Questions tagged [stellar-evolution]

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When do planets formed via core accretion in a proto-planetary disk stop gaining mass?

I was just trying to go over some of the contents in my exo planets course and wanted to know that if all the planets that form via core accretion continue to attract all the dust in a proto-planetary ...
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1answer
52 views

What will be the mass of the sun when the core is depleted of hydrogen about 5 billion years from now?

Our sun converts 600 million tons of H to He every second, that is 5 million tons of matter into energy through nuclear fission. However, as the core of the sun continues to shrink the outer layers of ...
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67 views

Understanding the Chandrasekhar limit for white dwarfs and its relation with supernovas

So if I understand correctly, the Chandrasekhar limit ($\sim 1.4 \ M_{\odot}$) is the maximum mass that a white dwarf can have. Beyond this mass, the degeneracy pressure of the electrons can no longer ...
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3answers
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Why do stars get bigger and brighter when older?

As stars age, the concentration of Hydrogen in the core decreases which lowers the power output, causing an imbalance between outward radiation pressure and inward gravitational pressure. This causes ...
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1answer
134 views

How long from star collapse to supernova explosion?

According to some reports, Betelgeuse might "be ready to explode into a supernova". It's luminosity has decreased "considerably" in the recent weeks. If we consider the "stable period" as that when ...
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1answer
67 views

Evolution of red dwarf stars

While low mass stars (initial mass approximately $0.1 M_\odot$ to $0.8 M_\odot$) are quite numerous, their evolution seems to draw relatively little attention. The lower central density and ...
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2answers
109 views

Why do later fusion stages in a star last shorter?

When most of the hydrogen in the core of a massive star has fused to form helium, the next fusion stages (helium, carbon, neon, oxygen, ...) produce less and less energy in a single fusion reaction. ...
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22 views

Existence and evolution of P-type “asymmetrical binaries”

I'm not sure how those are called so let me explain what I mean by "P-type asymmetrical binaries" - I'm thinking of two stars of very different masses (originally) that orbit each-other fairly closely....
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2answers
83 views

Why do Type II supernova happen? [duplicate]

I am an engineer and not a physicist. I am unable to understand why SuperNova happen. I understand that when the core is composed of high atomic number of elements like Iron and further fusion is not ...
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26 views

Temperature function for stars?

I was thinking that for a star to be stable, the rate of energy emittance through a shell of radius r is constant, otherwise there would be a buildup of energy which would change the temperature and ...
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2answers
63 views

What conditions provide the oldest star?

If we define the start of the lifetime the protostar and the end of the lifetime a red giant (at max volume), what conditions would make this time the longest when the star was first formed and ...
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M3 globular cluster: simple age determination

For my pre-university pupils I would like to find a simple way to determine the age of the globular cluster M3 using a colour-magnitude diagram (CMD, B-V horizontal axis and apparent visual magnitude ...
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1answer
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How do neutron star binaries form?

Do neutron star binary systems come from previously active-star binaries, where where both stars have gone supernova and left behind neutron stars that are still in orbit? Or do they form when two ...
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1answer
53 views

If I add more mass to a red giant, will it become a supergiant?

Let's say I have a red giant. If I start dumping more matter onto it, will it eventually become a red supergiant? I'm guessing the answer is "yes" because when I see this covered in textbooks, they ...
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1answer
27 views

Why does a drop in gravitational energy result in star contraction

Consider a gas cloud that is radiating away heat. From virial theorem we see that if the cloud radiates away heat and loses energy this will cause its gravitational energy to drop. Why does this mean ...
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92 views

How is black hole formed after a supernova explosion?

Does all the mass of a core collapsing star get scattered during a supernova explosion? If it does, then how can a black hole be formed without any remaining mass? Or are there remnants of the star ...
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Strength of core-envelope coupling in stars

For a star with a given Zero-Age Main Sequence (ZAMS) mass, as a function of metallicity how strongly is the star's core coupled to its envelope? I understand that the core-envelope boundary is only (...
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1answer
88 views

When a star undergo collapse in a binary system what effect it has on its companion star? [closed]

when a star in its lifetime fuses up all its hydrogen and then collapse under gravitational force, till the temperature inside become high enough to restart the fusion of helium and radiation pressure ...
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78 views

Why does a star with its core collapsing and about to undergo a supernova, explode, instead of rapidly collapsing all of its matter into a black hole? [duplicate]

I am guessing this has something to do with density. I would assume that a massive star that has its core collapsing would be a prime candidate for having its core turn into a black-hole. If the ...
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1answer
243 views

What causes a supernova explosion?

I know similar questions have been asked and answered. However, it is still not clear to me, so please bear with me if this is duplicate to some extent. The explanation goes like this - the core ...
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Do stellar model luminosities include neutrino losses?

I have had a sudden crisis in my understanding of the published outputs from stellar evolutionary model calculations. Usually these models output a "luminosity" that one can then use, along with the ...
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22 views

What is the process that leads to the volume expansion of the outer layers of a star when it becomes a red giant? [duplicate]

If a main sequence star runs out of hydrogen fuel in the core, the core collapses because of its own gravity, but what exactly leads to the expansion of the outer layers of the star when it is ...
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1answer
252 views

The PPI Chain is composed of 3 steps: Does only the 2nd step release energy?

The PPI chain is \begin{align} \rm\ ^1H + {}^1H &\rm\rightarrow {}^2D + e^+ + \nu_e \tag 1 \\ \rm\ ^2D + {}^1H &\rm\rightarrow {}^3He + \gamma \tag 2 \\ \rm\ ^3He + {}^3He &\rm\rightarrow {...
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Jupiter's formation

Two days ago i went to a mathematics conference where there was a paper presented on Jupiter's formation via disk-instability model. I know that there are two different theories for the formation ...
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1answer
146 views

Why does the H-burning Shell do the CNO cycle instead of the PP Chain?

