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This Is Your Life this is you life.

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Presentation on theme: "This Is Your Life this is you life."— Presentation transcript:

1 This Is Your Life this is you life

2 But first, a little background Kirchhoff's Laws 4

3 Kirchhoff's laws ,there are three types of spectra: continuum, emission line, and absorption line.
High pressure, high temperature gas Low pressure, high temperature gas Cool gas in front of continuous spectra source

4 Hydrogen Helium Oxygen Neon Iron


6 Hydrogen Continuum Absorption Lines


8 Doppler effect similar in light and sound
Waves compressed with source moving toward you Sound pitch is higher, light wavelength is compressed (bluer) Waves stretched with source moving away from you Sound pitch is lower, light wavelength is longer (redder)

9 Red Shift

10 Inverse square of light
If two stars are similar and one star is 3 times as far away, as the other, its intensity will be 1/9.

11 Spectra of Stars OBAFGKM

12 Stars are different colors, because they are different temperatures

13 Spectral Classification
Annie Cannon classified stars according to the strength of the hydrogen absorption lines in the sequence A, B, C….P These spectral classes were changed to a temperature-ordered sequence and some were discarded, finally leaving : Subclasses K7 A5 O B A F G K M Sun(G2) 35,000 K 3,000 K Oh, Be A Fine Girl (Guy) Kiss Me

14 O B A F G K M L The Spectral Sequence Bluest Reddest Hottest Coolest
Spectral Sequence is a Temperature Sequence

15 O Stars B Stars A Stars F Stars
Hottest Stars: T>30,000 K; Strong He+ lines; no H lines T = 11, ,000 K; Strong He lines; very weak H lines B Stars T = ,000 K; Strongest H lines, Weak Ca+ lines. A Stars T = K; H grows weaker Ca+ grows stronger, weak metals begin to emerge. F Stars

16 G Stars K Stars M Stars Solar Spectrum
T = K; Strong Ca+, Fe+ and other metals dominate, G Stars T = K; Strong metal lines, molecular bands begin to appear K Stars T = K; strong molecular absorption bands particularly of TiO M Stars 4000 A A Solar Spectrum

17 Quantum Mechanics Spectra Part II
Electrons can only orbit the nucleus in certain orbits. n =1 First orbital: Ground State) Lowest energy orbit .

18 Down emission Up absorption Hydrogen Spectrum
Hydrogen (1H) consists of: A single proton in the nucleus. A single electron orbiting the nucleus.

19 Emission Lines: Balmer Lines
When an electron jumps from a higher to a lower energy orbital, a single photon is emitted with exactly the energy difference between orbitals. No more, no less.

20 Absorption Lines: Balmer Lines
An electron absorbs a photon with exactly the energy needed to jump from a lower to a higher orbital. No more, no less.

21 Hydrogen lines absent in the hottest stars because, photons ionize electrons.
They are also absent in the coolest stars because, photons don’t have enough energy to move the electrons from n=2 to higher energy levels. No electrons, no lines.

22 HR Diagram In 1905, Danish astronomer Hertzsprung, and American astronomer Russell, noticed that the luminosity of stars decreased from spectral type O to M. To bring some order to the study of stars, they organize them in the HR diagram.

23 H–R Diagram Supergiants Luminosity (Lsun) Giants Main Sequence
40,000 20,000 10,000 5,000 2,500 106 104 102 1 10-2 10-4 Temperature (K) Luminosity (Lsun) Supergiants Giants Main Sequence White Dwarfs

24 As you move up the H-R diagram on the Main Sequence from M to O, the stars get hotter and larger

25 Back to this is your life
Star Formation “All we are is dust in the wind” Kansas

26 (GMC) in Orion Protostars form in cold, Giant Molecular Clouds
About 1000 GMCs are known in our galaxy These clouds lie in the spiral arms of the galaxy

27 The Cone Nebula Examining a Star Forming Region

28 Giant Molecular Clouds (GMC)
are mostly composed of molecular hydrogen. Properties: Radius ~50 pc (~160 ly) Mass ~105 Msun Temperature: K Also, small amounts of He,and others

29 Size of cloud – large, Compression area - small
GMC’s resist forming stars because of internal pressure (kinetic energy) so, a cooler gas is needed. A shockwave is needed to trigger formation, and to compress the material .

30 Sources of Shockwaves:
1.Supernova explosions: Massive stars die young . 2. Previous star formation can trigger more formations 3. Spiral arms in galaxies like our Milky Way: Spirals arms are probably rotating shock waves.

31                                                                                        View all images An expanding supernova explosion , occurring about 15,000 years ago.

32 Gravity Contraction As the cloud is compressed, cool blobs contract into individual stars. The blobs glow faintly in radio or microwave light. As they heat up, blobs glow in the infrared, but they remain hidden .

