Search for galactic in Topics


Have we see the event horizon of the Galactic black hole?

A preprint submitted to the Astrophysical Journal (Ap.J.) last week makes a compelling case for conclusive observational evidence for an event horizon at the compact object Sagittarius A* (Sgr A*) at the center of the Milky Way galaxy. Recent observations with mm radio waves have determined Sgr A*'s mass , distance and diameter (Nature 455, p.78), which make it "very likely" to be a black hole, unless there is some sort of exotic physics leading to a compact, but still extended and visible, object at that location.This new paper uses very general arguments from energy conservation and radiative efficiency to demonstrate that it is "impossible" for the object at Sgr A* to have a visible surface onto which accreting material collects and radiates. While the authors go through calculations in standard General Relativity for demonstration, their results hold much more broadly than that, covering any gravity theory which includes stationary solutions (i.e., horizons).If there is an object with a real surface at Sgr A*, then all the material falling in must either give up it's full potential energy into radiation as it is falling, or we should see a separate, thermal spectrum from the surface of the object itself. The Sgr A* spectrum is extremely non-thermal; any thermal component is less than 0.4% of the total luminosity we see. That is equivalent to saying that the accretion efficiency (how much radiation you get from the falling material) must be at least 99.6%, compared to the actual efficiency estimated at 0.01 to 1% for Sgr A*.On the other hand, a "horizon" by definition is a position in space "below" which photons just can't get out. Material can fall through a horizon with no difficulty, but we will never see it, or any radiation from it, again. Whether there is a black hole or some other exotic object inside the horizon, it is invisible. The accreting material's luminosity may well be "low" (as observed); the rest of its potential energy is "lost" to our observation when it falls through the horizon.

Topic by kelseymh    |  last reply


Spore v.s. Galactic Civilizations

The new spore expansion pack is coming out soon and I'm deciding between that and Galactic civilizations II with expansion packs. I think spore gets boring after a certain point and so have every civilization type game I've played. Which should I get?

Topic by starwing123    |  last reply


What would happen if you stopped a galaxies rotation?

I mean a total complete standstill, every dust particle and bit of matter stopped moving rotationally in relation to the galactic center. Would the gravitational effects drag everything to the center if it stopped rotating over a few million years or would everything fly off in a straight line if it stopped instantaneously and eventually fall back into the center? 

Question by The Ideanator    |  last reply


Finding googols without a search engine!

It is not often that you encounter a googol as a "measured" (or inferred) quantity referring to something physical. A preprint out today on arXiv:astro-ph presents a calculation of the total entropy of the observable Universe (in units of Boltzmann's constant, k), coming up with a result Sobs = 3 × 10104 k. The dominant contribution is from supermassive galactic black holes, for which the entropy is proportional to their surface area, which in turn scales like the mass squared.

Topic by kelseymh    |  last reply


Take over the world easily!

So you want to take over the world? Well here's the steps! 1. Genetically and cybeneticaly enhance an army of ducks 2.Create Orbital Tungsten Bombardment System (O.T.B.S)  3 Aim your O.T.B.S at major oil/uranium fields.  4 While superpowers try to stop you move in And eliminate most humans with your ducks. 5. Blow up the planet and move to Mars OR attempt Galactic Domination

Topic by Jack The Supreme Duck Overlord    |  last reply


universe expanding forever?

I saw this article on the BBC news site: http://www.bbc.co.uk/news/science-environment-11030889 which has some astronomers apparently claiming that they have now worked out the fate of the universe from measurements on distant stars magnified through a galactic cluster. The final quote is: Professor Priyamvada Natarajan of Yale University, a leading cosmologist and co-author of this study, said that the findings finally proved "exactly what the fate of the Universe will be". This seems like a pretty bold claim to me - I was thinking that even if we had a lot of such measurements then we would still only be working out the geometry of space/time in the region of our universe that we are capable of seeing. This is likely to be only a small part of the whole universe due to the galactic horizon imposed by the age of the universe against the speed of light. Also, even assuming that the whole universe of 3D space and time that we live in behaved the way they are saying, this is still only working out what would happen due to the universe's own internal dynamics - there are ideas coming out now about our universe being part of a wider multiverse outside the realm that we experience as normal space and time, so even if the universe did expand into a "cold dead wasteland", then something could possibly infringe upon it from outside space/time and make something different happen at any time in the future. Some of what's going on here is just bad journalism - there's a longer article here: http://pda.physorg.com/darkenergy-universe-magnifyinglens_news201427857.html which gives a fuller version of the same quote: "The geometry, the content and the fate of the Universe are all intricately linked," says Natarajan. "If you know two, you can deduce the third. We already have a pretty good knowledge of the Universe's mass-energy content, so if we can get a handle on its geometry then we will be able to work out exactly what the fate of the Universe will be." This is a bit more cautious but there's still this idea that by making measurements like this from just one point in space and time we can work out the fate of the whole universe, which I don't really believe. So I reckon these sort of predictions should be taken with a massive pinch of salt, rather than definite statements of what we know. Which may be obvious, but I wanted to say it and see what anyone else thinks?

