# Tag Info

6

What you need is a mass-luminosity relation combined with an expression for the tidal radius in terms of the stellar mass. The latter also depends on the mass of the planet, so when you say earth-sized, I'll assume that means mass and radius. So going through the calculation. Flux at the planet is $L/4\pi r^2$, where $L$ is the luminosity and $r$ the ...

5

I can't give a detailed answer; the details are buried in the depths of numerical stellar evolution models. The thing that changes most with the metallicity of a newborn star is the radiative opacity of the gas. Higher metallicity leads to more opacity. This has two immediate effects - it makes energy harder to get out of the stellar interior and makes it ...

4

The gap appears because of pair instability supernovae. In short, as one looks at such massive stellar cores at increasing temperatures, an ever-larger fraction of the photons are sufficiently energetic to spontaneously form electron-positron pairs. True, they soon recombine, but there is nevertheless a loss in (radiation) pressure, which causes contraction, ...

4

Estimates of star numbers are difficult to obtain. Red dwarfs are too dim to be seen as individual points so star counts cannot be obtained. The best guesses come from obtaining the mass of the galaxy and then guessing how much of that mass is made of stars. It is usually a low proportion, between 1 and 3%. You then guess how big the stars are on average to ...

3

Looking at the primary literature (and the source of the wikipedia information), it appears that Arroyo-Torres et al. (2013) have estimated a radius of $1708\pm 192R_{\odot}$, using an interferometric angular diameter and a highly uncertain distance (where I'm not sure the distance uncertainty has been adequately included). Using similar methods Wittkowski ...

3

The lines that appear in a stars spectrum mainly reflects its temperature not its composition, see here O-type stars start out with the same sort of composition as other stars, that is they are mainly H and He (approximately 75% and 25% by mass) with traces heavier elements.

3

I think the quick answer to this is no, at least, any solar-system around a Wolf-Rayet or similarly large star wouldn't have time to develop. I would think that large stars have solar-systems cause I see no reason why they wouldn't, but the stars don't last long enough for their solar-systems to develop much. The formation period, including bombardment ...

3

There can be no such thing as a "supermassive neutron star". The theoretical upper mass limit for a neutron star is somewhere between 2 and 3 solar masses. Any more massive and they inevitably form black holes. So I am not clear what kind of "neutron objects" you were thinking of? Nor is it clear what you mean by "non-stellar" objects that will have the ...

3

Protium is a proton + an electron. Under enormously high pressure, it's energetically favorable for electrons to merge with protons and become neutrons - see here. are stars mostly protons By mass, yes, at least before they get too old. The mass of the universe is more complicated, but anything solid that we think of as matter is made of ...

2

You are referring to pyconuclear reactions - these are reactions that are initiated even when the temperature is effectively zero. They are caused by zeropoint oscillations of particles that are trapped in a deep potential well and hence are purely a quantum mechanical effect. This is far from just of theoretical interest. It may be that pyconuclear ...

2

You are right that the stars seen on the sky are within the Milky Way. Only with a large telescope is it possible to resolve individual stars in other galaxies, and only for the nearest ones. I don't know which sources you refer to, by I think perhaps you are confusing the different types of gravitational lensing. I cannot explain them better than the ...

2

This is the full quote If, for example, the Sun were replaced by a black hole of equal mass, the orbits of the planets would be essentially unaffected. A black hole can act like a "cosmic vacuum cleaner" and pull a substantial inflow of matter, but only if the star it forms from is already having a similar effect on surrounding matter It's ...

2

This is really a computing problem, but I suppose the only point from an astronomical perspective is what the RA, Dec distributions of your catalogues look like. I'm not that familiar with optimal search techniques but I guess that you want roughly similar numbers of stars in each region. If your catalogue is just of the brightest stars, then these are ...

1

If you also have photometry, then there is a reasonably accurate conversion between the apparent magnitude and the continuum flux (per unit wavelength interval) at the wavelength of the photometry. Once you have this conversion factor, you multiply your equivalent width by it to get a flux.

1

I think that you mean to say: if the stars would disappear right now, but in case you meant to say if there had never been stars, here is an additional answer. Without stars human development would have followed completely different paths, and there's no way to know where we would have ended by now. Probably as long as human beings developed some form of ...

1

One example: there might be some effects on animal migration, as migrating species have been shown to respond to star patterns in a planetarium in various experiments over the years. Even dung beetles were found to respond to the "stripe" of the milky way across the sky, in an experiment publicised a few years ago. This was not for long distance migration ...

1

Do you mean if they disappeared now, or disappeared at some arbitrary time? If the latter, then I would say that if they had disappeared more than a few thousand years ago, we might still be living in mud huts. The movement of stars and planets in the heavens motivated many of the ancient scholars and led directly to things like Newton's laws and a theory ...

1

There are two main things we should look at here, because there are two main ways these distant stars can affect us: light and gravity. Light If all the stars in the universe disappeared (besides the Sun), the most of the luminous objects in the universe would simply vanish. There would still be objects emitting radiation - stellar remnants, accretion ...

1

Here's a very roughly calculated partial answer. A first generation star and solar-system would obviously not be a good candidate for life or even planets cause you can't do much with mostly hydrogen and helium. You can't even build an ocean with mostly those 2 elements. Stars do just fine, but planets don't. Gas Giants and Suns only. After the big ...

1

Most likely a satellite. They look exactly like stars, but they glide across the sky smoothly. Airplanes may have multiple light sources, some blinking lights, and you can definitely perceive how low it seems to be: An airplane somewhat seems to come from the horizon and disappear the same way, while a satellite "seems to always be at the same distance from ...

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What I do is compute the limiting magnitude for the position of the object I am interested in, and subtract it from the magnitude of the object (I call this the magnitude contrast). If negative, it should be visible with the naked eye. I use the function limmag_jd() in the Fortran library libTheSky for this. In order to find the best moment in a given ...

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