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1answer
16 views

Why do we ignore the Flux - Luminosity relation when deriving the Eddington Luminosity?

I was just doing the derivation for the Eddington Luminosity by considering the momentum equation, $$ -\frac{Gm}{4\pi r^4} = \frac{dP}{dm} $$ and the radiative transport pressure $$ \frac{dT}{dr} = ...
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1answer
64 views

Properties of a star made from water? [closed]

What would the properties of a star formed from a sphere a water/ice be? One large (massive) enough to collapse into an ordinary, mostly plasma star. I understand that it would have particularly high ...
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2answers
45 views

How to calculate radius of a sphere of Ideal gas?

The problem I am faced with is approximating the mass of the sun, and I thought that a fancy approach would be to approximate the sun as being made up entirely of hydrogen atoms, finding the resulting ...
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3answers
68 views

Negative density solutions of the Poisson's Equation for polytropic gas (aka Lane-Emden Equation)

Question: What does it mean by when we obtain negative density for specific region in space as a solution of Poisson's equations? I will explain the situation as detailed as possible, so that anyone ...
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1answer
41 views

What are some current models for neutron star core? [closed]

How are neutron star cores described today, do we use models of superfluidity/superconductivity for instance?
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2answers
49 views

Is it possible to calculate the radius of star?

Suppose I know the Luminosity $L$, temperature $T$ and Mass $M$ of star. Assuming the star is very heavy so that we can treat it to be radiation-dominated star. This would imply that pressure inside ...
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1answer
53 views

PP Chain and CNO cycle relationship

At what temperature would the energy generation rates of the PP-Chain and CNO cycles be roughly equivalent? The dependences are so vastly different that I am wondering how and by what equations they ...
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2answers
96 views

Harvesting hydrogen from a star

I've been thinking about what highly technologically advanced civilisations would do once their energy requirements become comparable to the total output of a star, and how such activity could be ...
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0answers
54 views

How is optical depth (opacity) related with gas pressure?

In stellar atmospheres, if we are given the gas pressure on the surface level of a star $P_{0}$ and we are expected to calculate the gas pressure on a deeper level (say 10000km) of the star, what kind ...
0
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1answer
40 views

What is the relation between Rössler attractor and thin accretion discs (like in the movie Interstellar)?

Is there any relationship between the Rössler attractor and thin accretion disks, like the accretion disk(s) in the movie Interstellar?
0
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1answer
34 views

Planetary nebulae, thermal pulses and mass loss

I'm reading about planetary nebulae and how they are formed, but as is sometimes the case, I've gotten a little confused. So, I have a star, let's say 5 times the mass of the sun. At some point, when ...
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2answers
84 views

Habitable zones around other stars

I have a question about measuring the boundaries of habitable zones on other planets. Is it okay to assume that, if Sun's habitable zone starts at a distance $R_0$ and its luminosity is $L_0$, we can ...
0
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1answer
26 views

Synthesising types of galaxies using various stellar spectra

I have been given the task of synthesising an elliptical galaxy, a starburst galaxy and a spiral galaxy (considering the arms and the bulge separately and adding them) using stellar spectra which I ...
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1answer
150 views

Do septuple (7), octuple (8) or nonuple (9) star system exist?

The highest I found so far is Castor, a sextuple star system. And there doesn't seem to be any other sextuple star system within at least 100 light-years...
0
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1answer
162 views

Can life exist in intergalactic space?

A terrifying idea I think, to be so utterly alone. Do you recon life could exist in intergalactic space? A lot of cosmic radiation is shielded from us by the Milky Way's magnetic field, but the ...
9
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2answers
477 views

What is the Sun's core made of?

The obvious answer is hydrogen and helium plasma but the nuclear fusion can also create heavier elements. Are these heavier elements a significant portion of the core? Do the heavier elements "sink" ...
3
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1answer
45 views

Sun energy production as a function of depth

I've heard a few times that the Sun's energy output per unit volume is less than that of a human, with the Sun's much higher power output being a result of its much greater size. In a blog post, ...
1
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1answer
41 views

Mass exchange between stars

I'm curious, are there specific conditions for a transfer of mass between two stars as they pass near each other? Its for my final project in computing, I'm writing a gravity simulation and thought ...
1
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1answer
189 views

Is there a simple formula for calculating semimajor axis bounds of “habitable zone”?

