Astronomy and Cosmology

First, is it valid that as an object gains momentum-energy, it also gains gravitational-mass? Second, if it does and you have very massive fast-moving object orbiting around a black hole, could the gravity stretch spacetime in a way that expands the black hole beyond its Schwarzschild radius? edit: if nothing else, could it decrease the relative density of the black hole in a way that would increase its rate of Hawking radiation?

If all EM interactions are conveyed w/ virtual photons, then does that imply that Gravity interactions are conveyed by virtual gravitons ?

Hi, I have a question: I read many place that space expansion is not proper motion. That faraway galaxies doesn't move but are caried by space expansion. So if today a galaxy is mesured to be 1G lightyears away, in 1 millions years that galaxy will still be 1G lightyears a way because she have no proper motion. If I go back in time, the same will be true. No need for a bigbang... where am I wrong in my reasonning ? Thanks

Imagine simulating the evolution, through time, of the Local Group (say). You create, in computer, several spiral galaxies, and a slew of spheroidals, and evolve them for billions of years. You plot their paths through space & time. Now, imagine re-doing that simulation, starting from the same initial conditions, but "jiggering" all the stars' initial positions, by +/- several light-years, in random directions. Then, re-run the simulation, for the same amount of time. Would varying all the positions, of all the billions of stars comprising a galaxy, by a few light-years, in varying directions, ultimately affect the global, bulk motion, of that galaxy, throu…

In this topic, I wish to discuss the many ways to potentially terraform Titan. I am pretty sure that this has been done, but two topics are better than one, are they not? And it will help me with a science fiction series I am writing. I wish to use the most scientifically accurate way to terraform Titan. Mars has already been done in this series but the human population has reached 15 billion at this point and we have already begun living under Europa's ice sheet. Please note I am only 15 at the moment but I do have an exceptional knowledge of astronomy and astrophysics compared to most people. I understand the basic concept of gravity and atmospheric pressure and so on.…

I am not sure where to post this thread. Sorry if it is the wrong place. If it is, please move it to the correct forum, thanks in advance Hey How come our universe still exists? According to what I know our universe was created from a singularity, the big bang, a so called explosion. If everything, including all matter and energy, was created at the time of the big bang, then all matter must have been squeezed together in the first nanoseconds of our universe. How come that there wasn't a black hole, when all the matter from our universe was squeezed into that small place in the first second? If there was a black hole, how come our universe still exis…

Splitted from a tooo long thread: That is correct. What happens to Minkowski spacetime when one dimension is taken away? From the 4 dimensions x,y,z & t, eliminate z for example. The resulting reduced spacetime x,y,t looks quite a lot with Euclidian space, or do I miss something?

In flat spacetime, differential distances & times are measured within the spacetime fabric. In the Schwarzschild spacetime, differential radial distances can be defined within the spacetime fabric, from [math]r \equiv circumference / 2 \pi[/math]. What about 'time', in the FRW cosmology solutions? Is 'time' measured fully within the spacetime fabric, so that the time is the 'integrated length' measured along the hyper-surface of spacetime? Or, is 'time' an 'absolute coordinate', measured along the 'vertical hyperspatial axis' of a closed cosmic spacetime??

Mass curves spacetime, and curved spacetime tells mass how to move (Wheeler. Journey into Gravity & Spacetime). Thus, when one witnesses an anomalous movement of matter (e.g., Galactic Rotation Curves), one is witnessing an anomalous curvature of spacetime, not an anomalous matter distribution directly. Therefore, is it possible to explain Galactic Rotation Curves, without invoking 'Dark Matter', so much as 'Dark Curvature' ??? Simply as a suggestion, if our Cosmos is closed, and if under-dense, evacuated, voids 'poof outward', wouldn't that extra 'outward swelling' of the spacetime, of voids surrounding some mass concentration (e.g. galactic group), impose a 'p…

Is there a differance between the geomagnetic field of the Earth,and the magnetic field of a magnet? And how far does the Earth's geomagnetic field reach into space?

Is it 'mere mortal-humanly feasible', to solve for the Schwarzschild metric, when the gravitating central mass, is embedded in a non-vacuum, uniform/isotropic/homogenous background closed cosmic spacetime ?? What is the metric? Naively, simply 'slapping the two together', one could come up with: [math]ds^2 \propto \frac{dr^2}{1-\frac{r}{R_C} - \frac{R_S}{r}}[/math] Such a solution would be 'Schwarzschild-like', near the gravitating body, but meld back into the 'Friedmann-like' background, at great distances. Note that if you could solve for the metric, you'd be able to tell, whether gravity over-densities, in a closed cosmos, 'sag down' radially inward, or 'po…

I suppose what I'm asking here is will there ever be preventive measures put in place to present a catastrophic event caused by asteroid impact such as what happened to the dinosaurs? Never mind that, to my knowledge, there isn't even any serious research being done on ways to re-plot the course of an asteroid away from Earth or destroy it, is there? How long will humanity cross there fingers and hope that such a thing doesn't happen without actually doing anything to prepare for if it does happen? I guess I should also ask, do any of you think its even worth it to put funding into research for this at this point? Our detection methods for detecting these things aren't …

