The science regarding the structure, formation and evolution of stars.

learn more… | top users | synonyms

-1
votes
1answer
50 views

How does the energy of a supernova compare to that of its parent star?

How can the energy produced in a supernova be quantified? And, if the energy of the supernova is not equal to the energy of the parent star, how do we account for this difference?
20
votes
2answers
3k views

Why is the cut off mass for massive stars 8 solar masses? Why can't it be 10-11 solar masses or so?

I know that stars having a mass greater than or equal to 8 solar masses are termed "massive stars". But why is the cut-off 8 solar masses?
3
votes
1answer
91 views

What causes the differential rotation of the Sun?

I have read the explanation in Wikipedia, but the problem is that because I'm a beginner in physics, I don't quite understand what more than half of the words mean! Here is the explanation from ...
1
vote
0answers
64 views

What is the metric at the center of a star? [duplicate]

If there is only one star in the universe then is the metric at the center of the star flat?
3
votes
2answers
467 views

How can a low-mass star increase its mass to 1.4 Msun?

In my astronomy class I learned that a only low-mass stars (< 0.5 Msun) will contract, and then become degenerate, until it is a white dwarf. However, we also learned about the Chandrasekhar limit, ...
9
votes
3answers
355 views

How to cut a stone on a White Dwarf?

I've heard that white dwarf stars are extremely dense and hard. So, if I had a piece of white dwarf matter, would it be possible to cut it (or otherwise) into a custom shape? How could one do that?
5
votes
1answer
1k views

Reason why stars do not produce elements heavier than iron

In his book "Origins", Neil deGrasse Tyson says that "if you seek to split iron nuclei apart, you must them with additional energy. On the other hand, if you combine iron atoms they will also absorb ...
2
votes
2answers
109 views

Why does the core of a low mass star contract after reaching electron degeneracy?

I am learning about the lives and deaths of stars with a solar mass of 0.4-2. What I understand is that once the star stops hydrogen fusion after using up all its hydrogen, the star leaves the main ...
0
votes
1answer
55 views

Heavy Element Production from Supernova

When considering super massive stars going supernova, what are the heaviest elements that are predicted to be able to be created? So if the star VY Canis Majoris (1200 suns) were to go supernova, what ...
2
votes
2answers
64 views

What would happen if I gathered stellar sized masses of iron?

Lets say I had a bag that when turned upside would start pouring out iron shavings and never ever stop. Viola, there's my infinite source of iron. Now, lets say I just continued to dump this iron ...
5
votes
2answers
832 views

How to calculate the force of gravity that wants to collapse a star?

In astrophysics, the pressure created by the outflow of energy from the interior of the star counteracts the force of gravity that wants to collapse the star. If I want to calculate this force for a ...
2
votes
0answers
33 views

How much energy does proton - carbon 12 fusion produce?

Page 25 of this document from the California Institute of Technology says that proton-carbon 12 fusion releases 7.54 MeV, while Wikipedia says it releases 1.95 MeV. Which one is correct?
13
votes
7answers
2k 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 ...
1
vote
2answers
46 views

Can solar flares affect gravity?

Can a large eruption of solar flares on our sun change the effects of its gravity ever so slightly, and is it possible to measure these changes with the equipment we have today.
3
votes
1answer
128 views

Looking for a resource that explains all colors and shapes of stars and galaxies

I've been looking at some of the astronomy pictures of the day from NASA. They all have content that is indicative of certain situations or events. Supernovas have the scattered lines look, new stars ...
0
votes
0answers
26 views

Period-Luminosity relationship in Cepheid variables

I'm investigating the period-luminosity relationship in Cepheid variables. I know such a relationship has already been discovered; however, I'm trying to figure it out by myself as part of a school ...
4
votes
2answers
98 views

How do we know what happens to stars during their life cycle?

It is common knowledge than Sun-sized stars will eventually become red giants, and later they will get gradually smaller again until they cool down into a brown dwarf, and that bigger stars can ...
1
vote
0answers
16 views

how to calculate the amount of mass ejected from a stellar system?

I need to write a python program to find the amount of mass ejected from a stellar system and how much is retained. for this I need to calculate the quantity $$\int \rho (\vec {r}) f (\vec {v} (\vec ...
2
votes
2answers
61 views

Measuring Rotation of Sun

If the sun had a uniform surface (i.e., if there were no sunspots to look at), is there a practical way to measure its rotation? In other words, if some external force flipped the sun's spin ...
1
vote
2answers
82 views

Good books or resources for Stellar Astrophysics at graduate level?

I wanted to know if there is a well established resource in the field of Stellar Astrophysics which is not very outdated. I have seen plenty of books at my university library but I do not know if ...
18
votes
4answers
2k views

How is hydrostatic pressure overcome when a star is formed?

