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The center of our galaxy is a strange place, inhabited by astronomical phenomena such as the Great Annihilator, where subatomic particles constantly destroy each other in huge bursts of energy.
Another inhabitant of our galaxy center is Sagittarius A*, a point-like, variable radio source. It is believed to be powered by gaseous matter falling into a supermassive black hole with around 3 million times the mass of our sun. The problem is, it doesn't always act like a black hole.
Charles H. Townes, a former MIT Institute Professor and provost, delivered the Ford/Nobel Laureate Lecture in physics on Monday to a full house in Rm 10-250 on "The Black Hole at the Center of our Galaxy."
Professor Townes received the Nobel Prize in 1964 "for fundamental work in quantum electronics which has led to the construction of oscillators and amplifiers based on the maser-laser principle." The maser (Microwave Amplification by Stimulated Emission of Radiation) works on same principle as a laser and emits coherent microwave radiation.
At the University of California at Berkeley, where he is now a professor, Professor Townes returned to full-time research and teaching and pursued new interests in astrophysics. His work there in radio astronomy resulted in the first detection of polyatomic molecules in interstellar clouds and the use of molecular spectra to characterize these dark clouds, now an important astronomical field. He and colleagues measured the velocity of gases at various points along the ellipse to help determine whether the black hole existed.
AN OUTER SPACE LAB
Our spiral, pancake-shaped galaxy, the Milky Way, is one of billions of galaxies in the universe. The Earth is around one-third to halfway out from the center, which is around 25,000 light years away, and we can't see the center with visual light because of the gas clouds filled with dust particles that block our view. So scientists rely on other forms of energy -- X-rays, radio waves, infrared and gamma rays -- to "see" the galaxy center.
The black hole at the center of our galaxy is perplexing because it produces intense radio waves but not much infrared radiation. Scientists were finally convinced of its existence when stars in the vicinity were shown to be moving around an ellipse, apparently affected by the monstrous gravitational pull of a nearby black hole.
Although researchers agree that a black hole inhabits the galactic center, many questions remain. "We don't understand the peculiar collection of hot stars there," Professor Townes said. "There are a lot of new stars and not many red giants.
"We don't understand the lack of luminosity from Sagittarius A*. Maybe nothing is falling in right now. Maybe material is falling straight in and not radiating around. Maybe material that falls in collides with gas and squirts out," he speculated. Like around 40 percent of black holes, maybe this black hole just doesn't radiate very intensely.
"We don't have a very satisfactory explanation right now," Professor Townes said. But as scientists continue to track the motion of nearby stars and as they continue to watch for a dramatic event such as a star falling into the black hole, they should have more detailed and precise information in the next 10 years.
"We keep watching," he said. "The galactic center is a wonderful laboratory to observe, to see what's new. It produces things we don't see anywhere else."
Professor Townes is known for research involving the interaction of electromagnetic waves and matter, and also as a teacher and government advisor.
From 1959-61, Professor Townes was vice president and director of research of the Institute for Defense Analysis. He was provost and Institute Professor at MIT from 1961-65.
Professor Townes's principal scientific work is in microwave spectroscopy, nuclear and molecular structure, quantum electronics, radioastronomy and infrared astronomy. He holds the original patent for the maser, and (with Arthur Schawlow) the original laser patent.
In addition to the Nobel Prize, Professor Townes received the 1982 National Medal of Science.
The Ford/MIT Nobel Laureate Lecture Series is part of a collaboration between the Ford Motor Co. and MIT. Several additional lectures are planned during the coming year, said former MIT President Paul E. Gray, professor of electrical engineering, in his introduction.
A version of this article appeared in MIT Tech Talk on April 25, 2001.