# Tag Info

16

In astronomy parlance, the Sun has a "metal"$^{1}$ mass fraction of about $0.02$. A solar mass is $\sim2\times10^{30}\;\rm{kg}$, so the sun contains about $4\times10^{28}\;{\rm kg}$ of "metals". That's about $20$ times the mass of Jupiter. A lot of that metal mass will be ${\rm C}$ and ${\rm O}$ and other elements a chemist would call non-metals, but I think ...

11

Estimating the mass of a "single star" can be a very difficult task, though perhaps your question is too pessimistic. There are a number of suggested relationships linking the mass of a star to its luminosity. These can of course come from stellar evolution models, but they can also be empirically calibrated using stars in resolved binary systems of known ...

7

Our primary method of understanding stars is using optical telescopes. We can directly measure the temperature of the "surface" of a star by fitting its spectrum to a blackbody. However, this gives us the temperature only at the "surface" or the optical depth of a visible photon. We know that stars are extremely hot through the hydrodynamic/thermodynamic ...

6

A binary star system, which is quite common, will allow us to determine mass with great accuracy, using Kepler's Third Law of Planetary Motion which is as follows: $$\frac{T^2}{r^3} = \frac{4 \pi^2}{GM_{sum}}$$ Using the orbital period, $T$, we can determine the acceleration and affect that stars have on one another to determine mass. Once we have the ...

5

"Storing" something implies the purpose is to put is somewhere safe so that it can eventually be retrieved. Heavy metals should eventually sink to the center of a star, but how are you going to retrieve it? Even in a science fiction context, it's hard to imagine a plausible means or retreiving a large pile of heavy metal from the center of a star. ...

4

The sun gets its energy from the pp-chain. The first step is the two protons forming the diproton (Helium-2): $$\,^1_1H+\,^1_1H\to\,^2_2He+\gamma$$ where the $\gamma$ is the photon (of energy about half an MeV). This quickly $\beta^+$-decays into a deuterium by converting a proton into a neutron: $$\,^2_2He\to\,^2_1D+e^++\nu_e$$ where $e^+$ is the ...

3

The first definition of $\mu=GM$ is the standard definition of the SGP. The second one comes from the velocity of a circular orbit. If you have an object in a circular orbit of radius $r$ and velocity $v$ around a body of mass $M$, then the velocity is given by $$v=\sqrt{\frac{GM}{r}}$$ From this you can see that $rv^2=GM$ for circularly orbiting objects. ...

3

The ejecta of a supernova does indeed move at a fraction of the speed of light (somewhere around the 10% mark). However, it does not remain at this speed forever. As the supernova ejecta expands outwards, it creates a shell of material that is actually gathering up particles in the ambient medium (typical interstellar densities are around 1 particle per ...

3

The resolution is much smaller than the granulation pattern. i.e. The granules are well resolved and are of order 500-1000 km in diameter, not 50 km. The sunspot is of order the diameter of the Earth. Granulation is caused by convective cells rising and falling such that they just poke up into the bottom of the photosphere - i.e. that region where most of ...

3

This is due to spinning forces, such as centrifuged force. Remember that galaxies form (at least the regular ones) from the spinning of matter around a galaxy nucleus. So, you're not wrong. Gravity is isotropic, but in this cases the spinning forces are the definition to the galaxy form.

3

I had a quick look at the paper - its mostly nonsense. The intrinsic light from a quasar is completely dominated by its emission line spectrum and a mostly featureless continuum. The emission lines give the true redshift of the quasar. Absorption lines in quasar spectra are predominantly due to foreground gas clouds at lower redshifts than the more distant ...

2

According to Wikipedia The Chandrasekhar limit is the maximum mass of a stable white dwarf star. The limit was first published by Wilhelm Anderson and E. C. Stoner, and was named after Subrahmanyan Chandrasekhar, the Indian-American astrophysicist who improved upon the accuracy of the calculation in 1930, at the age of 19. White dwarfs with masses greater ...

2

Elements heavier than iron are produced mainly by neutron-capture inside stars, although there are other more minor contributors (cosmic ray spallation, radioactive decay or even the collision of neutron stars). Neutron capture can occur rapidly (the r-process) and occurs mostly inside supernova explosions. The free neutrons are created by electron capture ...

2

Your first paragraph is not quite right. Gas pressure does not "stop" upon formation of an iron core, it is merely that the star cannot generate further heat from nuclear reactions and becomes unstable to collapse. i.e. The star does collapse! Perhaps what you mean is what halts the collapse (sometimes) before the star disappears inside its own event horizon ...

1

The core-collapse phase of a supernova commences once the final stages of nuclear burning are complete. This final phase of fusion reactions involving silicon, produce a core composed of iron-peak elements (not just iron). The cessation of nuclear burning leads to the contraction of the core. This happens relatively slowly at first, on a timescale given by ...

1

The apparent radial accelleration due to moving in a circle is ω2R. For earth, ω = 2π rad/24 h = 73 x 10-6 rad/s. Earth's radius is about 6.37 Mm. Therefore the upwards accelleration at the equator is 34 mm/s2. That's pretty small compared to the 9.8 m/s2 downwards accelleration due to gravity, so we generally ignore it. Then there is ...

1

This has a three-part answer. The first part concerns large-scale, quasi-static electric fields. The nice thing about electric fields is that one can always do a simple galilean transformation to a frame where this quasi-static electric field does not exist. So that is the first part (not very satisfactory, but true and practical). The second part ...

1

Here are the systems I found: 6: ADS 9731 Beta Tucanae Gamma Velorum Kappa Tauri Mu Sagittarii 7: AR Cassiopeiae Nu Scorpii ... no physical multiple stars of greater multiplicity yet found.

1

A "collision course" is a very fuzzy concept: if you are "barely going to hit" you are on a collision course but don't need a lot of deflection. However, let's assume for a moment a stationary earth, a meteorite of mass $m$ at distance $D$, heading for earth of radius $R$ with velocity $v$. The equations you need are conservation of angular momentum and ...

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