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STELLAR EVOLUTION AND LIFE! Linda Khandro, MAT www.lindakhandro.com Edmonds College Creative Retirement Institute Everett Astronomical Society Shoreline College Summer College Table Mtn. Star Party 2009-2010 PART THE FIRST: STELLAR EVOLUTION… “BIRTH, LIFE, AND DEATHS” OF STARS PART THE SECOND: …AND LIFE. WHAT DO STARS HAVE TO DO WITH LIFE PART THE FIRST: STELLAR EVOLUTION… “BIRTH, LIFE, AND DEATHS” OF STARS Our Galaxy, the Milky Way: where new stars are being born and old stars are dying in the spiral arms. The Andromeda Galaxy: our nearest galactic neighbour; stars birthing stars dying ~2.5 million light years away. Rosette Nebula: where new stars are being born, in the constellation Monoceros. Betelgeuse: a dying, red giant star, in the constellation Orion Eta Carinae: remnants of a dying star in the constellation Carinae. Crab Nebula: remnant of supernova 1054 AD, in the constellation Taurus. INTRODUCTION TO STARS important terms & definitions •BIRTH : Not from a “parent”, but from the gravitational collapse of a nebula. •NEBULA: cloud of gas and dust, itself a product of stellar deaths, including supernovae. •SUPERNOVAE: several types, either from dying binary stars, or deaths of single, massive stars at least 8x sun’s mass (these are the supernovae of interest to us here). INTRODUCTION TO STARS (2) •LIFE SPAN: longevity of a star depends entirely on its mass •Mass like our Sun = few billion years (Sun is 5 b.y. now, we expect 5 b.y. more) •Mass greater than Sun = less time than Sun to reach Red Giant stage •RED GIANT STAGE: star has consumed its core fuel, expands & contracts at the same time (!), grows larger, brighter, and cooler as outer layers expand outward to form Planetary Nebula, and core contracts to form a White Dwarf. •PLANETARY NEBULA: outer part of the end stage of sun-like star, outer regions continuing to cool and expand. •WHITE DWARF: core of sun-like star collapses, no fusion, no heat production, ultimately cools to “black dwarf”. INTRODUCTION TO STARS (3) •BRIGHTNESS: how bright a star appears to our eyes and instruments, function of distance as well as intrinsic brightness or luminosity. •LUMINOSITY: how much energy the star is actually generating is a function of its mass (or size) and temperature (the big vs small bonfire analogy). •TEMPERATURE: stars vary in temperature; more massive stars take a shorter time to burn core fuel and are hotter while doing do; less massive stars have less fuel, take longer, are cooler. Colour reflects temperature. INTRODUCTION TO STARS (4) •COLOUR: blue-white-yellow-orange and reddish coloured stars indicate temperatures from the hottest to the coolest. Colours, temperatures, and masses of stars are all plotted on an H&R diagram. Most stars we see are plotted on a graph on the H&R called the Main Sequence. Red Giants and White Dwarfs are no longer Main Sequence stars! •MAIN SEQUENCE STAGE: longest, most stable time of a stars ‘life’, when Hydrogen (H) fuses to form Helium (He) in the star’s core. STELLAR CLASSIFICATION SCHEME (general version) OBAFGK M Left to Right: Temperatures: hottest to coolest General Colours: blue,white,yellow,orange,red Oh Be A Fine Girl/Guy Kiss Me! MESSIER OBJECTS http://apod.nasa.gov/apod/messier.html MORE STARS FORM AS BINARIES OR TRINARIES THAN AS SINGLE STARS, LIKE OUR SUN AS FAR AS WE KNOW, OUR SUN HAS NO COMPANION STAR http://apod.nasa.gov/apod/ap050830.html COMPARING SIZES OF THE SUN AND PLANETS IN OUR SOLAR SYSTEM STELLAR BIRTH OUR SUN AND SOLAR SYSTEM FORMATION VIDEO http://www.youtube.com/watch?v=q5lc KLUvLzQ&feature=related COMPARING OUR SUN TO STARS OF DIFFERENT TYPES, AGES, AND SIZES SIRIUS (Canis Major): Younger than Sun, >2x mass, binary, brightest in sky, >8 LY, 25x luminosity, A class http://en.wikipedia.org/wiki/Sirius POLLUX (Gemini): Younger than sun, <2x mass, >34 LY, 32x luminosity, K class http://en.wikipedia.org/wiki/Pollux_%28star%29 ARCTURUS (Bootes): Age of sun, 3.5x mass, 37 LY, 210x luminosity, K class http://en.wikipedia.org/wiki/Arcturus BETELGUESE (Orion): Younger than Sun (few my), >18x mass, >640 LY, 