IPS

Astronomy: Birth and Life of a Star

I. Nebulas

    All stars start out as a nebula A nebula is a stellar nursery A nebula is a large amount of gas

and dust spread out in an immense (or big) volume

Don’t get a star and a nebula confused.

Nebula vs. Star

   Nebula –

Large

amount of gas in a

large

Star –

Large

Links: – – – amount of gas in a

small

Jellyfish nebula Eskimo nebula Horse head nebula volume volume

II. Protostar:

earliest star in Greek, “proto” means earliest. Protostar =

   

Gravity pulls gas and dust in (contracts)

A contracting cloud is called a protostar.

Pressure and temperature increase.

When the contracting gas and dust becomes so hot that nuclear fusion begins, a star is born!!

– Remember: nuclear fusion starts when hydrogen combines to form helium. During fusion, enormous amounts of energy are released.

– Link: Pillars of Creation nebula

III. Main Sequence

      The star is fusing (burning) H into He (produces

a lot of energy)

The star is now in the “prime of its life”; it is in

equilibrium.

Over time; temp, luminosity, color change.

Our sun is in the main sequence phase It will live for about 10 billion years Our sun is now about 4.6 billion years old – Links:    Planet swallower (artist) Sun Solar prominence

IV. Red Giant

(or supergiant)

     Stars begin to die when they run out of fuel

(hydrogen)

The center of the star shrinks and the outer

part expands

The star may fuse all the elements through

Fe Big, and bright, but low surface temp

All stars become a red giant or a supergiant – Camera Orion – Betelgeuse and Rigel

V. Death Phases of a Star

   A dying star will take one of three paths extinction

The mass of the star dictates which path it will take

After the fuel is used up, a star will become a… – White Dwarf, or – Neutron Star, or – Black Hole

Path #1: White Dwarfs

     White Dwarfs, small stars (1 X our Sun) The outer layers of the star grow bigger and slowly drift out into space. This material rejoins a

nebula to be recycled into a new star

The blue-white hot core is left and the “dead” star that is left behind is a white dwarf The glow coming from the core is left-over energy from the old star. The core is NOT making any more energy. (Like turning off a light bulb) Eventually, the energy glow is gone and the core is dark. It becomes a black dwarf.

– Links: Little Ghost Nebula , Helix Nebula , Eight-burst Nebula

Path #2: Neutron Stars

      Neutron stars, medium stars (5 X our sun) A supernova occurs when a supergiant star (5 X or more our sun) suddenly explodes

Some material rejoins a nebula

The remaining material from the star (or core) is a

neutron star

Neutron stars are even smaller and more dense

than white dwarfs

Some neutron stars spin, these are pulsars – Links: Cosmic Pearls supernova , Elusive Jellyfish nebula (neutron star), Tycho’s Supernova Remnant , A Dark Pulsar in CTA 1 , Crab Pulsar Wind Nebula

Path #3: Black Holes

     Black holes are the most massive stars (10-40 X

our sun)

The (red) supergiant goes supernova, throwing the outer layers into space to rejoin a nebula

The gravity of the remaining core is so

strong that the core collapses in on itself, creating an even stronger gravitational pull This gravity pulls everything to it – Nothing can escape its gravitational pull, not even light waves!!

Links: A view near a black hole , star ripped apart by BH , x-ray jet black hole , BH candidate Cygnus

VI. Lifetimes of Stars

  How long a star lives depends on how much mass it has

Small mass stars live longer than large mass stars

– Stars that have more mass than the sun live a shorter lifetime. Approx. 10 million years – Stars that have less mass than the sun live longer. Approx. 200 billion years  Example: A small car burns a gallon of gas more efficiently than a big SUV (exp 25/mpg vs 8/mpg) http://www.classzone.com/books/earth_science/terc/content/visualizations/es28 07/es2807page01.cfm?chapter_no=visualization