Stars and their Physical Properties Background Information Name: Isabel Baransky School: Fu Foundation of Engineering and Applied Science Major: Applied Physics Minor: Music OVERVIEW OF FORCE THE BIG BANG Big Bang Occurred 13.7 billion years ago. All matter, energy, and light were all compacted into an infinitely dense point It spread out rapidly in an explosion, similar to a “big bang” Formation of Hydrogen/Helium Around 300,000 years after the Big Bang, the universe was abundant with floating subatomic particles (electrons, protons, etc) The universe had cooled enough for the particles to come together to make the simplest elements: hydrogen and helium WHAT IS A STAR? BIRTH OF STARS Gas clouds •Dense clouds of gas, called nebulae or nebula, are the birthplace of stars •Due to gravity, the mass in the clouds collapses in on itself, creating something called a protostar Achieving equillibrium 1. Gravity pulls gas and dust inward toward the core. 2. Inside the core, temperature increases as gas atom collisions increase. 3. Density of the core increases as more atoms try to share the same space. 4. Gas pressure increases as atomic collisions and density (atoms/space) increase. 5. When gas pressure = gravity, the protostar has reached equilibrium Two options for a protostar 2 OPTION 1 If the critical temperature to counteract gravity is to counteract gravity is not reached, then the protostar begins nuclear fusion in its becomes a brown dwarf core This is the moment it becomes a real star! Brown Dwarfs •Brown dwarfs are not large enough to cause fusion in their core •Most brown dwarfs are 15 to 75 times the mass of Jupiter! •Brown dwarfs are considered failed stars MAIN SEQUENCE STARS Stars in the Main Sequence L = 4πR2 σT4 L ∝ M3.5 (proportional) Hydrogen Fusion When a star is in the main sequence, it will carry out something called hydrogen fusion Convert hydrogen molecules in its core to helium molecules Four hydrogen are combined to produce a helium atom According to Einstein, because we start out with more mass then we end up with, the mass is converted to massive amounts of energy This helps prevent the gravitational force from making the star collapse in on itself Hydrostatic Equillibrium 1. Gravity = gas pressure (equilibrium) 2. Out of fuel 3. Fusion stops, temperature drops 4. Gravity reduces core 5. Increased temperature 6. Provides enough energy for nuclear, and the cycle begins again at step 1 A little more information Because interstellar medium is 97% hydrogen and 3% helium, a star primarily burns hydrogen during its lifetime. Our sun, a medium-size star, will live in the hydrogen phase, called the main sequence phase, for about 10 billion years Once hydrogen fuel is gone, the star has entered “old age.” WHICH STARS “LIVE” LONGER: LARGE STARS OR SMALL STARS? VEERING FROM THE MAIN SEQUENCE New fuel is used! •The star begins fusing other elements •Helium •Carbon •Iron •The larger the star, the more gravitational energy, the more thermal energy, the heavier the fusion element •Once iron is reached, fusion is halted WHERE DO ALL THE ELEMENTS HEAVIER THAN IRON COME FROM? Supernova! •The core and outer layers of the star start to collapse at up to the speed of light! •The imploding matter hits the rigid core and bounces back •The energy released during this explosion is so immense that the star will out shine an entire galaxy for a few days. •Supernova are responsible for all elements heavier than iron •These are called supernovas Stars smaller than 1.44 Solar Masses These stars become white dwarfs! Very dense A teaspoon of a white dwarf would weigh 5 tons Electron Degeneracy keeps equilibrium Degeneracy •Paulis’ Exclusion Principle: no two identical fermions may occupy the same quantum state simultaneously •The resistance from particles to be in the same orbitals creates a pressure that can outstand gravitational force under 1.44 solar masses •If over 1.44 solar masses, electron degeneracy is overwhelmed and we enter neutron degeneracy, which is overwhelmed after 3 solar masses Neutron stars Neutron stars are so §1 billion tons per teaspoon massive that they have §Create pulsars overwhelmed electron §A 0.033 sec pulsar was degeneracy discovered in the Crab Nebula LITTLE GREEN MEN •Summer of 1967, approximately a radio transmission was discovered that pulsated consistantly once ever second •Attributed to intelligent life and labeled “LGI1” •Soon it was discovered to just be the signal given off from neutron stars What are black holes? An object so dense that even light cannot escape from it (hence the term “black”) They are so massive that they overwhelm neutron degeneracy Since black holes by their very definition cannot be directly observed, proving their existence is difficult The Schwarzschild Radius Also called the “event Any mass can become horizon” a black hole if it collapses down to the Schwarzschild radius How can we prove their existence? •X-ray emissions •Binary systems with no evidence of a secondary star ANY QUESTIONS?
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