105,000x luminosity, M class http://en.wikipedia.org/wiki/Betelgeuse RIGEL (Orion): Younger than Sun (8 my), trinary system, 17x mass, 800 LY, 40,000x luminosity, B class http://en.wikipedia.org/wiki/Rigel ALDEBARAN (Taurus): Binary, <2x mass, 65 LY, 150x luminosity, K class http://en.wikipedia.org/wiki/Aldebaran ANTARES (Scorpio): Binary, 15-18x mass, 600 LY, 10,000x luminosity, M class http://en.wikipedia.org/wiki/Antares STAR BIRTH REGIONS FROM ASTRONOMY PICTURE OF THE DAY http://apod.nasa.gov/apod/lib/aptree.html: THE PLEIDES OPEN STAR CLUSTER http://apod.nasa.gov/apod/ap060109.html M46 AND M47 (IN PUPPIS) http://apod.nasa.gov/apod/ap050804.html EAGLE NEBULA (M16 IN SAGITTARIUS) http://apod.nasa.gov/apod/ap050424.html ORION NEBULA (M42 IN ORION) http://apod.nasa.gov/apod/ap040713.html STAR FORMATION VIDEO: 12 BILLION YEARS IN 6 MINUTES! http://www.youtube.com/watch?v=mZ L7VBmeFxY&NR=1&feature=fvwp LIFE CYCLE OF OUR STAR http://en.wikipedia.org/wiki/Stellar_evolution http://www.astronomytoday.com/cosmology/evol.html STELLAR LIVES How hot, large, and long-lived will a star be once it enters its main sequence stage? That all depends on its mass… •Stars range in mass from about 0.08 to 100 solar masses, but most are similar to or less than that of the Sun and masses greater than 10 solar masses are rare. •However, the range of densities is very great. Red Giants, such as Betelgeuse, are less dense than the air we breathe, whereas a sugar- lump size of white dwarf material would, on Earth, weigh in excess of 1 ton. Avg. Mass Spectral class Avg. Lum Avg. Diameter MS lifetime 40 x Sol O5 500 000 x Sol 18 x Sol 1 million years 17 x Sol B0 20 000 x Sol 7.6 x Sol 10 million years 7 x Sol B5 800 x Sol 4.0 x Sol 100 million years 3.6 x Sol A0 80 x Sol 2.6 x Sol 500 million years 2.2 x Sol A5 20 x Sol 1.8 x Sol 1000 million years 1.0 x Sol G2 (sun) 1.0 x Sol 1.00 x Sol 12 000 million years 0.5 x Sol M0 0.03 x Sol 0.63 x Sol 75 000 million years 0.2 x Sol M5 0.008 x Sol 0.32 x Sol 200 000 million years Simplified illustration of the evolution of a star with the mass of the Sun •The star forms from a collapsing nebula, or cloud of gas (1) •then undergoes a contraction period as a protostar (2) •before joining the main sequence (3). •Once the Hydrogen at the core is consumed it expands into a red giant (4) •then sheds its envelope into a planetary nebula and degenerates into a white dwarf (5). •90% of stars fall plot on the Main Sequence of the H&R diagram (note that this is not an evolutionary sequence! A typical evolutionary sequence is shown by the red curve). •Hotter, massive Blue Giant stars are plotted in the upper left of the H&R (not MS). •Cooler more massive Red Giant stars are in upper right. •Hot but smaller-size White Dwarfs are in lower left. Main sequence/hydrogen to helium burning stage: the longest and most stable time in a star’s “life”. RED GIANT STAGE FORMATION (about 10% of MS lifetime): 1.H to Helium fusion slows as H is depleted, thus 2.Fusion pressure is reduced, thus 3.Gravity collapses core, but 4.Gravity causes heat increase to the point where 5.Renewed H fusion can occur around core, which produces 6.Renewed fusion pressure, which expands 7.Outer envelope which cools with distance from hot core 8.Star is more luminous (brighter) and larger (cooler and reddish) Post Main Sequence Star (Red Giant): G=gravity P=fusion pressure L=luminosity STELLAR DEATHS DEATH OF STARS ABOUT ONE SOLAR MASS FROM RED GIANT TO… WHITE DWARF AND PLANETARY NEBULA http://apod.nasa.gov/apod/ap030614.html http://apod.nasa.gov/apod/ap050612.html DEATH OF STARS GREATER THAN ABOUT 25 ORIGINAL SOLAR MASSES These massive stars may implode then explode as Supernovae (Type II) http://imagine.gsfc.nasa.gov/docs/science/know_l2/supernovae.html http://imagine.gsfc.nasa.gov/docs/science/know_l1/supernovae.html SUPERNOVA FORMATION The Red Giant-forming sequence of one element fusing to form another element, at successively higher temperatures and shorter times can result in a supernova as this process can repeat over and over again as: 1.Collapse and increased core temperature causes He to fuse to form