Astronomy 2022 October 24-26

giant molecular clouds collapse and form these, in hydrostatic equilibrium, heated through kelvin helmholtz mechanism, have not achieved thermal equilibrium. Hard to find

form as protostars, collapse and reach a temperature hot enough for core fusion, achieved hydrostatic equilibrium and thermal equilibrium. basic structure envelope, atmosphere, core

interstellar medium, giant molecular clouds, dense cores, protostar, pre main sequence star, zero age main sequence star

dust/ice/ gases found between stars, composed of molecules/ions/atoms. 70% hydrogen, 28% helium, 2% metals, some areas low density and hot, some high density and cool. Came from supernova remnants/planetary nebula

raw material, areas of star formation

cold, dense areas (10-20 K, density 10^5 atoms/cm^3), small portions of ISM are composed of this, 70% molecular hydrogen H2, 10-300 parsecs in length, composed of dust/ice grains. Ideal conditions for forming organic molecules

supernova shockwaves, radiation UV from newly formed stars, collisions of interstellar clouds

shockwaves from a supernova’s explosion, highly supersonic, henize 206

when galaxies collide, most stars miss each other, but clouds collide

UV, newly formed stars

gmc fragments are different sizes and masses, fragments/clumps have high density and low density areas, high density fragments with collapsing dense cores collapse and become protostars

they become open galactic clusters, clusters of newly formed hot, blue, and white stars. Found in spiral arms of galaxy

gas clouds collapse, gravity, pressure, and temperature increases. Resulting heat energy causes cloud to expand/emit light. Because of the expansion, interior pressure lowers/temperature drops. With lower pressure/temperature, gravity takes over and the cloud collapses. As the cycle continues the star gets smaller
As the transparent cores collapse, they heat up and most heat leaks out, as they continue to collapse, they become more dense and opaque. As a result they trap even more heat

gravity wants to collapse into a singularity, heat wants star to expand and blow apart, once there’s a balance the star achieves this and a protostar is born

around the equator of a protostar, materials in polar regions pulled in by gravity, and material along equator held up by equator effect

Continue to collapse, 50% of the heat created through Kelvin Helmholtz goes into heating core, remaining 50 released into space. Core gets hotter
Heat causes the star to expand, eventually surface area is large enough to let energy escape at the same rate its generated

achieved when the star’s surface area is large enough to let energy escape at the same rate it’s generated

the amount of time for protostars to collapse and become main sequence stars. The lower on the HR diagram, the longer it takes

a star that achieved hydrostatic equilibrium, thermal equilibrium, and hydrogen helium fusion to its core (minimum temperature 10 million k)

takes around 150M years to build a temperature of 10M K in their cores

takes 60k yeras to build a temperature of 10m K in their cores, eventually cores reach 18M K and the CNO fusion cycle begins (carbon, nitrogen, oxygen)

determines where a star lands on hr diagram and luminosity

Minimum for an object to become a star is mass of .08 mass. As the star collapses it heats with the kelvin helmholtz but never reaches a core temperature of 10 million kelvin. Achieves hydrostatic equilibrium but never thermal, becomes a brown dwarf

300 mass, any larger the pressure blows it apart, only 3 stars in LMC have masses greater than 200

a nuclear reaction: the nuclei of atoms are held together by the strong nuclear force

a nuclear reaction: the nuclei of atoms combine and some of their matter is converted into energy

hydrostatic eqilibrium (Balance between gravitational collapse and expansion from heat pressure ), thermal equilibrium (amount of energy generated in core is equal to amount radiated from surface), hydrogen-helium fusion in its core (creates energy)

in the early 1800s the known energy sources were chemical and gravitational energy, but it was found that the earth was millions of years old, which made it older than the sun (impossible)

Kelvin Helmholtz mechanism proposed as a solution, but geologists found the earth was more than 2 billion y/o. This could only account for 100 million. Age crisis continued

Wilhelm Rontgen and Henri Becquerel discovered radioactivity, and by 1927, using Radiometric dating, Arthur Holmes determined the solar system was about 3.2 billion years old. Age crisis continued

Albert Einstein discovered energy and mass are equivalent, E=mc^2, age crisis averted?

1930 Pauli proposed existence of neutrinos
1932 Chadwick discovered neutron
1932 Anderson discovered Positron

hydrogen fusion in a core extending to .25 solar radius, core surrounded by radiative zone extending to .71 SR, energy transfer through radiative diffusion. Radiative zone surrounded by convective zone of gas at low temperature/pressure, energy through convection

source of a main sequence stars energy, hydrogen-helium fusion. Temperature 12M k, density 150 g/cm^3, pressure 250 billion atms

energy is created out of matter. 4 hydrogen -> helium+gamma radiation+neutrino. E=(.007)(3 x 10^8 m/sec)^2. fuse 4 hydrogen nuclei into one helium nucleus. Produces 6 protons gamma radiation, 2 positrons, 2 neutrinos

fuse 4 hydrogens into helium using C N and O as catalysts

4 million tons a second converted into energy
Sun has been fusing hydrogen for 5 billion years and had enough to last another 5 billion years

in all fusion reactions the mass of the products is less than the mass of the reactants, lost mass converted into energy

evidence fusion happens in star interiors, very low mass and near massless particles. No electrical charge. Stream out of star near speed of light. Hard to detect…70% pass through wall of lead 3 light years thick. Different types electron, muon, and tau

1/M^3, dependent on stars mass (bigger mass has shorter life expectancy)