Airbrush

Akh, your links say nothing about what direction a comet can orbit the Sun. Does anyone know if all comets orbit the Sun the same direction as all the planets? I don't think so. Long-period comets come from the Oort cloud and I think they go around the Sun in irregular orbits, on any plane, and in any direction. "Long-period comets have highly eccentric orbits and periods ranging from 200 years to thousands or even millions of years..." http://en.wikipedia.org/wiki/Comet

Yes the great increase in surface area, in an instant, is what caused the HiroshimaX30 blast and shock wave, followed by a series of smaller sonic booms when the smaller pieces again fragmented.

Yes, I know, I was just joking. You can call me hairbrush if you like.

Wow, so that might be what it looks like to see a hyper velocity neutron star, punching thru Earth? Not quite, a neutron star at 12 miles across is VERY tiny compared to an 8,000 mile wide Earth. It would be a tiny dot with a thin tail (or how thick a tail could it create?) of Earth material following it. It would go thru Earth like a bullet thru a cloud. But nice poster, never-the-less. Thanks for posting that mountainman. Last I heard, Tunguska level events were every few hundred years for a meteor 50 YARDS across. The recent Siberian blast of 2-15-13 was said to happen once in a hundred years, and it is only 50 feet across.

That's a good question. Just how fast can a meteor or comet impact Earth? I would think it would be a comet orbiting the Sun in the opposite direction. How fast could that be? Halley's comet was moving 43 miles per second as it passed Earth. Probably the highest speed an object can be moving, relative to Earth, would be a high velocity neutron star 600 miles per second. At several solar masses, and only 12 miles wide, would it punch a hole thru the Earth and keep going leaving the Earth behind? Or would it drag the Earth along with it and completely absorb the Earth? Getting back to the recent Russian meteor impact, that was an extraordinary event, once in a hundred years, plus or minus a few decades. There could have been such a 30-Hiroshimas-bomb blast over the ocean or a desolate area, and the nearest human thought it was just lightning and thunder, especially if it impacted in the early 20th century, such as the Brazilian blast of 8-13-1930 which was between 0.1 and 5.0 megatons of TNT. http://en.wikipedia.org/wiki/List_of_meteor_air_bursts http://apod.nasa.gov/diamond_jubilee/papers/lamb/node3.html

The lesson to learn is that when you see a bright flash in the sky, GET AWAY FROM WINDOWS! Or you will have glass shards in your face and eyes. If I noticed such a flash, I confess I would have gazed out the window at it for several minutes, just long enough to get seriously injured. I wonder how many of over 1,000 injured were blinded for life? A report said the shock wave arrived "a couple minutes" after the flash. If the shock wave traveled at the speed of sound (approx 768mph) then 2 minutes would indicate the blast took place about 24 miles away.

It was a once in about a hundred years event. A meteor of 50 feet across, about 10,000 tons, traveling 11 miles per second before impact, exploded 9 - 12 miles high with the energy of 30 Hiroshima bombs or 500 kilotons. It blew out windows 23 miles away. Anyone find any other info about this? I suppose something this large could have crashed over the ocean or desolate area, since the Tunguska event of 1908, without getting any attention, or could be mistaken for lightning and thunder. http://en.wikipedia.org/wiki/2013_Russian_meteor_event http://phys.org/news/2013-02-russia-asteroid-impact-esa.html

"A NASA artist's concept of a vehicle which could provide an artificial-gravity environment of Mars exploration crews. The piloted vehicle rotates around the axis that contains the solar panels. Levels of artificial gravity vary according to the tether length and the rate at which the vehicle spans." This is exactly what I was thinking. It seems very simple to tether two compartments of equal mass by cables and rotate. This creates little stress, only one G. The hub/axis could be attached on any edge of the ISS. The compartments would each have small rockets to return to the ISS in the unlikely event the cables would break and they fly off in opposite directions. Also it would be nice if they don't have to go for a space walk outside to reach the outer compartments. That is why I propose a pressurized structure surrounding the cables. "Having a spinning section and a zero g section connected together makes for complications where they join. The bearing has to be both airtight, and low friction, and reliable, and long lived." I don't know what is so complicated about cables attached to a spinning axis. The cables are not supporting the Golden Gate bridge. Maybe you could elaborate?

Thanks for the info pwagen, very interesting links. However, I was thinking that rather than a spinning disk, like in the movie "2001" just 2 cabins with apartments for the astronauts linked by a long tether. Only the crew quarters would rotate. At the end of a work day, they would climb through a tunnel-tether to their compartments about 50 yards out for sleep and R&R. This would keep them fit for long periods.

"The meteor that crashed to earth in Russia was about 55 feet in diameter, weighed around 10,000 tons and was made from a stony material, scientists said, making it the largest such object to hit the Earth in more than a century." I also heard it was traveling 18 miles per second before hitting the atmosphere and it exploded about 6 miles high, 30 times the energy of the Hiroshima atomic bomb, and yet smaller than the Tunguska explosion of 1908. http://online.wsj.com/article/SB10001424127887323764804578312264130040432.html

Dark matter is so subtle that even our best detection devices are hard pressed to find any evidence of it. Voyager was not designed to find it. Interesting about Voyager's current distance.

