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# Tag Info

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Summary There's a 1 in 500 billion chance you're standing under a star outside the Milky Way, a 1 in 3.3 billion chance you're standing under a Milky Way star, and a 1 in 184 thousand chance you're standing under the Sun right now. Big, fat, stinking, Warning! I did my best to keep my math straight, but this is all stuff I just came up with. I make no ...

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There are three main space weathering processes that will affect the surface of the marble. Cosmic rays, high energy particle from the sun and beyond, will hit the surface. This can change the chemistry of the surface. Solar wind particles, hydrogen and helium, can become implanted in the surface Micrometeoroids will impact the surface, causing small ...

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I think your question is on topic, but @RhysW has linked a very helpful post in understanding why your question is a common misconception about the Big Bang. No Center There is no 'center' to the universe. At any point, a local observer will claim that they are at the center of the universe by the way galaxies move away from them. How can we possibly know ...

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The answer to this is surprising: We are. And many (if not all) other galaxies. And they move faster than light. See, the universe is expanding, at an accelerating rate. The fabric of spacetime itself stretches out, so that galaxies seem to move away from each other. The interesting thing is that relativity does not forbid these from moving away faster ...

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Galaxies move through space with velocities of the order of a several 100 km per second; small velocities for small groups (~100 km/s; e.g Carlberg et al. 2000) and large velocities for rich clusters (~1000 km/s; e.g Girardi et al. 1993). In addition to this so-called "peculiar velocity", galaxies also also carried away from each other due to the expansion ...

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A quick google gave me these (approximate) figures: 7.5 x 1018 grains of sand in all the beaches and deserts of the world 7 x 1022 stars in the observable universe If these are reasonable estimates, then there are approximately nine thousand stars in the observable universe for each grain of sand on Earth. (By observable universe, I mean in all the ...

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All Conselice et al. (2016) appear to suggest is that when you look at something like the Hubble deep field, there are many faint (and presumably low mass) galaxies that are not seen. This has absolutely no effect on the need for dark matter. The main results are: (i) as you look back in time, the overall (co-moving) density of galaxies (more massive than a ...

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Olber's Paradox was created at a time before the idea of a finite universe was accepted. (It was thought of in the 1600's). In order to resolve Olber's Paradox, you have to introduce the idea that either the universe had a beginning or it is of finite size. (Note: the solution does not require an expanding universe). So, at the time, it was a paradox. ...

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Here is an overview of different scales we may look at the universe. On scales beyond it's almost homogeneous, and we get at the border of the visible universe. Many detailed images are available, e.g. from the Hubble Space Telescope. If you need a three-dimensional description of the universe, your program will probably need to read portions of star, cloud,...

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Your are misunderstanding the expansion of the Universe. The Big-Bang is not an explosion: this is the moment in time when the Universe had an (near) infinite density. So there is no center in the Universe as there is no center of the SURFACE of the earth (this is the most popular 2-dimensional analog). Since this primordial ultra-high density state, the ...

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The easiest explanation for why the maximum distance one can see is not simply the product of the speed of light with the age of the universe is because the universe is non-static. Different things (i.e. matter vs. dark energy) have different effects on the coordinates of the universe, and their influence can change with time. A good starting point in ...

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Let us define this as the largest observable density of a stable object, in order to exclude black holes which may have a very large (infinite) density at their centers or objects collapsing towards a black hole status. If we restrict the definition in this way, then the answer should be the core of the most massive neutron star that we know about. At ...

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The answer is yes time dilation does affect how much time an observer experiences since the big bang until the present (cosmological) time. However there is a certain set of special observers called comoving observers, these are the observers to which the Universe appears isotropic to. For example we can tell the Earth is moving at about 350 km/s relative ...

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Later estimates shows that the star could be as old as 14.5 billion years (± 0.8 billion years), which is still it older than the universe's calculated age of about 13.8 billion years, an obvious dilemma. There is no dilemma. That ± 0.8 billion years is important. Subtract 0.8 billion years from that 14.5 billion year figure (later revised to 14.27 billion ...