33 As protostar compresses: Density increases
Temperature rises. Photospheres (~3000K) Rotation increases as it shrinks in size. What types of stars form ? OB - Few AFG - More KM - Many, Many

34 Many of the cooler stars, spectral classes G,K,M, become heavy gas-ejecting stars called T-Tauri stars. Stars blows away their cocoon Leave behind a T Tauri star with an accretion disk and a jet of hot gas.

35 A T-Tauri star can lose up to 50% of its mass before settling down as a main sequence star.
False Color: Green = scattered starlight and red = emission from hot gas.

36 Motion of Herbig-Haro 34 in Orion
You can actually see the knots, called Herbig-Haro objects, in the jet move with time They can have wind velocities of km/s. This phase lasts about 10 million years.

37 Collapse is slower for lower masses:
Low-Mass Protostars Collapse is slower for lower masses: 1 Msun (solar Mass) ~30 Myr 0.2 Msun ~1 Billion years When core temperature ~ 10 Million K: Core ignites, P-P chain fusion begins Settles slowly onto the Main Sequence Has a rotating disk, from which planets might form .

38 Actual Protoplanetary Disks
The disks are 99% gas and 1% dust. The dust shows as a dark silhouette against the glowing gas of the nebula.

39 High-Mass Protostars Collapse is very rapid: 30 solar mass protostar collapses in ~30,000 years When core Temperature >10 Million K: Ignite first P-P Chain then CNO fusion in the core.

40 Clouds are blown away from the new stars
near the stars


42 The Cocoons of proto-stars are exposed when the surrounding gas is blown away by winds and radiation from nearby massive stars. Protostars!

43 The Main Sequence Core temperature & pressure rise
Collapse begins to slow down Finally: Pressure=Gravity & collapse stops. Becomes a Zero-Age Main Sequence Star, (ZAMS).

44 Most everything about a star's life depends on its MASS.
Pre-main sequence evolutionary tracks Most everything about a star's life depends on its MASS.

45 Meanwhile, back in the GMC, things are still happening



48 The original stars are growing, especially O & B stars.


50 Stars Form in Clusters Our own Sun is part of an open cluster that includes Alpha Centauri and Barnard's star. Gravitational interactions will cause some stars to eventually leave over time

51 Resemble "Super Jupiters"
Extreme :Minimum Mass: ~0.08 Msun Below this mass, the core never gets hot enough to ignite H fusion. Star becomes a Brown Dwarf Resemble "Super Jupiters" Only about 100 are known Shine mostly in the infrared

52 Extreme :Maximum Mass: 60-100 Msun
The core of a very massive star gets so hot: Radiation pressure overcomes gravity, star becomes unstable & disrupts. Upper mass limit is not well known. Such stars are very rare.

53 Star spends 90% of their life on the MS
Main Sequence

54 Stars on the Main Sequence, are in Hydrostatic Equilibrium .
Gravity pulling inward wants to contract the star Pressure pushing outward wants to make the star expand The star neither expands nor contracts.

55 Core Core-Envelope Structure
Outer layers press down on the inner layers. The deeper you go, the greater the pressure. The star develops a : hot, dense, compact central CORE surrounded by a cooler, less dense, ENVELOPE                                                    Core CORE Envelope

56 Energy is transferred inside stars by: Radiation (core)
Energy is carried by photons from core. Photons hit atoms and get scattered. Slowly stagger to the surface Takes ~1 Million years to reach the surface.                                      Convection (Envelope) Energy carried from hotter regions to cooler regions above by the motions of the gas. Everyday examples of convection are boiling water.

57 Energy in a Main-Sequence star is generated by fusion of H into He
This process is performed in two ways 1. Proton-Proton (P-P) Chain: (Low mass stars) 4 1H into 1 4He. + energy. Efficient at low core Temperatures (TC<18M K) 2. CNO Cycle: (High mass stars) Carbon acts as a catalyst Efficient at high core Temperatures(TC>18MK)

58 Main Sequence Lifetimes Main sequence lifetime (million years)
More massive stars have the shorter life time O & B stars burn fuel like an airplane! M stars burn fuel like a compact car! Every M dwarf ever created is still on the main sequence!! Main Sequence Lifetimes Spectral Type Mass (Solar masses) Main sequence lifetime (million years) O5 40 1 B0 16 10 A0 3.3 500 F0 1.7 BY G0 1.1 BY K0 0.8 BY M0 0.4 BY

59 Death of Low Mass Star “It’s the end of the world as we know it” . REM

60 The End-States for Low and High Mass Stars
Initial Stellar Mass Final Core Mass Final State White dwarf 8 - 30 Neutron Star > 30 > 3.0 Black hole

61 Evolution of Low-Mass Stars
Main Sequence Phase Energy Source: H core fusion (P-P cycle) Slowly builds up an inert He core Lifetime: ~10 Byr for a 1 Msun star( Sun) ~10 Tyr for a 0.1 Msun star (red dwarf)