Why don't the crew in the spacestation have living quarters that rotate for artificial gravity?

"It may be that the universe we live in is inherently unstable and at some point billions of years from now it's all going to get wiped out," This seems similar to what I had suspected and proposed here many years ago, that another big bang could happen at any time, and I am not an expert at science, just a "hunch".

"As for the "Infinite mass and density" I could be wrong here but if something is infinitly dense, would that not mean that within it's confines it has infinite mass or atleast the most mass that it could possibly have?" ANY amount of matter, confined to zero volume, which is a singularity, has infinite density. Black holes masses is variable from stellar to supermassive, or maybe even microscopic primordial.

There is an episode of "Through the Wormhole with Morgan Freedman" that talks about the universe as a living being, figuratively speaking. Also the "Gaia Hypothesis" speaks about the Earth being a giant living organism that self-regulates to keep conditions optimal for life. http://en.wikipedia.org/wiki/Gaia_hypothesis "One thing we do know is that a black hole sucks in all the matter than comes into contact with it." Not so. Black holes are messy eaters. Most of the matter that comes in contact with them gets spit out in polar jets. "A commonly accepted theory on how the universe came to be is the big bang, which was a singularity of infinite mass and density." Not infinite mass, but perhaps infinite density.

Here is something I discovered on another web site, that refers to "physics.org". "13 light years away: Earth-like planets are right next door February 6th, 2013 "Astronomers have found that 6 percent of all red dwarf stars have an Earth-sized planet in the habitable zone, which is warm enough for liquid water on the planet's surface. Since red dwarf stars are so common, then statistically the closest Earth-like planet should be only 13 light-years away. Credit: David A. Aguilar (CfA) "Using publicly available data from NASA's Kepler space telescope, astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA) have found that six percent of red dwarf stars have habitable, Earth-sized planets. Since red dwarfs are the most common stars in our galaxy, the closest Earth-like planet could be just 13 light-years away. "We thought we would have to search vast distances to find an Earth-like planet. Now we realize another Earth is probably in our own backyard, waiting to be spotted," said Harvard astronomer and lead author Courtney Dressing (CfA). Dressing presented her findings today in a press conference at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. Red dwarf stars are smaller, cooler, and fainter than our Sun. An average red dwarf is only one-third as large and one-thousandth as bright as the Sun. From Earth, no red dwarf is visible to the naked eye. "Despite their dimness, these stars are good places to look for Earth-like planets. Red dwarfs make up three out of every four stars in our galaxy for a total of at least 75 billion. The signal of a transiting planet is larger since the star itself is smaller, so an Earth-sized world blocks more of the star's disk. And since a planet has to orbit a cool star closer in order to be in the habitable zone, it's more likely to transit from our point of view. "Dressing culled the Kepler catalog of 158,000 target stars to identify all the red dwarfs. She then reanalyzed those stars to calculate more accurate sizes and temperatures. She found that almost all of those stars were smaller and cooler than previously thought. When it's young, a red dwarf star frequently erupts with strong ultraviolet flares as shown in this artist's conception. Some have argued that life would be impossible on any planet orbiting in the star's habitable zone as a result. However, the planet's atmosphere could protect the surface, and in fact such stresses could help life to evolve. And when the star ages and settles down, its planet would enjoy billions of years of quiet, steady radiance. Credit: David A. Aguilar (CfA). Since the size of a transiting planet is determined relative to the star size, based on how much of the star's disk the planet covers, shrinking the star shrinks the planet. And a cooler star will have a tighter habitable zone. "Dressing identified 95 planetary candidates orbiting red dwarf stars. This implied that at least 60 percent of such stars have planets smaller than Neptune. However, most weren't quite the right size or temperature to be considered truly Earth-like. Three planetary candidates were both warm and approximately Earth-sized. Statistically, this means that six percent of all red dwarf stars should have an Earth-like planet. "We now know the rate of occurrence of habitable planets around the most common stars in our galaxy," said co-author David Charbonneau (CfA). "That rate implies that it will be significantly easier to search for life beyond the solar system than we previously thought." "Our Sun is surrounded by a swarm of red dwarf stars. About 75 percent of the closest stars are red dwarfs. Since 6 percent of those should host habitable planets, the closest Earth-like world is likely to be just 13 light-years away. Locating nearby, Earth-like worlds may require a dedicated small space telescope, or a large network of ground-based telescopes. Follow-up studies with instruments like the Giant Magellan Telescope and James Webb Space Telescope could tell us whether any warm, transiting planets have an atmosphere and further probe its chemistry. "Such a world would be different from our own. Orbiting so close to its star, the planet would probably be tidally locked. However, that doesn't prohibit life since a reasonably thick atmosphere or deep ocean could transport heat around the planet. And while young red dwarf stars emit strong flares of ultraviolet light, an atmosphere could protect life on the planet's surface. In fact, such stresses could help life to evolve. "You don't need an Earth clone to have life," said Dressing. "Since red dwarf stars live much longer than Sun-like stars, this discovery raises the interesting possibility that life on such a planet would be much older and more evolved than life on Earth. "We might find an Earth that's 10 billion years old," speculated Charbonneau. "The three habitable-zone planetary candidates identified in this study are Kepler Object of Interest (KOI) 1422.02, which is 90 percent the size of Earth in a 20-day orbit; KOI 2626.01, 1.4 times the size of Earth in a 38-day orbit; and KOI 854.01, 1.7 times the size of Earth in a 56-day orbit. All three are located about 300 to 600 light-years away and orbit stars with temperatures between 5,700 and 5,900 degrees Fahrenheit. (For comparison, our Sun's surface is 10,000 degrees F.) From phys.org"

