# Tag Info

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The universe now is expanding but its momentum will end and it will stop expanding and a reverse action will occur due to the force of gravitation . It is then when all the universe will shift gear backwards . Thus reversing the motion of the constellations , their stars and their planets . No body knows the speed of the expansion of universe or when it will ...

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New studies indicate that new, young stars, pulse and change size as ignition processes start. The pulsing and size changes, increasing and decreasing, aided by newly forming magnetic fields and gravitational forces, form strong vortexes around the new star. The vortex drag early gas and dust, present for the stars initial formation, together into gas giant ...

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We are continually told that the Universe will eventually be a void and everything will have burned up, no stars, no nothing. In my school days we were told that energy can neither be created or destroyed. So, if the universe does become "nothing" what has happened to the energy?

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Well i'm not into dark matter, but i am into entropy and stuff, so i will post an answer. How one is supposed to measure the entropy before and after, by counting micro-configurations, by counting volume/size, all these together? i suggest one or both of the above may give you an answer as to how the 2nd law may still be valid. No need for radiation (and ...

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Dark matter does not radiate photons by definition, but as I said in the comment to CuriousOne, dark matter may not have electromagnetic radiations to first order, but it does have gravitational radiation. The current Big Bang model accepts an effective gravitational interaction and thus the existence of gravitons, i.e. elementary particles of mass zero and ...

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A free dark matter cloud (without the presence of ordinary matter) will simply not "collapse" the same way a radiating gas cloud does. In both cases total momentum, angular momentum and energy are conserved, but in the case of a gas cloud the photons can carry away some of the angular momentum and most of the energy, in case of a dark matter cloud they ...

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I think the assumption that radiation is required for a collapse in general is mistaken. Think about a cloud of gas. If it is going to gravitationally collapse it must have a negative total energy; if it doesn't parts of the gas will fly off. If it has a negative total energy then there is some finite maximum size for the gas cloud, where it only has ...

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A brief overview of stellar evolution can be depicted in the following image: (From here which says it is originally from an encyclopedia; click here for larger image). The heavier stars (top track) have very short life times (a few million years) because they run through hydrogen, helium, carbon+oxygen, ..., iron fusion in the core. Once a particular ...

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You are neglecting two important facts. The first one is that stars, toward the end of their lives, return to the interstellar medium (ISM) a lot of their initial mass, but now enriched with heavy elements produced by nuclear reactions inside the stars themselves. In this way, younger stars which form from the ISM begin their life with a larger fraction ...

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It is convention and laziness (and I'm as guilty as anyone). In fact cgs units should not be used (according to the International Astronomical Union), in the same sense as Pluto should not be called a planet. Both were decisions made by the IAU. In the case of units, the IAU unambiguously endorsed the use of SI units, except for a short list of defined units ...

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Light with wavelength $\lambda\gg10\,\mathrm{km}$ can pass around a neutron star thanks to diffraction, even if the star is made of a perfectly absorbing material. That's exceptionally low-energy radio waves, though, and pretty different from what you probably had in mind.

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OK, let's try a back of the envelope... http://www.slac.stanford.edu/econf/C0805263/Slides/Budge.pdf states that the total anti-neutrino count from a supernova is on the order of 1e58 and the neutrino energy is on the order of 40MeV. Let's imagine all of these neutrinos would go trough earth, which is the worst case scenario. The nuclear cross section of ...

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It is difficult to keep track on these things, specially since quasars are also highly variable. Trying to answer the question of the post title, I found this example that sound pretty impressive: $7\times 10^{14}\,{\rm L_\odot}$, or $1.4\times 10^{41}$ W. The ESO press release refers to the kinetic luminosity, or the kinetic energy of the outflow per unit ...

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The Jeans equations can be a bit tricky. Their simplest form (in cartesian coordinates, with no particular assumptions) is: $$\frac{\partial\nu}{\partial t}+\frac{\partial(\nu\bar{v_i})}{\partial x_i} = 0$$ \nu\frac{\partial\bar{v_j}}{\partial t}+\nu\bar{v_i}\frac{\partial\bar{v_j}}{\partial x_i} = -\nu\frac{\partial\Phi}{\partial ...

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We do not know if the universe is closed or open, so space could very well be infinite. However, that does not mean that there is an infinite amount of space in anything. Such a conclusion does not quite make much sense in terms of a logical,mathematical (or even philosophical) argument. Take Zeno's paradox for instance: The paradox states(in summary) that ...

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Let's suppose the broadening mechanism is van der Waals or Stark broadening - something where the energy levels of individual atoms are perturbed. In this case you could use the following argument. Divide the line profile up into groups of atoms which share the same perturbation and treat each of these as a subpopulation with a different energy gap and ...

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The flux (defined as power per unit area) coming from the surface of the star is given by $\pi I_{\nu}$, where in the case of a blackbody, the specific intensity $I_{\nu}$ is given by the Planck function. The total luminosity of the star is therefore $\pi I_{\nu} 4\pi R^2$. At the earth, the received flux is therefore $\pi I_{\nu} 4 \pi R^2/(4\pi r^2)$, ...

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The answer given by Kyle refers of course only to the surface or photospheric temperature of the neutron star - the temperature of the layer from which photons can escape to reach an observer. In these outer layers the relationship between temperatures and particle motions is more-or-less consistent with the "everyday" Maxwell-Boltzmann picture referred to ...

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ever since the big bang,there universe has been expanding.other stars continues to burst and expand when they get hotter.so yes other stars wil disappear in the future and no longee be seen with naked eyes.

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