* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download The Life and Death of Stars
Survey
Document related concepts
Gravitational lens wikipedia , lookup
White dwarf wikipedia , lookup
Nuclear drip line wikipedia , lookup
First observation of gravitational waves wikipedia , lookup
Big Bang nucleosynthesis wikipedia , lookup
Planetary nebula wikipedia , lookup
Standard solar model wikipedia , lookup
Main sequence wikipedia , lookup
Chronology of the universe wikipedia , lookup
Nucleosynthesis wikipedia , lookup
Astronomical spectroscopy wikipedia , lookup
Transcript
The Life and Death of Stars John Irwin Low Gillerthwaite Field Centre Photo credits with thanks to NASA and Hubble telescope The Life and Death of Stars • • • • • Basic concepts How are stars formed? What provides a star’s fuel? What happens when the fuel runs out? Different types of star Basic Concepts • • • • • • What is light? Energy – Mass equivalence Atomic structure Fission and fusion Fundamental forces of nature Timeline of the Universe What is light • • • • • • • Ancient Greeks – a beam emitted from the eye 1000 Al-Haytham – streams of particles from the sun 1672 Isaac Newton – minute particles 1799 Thomas Young – wave 1846 Michael Faraday, 1873 Robert Maxwell – wave 1905 Albert Einstein – photon - particle and a wave Light is electromagnetic radiation: Radio – TV – Infra-red – Light – Ultra Violet – X-ray – Gamma ray Electromagnetic radiation gine.gsfc.nasa.gov/science/toolbox/emspectrum1.html Basic concepts - Speed of light • Light has a fixed speed in a vacuum • C = 300,000 km/sec or 186,000 miles/sec or 3 x 1010 cm/sec • Sun is 150 million km from earth • Sunlight takes 500 secs to reach earth An experiment to measure the speed of light • 3 everyday items to measure the speed of light – Measuring device – Source of electromagnetic radiation – Medium to see the effects of the radiation – Ruler – Microwave oven – Bar of chocolate An experiment to measure the speed of light λ = 6.5 x 2 cm =13cm ν = 2450 mhz = 2.45 x 10 9 cycles/sec c = λν = 13 x 2.45 x 10 9 = 31.85 x 10 9 cm/sec = 318,500 km/sec Basic concepts - What is a light year? • • • • • • The distance light travels in a year It is a measure of distance – not a measure of time Speed of light is 300,000 km/sec Light takes 500 secs to reach us from the sun A light year is 9.5 trillion km (9.5 x 1012 km) Alpha Centauri is 4.4 light years away Basic concepts - Energy – Mass equivalence • The most famous equation in Physics • E = mc2 E - energy (Joules) m - mass (kgm) c - speed of light (m/sec) Albert Einstein 1905 • Burn 1 kg coal -> 32 million Joules (3.2 x 107 Joules) • Convert 1kg coal to energy -> 9 x 1017 Joules Energy – Mass equivalence • 1000 MW Power Plant – – – – Coal Oil Gas U235 – 9000 tons/day – 40,000 barrels/day – 240 million cu.ft/day – 3 kg/day (2 train loads per day) (1 oil tanker per week) (30,000 barns/day) Basic concepts - Atomic structure • Atomic Nucleus contains most of the mass – Protons – positive charge – Neutrons – no charge • Orbiting the nucleus – Electrons – negative charge http://www.bbc.co.uk/schools/gcsebitesize/science/ add_aqa_pre_2011/atomic/atomstrucrev1.shtml Attribution: Yzmo Atom statistics • Atom • Nucleus 10-8 cm 10-13 cm (i.e. atom is about 100,000 times larger than the nucleus) • Proton and Neutron have similar mass (1.7 x 10-24 gm) • Electron is 1/2000 the mass of a proton • For an atom the size of this room the nucleus would be 1/100 cm • A Hydrogen atom is 99.9999999999 % empty space Basic concepts – Nuclear Fission and Fusion • Fission – An atom is split into two or more smaller atoms eg U235 + n -> Ba + Kr + 3n + 202 MeV • Fusion – Two or more atoms fuse to create a larger atom e.g. H2 + H3 -> He + n + 17.6MeV • Mass is lost and is released as energy : E = Mc2 Basic concepts – Fundamental Forces of Nature • • • • Strong nuclear force Electromagnetism Weak Nuclear force Gravity Basic concepts – Fundamental