The Heart of the Sun Energy Generation in Sun-like Stars

From whence it came… All energy generation occurs in the Core of the Sun ( and other stars) All energy generation occurs in the Core of the Sun ( and other stars) Nuclear Fusion (combining nuclei) Nuclear Fusion (combining nuclei) Lighter elements combine to make heavier ones Lighter elements combine to make heavier ones Some mass gets converted into energy! Some mass gets converted into energy!

Sun’s Fuel All stars are composed primarily of Hydrogen All stars are composed primarily of Hydrogen It is the most abundant element in the Universe It is the most abundant element in the Universe Sun is burning Hydrogen into Helium Sun is burning Hydrogen into Helium Nuclear Fusion! Nuclear Fusion!

Hydrogen Fusion Two mechanisms to burn Hydrogen Two mechanisms to burn Hydrogen Sun-like stars use Proton-Proton chain Sun-like stars use Proton-Proton chain Larger stars (1.4 times Sun size) use CNO cycle (carbon, nitrogen, oxygen) Larger stars (1.4 times Sun size) use CNO cycle (carbon, nitrogen, oxygen) Both are mechanisms to convert Hydrogen to Helium Both are mechanisms to convert Hydrogen to Helium

Proton-Proton Chain Net effect: Converts 4 Hydrogen to 1 Helium Net effect: Converts 4 Hydrogen to 1 Helium 1 H + 1 H  2 H + e + + (happens twice) 2 H + 1 H  3 He +  (happens twice) 2 H + 1 H  3 He +  (happens twice) 3 He + 3 He  4 He+ 1 H+ 1 H +  3 He + 3 He  4 He+ 1 H+ 1 H + 

Proton-Proton Chain There is a mass defect! There is a mass defect! The Helium-4 nucleus is 0.048x kg less massive than the 4 Hydrogen-1 nuclei The Helium-4 nucleus is 0.048x kg less massive than the 4 Hydrogen-1 nuclei This mass gets converted into energy This mass gets converted into energy The amount of energy for a housefly to jump.001 inches into the air! The amount of energy for a housefly to jump.001 inches into the air! Not much! Not much!

Proton-Proton Chain This reaction occurs times per second This reaction occurs times per second 5 million tons of Sun’s mass are converted to energy every second! 5 million tons of Sun’s mass are converted to energy every second! How much of total mass will get converted in the Sun’s lifetime? How much of total mass will get converted in the Sun’s lifetime? < 0.07% of its mass! < 0.07% of its mass!

Proton-Proton Chain Need high temperatures and high densities Need high temperatures and high densities Temp= 8 million K Temp= 8 million K Only core of Sun is hot and dense enough! Only core of Sun is hot and dense enough!

Matter and Antimatter Positron is antimatter Positron is antimatter Reacts with electrons Reacts with electrons Annihilates! Annihilates! Creates  -rays Creates  -rays

Solar Neutrinos Neutrino- “little neutral one” Neutrino- “little neutral one” Interact with almost nothing! Interact with almost nothing! Hard to detect Hard to detect Escape from Sun quickly! Escape from Sun quickly! Provide information about internal processes of the Sun Provide information about internal processes of the Sun Carry about 2% of energy from P-P chain Carry about 2% of energy from P-P chain

Solar Neutrinos Appear whenever reaction produces an electron or positron Appear whenever reaction produces an electron or positron 3 types of neutrinos exist 3 types of neutrinos exist Once believed to be massless Once believed to be massless But now… But now…

Solar Neutrino Problem 2 produced in every P-P chain 2 produced in every P-P chain chains/second chains/second Lots of ’s! Lots of ’s! Huge detectors on Earth didn’t detect enough (1/3 as many as predicted) Huge detectors on Earth didn’t detect enough (1/3 as many as predicted) Where are the ’s? Where are the ’s?

Solar Neutrino Solution! (Maybe) 3 kinds of neutrinos 3 kinds of neutrinos Not enough electron ’s, too many mu ’s Not enough electron ’s, too many mu ’s Some ’s have been detected changing varieties (oscillating) Some ’s have been detected changing varieties (oscillating) They must have mass to do this! They must have mass to do this! The solar type ’s have yet to been observed doing this The solar type ’s have yet to been observed doing this

Summary Sun generates energy via Hydrogen fusion Sun generates energy via Hydrogen fusion Uses Proton-proton chain Uses Proton-proton chain This process generates energy via mass defect This process generates energy via mass defect Antimatter exists Antimatter exists Solar neutrino problem solved? Solar neutrino problem solved?