Stars orbiting a supermassive black hole would affect the black hole as much as a fly buzzing around an elephant. In a binary system of black hole and star, the star would have negligible effect on the black hole, compared to the effects the black hole have on the star by eating it.

"Even an infintesimal force will change an orbit." An orbit is not the same as the GRAVITY in a galaxy, vs dark energy. "There is nothing in Wikpedia article that gives any logical answer to why galaxies are exempt from the expansion of space." - Yes it does, GRAVITY. "I originally asked for a logical explaination of why galaxies don't expand like everything else. No answer was forthcomming." - Yes it was, GRAVITY. I responded with a straighforward example." - No you didn't, your example is convoluted. "I am just asking for a believable reason." - Here it is again, GRAVITY. "All of the respondents must know that is not intuitive or kind to common sense that space is expanding along with everything in it except galaxies." - No we don't. It is perfect common sense that GRAVITY is stronger than dark energy on local scales. Not only don't galaxies expand but galaxy clusters don't expand, and galaxy superclusters don't expand. "My question has not been answered." - A number of people here believe your question has been answered redundantly. Everyone is crazy except for you? "Thanks to everyone that has posted or read this thread." - You are welcome, and I don't know why I bother to post this, I guess I like you in spite of your difficulty, and I don't understand the unlimited patience of those who made the effort to explain GRAVITY to you, but in vain, they must like you also.

Lazarus, your questions don't make sense. I don't know what you are talking about. Your question has been answered redundantly. Are you just trying to be difficult? I have no problem with the explanations given above by ACG & Zapatos, but your questions and speculations seem baseless. You want someone to draw you a map to a book about cosmology?

The question is what is at the center of a black hole if not a singularity? I think Hawking is an expert on black holes, and he refers to a singularity in a black hole. He does not refer to something with a size, unless I am mistaken.

"The force is inversely proportional to the square of the distance." Thank you for the correct answer to this question and the other information too.

"What is the rate at which a black hole's gravity weakens as one gets further away?" Gravity weakens at a rate directly proportional to the distance between the objects. "If I know my physics correctly, the singularity at the center of a black hole has infinite mass." Infinite density, not infinite mass. "If two black holes were to converge, would the black hole with less mass get drawn to the center of the larger one? Because, if entering an event horizon requires infinite energy or mass to escape, and two event horizons are slightly overlapping one another, would they stay locked together or would the smaller one collapse even further and reach the singularity at the center of the larger black hole?" The two would behave exactly the way any two massive objects (stars, planets, moons) would behave when they approach each other. Usually this results in them spiraling inwards until they merge, which must be an incredibly immense release of energy, however that energy is not "released" but mostly contained inside the new more massive black hole. I wonder if mere spin would be enough to stop two supermassive black holes (SBH) from eventually merging? Could masses that great avoid each other? But interesting concept nevertheless. "According to simulations made by G.A. Shields from the University of Texas, Austin, and E.W. Bonning, from Yale University, the result is often a powerful recoil. Instead of [sBH] coming together nicely, the forces are so extreme that one black holes is kicked away at a tremendous velocity. The maximum kick happens with the two black holes are spinning in opposite directions, but they’re on the same orbital plane – imagine two spinning tops coming together. In a fraction of a second, one black hole is given enough of a kick to send it right out of the newly merged galaxy, never to return...." That would be a hypervelocity SBH. Has anyone heard of that? "Do you think that nature has made it impossible for black holes to overlap to avoid the consequences of it by making them spin off of each other? Or do we just not have the ability to figure out what happens when they overlap." Not at all. SBHs probably merge most often when galaxies collide, with perhaps rare cases when both have extreme spins in opposite directions. If most SBHs did not merge when galaxies collide, then wouldn't there be evidence of wondering hypervelocity SBH?

Thanks for the link Arch, I intend to review that later. I do believe you are very near what I was looking for.

"...If something should travel faster than light inside the event horizon, then it would escape, which is not possible." The kind of faster-than-light travel the astonomer was referring to is in the other direction, inwards towards the singularity. Now I remember it was a guest astronomer on an episode of "Wonders of the Universe" with Brian Cox. The astronomer was standing next to a waterfall. The waterfall was a metaphor for matter flowing into a black hole.

No matter travels faster than light in space, but the region inside a black hole is not "normal" space. So faster than light speed for matter passing the event horizon onward to the singularity is plausible. That would be a kind of reverse inflation. The laws of Physics, as understood, can break down upon entering a black hole. Or at least the laws of physics inside a black hole are beyond us.