Astrophysics

How is a protostar formed?

Nebulae (giant clouds of dust and gas) are forced together via gravitational attraction, leading to an increase in density. The gravitational energy of the particles are converted to thermal energy. The resultant sphere of hot, dense gas is a prototar

How is a star formed from a protostar?

Temperature and pressure inside star must be high enough for hydrogen nuclei to overcome electrostatic forces of repulsion and undergo nuclear fusion. This fusion produces helium

What is the main phase of a star?

the star remains in stable equilibrium (gravitational force is equal to the radiation pressure). Larger stars have a short main phase since they are hotter and therefore fuse more often

What does a low mass star (0.5 to 10 solar masses)

As hydrogen depletes, star begins to collapse inwards and evolves into a red giant

Where does fusion take place within a red giant?

Outer shell since pressure is much greater than at the core (core is also too cool)

What happens after a red giant runs out of helium?

Star evolves into a white dwarf and the outer shell begins to drift off into space, forming a planetary nebula. Core becomes a white dwarf and releases photons that were produced earlier in it’s evolution.

What keeps white dwarves core’s from collapsing?

Electron degeneracy pressure

What is the Chandrasekhar limit?

The mass of a stars core that produces a stable white dwarf. This is any mass below 1.5 solar masses

What does a massive star evolve into?

As hydrogen supplies deplete, its temperature and pressure are high enough for helium to fuse into heavier elements. This is known as a red supergiant

What dose a red supergiant have?

Layers of increasingly heavy elements produced from fusion, with an inert iron core. (since iron does not release energy)

What happens when the iron core is produced within a red supergiant?

The star becomes unstable and a type 2 supernova occurs which ejects the materials into space

What happens if the mass of the core is greater than the Chandrasekhar limit and less than 3 solar masses?

The core collapses, forming a neutron star which is extremely small and dense

What keeps a neutron star from collapsing?

Neutron degeneracy pressure

What happens if the core of a red supergiant exceeds 3 solar masses?

Gravitational forces are strong enough so that the escape velocity of the core is greater than the speed of light. This is a black hole.

What do electrons exist as when bond to an atom?

discrete energy levels

What happens when the energy value is 0?

An electron is completely free from an atom

What is the negative sign used for in energy levels?

Used to indicate the energy required to be inputted to remove the electron from the atom

What is emission line spectra?

Each element produces a unique emission line spectrum since they all have unique sets of energy. It appears as a series of coloured lines on a black background

What is a continuous line spectra?

All visible wavelengths of light are present. produced by atoms of solid heated metals

What is an absorption line spectra?

A combination of a continuous line and emission line spectra. A continuous spectrum is divided by dark spectral lines which correspond to wavelengths of light that excite atoms of that element

What is a diffraction grating?

A component with regularly spaced slits

What are stars modelled as?

Idealised black bodies that emit radiation acrosss

What does the colour of a star depends on?

A peak in intensity of a specific wavelength

What is Wein’s law?

The black body radiation curve for different temperatures peaks at a wavelength inversely proportional to the temperature of the object

What is the value of Wein’s constant?

2.9 × 10^-3

What is stefan’s law?

the total radiant heat energy emitted from a surface is proportional to the fourth power of its absolute temperature

What is the luminosity of a star?

The radiant power output of a star

What is 1AU?

The distance from the sun to the earth. 1.5 × 10^11m or 150 million km

How many degrees is in one arcminute?

1/60 degrees

How many degrees is in one arcsecond?

1/3600 degrees

What is stellar parallax?

Used to measure the distance to nearby stars. It is the apparent shift in position of an object against a backdrop of distant objects

When is stellar parallax accurate?

For distances less than 100pc

What is the cosmological principle?

The universe is isotropic and homogeneous and the laws of physics are universal

What does isotropic mean?

The universe is the same in all directions to every observer and has no center or edge

What does homogeneous mean?

Matter is uniformly distributed. For a large volume of the universe = the density is the same

What is the doppler effect?

The apparent shift in wavelength occurring when the source of the wave is moving (the actually wavelength emitted by the source remains the same)

What happens when the source of a wave moves closer to the detector?

The wavelength will appear to decrease

What happens when the source of a wave moves closer to the detector?

The wavelength appears to increase

How does the doppler effect effect star light?

It shifts the position of spectral lines

What is hubble’s law?

The recession velocity of a galaxy is directly proportional to its distance from earth

What is the value of Hubble’s constant?

67.8km/s/Mpc

What does hubble’s constant provide evidence for?

The big bang (the fabric of space time is expanding, and any point in the universe is moving away from any other point)

What is the other piece of evidence of the big bang theory?

Cosmic microwave background radiation

What is cosmic microwave background radiation?

Originally, there were high energy photons , but as the universe expanded, the wavelengths were stretched into the microwave region. This now provides a constant signal

What is the big bang theory?

All objects were initially contained in a singularity, which suddenly expanded outwards. The universe has not stopped expanding since then

What is the order of things that happened after the big bang?

• Universe expands, no matter, only high energy gamma photons

• First fundamental particles gain mass

• Mass is created through pair production

• Production of mass is halted

• Protons and neutrons fuse into light nuclei

• After a long period of time, it is now cool enough for the first atoms to form

• Stars form

• Galaxies form

• Solar system forms

• Life begins of earth