Cosmology Flashcards

Flashcards covering key concepts in cosmology, including stellar parallax, the Big Bang theory, cosmic microwave background radiation, and celestial objects.

Stellar Parallax

Apparent motion or displacement of a star relative to the position of more distant stars, caused by the Earth’s orbit around the Sun. Used to measure distances in space.

Evolution of the Universe up to the formation of the first nuclei

At the Big Bang, the Universe is a singularity / very dense / very hot. Expansion / inflation / high energy (gamma) photons but no matter. Quarks and leptons form / Quark-Gluon Plasma phase. Quarks combine to form neutrons / protons / hadrons. Hadrons / neutrons and protons / nucleons combine to make nuclei.

Cosmic Microwave Background Radiation Support for the Big Bang Theory

Red Shift shows increase in wavelength. Change in wavelength caused by motion of galaxy or reference to Doppler Effect

Chandrasekhar Limit

The maximum mass of a white dwarf before it collapses under its own gravity; it is 1.4 solar masses.

EM radiation from stars

Only specific energy levels are allowed; the electron can only occupy the specific energy levels. The most negative energy level is the ground state. Energy levels have negative values because energy has to be inputted to remove electrons. Once an electron is removed, it will have 0 energy. If an electron jumps up an energy level, it means a photon has been absorbed.

Emission Spectrum

Caused when a hot gas emits photons; only certain energy levels are allowed, so only certain wavelengths are seen.

Absorption Spectrum

Caused when a hot gas absorbs photons. Only certain frequencies can be absorbed, hence dark lines on a continuous spectrum

1 AU

Average distance from the earth to the sun.

Light year

Distance travelled by moving at the speed of light for a year

1 arcminute

1/60th of a degree

1 arcsecond

1/3600th of a degree

1 parsec

The distance at which 1 AU subtends a parallax angle of 1 arcsecond

Cosmological Principles

Universe is isotropic (appears the same in all directions) and homogenous (has constant matter density) and the laws of physics are universal

Hubble’s law

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

Lemaitre’s Theory

Universe had its origin in a single point which was proposed to be extremely dense and hot, and as the universe expanded it cooled.

Cosmic Microwave Background Radiation

Radiation that was released as gamma rays but has stretched to microwaves, which accounts for temperature of 2.7k

Dark energy/ dark matter

Velocities did not decreases with distance, astronomers studying Doppler shifts in light from galaxies found that the orbital outside of the galaxies increasing the star’s velocities; proposed that there was some additional matter (mass) on the

Time after Big Bang: 0

Infinitely dense and hot.

Time after Big Bang: 10^-35 s

Inflation - Universe expands rapidly. No matter in the Universe only high energy gamma photons. T ≈ 10^28 K.

Time after Big Bang: 10^-6 s

First fundamental particles (quarks, leptons etc.) form

Time after Big Bang: 10^-3 s

Quarks combine to form hadrons (like protons and neutrons). Mass is produced through pair production (photons to particle-antiparticle pair)

Time after Big Bang: 1

Mass creation stops. T ≈ 10^9 K.

Time after Big Bang: 380,000 years

The Universe cools so the first atoms can form as nuclei capture electrons. The Universe is no longer opaque and the electromagnetic radiation from this stage becomes the detectable CMB.

Time after Big Bang: 30 million years

The first stars appear. Nuclear fusion begins to form elements heavier than lithium.

Time after Big Bang: 200 million years

Our galaxy, the milky way, forms. As gravitational forces pull clouds of hydrogen and existing stars together.

Time after Big Bang: 9 billion years

Our Solar System forms from the nebula left by supernova of a large star.

Time after Big Bang: 13.7 billion years (now)

T = 2.7 K.

Planets

Mass large enough for the force of gravity to make the object spherical. No fusion reactions. Not in an orbit with many other objects such as asteroids.

Planetary Satellites

Orbit around a planet. This includes moons and artificial satellites

Comets

Irregular shapes composed of ice, dust, and rock that Orbit the sun in highly eccentric orbits.