The Black Hole in the Galactic Center
Lifting the fog - the actual size of Sagittarius A*
Slide 12 of 16
Only after a lot of work and with the most accurate measurements
was it finally possible to peek through the interstellar fog that
blurred the image of Sagittarius A*. Such measurements eventually
succeeded in 2004 as reported in a paper by Bower, Falcke, Herrnstein,
Zhao, Goss and Backer published in Science (April 1, 2004). The
intrinsic size at 43 GHz was found to be only two astronomical units -
the diameter of the earth's orbit around the sun.
The image below is an artists impression and shows a comparison of the
sizes found: the blue blob represents the intrinsic size of Sgr A*
overlayed on a sketch of the solar system (planets not to scale!). On
the top right one can see the expected size of the shadow cast by the
event horizon of the black hole. This is only a factor 5 smaller then
the actually detected radio source. Never have we been so close to
this final frontier of our universe - the point of no return. Could it
be that in the near future we could actually see the elusive event
horizon? The answer is yes, as described on the following pages ...
(Figure: The intrinsic size of Sagittarius A* as measured with the VLBA at 43 GHz by Bower, Falcke, Herrnstein et al. (2004) compared to the expected visible size of the event horizon (click on image to get larger size version, or click here for a Corel Draw version, e.g. to change the text). The radio source would just fit inside the orbit of the earth. For an observer at earth the event horizon would look 40 times bigger than the sun on the sky if the black hole were at the position of the sun in our solar system! (Of course, the earth would be torn into pieces in this case ...).)
Slide 12 of 16
Contact: Heino Falcke
