Weber State University
Popular in Course
Popular in Physics 2
This 25 page Class Notes was uploaded by Guido Casper IV on Wednesday October 28, 2015. The Class Notes belongs to PHYS 1040 at Weber State University taught by Staff in Fall. Since its upload, it has received 10 views. For similar materials see /class/230790/phys-1040-weber-state-university in Physics 2 at Weber State University.
Reviews for PS
Report this Material
What is Karma?
Karma is the currency of StudySoup.
You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!
Date Created: 10/28/15
THE GALACTIC HALO 8c GLOBULAR CLUSTERS Lecture 16 PH 1040 Astronomy Shane L Larson Weber State University SCHEDULE Next week STAR WEEK Mon Mar 5 Review Day Wed Mar 5 lVIidterm Handed out Fri Mar 7 In class activity day before Spring Break LU NAR ECLIPS E LU NAR ECLIPS E LU NAR ECLIPS E STORYLINE 0 Halo de nition 0 Stellar metallicity and populations 0 Globular Clusters HALO DEFINED Galactic halo is physically quot1 i the largest component of most galaxies Primary content is dark matter but also contains stars and sometimes hot gas seen in Xrays Radial eXtent of halo is unknown SOM E HALO FACTS o Spherical or nearly so 0 Relatively quotusuallyquot free of gas and dust 0 Stars in halo seem to be older Population II than stars in the disk Population I 0 Tell stellar age by looking at how much hydrogen they have measure metallicity 0 Identify halo stars by high proper motion METALLICITY o For astronomers everything heavier than hydrogen is metal ag EE4 IEQQE Eamp METALLICITY o For astronomers everything heavier than hydrogen is metal METALLICITY Just after nucleosynthesis the Universe was mostly hydrogen With small quantities of other light elements helium mostly Early stars were composed mostly of hydrogen Heavier elements quotmetalsquot are created through stellar evolution Descendant populations of stars still contain a lot of hydrogen but are also rich in metals quotelements heavier than hydrogen and helium quot STELLAR POPULATIONS o Astronomers classify stars into three age groups 0 Population I Metal rich stars like the Sun these are the youngest stars in the Cosmos Population II Metal poor stars these are older stars and created most of the metals that are in the younger generation they are Pop I parents Population III The oldest stars consisting of Virtually nothing except hydrogen No known Population III star has been detected yet 0 In the IVIilky Way most stars in the disk are Pop I While most stars in the halo are Pop II HALO DARK MATTER We don39t know What all the dark matter in the halo is but some of the dark matter is MACHOS A microlensing search toward the Magellanic Clouds detected MACHOS Microlensing is gravitational lensin when the mass is small and can39t make multiple images Instead it brightens the star 0 Watch stars in the Magellanic Clouds every night 0 Wait for a MACHO to pass MICROLENSING Source Star HALO DARK MATTER MACHO EVENT Ia uhi w M a day hm 5791 E 8155 Ann wce 4 day bms MACHO RESULTS The MACHO Collaboration photographed the LMC for 57 years Detected enough MACHOs to account for 20 of the dark matter in 05 solar mass MACHOs Other groups did not detect such high rates The matter is still under debate and new observations are being done HALO HISTOR o How does a halo form o Haloes may form from galactic cannibalism of small satellites material is easily tidally stripped and fills halo c Halo may preserve a memory of those events 0 over dense remnants of tidal streams o kinematic memory speeds similar to parent GLOBULAR CLUSTERS Star clusters with hundreds of thousands of stars Typically very 15 Gravitationa y bound don t y apart GLOBULAR CLUSTERS Currently the Milky Way is the parent of 155 known globular clusters 200 are expected Why are 50 missing We think there are globulars living behind the Zone of Avoidance In 1917 Shapley was the rst person to measure the distance to the clusters using Cepheids and plot their positions GLOBULAR CLUSTERS 20 80 10 o 3353 3 0 3503 lm 3930 4o kpc O 9 0 10 D o 20 o Shapley discovered the globulars were not centered on the Earth This he argued was evidence that the Earth was not at the center of the Milky Way First determination of the Center of the lVIiiky Way in Sagittarius 4 0000 lyr away correct for dust 25000 lyr close to true value GLOBULAR CLUSTER MAKEUP o Globular clusters quotglobsquot are mostly Pop H stars 0 The glob is at least as old as the stars 0 Pop H stars in globs suggest age of 127 billion years making globs the oldest objects in the galaxy 0 Low metallicity and very little star formation 0 Both indications of extreme age 0 Circumstantial evidence for black holes at their cores 1000 to 10000 solar masses Globular clusters are quotall bulgequot 0 Still hotly debated GLOBULAR CLUSTER AGES At an age of 127 billion years globs are the oldest objects in the galaxy When Hubble constant is greater than 77 kmsMpc the Universe is younger than the globs o 1Ho is the Hubble Time For Ho 77 kmsMpc the Hubble Time is 127 billion years As late as 1996 some believed Ho 80 kmsMpc and some believed Ho 40 kmsMpc Age problem resolved by better Ho measurements Ho 71 kmsMpc
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'