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Introduction to Physical Science Monday, Wednesday, Thursday Tom Burbine tomburbine@astro.umass.edu. Schedule. December 8 - December 9 – Presentations 5-10 minutes On how you would teach something you learned in class to your students December 13 – Final Covers everything from midterm
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Introduction to Physical ScienceMonday, Wednesday, ThursdayTom Burbinetomburbine@astro.umass.edu
Schedule • December 8 - • December 9 – Presentations • 5-10 minutes • On how you would teach something you learned in class to your students • December 13 – Final • Covers everything from midterm • Can bring in one sheet of paper with anything you wanted written on it • Also, your mineral identification sheets
Unit of distance in Astronomy • A light-year is the distance that light travels in a year • 10,000,000,000,000,000 meters • 5,878,625,373,184 miles
Life of a Star • A star-forming cloud is called a molecular cloud because low temperatures allow Hydrogen to form Hydrogen molecules (H2) • Temperatures like 10-50 K
Condensing • Molecular clouds tends to be lumpy • These lumps tend to condense into stars • That is why stars tend to be found in clusters
Protostar • The dense cloud fragment gets hotter as it contracts • The cloud becomes denser and radiation cannot escape • The thermal pressure and gas temperature start to rise and rise • The dense cloud fragment becomes a protostar
When does a protostar become a star • When the core temperatures reaches 10 million K, hydrogen fusion can start occurring
Classification of Stars • Stars are classified according to luminosity and surface temperature • Luminosity is the amount of power it radiates into space • Surface temperature is the temperature of the surface
Hertzsprung-Russell Diagram • Ejnar Hertzsprung and Henry Norris Russell plotted spectral type (temperature) versus stellar luminosity • Saw trends in the plots • Stars did not plot randomly
OBAFGKM • Oh Be A Fine Girl/Gal Kiss Me • http://www.mtholyoke.edu/courses/tburbine/ASTR223/OBAFGKM.mp3
Hertzsprung-Russell Diagram • Most stars fall along the main sequence • Stars at the top above the main sequence are called Supergiants • Stars between the Supergiants and main sequence are called Giants • Stars below the Main Sequence are called White Dwarfs
giant – a star with a radius between 10 and 100 times that of the Sun • dwarf – any star with a radius comparable to, or smaller than, that of the Sun
Classifications • Sun is a G2 V • Betelgeuse is a M2 I
Main Sequence Stars • Fuse Hydrogen into Helium for energy • On main sequence, mass tends to decrease with decreasing temperature
Things to remember • 90% of classified stars are on main sequence • Main sequence stars are “young” stars • If a star is leaving the main sequence, it is at the end of its lifespan of burning hydrogen into helium
Stellar Classifications • O, B, A, F, G, K, M • A0, A1, A2, … A9 in the order from the hottest to the coolest
“Deaths” of Stars White Dwarfs Neutron Stars Black Holes
White Dwarfs White Dwarfs is the core left over when a star can no longer undergo fusion Most white dwarfs are composed of carbon and oxygen Very dense Some have densities of 3 million grams per cubic centimeter A teaspoon of a white dwarf would weigh as much as an elephant
White Dwarfs Some white dwarfs have the same mass as the Sun but slightly bigger than the Earth 200,000 times as dense as the earth
White Dwarfs Collapsing due to gravity The collapse is stopped by electron degeneracy pressure
Electron Degeneracy Pressure No two electrons can occupy the same quantum state
The Sun Will end up as a White Dwarf
Neutron Star Neutron stars are usually 10 kilometers across But more massive than the Sun Made almost entirely of neutrons Electrons and protons have fused together
How do you make a neutron star? Remnant of a Supernova
Supernova • A supernova is a stellar explosion. • Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months.
The last person to see and chronicle a supernova outburst in our galaxy was Johannes Kepler. • That was in 1604 rivaled Venus in brightness.
Density • You could take everybody on Earth and cram them into a volume the size of sugar cube
Explosion • The collapse of the core releases a huge amount of energy since the rest of the star collapses and then bounces off the neutron core • 1044-46 Joules • Annual energy generation of Sun is 1034 Joules
Black Hole • After a supernova if all the outer mass of the star is not blown off • The mass falls back on the neutron star • The gravity causes the neutron star to keep contracting
Black Hole • A black hole is a region where nothing can escape, even light.
Event Horizon • Event Horizon is the boundary between the inside and outside of the Black Hole • Within the Event Horizon, the escape velocity is greater than the speed of light • Nothing can escape once it enters the Event Horizon
No • Black Holes do not emit any light • So you must see them indirectly • You need to see the effects of their gravity
