* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download calculated using stefan`s law
Observational astronomy wikipedia , lookup
Auriga (constellation) wikipedia , lookup
Canis Minor wikipedia , lookup
Corona Australis wikipedia , lookup
Cassiopeia (constellation) wikipedia , lookup
Corona Borealis wikipedia , lookup
Planetary habitability wikipedia , lookup
Canis Major wikipedia , lookup
Stellar kinematics wikipedia , lookup
Cygnus (constellation) wikipedia , lookup
Astronomical spectroscopy wikipedia , lookup
Future of an expanding universe wikipedia , lookup
Star of Bethlehem wikipedia , lookup
Dyson sphere wikipedia , lookup
Timeline of astronomy wikipedia , lookup
Perseus (constellation) wikipedia , lookup
Aquarius (constellation) wikipedia , lookup
Hayashi track wikipedia , lookup
Corvus (constellation) wikipedia , lookup
ASTROPHYSICS Physical properties of star 1.SIZE spherical depends on mass, temperature, gravity & age Range- 0.2R to 220 R, R- solar radius = 6.96 x 108m [ calculated using stefan’s law] Physical properties of star 2. MASS: Range- 0.1 M to 50 M M – solar mass =1.99 x 1039 [ Keppler’s iii law] Physical properties of star 3. BRIGHTNESS / LUMINOSITY : • magnitude – measure of brightness when observed from earth • Faintest star observed in night sky – 6th • Brightest star observed in night sky – 1st 1st magnitude star is100 times brighter than 6th magnitude L2/L1= 2.512 m2 –m Stars having negative magnitude are brighter than 0 magnitude stars Magnitude of sun = -26.8 Absolute brightness of a star are defined by by placing all stars at a distance of 10 parsec 1 parsec = 3.260ly Physical properties of star 4. TEMPERATURE : • Surface temperature varies 3,000K to 30,000 K • Temperature is measured using spectral type MASS –LUMINOSITY RELATION • L α M3.9 As mass increases luminosity increases a graph of log M v/s log L is a straight line Spectral Classes Class colour temperature O Blue white 30,000 B Light Blue 20,000K A White 10,000K F Light yellow 7,000K G Yellow 6,000K K Orange 4,000K M Red 3,000K Absolute Luminosity of star V/S temperature graph of a star is called HR diagram Features • Most of the stars are concentrated in narrow band- called main sequence stars. • As one moves from O to M type stars mass, temperature and luminosity of the stars decrease in main sequence. • Stars spend most of their life span in regions e.g main sequence, giants, white dwarfs. • Super giants are thinly populated occupy the top. • White dwarfs lay left of the main sequence. TIME OF STAY IN THE MAIN SEQUENCE • More the mass, less is the time of stay Ex: sun life – about 10 billion years ½ the mass--- 200 billion years 3 times the mass--- 500 Million years Internal Temperature and Pressure of a Star • Pressure and the temperature are maximum at the stellar core and decrease towards the surface of the star. Photon diffusion Time • Time taken by a photon to defuse from the center of the star to its surface. - In a star energy generated at the core. - Energy spread in the form of photons - While moving towards the surface it faces a large number of frequent collision - Energy and direction of travel of the photon changes. • In case of sun T=30,000 years Stellar Evolution 1. Proto star • Large cloud of interstellar dust and gases mostly hydrogen compressed due to gravitational force. • High pressure and temperature are produced. • Nuclear fusion of hydrogen starts. • Gravitational contraction is balanced by outward pressure. Helium Star • As hydrogen fuel is exhausted, energy generation decreases • - star begins to contract. • Temperature increases and star becomes very hot. • Helium atoms begins to fuse to form carbon. Red giant • Fusion of helium continues at the centre. • Heat generated at the core expands the outer layer enormously ( 10 to 20 times the size of the sun ) • This cools the outer layer. • So star appears reddish and dim. White dwarf • After spending millions of years in red giant stage carbon fuses. • Radiation oozes the outer layer of the star. • As a result generation of energy further decreases, star collapses further. • Star sinks and acquire high density and high temperature. • This is the end stage of the star.l Chandrashekhar limit • If mass of the star at birth < 1.4Mo star ends with white dwarf stage. • If mass of the star at the time of its birth > 1.4 Mo the core of the star collapses further, temperature and pressure increases enormously results in explosion called supernova. • Debris of supernova has high temperature and pressure that electrons and protons fused into neutron called neutron star. • If the mass of the neutron star > 5Mo it further collapses under its own gravity. • Any radiation entering this mass can not come out. Which sucks everything like a hole- black hole. Stellar Evolution