United States-sized telescope views structure of Milky Way's black hole

William Atkins
Thursday, 04 September 2008 19:32

Science - Space

American-German-Dutch astronomers combined radio telescopes in California, Arizona, and Hawaii to make a very long baseline interferometer (VLBI)--a "virtual" telescope. It was able to measure the structure within Sagittarius A*, what is believed to be the supermassive black hole at the center of our galaxy, the Milky Way.


Two articles, which summarize the first-time measuring of the structure of the black hole at the center of our Milky Way Galaxy, were published in the August 4, 2008 issue of the journal Nature.

The two articles are entitled: (1) “Astrophysics: Bringing black holes into focus” by Christopher S. Reynolds and (2) “Event-horizon-scale structure in the supermassive black hole candidate at the Galactic Centre” by an international team of researchers (U.S.A., The Netherlands, and Germany) headed by Sheperd Doeleman of the Haystack Observatory, Massachusetts Institute of Technology (MIT), Westford, Massachusetts, U.S.A.

In the accompanying summary “Black hole physics: a new window on the Galactic Centre”, Reynolds states, “Using Very Long Baseline Interferometry (VLBI) at the relatively short radio wavelength of 1.3 mm [millimeter], a new intrinsic size estimate has been obtained for Sagittarius A*, the supermassive black hole candidate at the centre of the Milky Way.”

VLBI is an astronomical technique that makes observations of objects in deep space using many telescopes connected so they work simultaneously as one (“virtual”) telescope, which is in essence as large as the maximum distance between the telescopes.

The black hole--which is thought to be associated with the compact source of radio, infrared, and x-ray-emission, Sagittarius A* (Sgr A*)--is assumed to be at the center of our Milky Way galaxy. It, along with a disk of swirling gas and dust and maybe even a radio-emitting jet, is thought to be as massive as about four million stars the size of the Sun.

Reynolds continued to say, “The resulting lower limit on the size of Sgr A* is less than the predicted size of the event horizon of the presumed black hole, suggesting that Sgr A* emissions centre not on the black hole itself but on the surrounding accretion flow. VLBI observations of the Galactic Centre at around 1.3 mm, less influenced by interstellar scattering than those made at longer wavelengths, open a new window onto black-hole physics that will become even more sensitive as new VLBI stations are built.”

Please read page two about why this research is important to learning more about our black hole.