Galactic Center

The center of our galaxy is a fascinating and violent place. The evidence is now compelling that a black hole with a mass several million times greater than that of the Sun lurks there, almost invisible but for the effects of its gravity. This causes stars in the vicinity to orbit frantically around the hidden mass. But there is another signature of this exotic beast - radio emission. As material falls into the hole, energy is released, and some of this emerges as radio waves that can be detected by radio telescopes.

All this occurs, however, on very tiny angular scales. In addition, because the galactic center is such a dense, crowded environment, with lots of ionized gas, the radio waves are scattered, resulting in a blurring of any radio images that are made. This blurring, or scatter broadening, obscures structures that general relativity predicts will exist in the radio emission very close to the black hole.

The scattering is proportional to the square of the wavelength, so by going to very short wavelengths, it can be avoided. Also, by using very long baseline interferometry at such short wavelengths (for example, 1 mm), we can achieve sufficient angular resolution to image the predicted structures in detail. This is technically very challenging, however. In order to achieve sufficient sensitivity, the bandwidths and data recording rates of the VLBI systems must be greatly enhanced.

Haystack is taking a lead role in the development and deployment of new VLBI systems capable of pursuing this unique and fundamentally important scientific investigation. Eventually, the expectation is that high fidelity images of the immediate vicinity of the black hole at the galactic center will be produced, a region where general relativistic effects dominate.