Carbon… 2.C fuses to form next element in a… 3.Series of element formations ending in… 4.Silicon fusing to form Fe…end of the road…Fe will not fuse… The onion-like layers of a massive, evolved star just before core collapse. (Not to scale.) Eta Carinae… a dying star Eta Carinae http://apod. nasa.gov/ap od/ap980816 .html Crab Nebula… remnant of supernova 1054 AD PART THE SECOND: …AND LIFE. WHAT DO STARS HAVE TO DO WITH LIFE First of all, how do we know what we know about stars??? SPECTROSCOPY The study of light (spectra) “Spectroscopy pertains to the dispersion of an object's light into its component colors (i.e. energies). By performing this dissection and analysis of an object's light, astronomers can infer the physical properties of that object (such as temperature, mass, luminosity and composition)”. http://loke.as.arizona.edu/~ckulesa/camp/spectroscopy_intro.html That’s the short version! And what we are trying to do here is see how the composition of stars relates to the composition of life… So we’ll begin here… http://en.wikipedia.org/wiki/File:Light_dispersion_conceptual_waves.gif …to show what happens when white light is shone through a prism (later a spectroscope) Put on the glasses you have in front of you and look at various light sources in the room! Now we’ll look at a chart of the entire spectrum of electromagnetic radiation of which visible light is just one narrow band… …the wall chart please! There are different sources of light (or electromagnetic radiation) and different ways to look at those sources through a spectroscope (more complex but similar to a prism). We’ll keep it simple and just deal with visible light. (in each case, a unique type of spectrum is created) 1. Sources of light: a. Hot solid (i.e. light bulb) or hot, dense gas (i.e. surface of a star) b. Cooler or less dense gas (i.e. atmosphere of a star) 2. Ways to look at a light source through a spectroscope (and the spectrum produced): a. Hot solid or hot, dense gas: i. looking directly at the light source (produces a continuous spectrum, like a rainbow) ii. looking at the source through an intervening cloud of cooler or less dense gas (produces a dark line against a continuous spectrum; this is called an absorption spectrum) b. Cooler or less dense gas i. looking directly at the light source (produces a bright coloured line against a black background; this is called an emission spectrum) How does this happen? •Each of the absorption and emission spectra are produced by specific energies (wavelengths) of light interacting with the atoms that make up the elements of matter in the cool or less dense gas. •The gas can be any element heated to a gaseous state. •The end result is that each element of matter has its own unique spectrum that can be seen as either a bright (emission) or dark (absorption) line, depending on how it is viewed. •And since this can be done (and has been done) in laboratories with elements heated to gaseous states, we now have a catalog of elemental spectra. •Using this catalog, we now look at stars through a spectroscope and see what they’re made of… …the very same elements of which we are made! And since they came before we did in the history of the universe, we are made of star stuff! How did that star stuff turn into life? Go back to the beginning to see how stars form…from collapsing nebular clouds, which in turn, are produced by the expanding outer layers of sun-size stars, and the exploded remnants of supernovae! The grandest recycling program in the Universe! The elements of life, oxygen, hydrogen, carbon, nitrogen and more: http://www.seafriends.org.nz/oceano/abund.htm http://www.daviddarling.info/encyclopedia/E/elbio.html http://www.lpi.usra.edu/meetings/abscicon2010/pdf/5547.pdf And take a look again at the onion-like layers of a massive star about to “go” supernova… The onion-like layers of a massive, evolved star just before core collapse. (Not to scale.) With one important intermediate step yet to be discussed… …from stars to solar systems to planets to life… OUR SUN AND SOLAR SYSTEM FORMATION VIDEO http://www.youtube.com/watch?v =q5lcKLUvLzQ&feature=related