Copyright © 2009 Pearson Education, Inc.Europa: is there life here?Copyright © 2009 Pearson Education, Inc.Pathological Science1. Discoverers make their claims directly to the popular media, rather than tofellow scientists.2. Discoverers claim that a conspiracy has tried to suppress the discovery.3. The claimed effect appears so weak that observers can hardly distinguish itfrom noise. No amount of further work increases the signal.4. Anecdotal evidence is used to back up the claim.5. True believers cite ancient traditions in support of the new claim.6. The discoverer or discoverers work in isolation from the mainstreamscientific community.7. The discovery, if true, would require a change in the understanding of thefundamental laws of nature.From Robert ParkCopyright © 2009 Pearson Education, Inc.Pathalogical Science1. The maximum effect that is observed is produced by a causative agent ofbarely detectable intensity, and the magnitude of the effect is substantiallyindependent of the intensity of the cause.2. The effect is of a magnitude that remains close to the limit of detectability,or many measurements are necessary because of the very low statisticalsignificance of the results.3. There are claims of great accuracy.4. Fantastic theories contrary to experience are suggested.5. Criticisms are met by ad hoc excuses.6. The ratio of supporters to critics rises and then falls gradually to oblivion.From LangmuirCopyright © 2009 Pearson Education, Inc.Copyright © 2009 Pearson Education, Inc.11.2 Patterns Among StarsOur goals for learning:• What is a Hertzsprung–Russell diagram?• What is the significance of the mainsequence?• What are giants, supergiants, and whitedwarfs?Copyright © 2009 Pearson Education, Inc.What is a Hertzsprung–Russelldiagram?Copyright © 2009 Pearson Education, Inc.TemperatureLuminosityAn H-Rdiagram plotstheluminositiesandtemperaturesof stars.Copyright © 2009 Pearson Education, Inc.Generating an H-R DiagramCopyright © 2009 Pearson Education, Inc.Most stars fallsomewhere onthe mainsequence of theH-R diagram.Copyright © 2009 Pearson Education, Inc.Stars with lowerT and higher Lthan main-sequence starsmust have largerradii:giants andsupergiantslarge radiusCopyright © 2009 Pearson Education, Inc.small radiusStars withhigher T andlower L thanmain-sequencestars must havesmaller radii:white dwarfsCopyright © 2009 Pearson Education, Inc.A star’s full classification includes spectraltype (line identities) and luminosity class (lineshapes, related to the size of the star):I — supergiantII — bright giantIII — giantIV — subgiantV — main sequenceExamples: Sun — G2 VSirius — A1 VProxima Centauri — M5.5 VBetelgeuse — M2 ICopyright © 2009 Pearson Education, Inc.TemperatureLuminosityH-R diagramdepicts: Temperature Color Spectral type Luminosity RadiusCopyright © 2009 Pearson Education, Inc.Whichstar is thehottest?ABCDCopyright © 2009 Pearson Education, Inc.Whichstar is thehottest?AABCDCopyright © 2009 Pearson Education, Inc.Which staris the mostluminous?ABCDCopyright © 2009 Pearson Education, Inc.Which staris the mostluminous?CABCDCopyright © 2009 Pearson Education, Inc.Which star isa main-sequence star?ABCDCopyright © 2009 Pearson Education, Inc.Which star isa main-sequence star?DABCDCopyright © 2009 Pearson Education, Inc.Which starhas the largestradius?ABCDCopyright © 2009 Pearson Education, Inc.Which starhas the largestradius?CABCDCopyright © 2009 Pearson Education, Inc.What is the significance of themain sequence?Copyright © 2009 Pearson Education, Inc.Main-sequencestars are fusinghydrogen intohelium in theircores, like theSun.Luminous main-sequence stars arehot (blue).Less luminousones are cooler(yellow or red).Copyright © 2009 Pearson Education, Inc.Massmeasurements ofmain-sequencestars show thatthe hot, blue starsare much moremassive than thecool, red ones.High-mass starsLow-mass starsCopyright © 2009 Pearson Education, Inc.The mass of anormal,hydrogen-burningstar determines itsluminosity andspectral type.High-mass starsLow-mass starsCopyright © 2009 Pearson Education, Inc.The coretemperature of ahigher-mass starneeds to be higherin order tobalance gravity.A higher coretemperatureboosts the fusionrate, leading togreaterluminosity.Hydrostatic EquilibriumCopyright © 2009 Pearson Education, Inc.Stellar Properties Review Luminosity: from brightness and distance10!4LSun–106LSunTemperature: from color and spectral type3,000 K–50,000 KMass: from period (p) and average separation (a) of binary-star orbit0.08MSun–100MSunCopyright © 2009 Pearson Education, Inc.Stellar Properties Review Luminosity: from brightness and distance10!4LSun–106LSunTemperature: from color and spectral type3,000 K–50,000 KMass: from period (p) and average separation (a) of binary-star orbit0.08MSun–100MSun(0.08MSun)(100MSun)(100MSun)(0.08MSun)Copyright © 2009 Pearson Education, Inc.Mass and LifetimeSun’s life expectancy: 10 billion yearsCopyright © 2009 Pearson Education, Inc.Mass and LifetimeSun’s life expectancy: 10 billion yearsUntil core hydrogen(10% of total) is used upCopyright © 2009 Pearson Education, Inc.Mass and LifetimeSun’s life expectancy: 10 billion yearsLife expectancy of a 10MSun star:10 times as much fuel, uses it 104 times as fast10 million years ~ 10 billion years ´ 10/104Until core hydrogen(10% of total) is used upCopyright © 2009 Pearson Education, Inc.Mass and LifetimeSun’s life expectancy: 10 billion yearsLife expectancy of a 10MSun star:10 times as much fuel, uses it 104 times as fast10 million years ~ 10 billion years ´ 10/104Life expectancy of a 0.1MSun star:0.1 times as much fuel, uses it 0.01 times as fast 100 billion years ~ 10 billion years ´ 0.1/0.01Until core hydrogen(10% of total) is used upCopyright © 2009 Pearson Education, Inc.Main-Sequence Star SummaryHigh-mass: Low-mass: High luminosity Low luminosity Short-lived Long-lived Large radius Small radius Blue RedCopyright © 2009 Pearson Education, Inc.What are giants, supergiants, andwhite dwarfs?Copyright © 2009 Pearson Education, Inc.Off the Main Sequence• Stellar properties depend on both mass and age:those that have finished fusing H to He in theircores are no longer on the main sequence.• All stars become larger and redder afterexhausting their core hydrogen: giants andsupergiants.• Most stars end up small and white after fusion hasceased: white dwarfs.Copyright ©
View Full Document
Unlocking...