Hi, I understand that many of the plans to explore the solar system involve using a sling shot technique around other planets to increase speed to the more distant ones. In fact Nasa used this around the moon to get back to Earth. What I have trouble understanding is where this energy comes from. In effect energy (speed) is transfered from "somewhere" to the object that is sling shot'd. Gravity is used in a very specific way - close enough to feel effect but not too close to be caught in orbit etc. The object/craft has gained energy but nothing seems to have lost energy. Surely this breaks the "conservation of energy" rule ? Confused ! George

I hope I am posting in the right place. I want to know, why do I feel the warmth of the sun's rays when the sun is visible from my window, but not when the sun is the other side of the building? Like on the south side of the building, there is light, but not heat. On the north side, there is a lot of heat with the sun shine coming in. Like even if there is no heat with reflect sun light, why not? What happens to the heat?

This has been bothering me for a while. Funding aside (I think THE WORLD would be able to pull off enough cash for funding), why don't we build a larger, better International Space Station? One that ships could launch off of with ease (MUCH less fuel required because of low gravity), one with a top of the line observatory, one that could simply just do more: boarding, tourism, etc.

The International Astronomical Union has no Definition for Big Bang After putting in a bit of effort in getting answers and permissions and writing it up, I thought you might appreciate learning of two significant, related cosmology news events that occurred last week. 1. The International Astronomical Union confirmed that they have no definition for Big Bang, and their Cosmology Commission VP explained why they probably will not do so. 2. ". . . the [standard model] definition is a mess." according to perhaps the most cited cosmologist - P. James E. Peebles of Princeton (author of "Principles of Physical Cosmology") You can read about these on my Cosmolog…

During the 'Dark Ages', from roughly 400 Kyr to 400 Myr after the Big Bang, space was strewn with neutral primordial gas: So, if space was strewn with gobs of gas, how can we see through that gas, all the way back to the CMB last scattering surface ??? In the following figure, sight-lines, extending backwards in time, from the present epoch, to the CMB last scattering surface, must first pass through the Dark Ages, and their gobs of gas. How come those clumps of matter don't block LOS ???

The interior, of a spherical massive body of uniform density, has a constant radius of curvature. Thus, the interior of such objects satisfies all of the requirements, for the FRW cosmological metric (uniformity, isotropy, homogeneity, constant curvature). Now, the Schwarzschild solution is static -- the downward pull of 'gravity on the rubber sheet', is offset, by the upward pull of 'tension in the trampoline'. So, why can you not extend that interior solution 'around', into a closed 'mini cosmos', where the contractile tensions still exactly offset the oppositely directed 'gravity' ?? For example, our star, with R = 700 K-km, rS = 3 km, has a Radius of…

Let us think about big mass star. If star mass is bigger than the limit, the star will become a black hole. Then which phenomena will be happen before being a black hole? . ----------------------------------------------------------------------------------------------->mass increase planet------giant planet----------star----------------big star---------------black hole . Let us think it again related with mass from big star to black hole. Big star is reduced it's mass rapidly by fusion reaction. Very large amount of light energy is emitted, the light emitting force is bigger than gravity attraction force. And, the more bigger mass star, it's light intensity…

I got a rather simple question for everyone I was hoping someone would be able to clear up some confusion for me. I was watching a show on the science channel the other day and they mentioned the super massive black hole in the center of the galaxy. Im in agreeance that it exist but something they said struck me as odd. They stated that the size of the black hole was 15 thousand miles wide. This is where my current understanding falls apart. Im under the impression that a black hole is a singularity, so how could it have any dimensions other G and spin momentum? In an effort to not clutter up the forum with small questions I wanted to also ask another quick q…

I have heard there is very high energy cosmic ray in the universe. Where is the cosmic ray above 1x1020eV created? Which reaction make it possible? I think the reaction is not normal fusion reaction.

Astrology has been the domain of sages and Brahmins. Sages from pre Vedic era had very good knowledge of Astrology. There are three main sub-divisions of Astrology. (1) Samhita : This deals with collectivity or multitudes. It encompasses such varied areas as weather forecasts, agricultural produce, natural disasters, floods, famines, wars, earthquakes, cyclones, market trends, changes in government, national and international events, and virtually anything that influences the masses. The annual world predictions which are generally based either on Hindu New Year commencing on the Chaitra Shukla Pratipada, or on the solar Ingress into Mesha, fall under the Samhita astr…

Well, im somewhat skeptical on the theory of the Big Bang, because by everything i have heard, seen, or read, the gravity at the time everything were to explode outward would be so inconceivably vast that nothing could cause that to happen. Thoughts please.

As science,s general exceptance of the expanding universe and the vaccum is creating this no im not going to mention petry dish dooo, what is anti matter and what exists outside of space ? are we a molicule being vacummed into a hoover in another universe, were forever blowing bubbles springs to mind .

Our galaxy has maintained spiral style. But it is very large. How does it maintain a fixed shape? We know gravity speed is same as light speed. And, our galaxy diameter is known as about 100 thousand ly.