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Transcript
The Life Cycles of Stars
Your Questions first
1. Are we ever going to visit an Observatory?
The Ochard Hill Obvservatory
(http://www.astro.umass.edu/~rdubois/Observatory/index.htm)
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
NGC 4594
Optical
NGC 4594
8 mm
M51, 8.2 Mpc
Ha, R, 8mm
FUV, Ha, 24mm
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 = Ho d (Ho = 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.