I understand that an accurate determination of the bounds of the "habitable zone" for a given stellar system depends on a large number of factors, including many beyond characteristics of the parent ...
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1answer
94 views

How are stellar and galactic ages determined?

Being a 4th year undergraduate physicist, you'd think I'd know this! But it's never really taught in any detail, just vague mentions of metallicities and, in galactic case, redshift. So how exactly ...
3
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1answer
95 views

Mass loss in Red Giants via dusty-winds and chromosphere activity

I'm reading some literature on mass loss in the RGB/AGB branches and so far I'm getting a lot of information regarding mass loss via dusty-winds/pulsations but almost no explanation of mass loss by ...
3
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1answer
149 views

Predicting stellar evolution and life cycle of a star

Is there a way to model/predict the evolution and life cycle of a star based on certain initial conditions? That is, whether it will become a red giant, brown dwarf, etc. I'm basically looking for ...
2
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1answer
125 views

Dark Matter and Rotational Velocity Curves of Galaxies and Stellar Systems

The way dark matter is introduced to documentary watchers such as myself is to account for the difference between the rotational velocity of the stars in a galaxy compared to that of planets in ...
8
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1answer
145 views

Could micro black holes obey the Eddington limit?

A stellar-mass black hole has recently been discovered in the Andromeda galaxy. One interesting part of the release is that this black hole shines close to its Eddington limit. Quasars are ...
8
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1answer
1k views

How can such a high exponent arise in this physics equation?

This site http://what-if.xkcd.com/14/ states that during a helium flash, "the reaction rate is proportional to the 40th power of the temperature". Taking for granted that this is true, how can ...
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6answers
1k views

What is the easiest way to stop a star?

On long enough cosmological time scales, hydrogen and helium nucleii will become scarce in the Universe. It seems to me that any advanced civilisations that might exist in that epoch would have the ...
0
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2answers
92 views

Regarding binary systems (with pulsars)

Are binary systems (in case of stars and other celestial bodies) more favorable than independent existence? I've been going through an article regarding pulsars, where it was stated that 'many pulsars ...
3
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2answers
665 views

How were the heavy elements from iron to uranium made? [duplicate]

Possible Duplicate: Age of the Earth and the star that preceded the Sun How were the heavy elements from iron to uranium made? References: ...
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4answers
430 views

Could a Dyson sphere destroy a star?

Freeman Dyson proposed that the power needs of an advanced civilisation would eventually require the entire energy output of a star to be collected, so that the star would end up surrounded by a ...
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1answer
509 views

What proportion of a star's hydrogen is consumed in its life?

I've heard in a lecture that a star like the sun would burn 3% of its Hydrogen before expiring. I would have thought it would be much more.
7
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1answer
87 views

What's the most accepted theory for Blue Stragglers These Days?

I'm working on a post against a recent creationism article about blue stragglers. From when I was in undergrad, the general explanation was that they were likely second generation stars within ...
4
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2answers
410 views

The Opera Neutrino Experiment and the Supernova 1987

So this probably stems from my massive ignorance about post-Newtonian physics but the supernova results of 1987 which measured neutrinos arriving 3 hours before the light from the supernova have been ...
3
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1answer
20 views

Could asteroseismology have a significant potential to unravel the mechanisms of solar cycles that last thousands of years?

Could asteroseismology have a significant potential to unravel the mechanisms of solar cycles that last thousands of years? And what about solar cycles 1 billion years ago and 2 billion years ago ...
2
votes
2answers
454 views

Are there formulae for calculating stellar luminosity and effective temperature as a function of age?

Is there a manageable formula or set of formulas or simple algorithms that approximate stellar luminosity and effective temperature (or radius) as a function of stellar age? I'm aware that accurate ...
3
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1answer
172 views

Solar neutrino predictions

The solar neutrino problem has been "solved" by discovering that neutrinos have mass and they oscillate. So how accurate are now our predictions about the number and types of solar neutrinos that ...
4
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1answer
1k views

If Betelgeuse were to go supernova

If Betelgeuse were to go supernova would the sky be twice as bright, or day time extended, depending on what time of year it happened in. Basically when it does supernova how bright and large will it ...