My newest sketchbook page pictures Sagittarius, the largest constellation in the Southern Hemisphere. It has many bright stars and the most stars with known planets — 16 at present count. But perhaps its most celebrated feature is a bright astronomical radio source called Sagittarius A* (pronounced “Sagittarius A-star”), believed by scientists to be the site of our galaxy’s central supermassive black hole.
Sagittarius A* is invisible as all black holes are, but researchers are on course to observing the glow of matter near its edge — a region known as the event horizon — through an international effort called the Event Horizon Telescope (EHT). Led by MIT and and the Harvard-Smithsonian Center for Astrophysics, the project links several of the world’s most powerful radio dishes to create a telescope array that discerns detail 2,000 times finer than the Hubble Space Telescope can. As a result, the EHT is expected to offer mankind its first image of the black hole’s ridge, or “shadow,” located 26,000 light-years from Earth.
The array will include the South Pole Telescope operating at the Amundsen-Scott Research Station, as reported by Space.com. The SPT’s advanced capabilities and remote location are key to the array’s technique known as Very Long Baseline Interferometry. VLBI uses the distances between the EHT radio dishes — which stretch from Antarctica through Chile, Mexico, Hawaii, California, Spain, France, Greenland and beyond — to capture the black hole’s signals from several different angles which MIT’s supercomputers precisely combine to produce a data set with much higher resolution than any one dish can manage on its own. The EHT is, in effect, a virtual telescope the size of the Earth.
In observing the black hole’s dynamics, scientists also hope to test Einstein’s theory of general relativity which defines our contemporary understanding of gravity. While Einstein’s theories have been verified in low-gravitational situations such as on Earth and in the solar system, it remains to be seen whether they hold up under the extreme gravitational fields at a black hole’s edge. The EHT project will be conducting these studies in collaboration with BlackHoleCam, a European-led VLBI endeavor with similar objectives.