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Astronomers Find Star-Less Galaxy
Wohngebaeudeversicherung writes "Astronomers have discovered a galaxy about 50 million lightyears away from earth that appears to be composed entirly of dark matter. This galaxy, dubbed VIRGOHI21 is rotating like a real galaxy, at speeds only explainable through massive amounts of matter, thought no single visible star could be detected."
...and it doesn't require exotic quarks, leptons, or baryons to work.
Okay, that's an enormous (and highly unlikely) exaggeration, but I *have* thought of an interesting possibility. A Dyson Sphere surrounding several stars (or in a Type 3 civilization, an entire galaxy) would block visible light - the problem is it would glow in the infrared, so it wouldn't really be dark. Black holes are dark, but they tend to fling stuff around, and matter sucked into them gives off bursts of energy before they disappear.
The solution: a dark bubble. At the center of our galaxy there is a supermassive black hole, which is (according to some estimates) roughly three million solar masses. A civilization putting a bubble around it would have 1 (earth) gravity a little beyond the orbit of Pluto, perhaps 40-45 A.U. or so. The problem is that you still would need to stick some stars around it to supply energy, and a Klemperer rosette would be pretty noticeable.
Well, light falling onto a blackhole blue shifts, increasing its energy. Increase the bubble enough (remember, we're talking a civilization that can harness the energy of a galaxy), and the mass of the bubble itself starts to warp space around it. There comes a point where the size of the bubble and the mass that makes it up can be just under the Schwarzschild limit - a bit more massive and it would be a black hole - even without a central singularity. For humans, we'd want a bubble that has a surface gravity equal to earth's, and a blue-shifted energy equal to the average output from our sun.
As a back-of-the envelope calculation, using v^2=2*g*R, where v is the escape velocity, g is the gravitational attraction at the earth's surface, and R is the radius from the center of mass, and setting v=c (the speed of light) for the maximum size, you get a bubble with a diameter just a bit under a light-year across (354 light days, if I figured correctly). The surface area would be about 3 square light-years, 2.6 x 10^26 square kilometers, or 5.2 x 10^17 times the surface area of the earth. The mass would be equivalent to 1.5 trillion suns - roughly twice the mass of our galaxy. Assuming you use buckytubes as the material of choice, you'd have a shell 7000 kilometers thick of solid buckminsterfullerene.
Of course, this is the absolute maximum size and mass just before it becomes a black hole, so the actual construct would be a bit smaller and less massive, balancing surface gravity and blue-shifted energy hitting the surface. You'd also want to carve out mountain ranges and oceans for a bit of variety - a galactic Kansas would be kind of boring. For safety reasons, you would have to stick these bubbles in the empty space between galaxies, or just use all of the mass in one large galaxy (you'd have to be careful, though, to keep relativistic rocks from flying at the completed project). You'd have a sky that would look kind of like a slow-moving aurora, perhaps -- infrared would be shifted into visible light, visible stars would have their peak shifted to ultraviolet -- especially since the gravitational warping would slow down time considerably compared to the rest of the galaxy.
To detect them, you'd have to aim telescopes at the "empty" parts of the sky and see if there was any gravitational lensing. If something was there that was far too massive to be a neutron star but didn't have the characteristics of a supermassive black hole, that could be a sign of it. The largest ones would have the gravitational mass of a large galaxy, so if a supercluster appears to be missing a galaxy's worth of stars that stellar motions demand, it might not be exotic matter but instead bubbles of normal matter from some vast engineering project.
Of course, it might be too early in the evolution of the universe for a type 3 civilization to appear, or you might not be able to make a buckytube bubble big enough that would also support its own weight, so exotic forms of matter might still be necessary. One thing's for certain, though - a bubble like this would make Ringworld look as spacious as a phone booth.
It was easy to disprove the existence of aether with the Michelson-Morley experiment. Had that experiment not been possible it would have been very premature to jump to the conclusion that there is no aether. When it comes to dark matter, there is no easy experiment to disprove its existence and so it would be very rash to conclude that our understanding of gravity, which has worked extremely well for us for hundreds of years, is wrong.
Not really.
Serious scientist DO say when they have no idea.
Dark matter indicates that there is a whole field of physics out there and that we're in the state of peaking through the keyhole atm, before opening the door. BTW, this is what the article states, just worded differently when it says something about starting to understand things.
