# Tag Info

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No one ever sees a black hole form without going inside. Instead you see something evolve into something that looks more and more like a black hole. And eventually it looks so similar than if a friend casually asked about it you might tell your friend it is a black hole because the difference hardly matters to your friend. But you'd know that you haven't ...

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If by "general proximity" you mean "reasonably close", i.e. a few light minutes away (Earth is 8 light minutes away from the Sun), then people on Earth would see the star evolve in the future, the time dictated by how far away the star is. Our closest neighboring star (besides the Sun) is Alpha Centauri, around 4.37 light years away from Earth, so if it ...

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A star is modelled pretty well as a blackbody so you use the formula, $$P = 4\pi R^2 \sigma T^4$$ to estimate the luminosity and then divide by $4\pi r^2$ to find the flux incident on an object a distance $r$ from the star. $$\frac{dE}{dt dA}=F = \frac{4\pi R^2\sigma T^4}{4\pi r^2}$$ In repsonse to the comment: $T$ : is the temperature fo the star ...

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orbiting, graviting, means only mass maters. It could be gaz, diamon, a bag of cockroach, or even a black hole, it would not change gravitational behaviors that orbits are. ( NB: yes, black hole too. Nothing different occurs in gravity as well when a star turn into blackhole. And it was attracting distant matter before exactly as well.)

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If we assume all of the rest of the planets are neutral in charge, then only the mass of the sun matters for the Solar system. The gravity between the star and planets and other objects forms the main force that maintains the rotation of smaller objects around the sun and be stable for a long time. No matter what you fill in the sun, the mass of the sun ...

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I would guess that given that the book was designed to teach amateur astronomers that most of the book refers to measurements made with reference to earth. Now, you can measure the component of velocity along the distance line between the star and the earth by using the doppler effect and the adsorption lines for particular elements(measuring the adsorption ...

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It's pretty natural to think that a star can have velocity - there's no reason a star shouldn't be able to move. The first thing you need to know is "velocity relative to what?" Stars in our galaxy are all in some kind of orbit around the galaxy, so you can talk about velocity in galactic coordinates. Binary stars orbit each other, so you can talk about ...

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What we see from the Earth's surface with our eyes are just stars, any planets surrounding them - indeed, entire planetary systems are not visible by the naked eye. That does not mean that there aren't any planets around those stars, the exoplanets listed in this European based Exoplanet catalogue were detected using much more precise and sophisticated ...

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Altair, Vega, and Regulus A are perhaps the most famous examples of stars that have been "flattened" by rapid rotation. Some studies (mentioned in Yoon et al. (2010) suggest that Vega is rotating at 70-90% percent of the speed at which it would break up (its rotational velocity is about 20 km/s). Regulus is even closer to this breakup speed: If its ...

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You conclude: "My intuition is that with 100's of M's of years to even out and settle down, it would be surpassingly smooth and quiescent." According to the history of the universe here , the dark ages happen after the decoupling of photons and the Cosmic Microwave Background radiation which happened around 380.000 years after the Big Bang. CMB is ...

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I've located a paper that goes into great (excruciating?) detail on the 21cm power spectrum (of baryons) in the dark ages. I won't pretend to have the expertise to understand the whole thing, but I'll try to bring out a couple of relevant points here. Note that this is all theoretical work in the framework of the standard cosmological model since actual ...

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We can't observe the population III stars directly so our knowledge of them is based upon computer modelling. The modelling shows that the main problem is getting the collapsing clouds of hydrogen to cool enough to become dense. It might seem a bit odd to require that the clouds cool, because after all we want the forming star to get hot enough for fusion ...

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