Forces of Nature • • • • Strong nuclear force Electromagnetism Weak Nuclear force Gravity 1 10-6 10-16 10-41 Timeline since Big Bang Big Bang NASA/WMAP Science Team Sun and Earth formed 4.6 billion years 13.8 billion years Basic concepts – Timeline of the Universe • If the Universe were a year old, then it would have begun on January 1st at 00:00:00 with the Big Bang • Sept 1st – Solar System formed • Oct 1st – bacteria begin photosynthesis • Dec 18th – first animals moved from the sea to land • Dec 26th – first dinosaurs • Dec 30th – dinosaurs became extinct • Dec 31st 23:40 Neanderthals • Dec 31st 23:52 Homo sapiens • http://www.thestargarden.co.uk/Timeline.html Basic concepts – Timeline of the Universe • • • • • • • • Dec 31st 23:59:54 23:59:58 23:59:59.25 23:59:59.52 23:59:59.75 23:59:59.85 24:00:00.00 Pythagoras (537 BC) Battle of Hastings Newton’s theory of Gravity (1687) John Dalton – atomic structure (1805) Einstein – Special Relativity (1905) Most of us in this room were born Now! Stars • ~ 200 billion stars in our galaxy (The Milky Way) • ~ 200 billion galaxies • ~ 4 x 1022 stars • Grains of sand on all the World’s beaches ~ 2 x 1022 Formation of stars • Stars are formed in Nebulae • A nebula is a cloud of dust and gas • For example the Nebula in Orion – 1350 light years away • Dust and gas coalesce and becomes denser and denser • What force drives this collapse? GRAVITY Nasa Hubble Telesco Nasa Hubble Telescope Nasa Hubble Telesco Nasa Hubble Teles Nasa Hubble Telescope A star is born • • • • • • • • • Gas cloud temperature – a few degrees Kelvin Gravity causes the gas and dust to coalesce This compression causes the gas and dust to heat up A protostar is formed Eventually it reaches 12 million degrees Kelvin As this point nuclear fusion starts Protons are forced together and Helium nucleii are formed Nuclear fusion starts to fuel the star Starts main sequence phase Nuclear fusion in a star like our sun Attribution: Borb Energy released • Atomic bomb (fission) – Hiroshima 14 kilotons TNT = 1gm mass converted • Hydrogen bomb (fusion) 50 megatons TNT = 2.3kg mass converted • Sun burns 564 million tons Hydrogen/sec (564 billion kg) to create 560 million tons Helium/sec (560 billion kg) • So the sun loses 4.3 million tons/sec (4.3 billion kg) • Equivalent to 2 billion Hydrogen bombs every second Life sequence of a star All stars follow a similar life sequence: Gas cloud -> Protostar -> Main Sequence -> Giant / Supergiant -> Planetary Nebula or Supernova -> Remnant 90-95% of stars are Main Sequence stars Star size varies from 1/10 to 150 solar masses Brown dwarf - less than 1/10 solar mass Star sizes • Star size varies from 1/10 to 150 solar masses (SM) • The heavier the star: – the hotter it is – the bluer it is – the faster it burns – the shorter it exists • Examples – – – – – Proxima Centauri Sun Sirius Regulus Zeta Puppis 1/ 7 SM 1 SM 2 SM 3.5SM 22 SM 3000K red 6000K yellow 10,000K white 12,000K blue 42,000K blue trillion years 9 billion years 1 billion years 100m years 2-5m years • Star size determines what happens at the end of its life Our Sun • • • • The sun converts 4.3 million tons/sec into energy It has been doing this for 4.5 billion years Has enough Hydrogen in the core for 5 billion years What happens when all the core hydrogen is burnt? – the core will collapse, become denser and hotter – Helium starts to fuse into Carbon and Oxygen • It will expand enormously into a Red Giant • It will lose its outer layers as a Planetary Nebula • Ultimately it will cool and become a white dwarf which could last for trillions of years A Planetary Nebula – NGC6543 Nasa Hubble Telescope White dwarf • • • • • White dwarf created by stars after Red Giant phase Stars which have 1/10 to 8 solar masses Small – about the size of the earth Similar mass to our Sun Therefore very dense – A teaspoon of white dwarf matter weighs 5 tons (5000 kg) • Gravity is 200,000 x earth gravity • Lasts for billions/trillions of years • Will eventually lose all heat and become a black dwarf http://www.slideshare.net/Teach5ch/majorfeatures-of-the-universe-andie Massive stars • More than 8x mass of our sun • Examples – Antares – 700 times the diameter of our sun – Betelgeuse –10m years old – Rigel – 10m years old • Massive stars have short life span – 30 million down to a few hundred thousand years • Supergiant stars Relative sizes of stars Red Giants Pollux Arcturus Supergiants Rigel Betelgeuse Antares http://sci.gallaudet.edu/Science/ relativesizes.html What happens to Supergiants • • • • • • • • • Like our sun they fuse Hydrogen to Helium for fuel When core Hydrogen runs out the star collapses (cf our Sun) It will start fusing Helium to Carbon Eventually core Helium runs out and star collapses again Gets even hotter than before Carbon fuses into heavier elements Process of: star collapse – fusion keeps repeating This creates heavier and heavier elements in the core Stellar nucleosynthesis https://en.wikipedia.org/wiki/Stellar_nucleosynthesis The end of a Supergiant • • • • • Fusion of elements up to Iron releases energy This holds the star up against the pull of gravity Fusion of iron requires energy But there is nothing to burn The outer edge of the core collapses catastophically (.25 sec) • Bounces off the core creating an enormous shockwave The end of a Supergiant - Supernova • The shockwave travels to the surface of the star (2 hrs) • On its way it fuses elements heavier than iron – Gold, silver, platinum, uranium • The outer surface and the new elements are blasted into space • The supernova will be incredibly bright for a few months • After a few years it will fade away • It will leave a shockwave of gas and dust hurtling outwards • It will also leave a remnant of the star behind Supernovae remnants • A Supernova leaves behind a remnant of the star • Depending on the size of the remnant it will form: • Remnant size: – <1.4 SM – 1.4 – 3 SM – >3 SM White dwarf Neutron star Black hole Neutron star • • • • Created as remnant of a Supernova explosion Very small – about 10 miles across 1.4 to 3 x the mass of our Sun Therefore incredibly dense – A teaspoon of neutron star matter weighs 10 million tons • Gravity is 200 billion x earth gravity • Neutron stars also spin very rapidly – Up to 700 times per second What is a neutron star made of • Mainly neutrons !! • The protons and electrons are fused to create neutrons • It is held up against the force of Gravity by neutron pressure https://s-media-cacheak0.pinimg.com/originals/3d/24/b0/3d24b060731583cfc28e5ba6c1fe1223.jpg Black holes • • • • • • • Created as remnant of a Supernova explosion At least 3 x the mass of our Sun Gravity wins – it collapses to a point Singularity This is known as a Black Hole The escape velocity is greater than the speed of light Nothing can escape the Event Horizon, including light Black Holes • We can’t see Black Holes • We can detect their presence • Event Horizon size – From 6 miles up to the size of our Solar System • Black holes are very compact • At the centre of every galaxy is a Supermassive Black Hole Stardust The universe started with a Big Bang 13.8 bn years ago Shortly after the Big Bang by mass the Universe consisted of (by atoms): – 75% Hydrogen (92%) – 25% Helium (8%) – Traces of Lithium Today the mass of the Universe consists of (by atoms): – – – – – 74% Hydrogen (92%) 24% Helium (7%) 1% Oxygen (0.1%) 0.5% Carbon (.05%) 0.5% other elements (0.6%) Stellar Nucleosynthesis – Periodic Table Attribution: Cmglee Chemical elements in a human body https://askabiologist.asu.edu/content/atoms-life A final thought • We don’t know what most of the stuff in the Universe is ! • Stars, planets, gas clouds, dust etc make up 5% of the Universe • Dark Matter makes up 25% of the Universe • Dark Energy makes up 70% of the Universe • What is Dark Matter and Dark Energy? • Nobody knows!!! ANY QUESTIONS