62 Outer layer expands and cools
When all H in core converted to He He core collapses and heats up High temperatures ignites H burning in a shell Outer layer expands and cools Star becomes a Red Giant

63 Envelope ~ size of orbit of Venus
Outside:                                                                                          Envelope ~ size of orbit of Venus The star gets brighter and redder, climbs up the Giant Branch. (Takes 1 Byr)

64 *A secondary reaction forms Oxygen from Carbon & Helium:
At the top of the Red Giant Branch: Tcore reaches 100 Million K He fusion begins in core Fusion of three 4He nuclei into one 12C nucleus. *A secondary reaction forms Oxygen from Carbon & Helium:

65 Helium Flash in the core.
Short period of fast burning, then. star contracts, gets a little dimmer, but hotter . Moves onto the horizontal branch.

66 Horizontal Branch Phase
Structure: He-burning core H-burning shell Build up of a C-O core, still too cool to ignite Carbon

67 After 100 Myr, core runs out of He. C-O core collapses and heats up
Inside: C-O core collapses and heats up He burning shell outside the C-O core H burning shell outside the He shell                                       Outside: Star swells & cools

68 Climbs the Giant Branch again, slightly to the left of the original Giant Branch .

69 Core and Envelope separate.
Helium shell flash produces a new powerful explosion, that pushes the outer envelope outward. Core and Envelope separate. With weight of envelope gone, core never reaches 600 million K, no Carbon fusion Core contraction is stopped by electron degeneracy.

70 A Planetary Nebula forms Hot C-O core is exposed, moves to the left
                                                                                    Hot C-O core is exposed, moves to the left Becomes a White Dwarf

71 Expanding envelope forms a ring nebula around the White Dwarf core.
Ring is Ionized and heated by the hot central core of WD. Called planetary nebula because look like a tiny planet in a small telescope. The nebula expands at the ~ 35,000 to 70,000 miles/hour. Expands away in ~ 10,000 yrs

72 Planetary Nebulae Often asymmetric, possibly due to : Stellar rotation
Magnetic fields The Butterfly Nebula The Hour Glass Nebula

73 White Dwarf Properties Radii ~ 1000-5000 km (~ size of Earth. ) Temp
White Dwarf Properties Radii ~ km (~ size of Earth!) Temp. – from 100,000 to 2500 K. So small, that they can only be seen if close-by, or in a binary systems. White Dwarf’s mass < than the Chandrasekhar mass (1.4 Solar Masses).

74 White Dwarf Properties The core is tightly packed
One teaspoon weighs about 5 tons. Shine by leftover heat, no fusion. Fade slowly, becoming a "Black Dwarf“. Takes ~10 Tyr to cool off , so none exists yet.

75 Size: 92% Earth's diameter Mass: 1.2 solar masses
The most famous W.D. is Sirius’ companion . Sirius B Temp. 25,000 K Size: 92% Earth's diameter Mass: 1.2 solar masses The mass of a star, in the size of a planet. Sirius B

76 What about Binary Stars with one being a W.D. !
About half the stars in the sky are binaries. What about Binary Stars with one being a W.D. ! But wait that’s not all! Mass could transfer from the star to the W.D.

77 White Dwarf in a binary system…..
Evolving (dying) star Roche Lobes II Evolving (dying) star White Dwarf Accretion Disk III Evolving (dying) star Roche Lobe filled

78 A w. d. can take on material but , if the w. d. exceeds 1
A w.d. can take on material but , if the w.d. exceeds 1.4 solar masses, powerful explosions take place, and they can repeat. Type 1a super NOVA!!

79 Since the Type 1a supernova is always a white dwarf they can be used to judge very great distances (using the inverse square law).

80 Stellar Graveyard High Mass Stars Stellar Graveyard High Mass Stars

81 The End-States for Low and High Mass Stars
Initial Stellar Mass (Solar Mass) Final Core Mass Final State 1 - 8 White dwarf 8 - 30 Neutron Star > 30 > 3.0 Black hole

82 massive stars evolve more rapidly due to greater gravity.
Evolution of High Mass Stars Massive stars go through about the same internal changes as low mass stars, except : massive stars evolve more rapidly due to greater gravity. massive stars can produce heavier elements

83 Evolution of High-Mass Stars
O & B Stars (M > 8 Msun): (The James Dean of stars ) Burn Hot Live Fast Die Young Main Sequence Phase: Burn H to He in core using the CNO cycle Build up a He core, like low-mass stars But this lasts for only ~ 10 Myr

84 The Envelope expands and cools Envelope ~ size of orbit of Jupiter
After H core exhausted: Inert He core contracts & heats up H burning in a shell The Envelope expands and cools Envelope ~ size of orbit of Jupiter                                            

85 Moves horizontally across the H-R diagram, becoming a Red Super giant star
                                                                                    Takes about 1 Myr to cross the H-R diagram.

