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Announcements: -Public Viewing postponed to THIS Friday Evergreen Valley College http://www.evc.edu 7PM-10:30 check website for weather information maps available online Pick up copy of handout: required for credit!! Homework #9 due Thursday Exam #3: May 3. - PowerPoint PPT Presentation
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Announcements:
-Public Viewing postponed to THIS FridayEvergreen Valley Collegehttp://www.evc.edu7PM-10:30check website for weather informationmaps available online
Pick up copy of handout: required for credit!!
Homework #9 due ThursdayExam #3: May 3
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display2
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display3
5,000 stars with most accurate distances measured by Hipparcos.
85% lie on Main Sequence.
An actual HR Diagram
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Antares: M1IBetelgeuse: M2I
Aldebaran: K5IIIRigel B8I
Arcturus: KIIPollux: K0III
Relative Sizes
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What causes the red color?a) Hydrogen emissionb) Hydrogen absorptionc) Doppler shifted radiation
The cone shaped object isa) Cold dust and gas
obscuring radiationb) Bi-polar jet
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Chapter 13
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Introduction
• Where do stars come from?Giant Molecular CloudsBok GlobulesInterstellar Medium (ISM)ProtostarsPre-Main Sequence Stars
• How do they age (evolve)
• What is their fate?
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Where do Stars Come From?
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1. Giant Molecular Cloud breaks up into smaller clumps that collapse under their own gravity.
2. Rotation becomes more and more important as clump contracts.
3. Disk forms
4. Bi-polar jets are created; Cloud clears away
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Bipolar Flows, Jets, and Herbig-Haro ObjectsBipolar Flows, Jets, and Herbig-Haro Objects
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Bipolar Flows Easily Seen at Radio WavelengthsBipolar Flows Easily Seen at Radio Wavelengths
redshifted
blueshifted
Radio Image
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The nebulae around protostars are shaped into disks because of the same process that causes dough to become flat when it is
a) spun in the air like pizza doughb) rolled with a pin like pizza doughc) squashed between plates like dough for
a burritod) baked on a flat sheet like a cookie.
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The factors that tend to work against collapse areI. The magnetic field of the cloudII. The presence of a supernova nearbyIII. The existence of molecules in the gasIV. Heat in the gasV. rotation of the cloud
a) I, III, Vb) I, IV, Vc) II, III, Vd) II, IV, Ve) III, IV, V
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When will a protostar become an official star?When will a protostar become an official star?
Protostar continues to collapse, becoming Protostar continues to collapse, becoming denser and hotter in its interior.denser and hotter in its interior.
Once temperatures reach about 7 million Once temperatures reach about 7 million Kelvin, hydrogen fusion reactions begin to Kelvin, hydrogen fusion reactions begin to take place. take place.
Protostar becomes a star when fusion Protostar becomes a star when fusion begins. Process (protostar to star) takes begins. Process (protostar to star) takes about 1-100 million years.about 1-100 million years.
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Protostars in the HR DiagramProtostars in the HR Diagram
NGC 2264: a young clusterNGC 2264: a young clusterof stars (10 millionof stars (10 millionyears old)years old)
Note the large amount ofNote the large amount ofgas/dust left over fromgas/dust left over fromstar formation.star formation.
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Protostars in the HR DiagramProtostars in the HR Diagram
High-mass stars collapse faster than High-mass stars collapse faster than low-mass stars. (larger gravitational low-mass stars. (larger gravitational forces are involved).forces are involved).
The faster they collapse, the sooner The faster they collapse, the sooner core temperatures sufficient for core temperatures sufficient for hydrogen fusion are reached.hydrogen fusion are reached.
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Stellar Mass LimitsStellar Mass Limits
M < 0.08 solar masses:Not hot enough for fusionBrown Dwarfs (failed star)
M > 100 solar massesNot observedextreme temperatures/luminosityradiation pressure
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A Star’s Mass Determines its Core TemperatureA Star’s Mass Determines its Core Temperature
Hydrostatic Equilibrium:gas pressure balances gravity
higher gravity, higher internal pressure, higher internal temperature!
