The Sun, Formation of Elements, the Big Bang, and Black Holes Stars The Sun, Formation of Elements, the Big Bang, and Black Holes

Stars Mass of plasma held together by its own gravity and creating light and heat using nuclear fusion Make up galaxies Always there – don’t see them in daytime b/c sun is so bright, atmospheric skylight overwhelms star light.

Formation Most of Space = really empty 1 million times more empty than we can make on Earth Gas and Dust attract other gas and dust using gravity Nebula – Cloud of dust and gas More gas = more mass, more gravity, attracts more gas Makes a Protostar – forming star, huge cloud of gas and dust Cloud pulls together due to gravity, nuclear fusion occurs and makes a star

Lifetime Large stars = lots of gravity -> lots of nuclear reactions -> very bright -> burn out quickly Smaller stars = less bright, last longer Sun = avg. star, lasts around 10 billion years Has been around 5 billion years so halfway through its life.

Lifecycle of a star

Classification Determine what stars are made of by energy they emit. X-rays, light waves, radio waves Type of waves indicate what atoms are in star.

Classification: H-R Diagram Also classified by surface temp and brightness using the H-R Diagram

Our Sun Typical star – medium size, low mass Yellow star half way through main sequence stage 75% Hydrogen (H), 25% Helium (He) Similar to billions of other stars

Nuclear Fusion Nuclear fusion – small atoms combine into larger atoms, releasing huge amts. of energy Requires enormous heat and pressure – found in core of stars due to mass and gravity In sun, H fuses to form He, releasing energy as heat and light Changes more than 600 million tons of H into He each sec. When sun runs out of H in 5 billion years, it will start fusing He turning it into a red giant Nuclear fusion = start of star, how star makes energy

Nuclear Fusion H -> He

Formation of Elements All elements larger than H and He were formed by nuclear fusion in the core of stars At the end of the star life cycle, the star explodes in a Nova – star explosion Large elements are then released as star dust. Star dust comes together to form planets, rocks, etc. All oxygen, gold, iron, carbon, etc. formed in the core of stars by nuclear fusion So we’re all made of star dust!!! You’re a star, you’re a big, bright, shiny star!!!

Periodic Table of Elements

Big Bang - Evidence Red shift of distant galaxies indicates they’re all moving away from us So if we move them in “rewind” they get all get closer together Eventually, all converge at single point around 14.6 billion years ago – universe is 14.6 b.y. old Cosmic Background Radiation – very slight amt. of heat in deep space (3 K) Heat likely came from big bang and is slowly cooling

Big Bang 14.6 billion years ago, everything was in a single point No matter, just pure energy Point expanded, energy cooled, and matter was formed as Hydrogen and Helium H and He pulled together by gravity formed first generation of stars.

Black Holes Black hole – remains of giant star that has collapsed on itself So dense, such great gravity that nothing can escape, not even light Only form at end of stars life for REALLY big stars Once fusion is done, gravity is too great, has nothing left to fuse/burn so collapses on itself

Sun as Black hole Our sun cannot be a black hole – too small But if it could, it would shrink from 1,400,000 km across to infinitely small while keeping same mass Light within 3 km of center would be trapped Would Earth be sucked in?

Sun as Black Hole No. Mass of the sun (and gravity) would be the same, so our orbit would be unchanged. Would only affect things that got to where the center of the sun is now And it’d be really dark/cold We know they exist b/c we can see things react to their gravity, but can’t see them. NOT the same as a wormhole - won’t take you to another dimension/place. Will just crush you into a single point.