A star that initially produces energy through the PP Chain will eventually exhaust its Hydrogen leading to a core contraction in order to increase the temperature to generate again nuclear reactions. ...
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3answers
646 views

Does the Virial Theorem apply to degenerate matter?

I am trying to understand how the degenerated He core progressively increases its temperature as the star moves up through the Red Giant Branch. A well-known property of the degenerate He core is ...
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2answers
216 views

How can a red dwarf have such an immense lifetime?

I understand what a red dwarf is, and that it is dominated by convection. But I still don't understand how the fusion processes in such a tiny star can keep going for the immense time predicted. ...
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2answers
150 views

Why the He core gets hotter and hotter? Is it because it shrinks?

I know that after a star in the main sequence runs out of H in the core, it will start burning H in the shells surrounding the (now) He core. (1) Why now the Hydrogen shells are hot enough for ...
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2answers
759 views

Can a hydrogen cloud directly collapse to form a black hole?

Does a cloud (essentially a nebula) have to turn into a star or can it directly become a neutron star/black hole? I might've read somewhere that some primordial black holes might have formed this way, ...
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1answer
76 views

Star formation confusion

If gravity is really a weak force compared to other forces, then how does gravity pull hydrogen atoms in a nebula to from stars. I understand that hydrogen is in atomic or in the molecular state in ...
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1answer
65 views

How to find the current age of a star as a function of its luminosity

In my recent research, I have found the need to find an age of a star. But instead, I have found information telling me on how to calculate the age of a star cluster. Hence I wonder is there a formula ...
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2answers
78 views

Where do brown dwarfs get deuterium from?

Brown dwarfs don't have a high enough temperature to begin fusing hydrogen, but they can fuse deuterium or burn lithium, according to wikipedia. Where do they get the deuterium from? Is there just ...
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327 views

Slope of main sequence in HR diagram

In the HR diagram, what causes the change of slope (more flattened) around the area marked with $X$? This corresponds to luminosity of $\sim 1 L_{\odot}$ and temperature $~6000-8000 K$
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1answer
554 views

How much mass do stars lose when turning into black holes?

Is there any way to predict the amount of mass a star will lose when turning into a black hole? I know that the star loses it's outer layers, but is there any way to predict it's final mass?
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1answer
403 views

How many naked-eye stars have 'died' since they emitted the light we are seeing?

This question is sort of in the spirit of this xkcd: The light we get from stars was emitted many years in the past, but the distances to stars which are bright enough to be visible to the naked ...
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4answers
407 views

Can a star collapse into a black hole before it finishes burning its hydrogen fuel?

I don't see why a 50 solar mass star couldn't do so for the following reason. The pressure beyond some depth is so high that the matter below it is degenerate matter despite the very high temperature ...
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1answer
57 views

Is cosmology and evolution possible with anti-matter?

Suppose the universe had more anti-matter than matter. (I mean the exact reverse ratio to the real universe) Would there be galaxies? Would there be stars? Would there be heat and light? Would there ...
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2answers
571 views

Is the mass of an individual star almost constant throughout its life?

Could we say that an individual star is almost a closed system?, as many of the stars like the sun don't exchange significant amount of their mass with their environment (except solar flares & ...
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3answers
2k views

Why are pre-main sequence stars brighter than they will be on the main sequence?

Why is a pre-main sequence star brighter than it will be when it reaches the main sequence?
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660 views

Why is radiation pressure dominant at high temperatures?

In the ($\log\rho, \log T$) plane for stars, the lower right corner corresponds to the equation of state of radiation pressure. This means that as a star gets hotter and less dense, radiation pressure ...
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1answer
59 views

Is there a mass relation of the core left behind after ejection in a red giant?

Assuming that you have the mass of the star prior to the ejection of non-core material, is there any relation that can be used to approximate the mass of the resulting left behind core which will ...
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2answers
884 views

Why do only red dwarf stars have convective currents?

Stellar models indicate that red dwarfs less than 0.35 M☉ are fully convective.[3] Hence the helium produced by the thermonuclear fusion of hydrogen is constantly remixed throughout the star, avoiding ...
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2answers
196 views

Can a binary star system create a stationary black hole?

Research over the last 200 years suggests that half or more of visible stars are part of multiple star systems. I apologise for the number of assumptions in my question but, because of the numbers of ...
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2answers
2k views

How Long Did It Take For The Sun To Form?

I realise this may be a difficult question to answer because, AFAIK, we don't have an accurate estimate of the size of the protostellar cloud, or whether our sun formed from a subsection of a much ...
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1answer
243 views

Initial velocity of particles in a 2D gravity simulation

In $N$-body simulations of protostellar clouds (or similar objects), each particle is has a set of characteristics: mass, size, position, velocity, and (if the object is large enough or if we want to ...
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Why are some stars very large (i.e., $r \geq 1000 \ R_{\odot}$) but not super massive?

Background While I was in graduate school, I put together some cartoon-like comparisons of multiple stars to show the order of magnitude differences in radii. At the time, VY Canis Majoris was the ...
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2answers
275 views

Could planets survive their star becoming a black hole? [duplicate]

Would the supernova responsible for its formation destroy them. The question becomes one of how destructive the supernova event is to its own solar system - does it completely evaporate all planets up ...
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1answer
119 views

Will hydrogen die out? [duplicate]

Stars create heavy elements up to iron during their lifetimes, and heavier elements beyond iron during supernova events. Are there any processes which create new hydrogen? If not, will all (or most) ...
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2answers
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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 ...
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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 ...