http://www.youtube.com/watch?v=a19fhhJcs1E (life cycle of a star – 44 minutes)
07 stars, constellations, and asterisms
Stars, Asterisms, and Constellations
StarsA star is a massive, luminous sphere of plasma heldtogether by gravity. Ex: the sun is a star
Life Cycles of StarsEvery star has a life cycle: a beginning, a middleand an end. At the beginning, a star forms froma massive cloud of gases and dust called anebula (gases include hydrogen and helium).
Life Cycles of StarsThe gravitational forces begin to pull the gas anddust particles close together, creating clumps. Theclumps become more massive and gravity becomeseven stronger. Over time, a dense region forms,called the protostar.
Life Cycles of StarsGravity causes the core of the protostar tobecome very tightly packed and the pressurecauses nuclear fusion to begin. Hydrogen atomsin the core fuse to make helium atoms and as aconsequence, produce tremendous amounts ofenergy.
Life Cycles of StarsBillions of years after forming, the star beginsto burn out.
Life Cycles of Stars: Stars like the SunFor about 10 billion years, a star’s available hydrogenwill have been converted to helium. With lesshydrogen to burn, the core begins to contract andgets hotter, while the outer layers of the star expandand then cool. The star evolves into a red giant.
Life Cycles of Stars: Stars like the SunOur sun will become a red giant in 5 billion years.The outer layers of the star expand sharply, pouringsolar matter into space. This leaves a small, dim hotcore behind – a white dwarf.
Life Cycles of Stars: Stars like the SunAs the sun’s massreduces, the planetswill not be attracted tothe Sun as strongly asat present and theirorbits around the Sunwill shift furtheroutwards. The Earthwill gradually move towhere the planet Marsorbits today.
More massive starsStars that are moremassive than our Sun (i.e.10 times more larger) willbecome a red supergiant.Once fusion stops, thesupergiant will have itscontents collapse on itsself under its own gravity.The outer layers of thestar explode outwards –known as a supernova.
Supernova All the atoms we are made from came originally from these giant supernova explosions.
If a star’s initial mass was:• between 10 and 30 solar masses a neutron star is formed – an extremely dense star composed of tightly packed neutrons.• greater than 30 solar masses black hole is formed – a quantity of matter so dense and gravity so strong that not even light can escape.