# Tag Info

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Stars form from collapsing dust clouds, and since interstellar dust clouds are quite turbulent at interstellar length scales it is almost certain that the dust cloud forming the star will have a non-zero angular momentum, and hence the star will have a non-zero angular momentum i.e. it will be rotating. There are various ways we can measure the rotation of ...

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When you're asking a question about general relativity you need to state what coordinates you want to use. This isn't just a mathematical nicety - as you'll see shortly, the different coordinate systems attached to different observers will describe very different behviours. The obvious interpretation of your question is to ask what happens when an observer ...

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Plasma is considered as one of the 4 fundamental states of matter. Charged particles must be close enough together that each particle influences many nearby charged particles, rather than just interacting with the closest particle (these collective effects are a distinguishing feature of a plasma). The plasma approximation is valid when the number of charge ...

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You are a little confused in your stellar evolution model. After the ignition of hydrogen fusion in the core of a star, it will next progress to helium fusion, then to carbon/oxygen fusion via the triple-alpha process (I've skipped a lot of steps and details there, if you want the details you can look at either Hansen & Kawaler's Stellar Interiors text ...

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To address the actual question of how we know the composition of UHECR without relying on source information (of which we have none), we have to look at their extensive air showers (EAS). After an UHECR hits the top of the atmosphere an EAS is created in the air, but p and Fe will create EAS with different shapes. Properties of hadronic interactions are ...

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Since every particle attracts all other particles, there is a net force directed towards the center of the star (or any object), for any particle not at the center. Therefore, the particles will move towards the center (collapse), unless some opposing force prevents it. In the case of a star, the kinetic energy of the particles creates the opposing force, ...

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The known exoplanets are not representive. Each discovery technique has its own bias. For the transit of star technique, the probabilty that a planet transits the star, as observed from a distance, is proportional to the radius of the star and inversely proportional to the orbital radius (semi-major axis). Also, below a certain size, there will be ...

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Your What happens in high-energy physics experiments aside partially contradicts your final question But if we restrict the discussion to radioactive decay, fusion in stars, cosmic rays, is everything a lepton, baryon, or a photon? Radioctive decay has as end products photons, leptons and baryons. Fusion and cosmic rays are the realm of ...

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The Earth and the Sun has magnetic fields which shields us from cosmic rays, as a charged cosmic ray particle will loose kinetic energy when its direction is perpendicular to the magnetic field. So what happens to the kinetic energy of the cosmic ray particle? According to the first law of thermodynamics it can't just disappear. It goes to the magnetic ...

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Does it gain infinite momentum before it crosses the horizon? Momentum is frame dependent so, when asking for the momentum, one must specify according to whom? Since the Schwarzschild metric is independent of time, the time component of the four-momentum of freely falling particle is constant. $$p_0 = -E$$ Now, imagine that the particle is at some ...

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It would be more correct to say that distant galaxies appear than to say they disappear. Based upon the accepted big bang theory, there are galaxies that formed early in the universe from which light has not yet reached us, but that will reach us in the future. On the other hand, accelerating expansion of the universe could cause light emitted after a ...

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The density of a black hole is defined simply as the mass within the event horizon divided by the volume within the event horizon. This gives an average density, but doesn't imply that the density is uniform within the event horizon. So when you hear statements like the density of a supermassive black hole is the same as water don't take this too literally. ...

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