86 Core Temperature reaches 170 Million K
Helium Flash : Helium Ignites producing C & O Star becomes a Blue Supergiant.

87 Inert C-O core collapses & heats up H & He burning shells expand
He runs out in the core: Inert C-O core collapses & heats up H & He burning shells expand Star becomes a Red Supergiant again                                                                                    

88 C-O Core collapses until: Tcore > 600 Million K
Ignites Carbon Burning in the Core. Carbon Burning: 2- 12C fuse to form : Mg, Ne and O Carbon burning: 1000 years

89 End of the road ! Fusion now takes place rapidly
Neon burning: ~10 years Oxygen burning: ~1 year Silicon burning: ~1 day . Finally builds up an inert Iron core. End of the road !

90 Core of a massive star at the end of Silicon Burning:
                                                                                                    Onion Skin

91 Collapse is final :Protons & electrons form neutrons & neutrinos.
At the start of Iron Core collapse: Radius ~ 6000 km (~radius of earth) Density ~ 108 g/cc A second later!! , the properties are: Radius ~50 km Density ~1014 g/cc Collapse Speed ~0.25 c !

92 Material falling inwards is stopped by neutron degeneracy pressure .
This material rebounds, causing the outer atmosphere, and shells, to be blown off in a violent explosion called a supernova.

93 Elements heavier than Lead are produced in the explosion.
The supernova star will outshine all the other stars in the galaxy combined. The Famous Supernova SN 1987A type II Supernova


95 The Crab Nebula. This nebula is the result of a supernova that, exploded in 1054. The supernova was brighter than Venus for weeks before fading from view. The nebula is expanding at more than 3 million miles per hour.

96 Structure of a Neutron Star Diameter- 10 km in diameter
3> Mass > 1.4 times that of our Sun. One teaspoonful would weigh a billion tons! Rotation Rate: 1 to 100 rotations/sec Inside a Neutron Star

97 Pulsar Magnetic axis is not aligned with the rotation axis.
Lighthouse Model: Spinning magnetic field generates a a strong electric field. We will see regular, sharp pulses of light (optical, radio, X-ray) , if its pointed toward the earth.

98 The discovery of a pulsar in the crab nebula was the key connecting pulsars and neutron stars.

99 Black Holes We know of no mechanism to halt the collapse of a compact object with mass > 3 Msun.

100 The effect of gravity on light
Relativity implies nothing can go faster than light. As you travel faster, time slows down, you get more massive and your length appears to get shorter. The effect of gravity on light

101 Singularities If the core of a star collapses with more than 3 solar masses, electron degeneracy and neutron degeneracy can’t stop the gravitational collapse. The star collapses to a radius of zero , with infinite density and gravity—called a Singularity. Position Particle paths in a collapsing star singularity Event horizon Time

102 The Schwarzschild Black Hole The simplest of all black holes.
A static, non-rotating mass. The Schwarzschild Radius defines the Event Horizon. We have no way of finding out what’s happening inside the “Event horizon”

103 The Kerr Rotating Black Hole The singularity of a Kerr Black Hole is in infinitely thin ring around the center of the hole. The event horizon is surrounded by the ergosphere, where nothing can remain at rest. Here spacetime is being pulled around the rotating black hole.

104 It may be possible to avoid the singularity.
An object is moving fast enough, can enter the ergosphere and fly out again. If the object stops in the ergosphere, it must fall into the Black Hole. General Relativity predicts Wormholes for Kerr Black Holes, but Astrophysicists are skeptical. It may be possible to avoid the singularity.

105 Primordial – can be any size (created with Big Bang).
Various Black Holes Primordial – can be any size (created with Big Bang). “Stellar mass” black holes – must be at least 3 Mo – many examples are known Intermediate black holes – range from 100 to 1000 Mo - located in normal galaxies – many seen Massive black holes – about 106 Mo – such as in the center of the Milky Way – many seen Supermassive black holes – about Mo-located in Active Galactic Nuclei, have jets – many seen

106 Candidate For Black Hole Cygnus X-1 Binary Star w/ two objects:
M=30 Msun primary , M=7 Msun companion Bright in X-rays.                                                            Far too massive to be a white dwarf or neutron star. The simplest interpretation is : A 30 M star and a 7 M black hole Measured orbital motion of HDE

107 Evidence for BH A disk of dust fueling a massive black hole in the centre of a galaxy. The speed of the gas around the center indicates that the object at the centre is 1.2 billion times the mass of our Sun. 800 light years

108 Signature of a Black Hole

109 Thanks to the following for allowing me to use information from their web site :
Nick Stobel Bill Keel Richard Pogge NASA

110 the E n d

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