Stars, Galaxies, and the Universe

Definitions

• Solar system: A star and all orbiting objects, including planets, moons, asteroids, and comets.
• Galaxy: A massive system of stars, gas, and dust held by gravity, revolving around a black hole.
• Star: A hot gas ball, mainly hydrogen and helium, undergoing nuclear fusion.
• Universe: All space, time, matter, and energy, including galaxies, stars, and planets.
• Light year: The distance light travels in one year, about 9.46 trillion km.

Nebulae

• Hydrogen is the most abundant gas.
• Gravity and internal pressure cause the transition from a nebula to a protostar.
• A protostar forms when gravity overcomes pressure.

Star Life Cycle

• The main sequence is the most stable stage because the outward pressure from nuclear fusion balances gravity.
• White dwarfs are smaller and denser than red giants due to gravity compressing matter after outer layers are expelled.
• Iron forms through nuclear fusion in red supergiants where fusion can no longer generate energy beyond iron, leading to a supernova.
• Copper forms during supernova explosions with intense heat and pressure creating elements heavier than iron.

Big Bang Theory

• A singularity is a point of infinite density and temperature which spawned the Big Bang theory.
• The Big Bang Theory states the universe began from a singularity before expanding.
• 380,000 years after the Big Bang, atoms formed, allowing light to travel freely and can be observed today as Cosmic Microwave Background (CMB) Radiation.
• The universe's expansion can be visualized as dots on a balloon moving apart as it inflates.
• The Steady State Model suggests the universe has always existed, continuously creating matter as it expands.

Distance Conversions

• Earth to Sun: 150,000,000,000 m = 150,000,000 km = 1.5×10^8
 km
• Earth to Andromeda: 23,650,000,000,000,000,000 m = 23,650,000,000,000,000 km = 2.365×10^16 km

Red Shift and Blue Shift

• Red shift indicates a galaxy is moving away (longer wavelengths).
• Blue shift indicates a galaxy is moving toward us (shorter wavelengths).
• The Doppler Effect explains how waves change frequency based on motion.
• Light shifts toward red if a star is moving away.
• Light shifts toward blue if a star is moving closer.
• Greater red shift indicates that a galaxy is moving away faster and is farther.
• Parsecs are based on parallax measurements.
• Parsecs are more useful for large-scale distances in astronomy.
• One parsec equals 3.26 light-years.

Star Life Cycle Explanation

• It begins in a nebula, undergoes nuclear fusion, and spends most of its life as a main sequence star.
• It may become a red giant or red supergiant before ending as a white dwarf, neutron star, or black hole, depending on its size.

Nuclear Fusion in Stars

• Lighter elements fuse to form heavier elements, releasing energy.
• It occurs due to extreme heat and pressure in a star’s core. -Main Sequence Star: Hydrogen fuses into helium, releasing energy that counteracts gravity and keeps the star stable.
• Red Giant/Supergiant: Helium fuses into carbon and oxygen (for low-mass stars) or into heavier elements (for massive stars) once hydrogen runs out.
• Supernova (for high-mass stars): Fusion continues up to iron, where the core collapses, and the explosion creates elements heavier than iron.
• Nuclear fusion powers stars and creates the elements that make up the universe.

Redshift and Blueshift

• Red shift occurs when light from a galaxy or star stretches to longer wavelengths
• It indicates the galaxy is moving away from us.
• Blue shift occurs when light compresses to shorter wavelengths
• It indicates the galaxy is moving toward us.

Red Shift and the Big Bang

• Most galaxies show red shift, suggesting the universe is expanding.
• This supports the Big Bang Theory, which states the universe started from a small, dense state and has been expanding ever since.

Doppler Effect in Astronomy

• The Doppler Effect describes how waves change in frequency based on the motion of the source
• If a star or galaxy moves away, its light is red shifted (lower frequency).
• If it moves closer, its light is blue shifted (higher frequency).

Red Shift Magnitude

• A greater red shift means a distant galaxy is moving away faster than a nearby one, showing an increasing expansion rate.
• If all galaxies showed blue shift, it would mean the universe is collapsing.
• Edwin Hubble’s observations of distant galaxies showed red shift, leading to Hubble’s Law.
• The amount of red shift correlates to the speed of a galaxy.
• Galaxies with spectral lines shifted slightly to the red are moving away slower than those with greater red shift.
• Astronomers measure red shift to calculate the rate of expansion, estimating the universe's age at 13.8 billion years.

Stages of the Big Bang

• Everything erupted from a single point called the singularity
• Includes time, space, energy and matter.
• In 10^−33 seconds Inflation occurred.
• Gravitational, electromagnetic, and strong and weak nuclear forces appeared in Planck Era 10⁻⁴³ seconds.
• Before subatomic particles formed, quark-gluon plasma (QGP) occurred within 10−12 seconds.
• During the particle era matter was formed from energy within 10⁻¹⁰ to 10⁻³ seconds.
• Protons, neutrons and electrons were created, but could not combine yet.
• The first atoms, helium and hydrogen were created within 3 seconds after the Big Bang.
• 10,000 years after the Big Bang photons could move freely and light shone.
• 300 million years after the Big Bang, the first stars and galaxies formed which included the Milky Way.
• 5 BYA, the solar nebula formed our Sun and Solar System.
• 4.5BYA Previously dying stars created heavy elements that produce Earth.
• 3.8 BYA the first microscopic bacteria-like organisms appeared on Earth.
• 700 MYA the first animals appeared.
• 200 MYA the first mammals appeared.
• 65 MYA Dinosaurs extinct
• 600,000 YA the first humans appeared.

Astronomical Unit

• 1 astronomical unit (AU) is the average distance from the Earth to the Sun.
• = 150,000,000,000m is the same as 150 x 10⁹m (in standard form).

Light Year

• 1 Light year = how far light travels in 1 year
• 9.5 trillion kilometres or 9.5 × 10¹² (in standard form).

Parsec

• The distance is based on a star that would need to be from our sun if it were to have a stella parallax of exactly 1 arcsecond (1 degree/3600).
• Distance in parsecs = distance in light years / 3.26
• It is calculated by using parallax.

Parallax

• Parallax causes you to see different views of the same object. By comparing the position of a star in the sky 6 months (and 300 million kilometers) apart.
• We can calculate how far a star needs to be away to have a parallax angle of 1 arcsecond.