# Tag Info

## Hot answers tagged star

8

Yes, there is a limit. If the radiation pressure gradient exceeds the local density multiplied by the local gravity, then no equilibrium is possible. Radiation pressure depends on the fourth power of temperature. Radiation pressure gradient therefore depends on the third power of temperature multiplied by the temperature gradient. Hence for stability  ...

7

Indeed conservation of angular momentum dictates that in a single star like the the Sun, rotation should be much slower when it becomes a red giant. This is because at the present time the Sun does not rotate at vastly different rates with depth, thus when it expands, the moment of inertia increases drastically and convection in the outer envelope will ...

6

There aren't any. A 25-30 $M_{\odot}$ main sequence star would have a spectral type of $\sim$ O7 and an absolute $V$ magnitude $M_V \simeq -5$ (see Zombeck 1982). A giant star with this mass would be even more luminous. At a distance of 30pc, the apparent magnitude of such a star would be $V=-2.6$. Closer examples would of course be brighter. Sirius is the ...

5

It really depends what you mean by "rock". At the temperatures and pressures at the cores of stars (and at which nuclear fusion reactions are possible), "rocks" as I suspect you are thinking of, do not exist. Thermonuclear reactions do not occur because the gas is "flammable", they occur because the kinetic energies of the nuclei in the gas (at these ...

4

They are called diffraction spikes, and they're artifacts from a supporting structure inside a reflector-type telescope.

3

NASA mission data is archived at a handful of NASA archives. If you do not know which archive a data set is in, then you can search the Master Catalog at the NASA Space Science Data Coordinated Archive (NSSDC). The main astrophysics archives are: HEASARC (High Energy Astrophysics Science Archive Research Center) IRSA (Infrared Science Archives) LAMBDA ...

3

The Hipparcos catalogue (use the revision by van Leeuwen 2007) contains trigonometric parallaxes and is complete down to about 9th magnitude. What this means is that you will have a complete set of measurements for F-type main sequence stars and hotter, and all giant stars within 450 light years. However, the sample will not be complete for G dwarfs or ...

2

Mu Sagittarii is a star system, not a single star. If that can be included, then Eta Carinae should be included, and it has an absolute magnitude of -12.0. It's a star system about 7,500 light-years from Earth. It looks like the brightest (absolute magnitude) single star visible to the unaided eye is WR 24 (in Carina Nebula). Its absolute magnitude is −11.1 ...

2

No. The sun does not revolve around another big star. It revolves around the center of our galaxy along with the whole solar system, including comets, asteroids, and a large amount of other stars and stellar systems. As per some theories, however, at the center of our Milky Way galaxy lies a Super Massive black hole, which was essentially once a huge ...

2

The endpoint in the lives of massive stars between about 10 and 25 solar masses is thought to be a core-collapse supernova that produces a condensed remnant called a neutron star. The lower mass limit for neutron star progenitors is reasonably well known and due to the evolutionary paths taken by stars of differing masses. Below 10 solar masses it is ...

2

You cannot just add the ideal gas pressure and degeneracy pressure together for any particular species of particle. (Well, you can, but it would be a poor approximation to the actual pressure). The trouble is that they are not separate things. In general, the electrons in the gas are partially degenerate and always obey Fermi-Dirac statistics. Unfortunately ...

1

Rob Jeffries nailed it, but I'll add a few points. 25-30 stellar mass stars are quite rare. O-type stars begin at a mass of about 16 suns and they're about 0.00003% of the main sequence (that's 1 in 3 million). They're also short lived, a few million to maybe 10 million years in main sequence. That's part of the reason there are so few of them. If ...

1

Using a mass-luminosity relation will give you a decent estimate on the mass (probably within a magnitude), but as usual, the more data you have on the stars, the better your estimate will be. There are a lot of sources of error (for example, age and metallicity), and whatever errors on your luminosity measurement will be propagated to your mass measurement. ...

1

You don't say what other information you have for the "several stars". Yes, you can use a mass-luminosity relationship if the stars are on the main sequence. In terms of mass uncertainties I would estimate that you might be at the level of 20% unless you can absolutely pinpoint them on a Hertzsprung-Russell diagram, because the luminosity of a (fixed mass) ...

1

This idea has been around for decades, so I'm not sure who first came up with it. Here's a reasonably sourced article on the involvement of supernova in solar system formation:Exploding Star May Have Sparked Formation of Our Solar System The shock wave from an exploding star likely helped trigger the formation of our solar system, according to a new 3D ...

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