass star after it runs out of fuel

Answer 15

It is an object of which has a known absolute magnitude

Answer 16

* All types of supernovae occur at the same critical mass, meaning they all have a very similar peak absolute magnitude and produce very consistent light curves * This allowing astronomers to use them as standard candles to calculate distances to far-off galaxies

Answer 17

When the white dwarf star reaches a critical mass, fusion begins and becomes unstoppable as the mass continues to increase, eventually causing the white dwarf to explode in a supernova

Answer 18

* Scientists believe that there are supermassive black holes at the centre of every galaxy * This is because stars and gas near the centre of galaxies appear to be orbiting very quickly * They concluded that there must be a supermassive object at the centre with a very strong gravitational field attracting them

Answer 19

* Dark energy is thought to be the reason behind the universe accelerating * It is described as having an overall repulsive effect throughout the whole universe. Since gravity follows the inverse square law, it decreases with distance * Dark energy however remains constant all throughout the universe, meaning it has a greater effect than gravity and is therefore causing expansion speed to increase

Answer 20

Dark energy is controversial because there is evidence for its existence but no one knows what it is or what is causing it