‘The life-cycle of stars’ Stellar Evolution ‘The life-cycle of stars’

What is a star? LARGE GLOWING BALL OF GAS Composed of H and He Fixed points of light in space Undergo fusion in their cores Generate heat and light Give off tremendous radiation

Star Energy Nuclear Fusion – a nuclear reaction in which to atoms are fused together… New elements are created and energy is released. This process is responsible for creating ALL elements found in the universe… in other words, we are all made from star dust.

Star Energy (con’t) Hydrogen fusion Helium fusion H + H  He + He + He  Be + As the mass of elements increases, energy production increases Energy More Energy

Properties of Stars Color & Temperature Brightness Size & Mass Apparent vs. Absolute Size & Mass Composition

Hertzsprung-Russel Diagram A graph showing the surface temperature and absolute brightness of a group of stars Used to compare several properties of stars and estimate their sizes and distances Shows star color, size, temperature and brightness

H-R Diagram

Low mass Protostar High mass

Nebula A cloud of gas and dust Gravity causes the cloud to collapse and condense Temperatures begin to increase = Glows Fusion begins at VERY high temps. (Some of the extra gas and dust may form planets)

Protostar Gravity pulls a nebula’s dust and gas into a denser cloud As a nebula heats up, it contracts A contracting cloud of dust with enough mass to form a star

Main Sequence Stars Core reaches a temp of ~15 million K. Hydrogen begins to fuse into Helium in the core. ~90% of stars lifetime is spent in the main sequence stage. Classified based on temperature and luminosity

Giant Stars Core decreases in size as all (or most) H is consumed He fusion is occurring – producing more energy Diameter increases x10 Surface temp decreases as star expands

Super Giants Form from massive stars A chain of reactions take place in the core producing He, C, O, Ne, Mg, Si, S, Ar, Ca, Ti, Cr, Fe Highest temperature = Blue Super Giants Usually explode in a tremendous event called a supernova

Planetary Nebula Energy from star becomes to decrease; no more elements to fuse Star begins to collapse Dying star surrounded by gases

Nova/Super Nova The core of a giant star produces too much energy in it’s core and causes the outside of the star to expand. The outer layer of gasses are blown out to space (nova, or supernova), leaving behind a small, hot core…

White Dwarf Stars decrease in size ~ same diameter as earth, mass stays the same Mass of sun, size of Earth DENSITY INCREASES TREMENDOUSLY Solid, but still hot, so it is glowing Luminosity decreases

Neutron stars Form from the remains of extremely massive stars after a supernova. Very small ~ 30 km across Density of 2 x 1014 Would be comparative to 1 sugar cube = mass of humanity

Black hole If the core’s mass is even greater/denser than a neutron star, it collapses. Surface gravity is so great that no matter can escape it…not even electromagnetic waves!

The fate of our Sun