The Life Cycles of Stars

Your Questions first 1.Are we ever going to visit an Observatory? The Ochard Hill Obvservatory ( is open every Thursday night, weather conditions permitting.

2. What is your research about? I study nearby (distances larger than 3,000,000 ly) galaxies. In particular, I study the events that produced their stellar populations. And how these events evolved with cosmic time. The Antennae galaxy (Arp 244) is a galaxy that is forming new stars at a torrid pace. It is located about 45 Mpc ~150 million ly away. I use a combination of space and ground telescopes

SINGS (Spitzer Infrared Nearby Galaxies Survey) Cambridge Rob Kennicutt (PI) STScI Daniela Calzetti (Deputy PI), Claus Leitherer, Michael Regan, Martin Meyer Caltech/IPAC/SSC Lee Armus, Brent Buckalew, George Helou, Tom Jarrett, Kartik Sheth, Eric Murphy (Yale) Arizona Chad Engelbracht, Karl Gordon, Moire Prescott, George Rieke, Marcia Rieke, JD Smith Arizona State Sangeeta Malhotra Bucknell Michele Thornley Hawaii Lisa Kewley MPIA Fabian Walter, John Cannon, Helene Roussel NASA Ames David Hollenbach Princeton Bruce Draine Wyoming Danny Dale

3.6/8.0/24  m M81 = NGC 3031

NGC 4594 Optical

NGC  m

H , R, 8  m FUV, H , 24  m M51, 8.2 Mpc GALEX + ground + Spitzer

NGC 628 (M74)

3. Why does the theory of relativity not apply to light in vacuum? The fundaments of the theory of relativity is that the speed of light (or any electromagnetic wave) is always the same, whatever the reference frame you use. The reference frame must be at rest or in uniform motion. There have been many experiments to test this, and it appears to hold true to the extent scientists can establish. One important consequence is the dilation of time, and the shortening of distances for `rockets’ travelling close to the speed of light (nothing with mass>0 can travel *at the speed of light*).

4. How are distances between galaxies and between galaxy clusters calculated? This is one of the fundamental questions of astronomy: how distances are calculated. For distant objects, the `Hubble Flow’ relation provides accurate estimates: v = H o d (H o = 71 km/s/Mpc)

For closer objects (closer than about 100 Mpc), local gravitational perturbations to the Hubble Flow render that relation less powerful. `Standard candles’ are often used (e.g., Cepheids, supernovae, etc.) together with other methods (e.g., surface brightness fluctuations, etc.)

5. What is the Chandrasekhar limit? It is the maximum limit for which a non-rotating white dwarf (a dying star supported by electron’s repulsion forces) can exist.

Astronomy Picture of the Day Oct 1st, 2007: An optical image of the Small Magellanic Cloud (the 4th closest galaxy to our Milky Way) located at 210,000 ly = 64,000 pc = 64 kpc. Two MW Globular Clusters, NGC362 and 47 Tucanae, can also be seen.