Topic by ganglion    |  last reply


Dance of the Scientists

So you think you can defend your research in front of a panel of experts? How about if you had to do it... with interpretive dance.No, this is not a joke. This is the first annual Dance Your Ph.D. Contest. Read this description and hit the link for videos of the dances....the diversity of the dancers was nothing compared with the diversity of their output. The graduate student category is a case in point. The first dance, Gruetzbauch's 30-second galactic tango, focused on one phenomenon: the capture of a galaxy by a larger one. Schraffl gave us raw data—a small scene from Il pittore parigino by Domenico Cimarosa—without analysis or metaphor. Sven Ramelow did a bit of both. His quantum physics Ph.D. title allowed him to make a play on words: The acronym SPUC is a homophone of a German word for ghost, and hence the scary sheet dance. Meanwhile, he used a laser light attached to his head to illustrate the strangely behaving photons he studies. (Very clever.) But then came Brian Stewart.No one was surprised when he scooped the prize. For one thing, Stewart wore nothing but a shimmering, translucent loin cloth. (That's worth a few bonus points in my book.) But the judges told me afterward that his dance stood out because it accomplished two things at once. Most importantly, "he connected with the audience," said Pastorini. "That is the purpose of dance: to create emotions." A big help was his choice of music a jazz interpretation of African Pygmy tribal music by Herbie Hancock which created an atmosphere of funky ancientness. Dance Your Ph.D. Contestvia Neatorama

Topic by fungus amungus    |  last reply


Designing a different / customized kind of computer system?

I've read about how when you Install the windows OS onto a usb stick It's unique to that computer (b/c of specific drivers, specs, hardware etc... and yes, It Is possible with some tweaking, don't spout out propaganda you're fed from Microsoft and apple). I'd like to know what it would take to design a generic computer that all you would have to do is plug in your personal drive and your OS (whichever it may be) and files are programs all there ready for use. And also be made in such a way that if the 'terminal' were duplicated part for part, no matter which one your drive was plugged Into It, would work the same. I'm thinking of designing a kind of system like this- drawing on elements from sci-fi (which is obversely based on the real world) In Stargate Atlantis and Battlestar Galactica (reimagined version). In Stargate Atlantis, Atlantis Is a cIty-shIp that has In Its Infrastructure the hardware, database, and OS, which is accessible from the hundreds of terminals throughout; each one is like a separate pc but are all connected to the database and processing power of the city as a whole. In a similar way, In Battlestar Galactic, the Galactica class Battlestar has a closed network which they rely on Instead of wireless to prevent cyber-attacks from the cylons... but the only advantage I care about Is that data transfer Is much faster via wires, and fiber optic cable even more so. With the amount of products and parts available on the market today, budget is the only limiting factor. I know many people are programmed to say, "It’s not possible" or immediately shoot it down by saying how hard it would be, and that I should just buy a computer and be happy. But I am not just a consumer, I’m an artist, a designer, I’m not going to let other people call the shots just so they get a profit. Now I know Linux has the sort of open source availability I like, but I’m not too familiar with It and I’d like the project to be user friendly as well as geek friendly If the user so chooses (like an optimized combination of apple, Microsoft, and Linux). I will no doubt read around at the library and online, but I wanted to hear from people who already have experience and know what I’d be better off learning and what I’d be better off skipping altogether.

Question by ranosonar