Star and Planet Formation; Nucleosynthesis

• The module discusses the formation of stars and planets and nucleosynthesis

Formation of Stars

• Covers topics about the first stars, formation of protogalaxies, and star formation today

First Stars in the Universe

• Early stars were massive and luminous
• The formation led to the production and dispersion of heavier elements; leading to forming the solar system today
• Density fluctuation left over from the Big Bang could have evolved into the first stars
• Distant quasars have allowed scientists to glimpse the final days of the cosmic dark ages

Quasars (Quasi-stellar radio sources)

• These are luminous and far celestial objects detected because of the large electromagnetic radiation emitted
• It is thought they are powered by supermassive black holes at the centers of galaxies

Protogalaxies

• The star-forming system is much smaller and less organized than modern galaxies
• They do not contain significant amounts of elements besides hydrogen and helium
• Protogalaxies merge to form galaxies and gather into galaxy clusters

Formation of Protogalaxies

• Clouds of gas and dust slowly aggregate to form more matter
• As they evolve, they will merge with each other and form larger structures like modern galaxies

Star Formation

• Stars are formed from a cloud of dust and hydrogen gas called nebuli
• The life of a star begins as a protostar: a hot core formed from a collection of dust and gas
• Accretion is the growing of a protostar by adsorbing more material from its surroundings; results in an increase of temperature and density
• Hydrogen molecules in these clouds begin to react with each other to form Helium gas through thermonuclear fusion
• The protostar eventually collapses into its own gravitational force and forms a hot ball of gas with enough mass and energy

Role of First Stars in Formation of Later Stars and Planets

• Re-ionization: Emission of ultraviolet radiation, ionizing surrounding neutral hydrogen gas in the universe
• Chemical Enrichment: First stars ended their lives after supernova explosions, releasing heavy elements into the surrounding gas clouds, chemically enriching the interstellar medium
• This lead to forming later generations of stars that could form smaller stars, planets and complex molecules needed for life
• Galactic Evolution: The presence of metals made it possible for subsequent generations of stars to form planets and other structures more easily

Classification of Stars

• Surface temperature
• Luminosity

Categories for Stars Formation

• Microphysics: Deals with how individual stars form
• Macrophysics: Deals with how systems of stars form, ranging from clusters to galaxies

Lifespan of Stars

• Lifespan depends on the amount of hydrogen present, and ends when the hydrogen is consumed
• Less Massive Stars: Emit their stellar material into space and leaves behind a white dwarf surrounded by a planetary nebula
• Massive Stars: Blast matter in the solar space in a bright supernova and leaves behind a highly dense body called a neutron star
• Most Massive Stars: Collapse into themselves and creates a black hole; minimum 3x the mass of the sun

Formation of Planets

• The Solar System consists of a star, eight planets, countless smaller bodies, dwarf planets, asteroids and comets
• The order of the planets in the Solar System includes: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
• 4.6 billion years ago, part of a wilsy cloud of gas and dust collapsed
• Result: A flat, spinning disk of dust and gas
• When enough material collected at this disk's center, nuclear fusion begins; the Sun was born
• The material left behind by the sun clumped together into bigger and bigger pieces
• Rocky things survived close to the sun, so gaseous and icy material collected further away

Planetary Formation stages

• Protoplanetary disk formation: Includes rotating disk of gas and dust
• Dust grain growth: Dust grains collide and stick together due to Van der Waals forces forming larger particles
• Planetesimals formation: Larger dust aggregates accumulate and form larger objects. Continues to grow through collisions and gravitational interaction
• Protoplanetary cores: Massive planetesimals attract significant amounts of gas from the protoplanetary disk, building blocks of gas giants planets
• Terrestrial planet formation: Planetesimals collide and merge in the inner regions of protoplanetary disk; closer to the sun
• Clearing the disk: Protoplanets interact with surrounding gas which either accretions more materials or clear out their paths
• Stabilization and Evolution: Planets stabilize in their orbits, and the protoplanetary disk gradually dissipates
• Mature Planetary System: Protoplanetary disk is gone and planets are in stable orbits around the sun

How planets form

• Small objects in space coalesce and form planet precursors called planetesimals
• Planetesimals gather together from common gravity and form a planet

Terrestrial Planets

• Made of rocky material
• Solid surface
• No ring systems
• Few moons
• Relatively small

