Questions tagged [stellar-evolution]

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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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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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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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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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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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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
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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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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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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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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
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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
647 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
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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
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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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1answer
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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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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
485 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
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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
373 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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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
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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
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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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2answers
562 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
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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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1answer
614 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
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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
1k 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
206 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 be ...
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5answers
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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
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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
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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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3answers
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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 ...
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1answer
2k 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?
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85 views

Origin of Stellar Nurseries

What is the mechanism thought to cause huge stellar nurseries to form e.g. eagle nebula?
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How much of this 'Slow Death of the Universe' was predicted?

In short: the energy generated in today's universe, is "about half of the produced two billion years ago" and found that "this fading occurs at all wavelengths" as yesterday news: ESO - Charting the ...
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3answers
566 views

Can there be eternal stars?

the question is quite straightforward: Can there be stars that shine forever without ever collapsing nor growing? Do we know some really, really old stars? (whatever age that might be) I hope to get ...
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1answer
276 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 ...
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1answer
673 views

What is the largest possible mass for a stable planet made of iron?

Consider a large spherical planet made of pure iron. Think of something similar to Mercury or Earth without its mantle, only much bigger, though those planets have elements other than iron mixed in ...
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1answer
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Do trace elements in a stellar proto-cloud affect the spectrum of the resulting star?

Two quick questions regarding the origin of our Sun: Our own Sun was probably part of a much larger gas cloud and I wonder, if two distinct stars condense from a homogenous protocloud, do very slight ...
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5answers
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Did the Sun form around a solid core?

When Jupiter formed I assume like the other planets it started as tiny clumps of matter that eventually came together, became gravitationally bound and then eventually captured a lot of gas. I've also ...
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3answers
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Pure hydrogen star

What is the smallest mass of pure hydrogen that can ignite fusion? That is can population III stars have tiny masses? How would such stars develop? How long would such a star last?
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Why do elements on the Binding Energy per Nuclear Molecule after Iron (most stable) even form?

So I was reading about the stability of elements based on Nuclear Binding Energy, and I saw that the 'Iron group' of elements were most tightly bound and hence most stable, and that is why the graph ...
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2answers
363 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 ...
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2answers
730 views

Why are neutron stars mostly composed of neutrons?

I understand that it is due to electron capture $(p + e \rightarrow n + v_e)$. My precise question is: What are the conditions needed for a star core to start undergoing this process at a large scale?...
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4answers
751 views

Why is the release of energy during the He-flash in stars almost explosive?

Can't really put 2-2 and together as to how having an inert degenerate He core translates to a He-flash. Also, at which points exactly do degeneracy and the He-flash start occurring?
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1answer
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How much mass is typically ejected from a supernova?

How much mass is released from a supernova of a 15 solar-mass star? 20? 25? What is the relation between star mass and mass ejected?