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How we discovered the black hole in the center of our galaxy

On Thursday, astronomers announced the first observations of the effect of the gravitational redshift of a black hole – light from a star in the gravitational field near a black hole looked redder than outside the black hole.

The responsible black hole was Sagittarius A * (pronounced "Sagittarius A-Star"), the supermassive black hole in the center of our Milky Way. Astronomers believe that most large galaxies like the Milky Way should have supermassive black holes in their centers, but only in the last few decades did they have convincing evidence that Sgr A * is our supermassive black hole.

The discovery of Sgr A * is attributed to two astronomers, Bruce Balick and Robert L. Brown, who in 1

974 published a paper describing a bright radio source in a small region in the center of the Milky Way.

Astronomers have known for a long time that there were many radio waves near the center of the Milky Way. Karl G. Jansky, a physicist who works for Bell Telephone Laboratories, tried to figure out which static sources the telephone company would face when stumbling over the discovery in the early 1930s. Jansky wanted to continue researching to find out why radio waves came from interstellar space, but Bell Labs was not interested and no one followed this discovery for several years.

Although the radio source was discovered in 1974, the name Sgr A * did not appear until 1982. Astronomers had suggested a few other names, like GCCRS (for Galactic Center Compact Radio Source), but they did not understand each other. Brown proposed the name Sagittarius A *, as the source was in a larger radioactive structure called Sagittarius A. The star notation was used in atomic physics for atoms in a high-energy state, and Brown considered this a good analogy for the compact radio source that supplies energy to its environment.

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