Star and Planet Formation: Module 3

• Module 3 is about the formation of stars and planets

Formation of Stars

• The first stars were massive and luminous

• The first stars’ formation led to the production and dispersion of heavier elements

• These heavier elements led to the formation of the solar system

• Density fluctuation left over from the Big Bang evolved into the first stars

• Observations of distant quasars allowed scientists to catch a glimpse of the final days of the cosmic dark ages

• Quasars are luminous and far celestial objects in the universe

• Protogalaxies are star-forming systems smaller and less organized than modern galaxies

• Protogalaxies do not contain significant amounts of any elements besides hydrogen and helium

• Protogalaxies merge to form galaxies and would gather into galaxy clusters

• Jeans mass is the minimum mass that a clump of gas must have to collapse under its gravity

• Clouds of gas and dust slowly aggregate to form matter

• As they evolve, they merge with each other and form larger structures like present-day galaxies

• Stars form from a cloud of dust and hydrogen gas called nebuli

• A protostar is a hot core formed from the collection of dust and gas

• Protostars become stars by accreting more material from their surroundings

• As they accrete, temperature and density increases

• Hydrogen molecules react with one another to form Helium gas through thermonuclear fusion

• With enough mass and energy, the protostar collapses into its own gravitational force

• The first stars emitted ultraviolet radiation, ionizing surrounding neutral hydrogen gas in the universe

• First stars were massive and ended their lives in powerful supernova explosions

• Supernova explosions released heavy elements into the surrounding gas clouds, chemically enriching the interstellar medium

• This chemical enrichment allowed for the formation of later generations of stars, planets, and complex molecules necessary for life

• Metals made it possible for subsequent generations of stars to form planets and other structures more easily

• Stars are classified by surface temperature and luminosity

• Microphysics deals with how individual stars form

• Macrophysics deals with how systems of stars form, ranging from clusters to galaxies

• A star's lifespan depends on the amount of hydrogen present

• Less massive stars emit their stellar material into space, leaving behind a white dwarf surrounded by a planetary nebula

• Massive stars blast matter in the solar space in a bright supernova, leaving behind a highly dense body called a neutron star

• Most massive stars, three times the mass of the sun, collapse into themselves and create a black hole

Formation of Planets

• The solar system consists of a star, eight planets and countless smaller bodies, such as dwarf planets, asteroids and comets

• In order from the sun, the planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune

• The solar system began about 4.6 billion years ago in a wispy cloud of gas and dust

• Part of the cloud collapsed in on itself, possibly due to the shockwave of a nearby supernova explosion

• This collapse created a flat spinning disk of dust and gas

• When enough material collected at the disk's center, nuclear fusion began, creating the sun

• The material left behind by the sun clumped together into bigger and bigger pieces, becoming planets, dwarf planets, asteroids, comets, and moons

• Rocky things survive close to the sun, and gaseous and icy material accumulate further away, as happened in our solar system

• Planetary formation occurs through protoplanetary disk formation, dust grain growth, planetesimals formation, protoplanetary cores, and terrestrial planet formation

• The protoplanetary disk contains the rotating disk of gas and dust

• Dust grain growth collides and sticks together due to Van der Waals forces, forming larger particles

• Larger dust aggregates accumulate and form larger objects

• Massive planetesimals attract significant amounts of gas from the protoplanetary disk to become the building blocks of the gas giant planets

• Planetesimals collide and merge in the inner regions of the protoplanetary disk, closer to the sun, to form terrestrial planets

• Protoplanets interact with surrounding gas to accrete more materials or clear out their paths

• After the planets stabilize into their orbits, the protoplanetary disk gradually dissipates

• The protoplanetary disk is gone and planets are in stable orbits around the sun in a mature planetary system

• Small objects in space coalesce and form planet precursors called planetesimals

• Planetesimals gather together due to common gravity and form a planet

• Mercury is known as a shrinking planet because its iron core is slowly cooling, affecting overall size

• Mercury does not contain an atmosphere, just a thin layer of exosphere

• Venus' Maxwell Montes volcano is almost as high as Mount Everest

• Rain in Venus comprises sulfuric acid (H2SO4)

• Venus reflects 70% of all of sunlight. giving it a brighter appearance

• Venus, Mercury, Earth and Mars are terrestrial planets consisting of rocky material and a solid surface

• Terrestrial planets do not have ring systems, few moons and are relatively small

