I’ve been cleaning out my filing cabinets lately, trying to rid myself of the paper and other stuff that accumulates through the mail, meetings, etc. I had two filing cabinets full of old press releases from science institutions. Most of them came my way at American Astronomical Society meetings. I usually register as press when I go (usually because I AM writing something for somebody), and thus these tidbits of research come my way.

One that I ran across that I decided to keep was a story about wide-field images of the center of the Milky Way taken using the Very Large Array radio telescopes. Nowadays it’s an accepted fact that there is a black hole in the center of the Milky Way. The past few years, astronomers have been perfecting techniques to zero in on the culprit and take the measure of its size and mass. You don’t actually see the black hole because — well… it’s black. Or, rather, it’s not allowing any light to escape from itself. But, you CAN see its effects on surrounding material — stars, gas, and dust. They give off emissions for various reasons related to the existence of the black hole — such as heating due to the strong radiation given off by material as it spirals into the hole. And some things here glow due to a whole raft of other causes. Unraveling what’s what in this area is a full-time job for a lot of astronomers!

However, much of this activity is still invisible to us at optical wavelengths (that which we see with our eyes) because the middle of the Milky Way is hidden behind a veil of gas and dust. So, astronomers use radio and infrared and other “probes” to peer behind that veil. All the features you see in the image radiate at a wavelength of 90 centimeters (in the radio portion of the electromagnetic spectrum), and these features are related to the black hole — which is the largest, brightest object, labeled Sgr A. The actual black hole is hidden deep within that blare of light, and it is called Sagittarius A*.

As you can see, Sgr A is clearly not the only source of emissions in this image. Hot young stars form in this region, and as they do, they heat the gas around them. Eventually, the gas becomes hot enough that it glows, giving away the position of starforming regions. These are labeled Sgr B1 and B2 and part of Sgr D. When these same stars run out of fuel, they explode as supernovae, spreading debris in shock waves, and glowing in emissions given off as high-speed electrons spiral around magnetic fields. There are several supernova remnants in this image — look for the objects with the letters SNR in front of them. This radiation (called synchrotron radiation) may also be what’s causing a collection of sources known as the Galactic center arc, filaments, and threads to glow.

Since I received that press release (in 1999) more research into the goings-on at the center of the Milky Way is zeroing in on details in these structures. If you’re interested in learning more, you can visit the web page where this image is posted: The Galactic Center or there’s a good book out from a guy named Fulvio Melia called “The Black Hole at the Center of our Galaxy” (Princeton University Press, 2003) that takes the reader on an amazing journey to visit this cosmic beast that is the center of so much activity!