The Life Cycles of Stars RVCC Planetarium - Last updated 7/23/03

Twinkle, Twinkle, Little Star...

How I Wonder What You Are... Stars have Different colors  Which indicate different temperatures Different sizes Different masses The bigger it is, the hotter and the faster a star burns its life away.

Stellar Evolution Stars begin their lives as clouds of gas and dust called Nebulas Clouds Contain: 70% H 28% He 2% Heavier Elements

Stars start from Nebula Clouds

Collapse to Protostar Nebula compresses Gravitational pull attracts more material. Temperature and pressure increases Nebula shrinks and begins to spin Spinning nebula begins to flatten into a disk ….A protostar is formed

Protostars are forming in Orion Protostars are forming in the Orion Nebula

Pressure builds inside the protostar over millions of years creating heat Temp increases to 10 million°C Nuclear fusion begins….A star is born!! Main Sequence stage of a star begins It is the longest stage in life of a star

Nuclear Fusion ! At 15 million degrees Celsius in the center of the star, Hydrogen Atoms fuses into Helium. It takes 4 Hydrogen atoms to make one Helium atom Sun has H atoms to burn which would last 8 billions year!

The Beginning of the End: Red Giants After Hydrogen is exhausted in core: Core collapses, releasing energy to the outer layers Outer layers expand

The Core of a Red Giant Giants are 10 times bigger than the sun Supergiants are 100 times bigger than the sun

Expansion of the outer Layers

Betelgeuse – A Red Giant Star

Outer Layers are Expelled …

… And a Planetary Nebula forms Planetary Nebulae After Helium exhausted, outer layers of star expelled

Some Planetary Nebulae are Round As the dead core of the star cools, the nebula continues to expand, and dissipates into the surroundings.

… and Bipolar

Some look like an Hourglass …

.. or a Cat’s Eye …

… or even look like an Eskimo!

White Dwarfs At Center of a Planetary Nebula … … sits a White Dwarfs White dwarfs shine for billions of years before they cool completely.

The Hubble Space Telescope has detected white dwarf stars (circled) in globular clusters:

White Dwarfs are Small and Heavy Size of the Earth with the Mass of the Sun “A ton per teaspoon”

Nova is a white dwarf star that suddenly increases in brightness by several magnitudes. It fades very slowly. white dwarf star

Fate of High Mass Stars After Helium is exhausted, core collapses again until it becomes hot enough to fuse Carbon into Magnesium or Oxygen. Through a combination of processes, successively heavier elements are formed and burned.

The End of the Line for Massive Stars Massive stars burn a succession of elements. Iron is the most stable element and cannot be fused further.

A Massive Star Explodes A Supernova is an exploding massive star

Supernova 1987a

What’s Left After the Supernova Neutron Star (If mass of core < 5) Under collapse, protons and electrons combine to form neutrons. Black Hole (If mass of core > 5) The force of contraction crushes the dense core of the star The gravity of a black hole is so great that not even light can escape from it.

Supernova interaction This compression starts the collapse of gas and dust to form new stars. Supernovae compress gas and dust which lie between the stars.

Which brings us back to … Sun-like StarsMassive Stars Stellar Recycling Nebula Protostar Low mass main sequence star Red Giant Planetary Nebula White Dwarf Nova High mass main sequence star Supergiant Supernova Neutron Star Black Hole