It takes a man to suffer ignorance and smile
Be yourself no matter what they say
This may or may not be true - for example, for my personal Dyson sphere I was displeased by the loss of energy caused by alowing the radiatated energy from the sun to spread over the large volume of my sphere (The effective temperature goes down as you get farther away from the sun), so I made my Dyson's sphere reflective on the inside - focusing the light towards two points on the top and bottom of the sphere. That lead my sphere to emit strongly from the top and bottom, but not at all from the sides.
It increased thermal conversion effeciency by 50%, making me the envy of all the other Spheriods.
while (sig==sig) sig=!sig;
If you then made one of those points perfectly reflective and radiated all extra energy out the one point, you could use it as a method of propulsion. You'll that the fastest spheroid around.
...or they could be a Type III civilization, capturing the energy output of that entire galaxy with one giant device.
"...always new atoms but always doing the same dance, remembering what the dance was yesterday." -Richard Feynman
TFA says this object is "a mass of hydrogen atoms a hundred million times the mass of the Sun."
It may be unusual that none of this hydrogen has ignited in a fusion reaction, but that doesn't change the fact that hydrogen atoms are baryonic matter, quite common here on earth. (There are quadrillions of them in my body right now.)
Later, TFA says "according to cosmological models, dark matter is five times more abundant than the ordinary (baryonic) matter that makes up everything we can see and touch."
So this object is "dark" in the sense that it doesn't emit visible light, but it's not Dark Matter.
Or am I missing something here?
That that is is that that that that is not is not.
There is both baryonic and non-baryonic dark matter. Astronomers worry about understanding both. HI isn't bad because it emits 21 cm radiation (although very weakly), but things like black holes, low-mass dwarf stars, cool white dwarfs and neutron stars, all count toward dark matter. There is a lot more non-baryonic dark matter, absolutely, and it dominates galaxy masses and is indeed the primary thing of interest here.
Professor of Astronomy, Author of Spider Star & Star Dragon (Tor)
Don't confuse people with the religion they practice. Bear in mind that Copernicus was scared to death of the church and wouldn't come out with his actual findings, one of his friends had to do it for him after he died. When Giordano Bruno not only pushed them publically, but suggested that other worlds and life may exist somewhere off of earth, he was tried by church and burned alive. Galileo was tortured and tried and forced to renounce his belief in Copernican theories for going against the church's geocentric view of the universe.
Further, bear in mind that Isaac Newton lived at a time when the church was under greater state control than was typical throughout its history and even received special treatment from the Church of Englad (courtesy of the King) such as the decree - still in effect today, currently on Stephen Hawking - that the Lucasian professor need not take Holy Orders, something nobody else can do. Furthermore, Newton's findings on gravitational fields did not directly challenge any particular belief held by the church.
The notion that science benefits significantly from religion is idiotic. It suggests in a subtle manner that the reason scientists succeed is that they're given baseless conclusions to smash, but that's not the case. Copernicus didn't go looking to beat up the Ptolemic model for the universe and didn't even want to accept his own findings. Galileo didn't go looking to beat up the Geocentric model of the universe. Einstien even rejected some of his discoveries - which are now turning out to be accurate to varying degress - with the famous quip "god doesn't play dice".
Religion is a crutch for people who want to know the "why" of something but don't want to go to all the trouble of following the "how" backwards long enough to get a real answer. People wouldn't be religious if they were clear, critical thinkers because the idea of making non-time-sensitive judgements on faith is an absurd thing born of ignorance and fear. Taking on religious beliefs is like wandering around in the dark and coming to a pit in the floor. Religious people would just back up and take a running jump not know how wide or deep it. Smart people would run some tests like dropping pebbles into it to depth test and trying to determine the width before they jumped. Rare is the case where you'd be forced to simply jump on faith and not be stupid for doing so such as, for example, because you are being chased by a wild animal or something.
Alito: A vote for Alito is a punch in the eye to put that bitch back in her place!
It's a very well supported hypothesis based on empirical evidence. The only viable alternative would be that we have gravity very, very wrong on large scales, and the evidence is against that. On the other hand, the evidence for non-baryonic dark matter comes from a number of areas, not just galactic motions. One form of non-baryonic dark matter you probably know something about is the neutrino, which apparently does have a tiny mass based on recent experiments demonstrating oscillations, but other considerations indicate that neutrinos are far from the dominant type of dark matter. Thirty years ago, your level of skepticism would have been appropriate. To experts in the field today, it's a no-brainer. What the stuff actually is, however, is still largeley unknown.
Professor of Astronomy, Author of Spider Star & Star Dragon (Tor)