The Life History of Stars How stars form and die

Origin of Stars; Nebulas Been studied as separate from individual stars for almost 2000 years Comes from Latin for a cloud, or mist It is from these clouds that stars get their materials to start

Nebula Stars begin their lives as clouds of gases and dust Areas of locally dense gases begin to accumulate due to gravity An area like this is known as a Nebula A Nebula can result in one or many stars

Stellar Disk and Protostar Forms Gravity draws gases and dust into center The material is drawn in tighter and tighter by the increasing gravity Protostar forms as increasing heat results in the emission of light

Star Ignites Temperature and pressure continue to increase Eventually Hydrogen is forced together and begins fusing into Helium These thermonuclear fusion reacts generate huge quantities of heat and light

Star continues to grow Gravity continues to pull material into the star faster than the pressure of the nuclear reactions can eject it The more that comes in the larger the star Eventually the amount being ejected is equal to the amount being pulled inward

Stable Star Forms Also known as Main Sequence This is when the gravity of the star is equal to the ejection rate of the nuclear reactions A stable star can last for billions of years while fusing Hydrogen

Solar System Forms Left over material in orbiting the new star will begin to accumulate due to local gravity into protoplanets Some will form large planets Others will become moons, asteroids, and comets

Inside a Stable Star The Core The Radiative Zone The Convective Zone The Photosphere The Chromosphere The Corona Solar Wind The Heliosphere

Star begins decline As the star begins to run out of Hydrogen, it begins to decline The star then starts fusing Helium instead Fusing Helium generates more energy, but there is less of it

Red Giant Forms The outer most layer spreads way out into space because of Helium fusion The sun will grow so large it will envelop Mercury and Venus The Earth will be fried to a crisp

Eventually the Helium will run out The Helium is fused into Carbon Carbon does not fuse well, so eventually the star starts to run out of fuel The star will cool and dim It also condenses due to gravity into a dwarf star These stars are about the size of the Earth

Black Dwarf, the end… When the star runs out of juice, it will cool to temperatures lower than that need to emit light As they go dark, they can no longer be seen These are known as Black dwarfs and this ball of Carbon is done

Super Red Giant Big stars die differently than medium or little ones do If the mass is large enough and the gravity is strong enough, Carbon can be fused into Si, Ne, S, or Fe This provides extra energy and the star grows enormously large

Death of a Super Red Giant All good things must come to an end. Iron can not be fused any further. Thus, when all of the Carbon is used up, the Super Red Giant condenses into an Iron ball due to gravity. But, the force of gravity of this star is so great that Protons and Electrons fuse to become Neutrons.

Supernova Eventually the crushing force of all of this iron and neutrons causes a giant explosion. This is a Supernova. It is one of the most powerful explosions in the universe. The light is very bright and can last for months. A major supernova exploded in 1054 AD that lit the sky as bright as a full moon for months.

Neutron Star After the supernova, whatever is left over condenses back into a very small dense sphere. This massive ball of neutrons is a neutron star. It is very small, only about 6 miles across. One teaspoon of a Neutron star would weigh 1 billion tons!

Blue Giants Largest and hottest burning stars These are often so massive that they no longer use hydrogen as fuel These stars will always supernova at the end of their life cycle and become neutron stars

The Largest Stars Only a few stars can be called ‘hyper giants’ Several orders of magnitude larger, brighter, and hotter than our sun

Pulsars If a Neutron star is spinning, it will release radiation (radiowaves) in pulses, almost like a lighthouse. These pulsars have regular patterns of a few seconds. The crab nebula pulsar is the neutron star remnant of a massive supernova in 1054 AD, that many people saw and wrote about. Crab nebula Pulsar “on” and “off”

Black Holes When a Neutron star is massive enough, it can actually have enough gravitational pull to suck everything in around it Even light can not escape The Event Horizon is the area at which once something enters, it can not ever escape The black ball in the center is the Event Horizon, as matter and energy enter it, they disappear

Quasars A Quasar is associated with a supermassive black hole that actually devours stars. They are almost always located at the center of a galaxy As the stars are ripped apart by the black hole, they heat up and emit enormous quantities of energy Quasars are the brightest, hottest things in the universe

The End