Mercury

• Revolution: 88 days/year
• Known as a shrinking planet since the iron core is slowly cooling, affecting its size decrease
• Does not contain an atmosphere, but a thin layer of exosphere

Venus

• Maxwell Montes is a volcano; almost as tall as Mount Everest
• Rain is made up of Sulfuric Acid (H2SO4)
• Reflects 70% of all sunlight that reaches the planet, making its brightness

Earth

• It contains water in all of its forms
• Only planet known to sustain life
• Life first began in the oceans in the form of microorganisms

Mars

• Also known as the red planet
• Seasons are the same as on Earth, but they last longer
• The gravity is weaker
• Atmosphere is mostly composed of carbon dioxide

Jovian Planets

• Multiple moons
• No solid surface
• Has ring systems
• Large in size

Jupiter

• Largest planet in the solar system
• Contains 79 moons
• Features the Great Red Spot; the most iconic storm raging for 300 years, known as a giant collection of swirling clouds

Saturn

• Lightest Planet; less dense than water
• Its largest storm is located on its north pole and has a hexagonal shape
• Has a ring system: 7 layers & composed of icy remnants, stays on track from its smallest moons, which orbits between the rings and uses gravity to shape it

Uranus

• Coldest planet
• Rotates vertically along its equator
• Contains 13 rings and 27 moons
• The cause of the planet's blue color: its surface is made up of water, ammonia, methane

Neptune

• Cold, dark and icy due to its far distance from the sun
• Contains 6 rings and 14 moons
• Triton is Neptune's largest moon

Pluto

• Pluto is a dwarf planet with: core, mantle, and crust
• Contains 5 moons
• Lost its status as a planet for failing to clear its orbit of debris

Characteristics of a Planet

• Orbits the Sun
• Not a moon
• Enough mass to be round
• Able to clear orbit of debris

Nucleosynthesis

• It is the forming process of a new atomic nuclei from existing smaller nuclei
• Atomic nuclei are formed through combining light elements or breaking down heavier elements
• Nuclear Fusion: Combination of two or more atomic nuclei to form one or more new atomic nuclei
• Nuclear Fission: Breakdown of nuclei into two or more separate nuclei

Types of Nucleosynthesis

• Big-Bang: Lighter elements such as Hydrogen and Helium were formed, along with traces of Lithium, Beryllium, and Boron (3 minutes - 300,000 years after the Big Bang)
• Stellar: Elements are synthesize in young stars thru fusion. The extreme temperature is needed at the core
• Supernova: Heavier elements are formed during supernova explosions of stars; Extremely high temperatures (100 billions degree C) and abundant neutrons

Atom structure

• Atoms are is the basic unit of an element that can enter into chemical reaction
• Contains a nucleus (protons and neutrons), surrounded by electrons
• Protons have a positive charge
• Electrons are negatively charged particles
• Neutrons are neutral (no charge) particles

Atomic Number and Mass Number

• Atomic number (Z) is the number of protons
• Mass number (A) = The number of protons + the number of neutrons, or the Atomic number + number of neutrons
• In a neutral atom, the number of protons is equal to the number of electrons
• All atoms may be identified from the number of protons and neutrons they contain
• The chemical identity of an atom may be determined from its atomic number alone

Isotopes

• Atoms of the same number atomic number (Z) but different mass numbers (A)

Radioactivity

• The 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
• Three rays are emitted by radioactive elements:
  • Alpha (α) is positively charged particles
  • Beta (β) is an electron
  • Gamma (γ) is high energy and does not have a charge

Nuclear Stability

• An isotopes need to have a stable nuceli to stay in area of the the belt of stability
• Radioactive isotopes are found outside the belt, indicating the need for undergoes radioactive decay
• Above the belt: The isotopes need to lower its ratio by undergoing beta-decay
• Below the belt: The isotopes need to increase in either positron emission or electron capture
• Heavy nuclei w atomic numbers over 83 are naturally radioactive; they would need to undergo alpha decay to decrease both the number of protons and neutrons

Types of Radioactive decay

• Alpha decay (or emission): A Helium is emitted
• Beta (β) decay: An electron is emitted number
• Positron (e) emission: A positron is emitted when an atom decays to produce a neutron and a positron
• Gamma (y) decay: High-energy photons or gamma rays are emitted
• Electron capture: An electron falls into the nucleus and fuses with a proton to form a neutron