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There is also another mediator particle which moves at the speed of light other than the photon. This is the gluon, which is the exchange particle for the strong force. The odd thing about the gluon is that it's never seen by itself (that is, outside of collections of other gluons). Also, though neutrinos do in fact have mass, they are neutral particles. ...

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Dark Matter Your understanding of dark matter isn't bad, but here's a few clarifying details. Orbits: The speed of an object's orbit is related to 2 things: the radius of its orbit and the mass inside of it. In the solar system, over 99% of the mass is concentrated at the centre, so radius is the dominant effect on orbital speed. As we look at planets ...

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Without checking the numbers in detail, according to Wikipedia, the volume of the observable universe is about $3.5\cdot 10^{80} \mbox{ m}^3$, and the volume of Earth is about $1.08321\cdot 10^{21} \mbox{ m}^3$. By dividing the two volumes we get a factor of $3.2\cdot 10^{59}$, or written as decimal number: The observable comoving volume of the universe is ...

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This question begs the question, does everything need a practical use? The answer is a resounding no. What's the practical use of the Louvre, or of your local neighborhood public park where you enjoy weekend barbecues? There are some things that are very worthwhile that have little or no economical gain. Your local neighborhood public park in fact has ...

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Under General Relativity (GR) alone, a Black Hole's (BH's) event horizon is a point of no return -- anything that passes through the event horizon is lost and gone forever, and nothing comes out. Hence, under GR alone, BHs are utterly black and don't have a temperature at all. This is why the absorption of radiation (or anything else) by a BH doesn't raise ...

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In short: no one knows for sure, but currently it looks that the probability is 1. Longer: On our current understanding, the Universe is probably infinite in space. This depends on the recent WMAP satellite results, which have shown a zero curvature of the Universe below measurement precision. The other two options were a positive curvature (thus, we would ...

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This is a question that concerns the initial mass function (IMF) - an empirical (that is, defined by observations rather than theory) function that describes the statistical distribution of stellar masses. Edwin Salpeter (1955) was the first to describe the IMF, though if you read Chabrier (2003) there are some reasonably comprehensive explanations of the ...

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There are only two types of neutrino source that are "bright" enough to be reliably detected. The sun and nearby supernovae. The source of solar neutrinos is nuclear fusion, which is also the source of most of the star's energy. Neutrinos also spread out in all directions, so their intensity follows an inverse square law. So the amount of neutrinos is ...

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You are labouring under the misapprehension that how far we can see directly gives the age of the universe. Whilst it is true that the oldest light we can see was emitted some 13.7 billion years ago, the stuff that emitted that light is now roughly 46 billion light years away, thanks to expansion of the universe. The universe itself probably extends ...

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There are plenty of rapidly moving objects in astrophysics. A good place where one can get moving relativistically is near an event horizon of a black hole. A simple Newtonian estimate illustrates the point. Black hole has all its mass $M$ hidden under an event horizon of the radius of order $r_{g}=\dfrac{2GM}{c^2}$. An object moving circularly in the ...

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The largest sub-galactic astronomical object (in volume) that we know of is the Carina Nebula, which is a non-spherical diffuse nebula. The Carina Nebula has a radius of about 100 parsecs. Image credit: ESA If you consider astronomical objects of the galactic scale, then the galaxy IC 1101 is the largest astronomical object (in volume) that we know of. ...

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In one sense any point you choose is at "the centre" of the universe and at any point in the universe, at a large scale, the universe looks the same as at any other point. This is not the same as saying the universe is infinite, though (but it could be). The analogy with an explosion is a poor one, as explosions expand into existing space. With the Big Bang ...

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The short answer is: gravitationally bound system will not be ripped by the accelerated expansion. A longer answer: The current standard model ($\Lambda$CDM model) says that everything started with the big bang. It released a lot of energy that pushed the Universe and is since then expanding. While it's expanding, gravitational attraction has been working ...

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The simple answer is (as with so much in astronomy): We Don't Know Parallel universes may or may not exist. There is no definitive way to prove that these universes do or don't exist. A parallel universe is a separate existence to ours. The Theories that suggest that there may be parallel universes are classified as theories of multiverses. There are many ...

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