# Tag Info

## New answers tagged stars

3

In answer to the edit, any transitions due to single-graviton exchange will involve energies that are just impossibly small. To convince yourself of this, remember that the energy levels of the hydrogen atom are given by: $$E = \frac{\mu k^{2}e^{4}}{2\hbar^{2}n^{2}} = \frac{13.6\,\,{\rm eV}}{n^{2}}$$ If you do the same for two solar mass neutron stars ...

21

Yes indeed to all your questions: mutually orbitting binaries do spin down, the system's orbital angular momentum thus decreases with time and the loss of energy and angular momentum is almost certainly owing to the emission of gravitational waves. Look up the Hulse-Taylor binary system: its spin-down has been carefully observed and measured since its ...

0

Red giants are caused as outward forces become greater than gravity can pull inwards. This could be caused by stars loosing mass as the reactions take place or through more energetic reactions starting.

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Is it just after they have finished core H burning and the core contracts creating high temperatures which result in core He burning...? It is after the core finishes H burning, but He burning is not required. Hydrogen shell burning is sufficient to make it a red giant. Helium burning would make it a Horizontal Branch Star. See good explanation here: ...

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A good question for anyone who has thought about the big bang,red shift and Hubble etc. There are valid questions to be raised concerning Hubble's red shift leading to the big bang theory. Firstly, space is commonly regarded as a vacuum but this is not the case. Space contains a variety of matter ranging from atoms, to molecules, gases and solids and myriad ...

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Question: How many stars are in the Milky Way Galaxy? Answer: As many as there are! Why this answer? Answer: Even the stars that are close to us are eons older than when their light approximately began to journey toward all directions including Earth. Unknown & thus far unprovable amount of celestial activity continues from when ever it ...

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There is a reasonable chance that yes, planets can form before the star "ignites" (which I take to mean the fusion of hydrogen into helium, not the very brief phase of deuterium burning which certainly will take place before planets can form). Planets form in a disk of circumstellar material around their parent protostars. The "core-accretion" model of ...

1

Indeed, what we infer about stars from the light we see at the Earth is "old news". However for almost all practical purposes in stellar astrophysics this doesn't matter. The phases of a star's life last millions if not billions of years and most of the individual stars that are studied are within say 30 thousand light years of the Earth. The example you ...

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Given the huge reservoir of angular momentum stars are born with it is more a question of how is it that stars can get rid of most of this angular momentum to become the relatively slowly rotating objects we see? One of the best and most comprehensive pictures of stellar rotation that we have comes from the periodic modulation of a star's light caused by ...

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Here is an example for the Sun. The figure below plots a (reliable) estimate for the interior density profile of the Sun, $\rho(r)$. So for a given radius $a$, the mass interior to that radius is given by $$M(a) = \int^{a}_{0} 4\pi r^2 \rho(r)\ dr$$ And of course the gravitational field strength assuming spherical symmetry will be g(a) = - G ...

3

Most of the brightest stars are spectral types B,A,F main sequence stars (50%), but there are also a bunch of O-type main sequence and giant stars (5%) and another big clump of red giants (about 35%) and a few percent are supergiants. There are no white dwarfs, and definitely no neutron stars! I have attached an image which I created by selecting 4992 ...

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This was more a comment than an answer, but I can not comment due to lack of reputation. Stars can exchange mass either by stellar wind, or by Roche lobe overflow: It basically depends on the separation, on the masses, and on the star type.

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