Fall 2013Astrophysics of Stars and the Galaxy33467, TR 12:00-1:20pmProfessor Shirley HoCome discover how the Milky Way forms, how our own star (aka the Sun) would evolve, how we hunt extra-solar planets, what black holes do in centers of galaxies! The class will be mostly project-based, and we will also learn to data-mine large databases of galactic and extragalactic objects like a modern day astrophysicist!
ASTR 3730: Fall 2003Distribution of radio pulsarsCan detect pulsars that are much older than the oldest distinct supernova remnants. So most pulsars are not in supernovaremnants.More interestingly: not all supernova remnants have pulsars at their center.centeredoff center
ASTR 3730: Fall 2003Together with observations of the distribution and proper motion of radio pulsars across the sky, this suggests that pulsars have velocities that can be as large as 103km s-1.Much larger than the space velocities of massive stars - suggests neutron stars receive a kickat time of formation.
ASTR 3730: Fall 2003Producing neutron star kicksBinding energy of a neutron star is:~GM2R~ 5"1053ergKinetic energy of a neutron star moving at 1000 km s-1is:12Mv2=1.5"1049ergNo energetic problem: small asymmetry in the emissionof neutrinos or mass from the supernova would be enough to give the neutron star enough kick energy.Can repeat exercise for momentum as well as energy.Seems plausible, but no definite mechanism is known:• asymmetry in the supernova explosion• irregularities in the progenitor star• …
ASTR 3730: Fall 2003Glitchespulse arrival timeIn some pulsars, the steady spin down is sometimes interruptedby a sudden, almost instantaneous, spin up - a glitch.Thought to arise because the neutron star has a fluid interior which is only weakly coupled to the crust. As the crust is braked, a mismatch in angular velocity develops which is suddenly corrected.
ASTR 3730: Fall 2003Binary pulsarIn 1974, Russell Hulse and Joe Taylor discovered a pulsar in a close binary system. From analysis of the arrival time of thepulses, they determined that the orbit was eccentric (e = 0.62),with a period of 7.8 hours.
ASTR 3730: Fall 2003Observations of this system provide very accurate masses forthe stars:M1=1.442±0.003MsunM2=1.386±0.003MsunTo a very good approximation this is a system of two pointmasses in orbit around each other.
This is the end of the preview. Sign up to
access the rest of the document.