Dirt and Stars The Life of a Star Dirt, Nebulae Collapse proto-stars and stars

Caterpillars, dirt and butterflies The interstellar medium - a dirty place! Consists of gas and dust (dirt type stuff) What is there to do in space for dirty things? 1. Sit around ( redden incoming radiation & hide things) 2. Perform photon screenings (in some cases only certain polarized types of photons get to move on thru). 3. Suck up a bit and start doing some emitting, maybe a little absorbing. 4. Some gas clouds will actually get on with their lives; collapse, swirl around some, get lumpy and eventually form Stars (butterflies) with little planets swinging around them. Stage 1

Speaking of Star Formation The molecular cloud collapses into many stars. It fragments into many clumps. These clumps can further collapse to form stars stars can be formed from the cloud.

More Star formation When a fragment of a molecular cloud reaches a critical mass, it collapses to form a star. Stage 2 Gas and dust are pulled together by gravity until a star is formed. Gravity makes the cloud collapse. Two hindrances to collapse, both which favor expansion of the cloud: 1.Internal heating which causes pressure to build- up. 2. Angular momentum (rotation at high speeds) (ex: figure skater)

Are we there yet? Not yet, Joey Cloud fragments continuing to collapse Potential energy => Kinetic Energy Gas particles speed up and collide. The temperature increases. This causes a pressure build-up which slows (or stops) the collapse. Stage 3 Energy is radiated away.

We’re getting closer.. Joey More on Stage 3: The cloud fragment has collapsed into a central core surrounded by a disk of lumpy like material. Our fragment somewhat resembles a star.

And closer … Due to proto-stellar wind and strong heating Orion Nebula proto-stellar disk

And we’re here, we are a Star ! The proto-star (which now has a surface – photosphere) continues to shrink. The central core heats up to millions of degrees. Collapse is halted by the pressure of the heated gas and radiation which counteracts gravity. Pressure is force in outward direction, gravity is force pulling star in. An equilibrium is reached between opposing forces. Fusion reactions start => A star is born ! Stage 5/6 Commence fusion! Forces in balance => no collapse or expansion Stage 4

Evolution of 1 Star : ( better yet, lets see if this link works.) file:///E:/Chaisson/AT419/HTML/AT41902.HTM#Anchor-23240

Pretty picture The Pleiades star cluster. ~ 120 pc away, It is an Open Cluster { a cluster lying in the plane of the Milky Way, may have a 100 to ~10,000 stars} these 6 to 7 stars have just been booted out of The Main Sequence neighborhood! Everyone in this cluster is about the same age. Young bunch ~ 100 million years old.