ASTRON 89 1st Edition Lecture 19Outline of Last Lecture I. Center of Mass in Binary Stars II. The Hertzsprung Russell Diagram Binary Stars Outline of Current Lecture I. Stellar MassesII. Correlations and Relationships Important to Stellar MassesIII. The Interstellar Medium Current LectureI. Stellar Massesa. Most common type of star: red dwarf b. 8% of stars in our galaxy have masses larger than the Sun c. Only .06% of stars in galaxy have masses much larger than the Sund. Why do we see them? Because they’re so bright! The more massive a star is, the more luminous it isII. Correlations and Relationships Important to Stellar Massesa. Luminosity is approximately equal to about Mass^4 b. Radius of a star is approximately equal to the massi. From bottom right to top left of the band, the following is true:c. LUMINOSITY, TEMPERATURE, RADIUS, MASS ALLINCREASEd. Red Giants are not on the main sequence! i. So the relationships do not apply to red giants! Only for the stars on the main sequencee. The consequences of the relationshipsi. Mass is related to stellar lifetime. The more massive, the more fuel it has, the longer it will live. BUT the luminosity also plays a roll because the more massive, the more luminosity it has to generate in order to hold itself up against gravity1. If it can’t hold its luminosity, the star will start to shrink. It’s a balance between gravity and radiation pressureii. How long a star lives depends on how much mass it as, but INVERSELY proportional to luminosity. More massive, the more fuel is used up, so actually lifetime shortens by luminosityThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.1. So stellar lifetime is inversely proportional to the CUBE of the MASS. The more massive a star is, the shorter its lifetime, they willburn up more quickly2. The most massive stars have the shortest lifetimes, they have a lotof fuel, but burn it at a very rapid pace3. On the other hand, small red dwarfs burn their fuel extremely slowly and can have lifetimes of a trillion years or moreIII. The Interstellar Medium a. Gas: atoms and small molecules, mostly H and He. The gas is cold (less than 100 Kb. Dust: grains of particles c. ISM gas is very DIFFUSE, it extends over many light yearsi. Atmosphere is very thin d. Interstellar space: dust cumulatively causes things to be hidden behind it i. Nebula = general term used for fuzzy objects in the sky 1. Dark nebula: dust cloud 2. Emission nebula: glows, due to hot stars nearby3. Reflection nebula: Blue, due to light scattering by dust. Reflection nebulae have lower concentrations of dust than dark nebulaeii. Looking through a dust cloud with IR light, the stars look redder (reddering) NOT the same as Doppler Shiftiii. It looks red because there are lines in the middle, and the star itself doesn’t move towards or away from anything, spectral lines don’t shift, its just the light goes through a dust cloud (no lines are shiftede. When you have light passing through dust, peak MOVES to the red side and TOTAL INTENSITY goes downi. Called extinction and reddening. Extinction (light has been extinguished) and reddening (has become red in