Transcript PowerPoint File

Lecture 30- The Structure of the
Milky Way Galaxy
Distance to the center of the globular
cluster distribution: 8500 parsecs =
8.5 kiloparsecs
How far is 8.5 kiloparsecs?
• Let 1 au = 1cm
• Nearest star (1.3 parsecs) = 2.68 km = 1.66
miles
• 8.5 kiloparsecs = 17,532 km = 10,870 miles
(2.74 Earth radii)
• Light signal transmitted from the GC would
take 27,700 years to reach us
Where (on the sky) is the galactic
center?
In Sagittarius
RA = 17h45m
DEC=-28.3 degrees
Position on SC1 Chart
Location on Sky of Galactic Center
At radio wavelengths, we can see
to the galactic center. Interstellar
dust has very little effect on radio
waves
The Galactic Center
Lang, Lazio, et al
At the Very Center
What do we see at the galactic
center (radio and infrared
wavelengths?
• Strong radio source (synchrotron radiation)
• At infrared wavelengths, can see stars
orbiting very vast around Sgr A
• http://antwrp.gsfc.nasa.gov/apod/ap001220.
html
• Ten years of observations speeded up
The Orbit of Star S2
Star S2 passes about as close to
Sagittarius A* as the planet Pluto
passes to the Sun. Indicates
supermassive object in a very
small region
Andrea Ghez paper