# Astronomy 100 Tuesday, Thursday 2:30 - 3:45 pm Tom Burbine

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Astronomy 100 Tuesday, Thursday 2:30 - 3:45 pm Tom Burbine tburbine@mtholyoke.edu www.xanga.com/astronomy100

Scores The highest score in the class currently is a 97% The lowest score in the class currently is a 33% (Assuming their test grades remain the same for the rest of the class and actually calculating their HW and PRS scores)

Class Average The exam average for the class is 72.2%. If I assume everybody gets 100% for HW and PRS scores and that this exam average does not change for the remaining tests: Class average = 80% x 72.2% + 20% x 100% Class average = 77.8% After all the exams, this class average should rise to above 80%

Schedule Today (Quasars, Dark Matter) Thursday (end and beginning of the universe) May 3 (Does Life Exist Elsewhere in the Universe) May 5 (Review) May 10 (Exam 4) May 12 (Exam 5) (optional) May 20 (Final) (optional)

Exam 4 Know the class notes Know all the definitions on the website Know the Summary of Key Concepts at the end of every chapter

Exam 5 and Final Know the class notes Know how to do every question on the 1 st 4 exams Know the Summary of Key Concepts at the end of every chapter

OWL assignment (Due Thursday) There is be an OWL assignment due on Thursday April 28 at 11:59 pm. There are 15 questions and a perfect score will give you 2 homework points.

Homework Assignment (Due by May 3) Make up a test question for next test Multiple Choice A-E possible answers 1 point for handing it in 1 point for me using it on test The question needs to be on material that will be on the 4th exam

Homework Assignment (Due by May 5) I have placed 40 terms on the website You get 0.1 of a HW point for each of these you define and hand in to me Definitions need to be hand-written or hand-typed A lot of these definitions will be on next test

Drake Equation Dark Energy Tully-Fisher Relation ALH84001 Cepheid Variable White Dwarf Jocelyn Bell Viking Mission Hubble’s Law SETI Big Bang COBE Standard Candle Quasar Planck Time Inflation in the Early Universe Olber’s Paradox Cosmic Microwave Background Isotope Baryon Percival Lowell Redshift Dark Matter MACHO Critical Density Radio Galaxy Main Sequence Fitting Cosmological Horizon White Dwarf Supernova Interstellar Medium Supercluster WIMPS Pulsar Habitable Zone Maunder Minimum Convection Zone Radiation Zone Hubble’s Constant Starburst Galaxy Europa

Astronomy Help Desk There is an Astronomy Help Desk in Hasbrouck 205. It is open Monday through Thursday from 7-9 pm.

Hubble’s Constant v = d x H o d = v/H o d = distance the galaxy is from you v = velocity the galaxy is moving away from us

Example A galaxy is moving away from us at a speed of 6,000 km/s How far is it away from us? H o = 71 km/s/megaparsec d = v/H o d = (6,000 km/s)/(71 km/s/megaparsec) D = 84.5 megaparsecs

Active Galactic Nuclei Active Galactic Nuclei are the unusually bright centers found in some galaxies

M87 Elliptical Galaxy

Quasars Quasars are the brightest active galactic nuclei Emit immense amounts of radiation Some are brighter than 1,000 Milky Ways

Quasars Look like stars But have huge redshifts

Radio Galaxies A galaxy that emits unusually large quantities of radio waves Thought to contain an active galactic nuclei

Power Active Galactic Nuclei, Quasars, and Radio Galaxies are thought to be powered by supermassive black holes They can exceed 1 billion solar masses

Energy Energy from the black holes comes from its gravity Gravity converts potential into kinetic Collisions convert kinetic into thermal energy Photons carry this thermal energy away

Very Efficient E=mc 2 10-40% of the energy of the accreting material is released as radiation before the matter crosses the event horizon More efficient than fusion, which turns less than 1% of the mass of the material into energy

Dark Matter Matter we infer to exist from its gravitational affects but from what we detect no light Dark matter dominates the mass of the Universe

Rotation curve Plot showing orbital velocities Of gas and stars

Milky Way Galaxy The mass of dark matter may be 10 times the mass of visible matter Visible matter is stars

Spiral Galaxies

Why is Dark Matter Important? The Universe is believed to proceed along two paths It may continue to expand forever Or it may stop expanding and collapse Its fate is dependent on the density of matter

Elliptical Galaxies The orbits of stars in elliptical galaxies are disorganized

Elliptical Galaxies Since some stars are moving towards us and some are moving away from us Spectral lines are broadened

Elliptical Galaxies Velocities of stars stay relatively constant as you move from galactic center Ellipticals contain dark matter

However We can’t determine the amount of dark matter in an elliptical galaxy Because we can’t measure their masses as far from their centers

Mass-to-Light Ratio You can compare the measured mass to the luminosity of a galaxy

Milky Way Milky Way contains 90 billion solar masses of material within the Sun’s orbit Luminosity of Milky Way at this orbit is 15 billion solar luminosities Mass-to-Light ratio of our Galaxy at this orbit is 6 solar masses per solar luminosities

This tells us that … The value of 6 solar masses per solar luminosity tells us that most of the matter is dimmer than the Sun out to the Sun’s orbit Mass-to-Light ratio of our Sun is 1 solar mass per solar luminosity So most matter is dimmer than the Sun

For some.. For some galaxies, they have mass-to-light ratios of 50 solar masses to solar luminosity This is too high to be accounted for by stars alone

Fritz Zwicky (1898-1974) Was among the first to suggest that there is a relationship between supernovae and neutron stars Suggested in the 1930s that dark matter was found in Galactic Clusters

Cluster Cluster is a collection of galaxies (that can number dozens to thousands) that are gravitationally bound

Zwicky By calculating the speed of galaxies as the rotate around in a cluster He found that galaxies in the clusters had huge mass-to-light ratios

Types of Dark Matter MACHOs WIMPS

MACHOs Massive Compact Halo Objects Includes –Brown Dwarfs – failed stars –Faint red stars –Jupiter-sized objects

WIMPs Weakly interacting massive particles –No electrical charge –Do not emit electromagnetic radiation –Have mass so do interact some with matter

Neutrinos Dark matter in galaxies can’t be neutrinos because neutrinos escape from galaxies with enormous speeds

WIMPS Have to have masses larger than neutrinos Have not been discovered yet

Questions

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