Astronomers are closing in on the dark monster at the center of our galaxy. New radio telescope images indicate that an invisible concentration of material at the Milky Way's core is some 4 million times as heavy as the sun and squeezed into a region no larger than the distance between the sun and Earth. That's half the distance that previous observations had indicated, making a more compelling case that the concentrated mass must be a black hole.
Zhi-Qiang Shen of the Shanghai Astronomical Observatory in China and his colleagues homed in on Sagittarius A*, a radio-emitting structure powered by the giant black hole proposed to reside at the galactic center. Using the Very Large Baseline Array of radio telescopes, the researchers obtained the highest-resolution image ever recorded of Sagittarius A*.