3Create a ChartIn your note book create a KWL chart and write what you know about how stars are formed. Also summarize what you know about the life cycle of a star? Next fill in the W.KWhat do you know?WWhat do you want to know?LWhat did you learn?
4Objectives Describe the different types of stars Describe how color indicates the temperature of a starDescribe the quantities that are plotted in the H-R diagram
5How is a star born? Chapter 2: Section 2&3 begins as a ball of gas and dustGravity causes the debris to form a sphereAs it gets denser it becomes hotter creating the right setting for nuclear fusion to occur.Hydrogen begins to change into Helium
8- Stars are classified by their size, brightness, color, temperature, spectrum and age. - Stars progress through the same life cycle, but the larger, hotter, and brighter stars progress much faster.Life Cycle of a Star:
9Life cycle sequenceStars begin as a large cloud of gas and dust called a nebulaOnce stars are formed they enter the main sequence stage. In this stage they continuously generate energy in the core through nuclear fusion.Size, structure and composition change very little during this stage.Eskimo Nebula
10A Tool for Studying Stars The H-R diagram is a graph that shows the relationship between a star’s surface temperature and its absolute magnitude.
12HR Diagram: The abundance of main sequence stars
13Life sequence continued… The third stage occurs when a star becomes a Red Giant or a Red Super Giant.This occurs when a star has used all of it’s hydrogen and begins to expand and cool. This causes the core to shrink, which then causes the rest of the sun’s atmosphere to expand.Red Giants can about ten times larger than the sun.Super giants are at least 100 times larger than the sun.
14Important terms Nebula Ball of dust and gas- beginning of a star. Main sequenceRed/Super GiantBall of dust and gas- beginning of a star.Constant Energy generated through nuclear fusion. The longest stage of a star.A star that is expanding and cooling; hydrogen is no longer generating energy. 10x larger /100x larger than sun.
17Life sequence continued… The final stage of a star’s life cycle is a white dwarf.A white dwarf is an old star’s leftover center that is no longer generating energy (no hydrogen left)White dwarfs can shine for billions of years before cooling completely
19Life cycle of a Star: Death of a Star Stars usually lose material slowly unless they are blue stars.Blue stars lose their energy fast and can sometimes explode in a bright flash called a Supernova, which is actually the collapse of the star.
21Super Novas can become: Neutron stars-stars that have collapsed under gravityPulsar stars –-spinning neutron stars that have jets of particles moving almost at the speed of light streaming out above their magnetic poles.-The beams of light sweep around as the pulsar rotates, just as the spotlight in a lighthouse does.-Like a ship in the ocean that sees only regular flashes of light, we see pulsars turn on and off as the beam sweeps over the Earth.-This along with the light being refracted by Earth’s atmosphere creates a stars “Twinkling” appearance
27Interesting triviaPulsars spin fast for the same reason ice skaters pull in their arms to spin. This is conservation of angular momentum. Pulsars are formed with a certain amount of angular momentum. As gravity causes them to shrink (and thus have a smaller radius) they must spin faster in order to conserve angular momentum.
29Black HolesLeftover supernovas that are so massive they collapse into an object called a black holeLight can not escape a black holes gravity because it is so massiveThey are only detected through x-rays that can determine a black hole through materials from stars filtering through it
33Important termsFinal stage, no hydrogen left. Can shine for billions of yrs.Blue stars that explode in a bright flash.Stars that collapse from the gravity-pulsars spin.Leftover supernovas that collapse into themselves forming gravity so massive that no light can escape.White DwarfSupernovaNeutron/Pulsar starBlack hole
34This artist's concept depicts a super massive black hole at the center of a galaxy. NASA's Galaxy Evolution Explorer found evidence that black holes -- once they grow to a critical size -- stifle the formation of new stars in elliptical galaxies. Black holes are thought to do this by heating up and blasting away the gas that fuels star formation.The blue color here represents radiation pouring out from material very close to the black hole. The grayish structure surrounding the black hole, called a torus, is made up of gas and dust. Beyond the torus, only the old red-colored stars that make up the galaxy can be seen. There are no new stars in the galaxy. Image Credit:NASA/JPL-Caltech
35Color of StarsWhat Is the Color of Hot? Although red and yellow may be thought of as “warm” colors and blue may be thought of as a “cool” color, scientists consider red and yellow to be cool colors and blue to be a warm color.
37How Bright Is That Star?Apparent Magnitude The brightness of a light or star is called apparent magnitude. How luminous the star is as it is viewed from Earth.Absolute Magnitude Absolute magnitude is the actual brightness of a star. Measurement of stars luminosity when placed at the same distance, absolute magnitudes show differences in actual luminosities.