THE USM SOUTHWORTH PLANETARIUM
70 Falmouth Street Portland, Maine 04103
43.6667° N 70.2667° W
Altitude: 10 feet below sea level
Founded January 1970
Julian date: 2458588.35
"Heavens above!!!"
THE DAILY ASTRONOMER
Monday, April 15, 2019
Black Holes I
Well, we are delighted to report that our invitation to send black hole questions elicited such a response that we will have to devote two DA's to answering them! Thank you to the subscribers who submitted these queries. I hope the responses prove helpful.
As always, please keep those cards and letters coming! I am only using the subscribers' initials for attribution.
"I have a silly question about the black hole: Is it something of concern for our planet either in the near future or thousands of years from now?" -M.H.
First, there are no silly questions! Einstein once asked the 'silly' question, "What would light beam look like if I could run next to one?" We see where that question lead him.
Now, as to your question. The closest known black hole, V616 Monocerotis, is 3,460 light years away. If that, indeed, is the closest black hole to the solar system, we can breathe easy, at least about black holes. Our solar system and V616 Mon will come nowhere near each other. That having been said, it is possible that other black holes are closer. We know about the black hole within the V616 system because it has a visible companion that exhibits motions that indicate the presence of a nearby black hole. We wouldn't be able to observe any isolated black holes that might be closer. However, we really shouldn't worry about them because there are about 100 million scattered over the entire galaxy, which is unfathomably large. Also, notice that Earth is about 4.5 billion years old -if you believe the heretics-. If a black hole had ventured close to our planet at all during those 4.5 billion years, Earth would have been ripped apart. No black hole yet and I do believe we're safe.
"Why haven't they photographed the black hole in the center of our galaxy? Is that farther away than the black hole they did photograph?" - C.S.
Strangely enough, the black hole in the center of our galaxy, Sagittarius A*, isn't massive enough to have been imaged in the same way that astronomers imaged the supermassive black hole in the center of M87. The M87 black hole is 6.5 billion times more massive than the Sun, whereas Sagittarius A* is about 4 million times more massive than our parent star. Consequently, the M87 black hole isn't nearly as turbulent as the one in the center of the Milky Way. In order to image such a black hole using the array of telescopes, it must remain "still." A highly massive black hole will be stationary, whereas a "lighter" one will not, making it exceedingly difficult to image.
"Why are black holes located in the center of galaxies?"
-W.L.
Astronomers are now convinced that each galaxy contains a supermassive black hole in its center. It turns out that one cannot have a galaxy without a supermassive black hole to provide the gravitational pull necessary to maintain the galaxy's cohesion. The supermassive black hole forms from the inner material contained with the galaxy. One cannot have one without the other. The unresolved issue pertains to the formation order: do they form together or does the supermassive black hole form first? We don't know.
