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Have you ever wondered what is at the center of the Milky Way? Don’t worry, you are not alone. Scientist have wondered that since our galaxy was named. Well, it is believed to be a supermassive black hole and it is named Sagittarius A-star(Sgr A*). The phenomenon is about 26,000 light years from Earth. Astronomers believe that there is a supermassive black hole at t eh center of all galaxies.
Sgr A* is an astronomical radio source that is believed to be 4 million more times massive than our Sun, but on takes up about 1 AU in diameter. If it is not a supermassive black hole, then it would have to be a few million stellar remnants all compacted in one area. So many remnants could only survive several thousand years before becoming a black hole anyway, so to differentiate could only be playing with semantics.
The mass of Sgr A* has been estimated in two different ways. One method monitored the orbits of stars very near the black hole and applied Kepler’s laws to calculate the enclosed mass. This rendered two values: 4.31 ± 0.38 million solar masses and 4.1 ± 0.6 million solar masses. This mass is confined to a 44 million km diameter, so either estimate yields a density ten times higher than previous estimated. The second method measured the proper motions of several thousand stars within one parsec of the black hole, applied some statistics, and yielded the black hole’s mass and the distributed mass in this region. The black hole mass was found to be consistent with the first method and the distributed mass was found to be 1 to 1.5 solar masses.
The black hole itself is never seen, but the observations are only consistent if there is a black hole present near Sgr A*. The observed radio and infrared energy emanates from gas and dust heated to millions of degrees while falling into the black hole. Although other possibilities exist for how these gases emanate energy, interaction with a massive source of gravity is the simplest explanation known to man.
It would be great if you asked ‘what is at the center of the Milky Way’ and it was some one of a kind phenomenon, but a supermassive black hole is probably at the center of every other galaxy we will ever discover.
We’ve also recorded an episode of Astronomy Cast about the Milky Way. Listen here, Episode 99: The Milky Way.