Inventory of the Galactic Center

How do we study the center of the Galaxy?

28 magnitudes of optical extinction -- can't do it in visible light
infrared emission (2.2 microns - K band)

much less obscured
old red giant stars (T ~ 4000 K) are brightest in the infrared.

radio emission

unobscured
not emission from stars

synchrotron emission: charged particles spiraling around magnetic fields
free-free emission: charged particles interacting with one another

At the distance of the Galactic Center, 1" is about 0.05 parsecs.

What do we see?

In the infrared: A rising density of stars towards the center: $ρ (r)$ ~ r^-2 from 1 parsec to 0.1 parsec. Stars are very close together, so close interactions are common.

In the radio: Lots of non-thermal synchrotron radio emission showing ionized gas and magnetic fields:

(Picture spans ~ 60 pc across)

The brightest radio source is called Sagittarius A (Sgr A). Sgr A is not a single object, but a complex region at the center of the Galaxy:

VLA radio image (Farhad-Zadeh & Morris)

Sgr A East (left side, light blue) is hot explosion remnant, perhaps from a supernova or something else?
Sgr A West (center, red) is a region of ionized gas which shows a mini-spiral pattern
Sgr A* is a very bright, compact radio source located in the center of Sgr A West.