During the history of humankind, we have looked up and stared at the center of our galaxy. Most of that time we created stories about it, but now we know some of the facts. If you’re not a space geek, astronomer, or science nut, you may not know what new information has been discovered about the center of the Milky Way. A lot of information has been learned in the course of our lifetime, even if you are only 16 years old.
Dust in the Wind
To see the Milky Way Galaxy requires getting away from bright city lights on a clear night. It looks like a faint cloud running across the sky at an odd angle. What a person sees is light that has traveled from the center of our galaxy for about 26,000 years. Some of those stars are gone, and new stars have formed.
What you may not know is the dim light coming from the central bulge at the center would be brighter than the full Moon if it weren’t for space dust. Near the center of the Milky Way are over ten million stars. If there were no dust we would just see a dazzling glow from the central bulge.
The Story of Black Holes
Our understanding of the Milky Way has coincided with our awareness and understanding of black holes in space. The idea of a black hole was first suggested in a letter by John Michell published in November 1784. The work of Albert Einstein on general relativity led to theoretical work confirming the mathematical possibility of black holes during the first half of the 20th century.
However, the first prospective black hole wasn’t discovered until 1971. At this point, no one suspected that the centers of all galaxies were black holes. It would be 2002 before Max Planck Institute for Extraterrestrial Physics in Germany would produce evidence that a black hole was at the center of the Milky Way Galaxy.
What You Can’t See
The problems with determining a potential black hole are that, 1) as mentioned before, there is too much dust between Earth and the center of the Milky Way galaxy and, 2) a black hole doesn’t emit light. The first problem is solvable by using different wavelengths of radiation other than visible light. Gamma, infrared, and radio waves pass through space dust and allow astronomers to see their source.
The second problem in revealing a black hole is not what they are, but what they do. What black holes do best is produce the pull of gravity. Their gravitational effect is so strong that stars orbit black holes…before they are eaten by it. All astronomers had to do is find an invisible point that stars are orbiting.
Really, Really Fast Stars
It wasn’t as easy as it sounds, but they did it. What is now known as the supermassive black hole called Sagittarius A is at the center of our galaxy. A close group of stars orbit this invisible point at incredible speeds. Astronomers estimate the size of the black hole is big enough to encompass our Sun and extend almost to the orbit of Mercury.
One of the orbiting stars known as S2 comes only as close to Sagittarius A as four times the distance of Neptune is from our Sun. Despite that distance, S2 reaches speeds of 5000 km/s (11 million mph) as it swoops by Sagittarius A and heads back out in a highly elliptical orbit. S2’s orbit takes less than 16 years to make one complete orbit. S2 will make it’s next closest approach in a few months….well, it actually will have happened 26,000 years ago.