• Earth is the only planet known to sustain life

• Its distance from the sun allows it to contain water in all of its forms

• Life on Earth first began in the oceans in the form of microorganisms

• Mars is known as the Red Planet with atmosphere of carbon dioxide

• Seasons on Mars lasts longer than on Earth, and gravity is weaker

• Jupiter and Saturn are Jovian Planets, with multiple moons, have ring systems, no solid surface and large in size

• Jupiter is the solar system’s first planet, the largest in the solar system, and contains 79 moons

• The Great Red Spot is the most iconic feature of Jupiter, a crimson brown storm raging for 300 years as a giant collection of swirling clouds

• Saturn is the lightest planet and less dense than water

• Saturn’s largest storm is located on its north pole and has a hexagonal shape

• Saturn's ring system has 7 layers and comprises icy remnants of comets, asteroids and moons

• Saturn’s smallest moons orbit between the rings and use their gravity to keep the rings on track and intact.

• Uranus and Neptune are Jovian Planets, with multiple moons, has ring systems, no solid surface and large in size

• Uranus is the coldest planet, rotates vertically along its equator, and contains 13 rings and 27 moons, and its blue colour comes from its water, ammonia, and methane surface

• Neptune is cold, dark and icy due to its far distance from the sun and contains 6 rings and 14 moons

• Triton is Neptune's largest moon

• Pluto is a dwarf planet with a core, mantle and crust structure and contains 5 moons

• Pluto Inability to clear its orbit of debris caused it to lose its status as a planet

• In order to be categorized as a planet, an object must orbit the sun, not be a moon, have enough mass to be round, and be able to clear orbit of debris

Nucleosynthesis

• Nucleosynthesis is the process of forming a new atomic nuclei from existing smaller nuclei

• Atomic nuclei may be formed through the combination of light elements or from the breakdown of heavier elements

• Nuclear fusion is the combination of two or more atomic nuclei to form one or more new atomic nuclei

• Nuclear fission is the breakdown of a nuclei into two or more separate nuclei

• Big-bang nucleosynthesis formed lighter elements, such as hydrogen and helium, and traces of lithium, beryllium, and boron, in under 3 minutes to 300,000 years after the Bigbang

• Stellar nucleosynthesis occurs in young stars where extreme temperature is required at the core and form heavier elements

• Supernova nucleosynthesis form heavier elements during supernova explosions of stars

• Supernova nucleosynthesis happens under extremely high temperature (100 billions degree C) and abundant neutrons

• An atom is the basic unit of an element that can enter into chemical reaction

• The structure of an atom contains a nucleus that is composed of a proton and a neutron that is surrounded by electrons

• A proton is a positively charged particle, an electron is a negatively charged particle, and a neutron is a neutral (no charge) particle

• The atomic number indicates the number of protons in an atom and is noted with the letter Z

• The mass number indicates the number of protons plus the number of neutrons in an atom and is denoted with the letter A

• All atoms may be identified from the number of protons and neutrons they contain

• In a neutral atom, the number of protons is equal to the number of electrons

• The chemical identity of an atom may be determined from its atomic number alone

• Isotopes are atoms of the same element with the same atomic number but different mass numbers

• Radioactivity is a phenomenon when unstable nuclei emit particles and/or electromagnetic radiation spontaneously

• Any element that spontaneously emits radiation is said to be radioactive

• Elements with an atomic number greater than or equal to 83 are radioactive

• The three rays are emitted by radioactive elements

• The alpha (a) ray consists of positively charged particles called a particles

• The beta (β) ray or B particles are electrons

• Gamma (y) rays are high energy rays that has no charge

• In Nuclear Stability, a stable nuclei is found on the area of the graph known as the belt of stability (solid line)

• Radioactive isotopes are found outside this belt. In order to obtain stability, these isotopes must undergo radioactive decay

• Above the belt of stability is a higher neutron-to-proton ratio. In order to reach the belt of stability, isotopes with higher neutron-to-proton ratios, needs to lower by undergoing beta-decay

• Below the belt of stability is a lower neutron-to-proton ratio. To reach the belt of stability, these isotopes needs to move upward by increasing this ratio either through positron emission or electron capture

• Heavy nuclei with atomic numbers greater than 83) are naturally radioactive and are found above the belt of stability

• Heavy nuclei needs to undergo alpha decay in order to decrease both the number of protons and neutrons to reach belt of stability

• Types of Radioactive decay includes Alpha decay (or emission), Beta (β) decay, Positron (e) emission, Gamma (y) decay, Electron capture