The Lives of the Stars

1. The Lives of the Stars

2. What’s Out there in Space? • Space itself • Gases • Hydrogen (~73%) • Helium (~25%) • All other elements (<~2%) • Solids – ‘spacedust’ or ‘stardust’ – grains of heavier elements, like sand

3. Start with a Nebula A Large Cloud! • Mass  100-1000 M¤ (solar masses) (BIG) • A temperatureof  20K to 100K (-279 F) (pretty cool) • A density of about 10 atoms/cm3(that’s not many!)

11. 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

12. A Star is Born • Cloud begins to collapse. The density and temp begin to rise! • Core of the cloud heats up to about 1000K (1340 F)  2000K (3140 F). Density rises further. • The cloud begins to glow as it gets hot. The protostar now has a luminosity. • Core collapses until Temp = 10-15 million K FUSION begins and the star Ignites. • A star is born!!

15. 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.

16. Stars fuse Hydrogen into Helium during their Main Sequence life…. Initial Composition 70% H 27% He H He He After 5 Billion years of fusion Core Composition 65% H 35% He What happens when Hydrogen runs out?

17. 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

20. He C, O HHe C, O 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

21. Then the HELIUM RUNS OUT Core collapses again – becomes hotter & denser then For a Sun-Sized Star: • Fusion Ends • Core gets degenerate • Outer layers of star are blown off, forming a planetary nebula • Star becomes white dwarf • Cools to a black dwarf

22. Planetary Nebulas

27. Hour Glass Nebula

31. Then the HELIUM RUNS OUT – Take 2 Core collapses again – becomes hotter & denser then For a Massive/SuperMassive Stars (starting at 100x more mass than Sun): • Fusion begins again • C fuses to O • O fuses to S, Si, and Ar • Si fuses to Fe, Cr • Heat from new fusion causes 2nd red giant phase – Red Supergiant. • After Fe, fusion must stop. Core collapses and gets degenerate

32. Outer layers of star are blown off spectacularly in a supernova. • Massive star becomes neutron star • Supermassive star becomes ablack hole

33. SUPERNOVA Brightest objects in the universe Can outshine an entire galaxy for a few weeks Fairly rare – 1-10 per century per galaxy.

34. 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).

36. Then one day in 1987 (February 23, 1987 to be exact) Watch This area Tarantula Nebula in LMC (constellation Dorado, southern hemisphere) size: ~2000ly (1ly ~ 6 trillion miles), distance: ~180000 ly

37. Then one day in 1987 (February 23, 1987 to be exact) Tarantula Nebula in LMC (constellation Dorado, southern hemisphere) size: ~2000ly (1ly ~ 6 trillion miles), distance: ~180000 ly

38. Supernova Remnants Hot gas cloud left behind remains hot for a long time Sometimes visible in x-rays, many visible in radio Size of remnant and expansion velocity tell us the age

40. HST picture Crab nebula SN July 1054 AD Dist: 6500 ly Diam: 10 ly, pic size: 3 ly Expansion: 3 mill. Mph (1700 km/s)

44. A SUPERNOVA LEADS TO ONE OF TWO ENDS… • Massive stars – the core of the star collapses into a neutron star – an incredibly dense star made only of neutrons.

45. Supernova remnants – neutron stars SN remnant Puppis A (Rosat)

46. Iisolated neutron star seen with Hubble Space Telescope Supernova remnants – neutron stars

47. Supernova remnants – neutron stars

48. A SUPERNOVA LEADS TO ONE OF TWO ENDS… • Supermassive stars – the core of the star collapses into a black hole, a dead star so dense and massive that nothing can escape its gravity, not even light.

49. Supernova remnant – black hole

50. Supernova remnant – black hole