Menacingly dark disk of the Milky Way galaxy's central black hole, and the hot gas caught in its gravity, could look like this computer simulation when a network of radio telescopes begins observing next year. Interstellar gas will, however, blur the finer details.
Courtesy of Avery E. Broderick

Key Concepts

• Black holes are among the most mysterious objects in the universe. So far astronomers have observed them only indirectly, from their gravitational effects on stars and from the radiation emitted by hot gas spiraling toward them.
• Astronomers are adapting a network of radio telescopes to produce images of the supermassive black holes that lie at the center of the Milky Way and M87 galaxies.
• Better studies of black holes not only would help explain unusual phenomena produced by the holes but also could test Einstein’s theory of general relativity and provide vital insights into the nature of gravity in extreme situations.

You have probably seen the TV commercial in which a cell phone technician travels to remote places and asks on his phone, “Can you hear me now?” Imagine this technician traveling to the center of our Milky Way galaxy, wherein lurks a massive black hole, Sagittarius A* (Sgr A*), weighing as much as 4.5 million suns. As the technician approached within 10 million kilometers of the black hole, we would hear his cadence slow down and his voice deepen and fade, eventually turning to a monotone whisper with diminishing reception. If we were to look, we would see his image turn increasingly red and dim as he became frozen in time near the black hole’s boundary, known as the event horizon.

The technician himself, however, would experience no slowing of time and would see nothing strange at the location of the event horizon. He would know he had crossed the horizon only when he heard us say, “No, we cannot hear you very well!” He would have no way of sharing his last impressions with us—nothing, not even light, can escape from gravity’s extreme pull inside the event horizon. A minute after he crossed the horizon, the gravitational forces deep inside the hole would tear him apart.

   
Already a Digital subscriber? Sign-in Now
If your institution has site license access, enter here.