Amusing Information About Stars
Our sun is a dwarf star. We are accustomed to think of the sun as a “normal” star, and in many respects, it is. But did you know that it is a “dwarf” star? You may have heard of a “white dwarf,” but that is not a regular star at all, but the corpse of a dead star. Technically, as far as “normal” stars go (that is, astronomical objects that produce their own energy through sustained and stable hydrogen fusion), there are only “dwarfs,” “giants” and “supergiants.” The giants and supergiants represent the terminal (old age) stages of stars, but the vast majority of stars, those in the long, mature stage of evolution (Main Sequence) are all called “dwarfs.” There is quite a bit of range in size here, but they are all much smaller than the giants and supergiants. So technically, the sun is a dwarf star, sometimes called “Yellow Dwarf” in contradiction to the entry above!
Stars don’t twinkle. Stars appear to twinkle (“scintillate”), especially when they are near the horizon. One star, Sirius, twinkles, sparkles and flashes so much some times that people actually report it as a UFO. But in fact, the twinkling is not a property of the stars, but of Earth’s turbulent atmosphere. As the light from a star passes through the atmosphere, especially when the star appears near the horizon, it must pass through many layers of often rapidly differing density. This has the effect of deflecting the light slightly as it were a ball in a pinball machine. The light eventually gets to your eyes, but every deflection causes it to change slightly in color and intensity. The result is “twinkling.” Above the Earth’s atmosphere, stars do not twinkle.
You can see 20 quadrillion miles, at least. On a good night, you can see about 19,000,000,000,000,000 miles, easily. That’s 19 quadrillion miles, the approximate distance to the bright star Deneb in Cygnus. which is prominent in the evening skies of Fall and Winter. Deneb is bright enough to be seen virtually anywhere in the Northern hemisphere, and in fact from almost anywhere in the inhabited world. There is another star, Eta Carina, that is a little more than twice as far away, or about 44 quadrillion miles. But Eta Carina is faint, and not well placed for observers in most of the Northern hemisphere. Those are stars, but both the Andromeda Galaxy and the Triangulum Galaxy are also visible under certain conditions, and are roughly 15 and 18 quintillion miles away! (One quintillion is 10^18!)
Black holes don’t suck. Many writers frequently describe black holes as “sucking” in everything around them. And it is a common worry among the ill-informed that the so-far hypothetical “mini” black holes that may be produced by the Large Hadron Collider would suck in everything around them in an ever increasing vortex that would consume the Earth! “Say it ain’t so, Joe!” Well, I am not Shoeless Joe Jackson, but it ain’t so. In the case of the LHC, it isn’t true for a number of reasons, but black holes in general do not “suck.”
This not just a semantic distinction, but one of process and consequence as well. The word “suck” via suction, as in the way vacuum cleaners work, is not how black holes attract matter. In a vacuum cleaner, the fan produces a partial vacuum (really, just a slightly lower pressure) at the floor end of the vacuum, and regular air pressure outside, being greater, pushes the air into it, carrying along loose dirt and dust.
In the case of black holes, there is no suction involved. Instead, matter is pulled into the black hole by a very strong gravitational attraction. In one way of visualizing it, it really is a bit like falling into a hole, but not like being hoovered into it. Gravity is a fundamental force of Nature, and all matter has it. When something is pulled into a black hole, the process is more like being pulled into like a fish being reeled in by an angler, rather than being pushed along like a rafter inexorably being dragged over a waterfall.
The difference may seem trivial, but from a physical standpoint it is fundamental.
So black holes don’t suck, but they are very cool. Actually, they are cold. Very, very cold. But that’s a story for another time.