Presentation on theme: "The Lives of the Stars. 1.Space itself 2.Gases a.Hydrogen (~73%) b.Helium (~25%) c.All other elements (<~2%) 3.Solids – ‘spacedust’ or ‘stardust’ – grains."— Presentation transcript:
Disturb the Nebula Somehow Areas in the nebula collapse due to: Cloud to Cloud Collisions: Two clouds collide and interfere with each other Supernova Shock Waves: The violent death of a nearby star blasts the cloud and sends it swirling Density Wave: dense areas in the galaxy interact with the cloud No good reason at all: The cloud just finds the conditions right for collapse
A Star is Born 1.Cloud begins to collapse. The density and temp begin to rise! 2.Core of the cloud heats up to about 1000K (1340 F) 2000K (3140 F). Density rises further. 3.The cloud begins to glow as it gets hot. The protostar now has a luminosity. 4.Core collapses until Temp = 10-15 million K FUSION begins and the star Ignites. 5.A star is born!!
Stars live on average from a few million years to 10 or more billion years. Stars live on average from a few million years to 10 or more billion years. How a star lives and dies depends on how much mass it has.
Stars fuse Hydrogen into Helium during their Main Sequence life…. H He Initial Composition 70% H 27% He After 5 Billion years of fusion Core Composition 65% H 35% He He What happens when Hydrogen runs out?
Main Sequence Phase Ends Core is hot & helium rich. Energy output down – no fusion in the core Core begins to collapse under gravity – this makes the core hotter and denser Hotter core causes star to expand up to 100x original size due to ‘radiative pressure’ Surface temp gets cooler – star becomes red Core becomes “degenerate” - can’t be crushed any more. the star becomes a RED GIANT
He C, O C, O H He Red Giant Core temp = 100 Million K then Helium Flash!!! Helium Fusion Starts and the star has a ‘second life’! Star fuses Helium into C & O
Core collapses again – becomes hotter & denser then Then the HELIUM RUNS OUT For a Sun-Sized Star: 1.Fusion Ends 2.Core gets degenerate 3.Outer layers of star are blown off, forming a planetary nebula 4.Star becomes white dwarf 5.Cools to a black dwarf
Then the HELIUM RUNS OUT – Take 2 For a Massive/SuperMassive Stars (starting at 100x more mass than Sun): 1.Fusion begins again 1.C fuses to O 2.O fuses to S, Si, and Ar 3.Si fuses to Fe, Cr 2.Heat from new fusion causes 2 nd red giant phase – Red Supergiant. 3.After Fe, fusion must stop. Core collapses and gets degenerate Core collapses again – becomes hotter & denser then
4.Outer layers of star are blown off spectacularly in a supernova. 5.Massive star becomes neutron star 6.Supermassiv e star becomes a black hole
SUPERNOVA Brightest objects in the universe Can outshine an entire galaxy for a few weeks Fairly rare – 1-10 per century per galaxy.
Supernova’s are important! They: Are very bright - visible over a great distance, for a long time spread new material out – “stardust” that goes into making new stars can trigger new star formation Produce the heavy elements – all the elements from Iron (Fe) up to Uranium (U).