If stars are formed by the collapse of dust clouds under gravity, how is the pressure of the dust cloud overcome? As more material gathers together, gravity will increase, but pressure will also ...
0
votes
1answer
89 views

What is the bigger number of particles crossing an area: the number of photons or the number of neutrinos? [closed]

Take an squared area with (10²)² m² in front of the sun. What is the bigger number of particles crossing an area: the number of photons or the number of neutrinos? Just for clarification: you can ...
0
votes
2answers
30 views

How to measure the spectra of the stars

I recently made a mini spectrometer using a CD. I have used that to measure the spectrum of the Sun, moon and various artificial light sources. My question is how can I use it or modify it to measure ...
52
votes
2answers
7k views

Why is the Sun almost perfectly spherical?

Relatively recent measurements indicate that the Sun is nearly the roundest object ever measured. If scaled to the size of a beach ball, it would be so round that the difference between the widest ...
-1
votes
1answer
76 views

In what ways does the sun output energy?

I'm curious about the energy output of the sun, and how it breaks down. What fraction is from EM radiation, solar wind, neutrinos, et cetera? How does energy output vary over the EM spectrum? I was ...
2
votes
1answer
204 views

How to calculate the radius of a main sequence star based on mass?

What would I need in addition to the mass to figure out the radius of a main sequence star?
1
vote
1answer
64 views

How does fusion work in the Sun if neutrons have more mass than protons?

According to my textbook, the next result of the fusion reactions in the Sun is: 4H -> He + neutrinos + gamma photons However, if hydrogen atoms are basically a proton and helium atoms are 2 protons ...
0
votes
1answer
83 views

How do inert helium cores in sub giant stars create a pressure force?

I'm reading about the sub giant branch (SGB) and the evolution to the red giant branch (RGB). On the SGB stars have burned all hydrogen into helium, as a result, they have an inert helium core. The ...
1
vote
0answers
46 views

What is the definition of the “stellar angular diameter” in stellar astronomy?

(Following the definitions here: http://arxiv.org/pdf/astro-ph/0509535.pdf ) What is the "stellar angular diameter", as measured by astronomers specializing in stellar astrophysics? Using the ...
1
vote
0answers
53 views

Using stellar spectroscopy to measure stellar parameters, why is it log g?

Stellar spectroscopy can in principle measure the stellar surface gravity, radii, effective temperature, and stellar rotation. Why is it that surface gravity g is ...
4
votes
4answers
722 views

What happens if a black hole sucks up a massive amount of oxygen and hydrogen?

Suppose a black hole were to suck up a massive amount of surrounding oxygen and hydrogen. Would this ignite inside the black hole and turn it back into a star?
1
vote
2answers
100 views

What causes the death of the Sun?

In a previous question I learned that in each second only a miniscule portion of the total hydrogen in the Sun is converted to helium and that the number is 1/10^18 of its mass converted each second. ...
1
vote
2answers
114 views

Density of the Sun

Being either on the surface or somewhere inside; where is the density of the gases of the Sun equal to the density of the ground we stand on here on earth?
2
votes
3answers
154 views

Are there more photons than nuclei within the Sun?

Are there more photons than nuclei within the Sun? Is there a good way to estimate what the ratio would be?
0
votes
1answer
127 views

Where is the Hydrogen the Sun consumes?

I understand the Sun consumes 600,000,000 tons of Hydrogen each second. Where is this Hydrogen? Is all the Hydrogen the Sun will ever consume inside it or are there vast amounts of Hydrogen in space ...
0
votes
0answers
20 views

How do exoplanet surveys precisely measure stellar properties?

All measurements in exoplanetary studies (e.g. the Kepler study) depend on how precisely we know the properties of a star. For instance, the planet mass and radius is known only as well as the star's ...
0
votes
2answers
50 views

In stellar astrophysics, what is the difference between protostellar disk and circumstellar disk?

I have noticed both the terms "protostellar disk" and "circumstellar disk" in the stellar astrophysics and exoplanet literature. What exactly is the difference?
3
votes
3answers
207 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 ...
5
votes
2answers
69 views

Why are stellar clusters useful for developing stellar evolution models?

I know that for globular clusters it is assumed that the stars developed around the same time thus their initial chemical compositions are roughly the same. My question is how does this tell us about ...
1
vote
1answer
23 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} = ...
2
votes
1answer
236 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 ...
1
vote
2answers
427 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 ...
0
votes
3answers
129 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 ...
1
vote
1answer
64 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?
4
votes
1answer
177 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 ...
9
votes
2answers
1k 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" ...
2
votes
2answers
154 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 ...
8
votes
4answers
478 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 ...
0
votes
1answer
35 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 ...
0
votes
2answers
107 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 ...