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What is the supernovae? [on hold]

Supernovae are exploding stars. They represent the very final stages of evolution for some stars. Supernovae, as celestial events, are huge releases of tremendous energy, as the star ceases to exist, ...
2
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1answer
20 views

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
1k views

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 ...
2
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3answers
582 views

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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1answer
27 views

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
34 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
179 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 ...
0
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0answers
28 views

In a supergiant star, is the energy transport inside the star mostly convective or radiative?

I know this has to do with the super-adiabatic and adiabatic characteristics in stars, but I'm unfamiliar with them. I'd love some discussion on this topic. Additionally, what determines the ...
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3answers
82 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
78 views

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?
1
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0answers
53 views

The standard textbook on supernovae?

This is a straightforward question: What is considered to be the standard treatment of supernovae? Could be a textbook, lecture notes, review article, etc.
5
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3answers
238 views

Why does fusion stop at iron when nickel is most tightly bound?

My understanding is that stellar fusion naturally stops at iron because it is energetically unfavourable to grow the nucleus further. But iron is only the third most tightly-bound nucleus, nickel is ...
2
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4answers
456 views

What happens during gravitational collapse to cause the formation of a star?

I know that stars are formed from dense regions in large gas clouds. I know that when gravity causes the mass of the clump to get so big that its internal pressure can't sustain it, it collapses and ...
2
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2answers
85 views

What is the process by which the density fluctuations that were detected in the CMB evolved into the first stars?

We can detect very slight fluctuations in the temperature (mass distribution) when the CMB was released (decoupling). It is believed that these fluctuations led to the first stars. However, these ...
2
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1answer
63 views

Electron degeneracy and helium flashes in stars

I have a question regarding the above mentioned. When a star have a mass of about 3-8 it does not go through the so-called helium flash phase, but instead just run along as nothing had happened, turn ...
0
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1answer
40 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 ...
4
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1answer
185 views

Chemical and stellar evolution in stars

I'm having an exam soon where I have to discuss/describe the follow figure: It's the first figure I have to explain, and it was on the same slide as the one below, so I'm thinking they are somewhat ...
0
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2answers
53 views

Photon walk in stars with convection

I'm having trouble figuring this out. I've read, that when photons are created via nuclear processes inside a star, it can take about 1 million years for photons to actually reach the surface of a ...
3
votes
1answer
109 views

Is there a scientific term for star formation?

It might be my stupidity to think that many laymen terms that most people use to describe some physics phenomena usually have a scientifically accepted term or name? The process of star formation, ...
5
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1answer
135 views

Has the number of new stars born decreased over time?

Has the number of new stars being formed decreased at all over the age of the universe? Would this be because the average density of the universe is decreasing due to the expansion of the universe, it ...
7
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3answers
501 views

Why does a star's core not cool when it expands as a red giant?

When a star starts to run out of hydrogen to fuse, it begins to collapse due to gravity until the central core temperature rises to $10^8~\text{K}$ Then due the force generated by the fusion of ...
13
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1answer
1k views

What is the theoretical lower mass limit for a gravitationally stable neutron star?

I ask here intentionally not for the size of the smallest possible observed size of neutron stars, which corresponds approximately to the well-known Chandrasekhar-limit for the upper limit of the ...
2
votes
1answer
202 views

What prevents a star from collapsing after stellar death?

When the star stops burning because heavier elements like Iron are formed in its core. Then the gas pressure stops and as you know the gas pressure helps keep a star in equilibrium because it provides ...
2
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2answers
178 views

What happens to a white dwarf star if it has mass higher than the Chandrashekhar limit? [duplicate]

What will happen if a white dwarf star has mass higher than the Chandrasekhar limit, i.e. 1.4 times the mass of the Sun?
2
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3answers
167 views

Are stars getting more metal-rich, less massive and shorter-lived with cosmic time?

A star produces energy through nuclear fusion with the 2H and 3H isotopes to create 4He for example. I read that there is a mass loss of 0.018884 (in atomic mass units). Of course this mass loss is ...
5
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1answer
282 views

Gravitational binding energy of a white dwarf at Chandrasekhar limit?

I was trying to calculate the gravitational binding energy of a white dwarf just before it went on a type Ia supernova in order to calculate the kinetic energy of the ejecta, but I wasn't able to get ...
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2answers
153 views

Why aren't all large stars black holes?

Like all stars, large ones are stable as long as there is a sufficient amount of hydrogen (or helium) to fuse. This fusion process is what prevents them from collapsing in on themselves. However, ...
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4answers
5k views

When a star becomes a black hole, does its gravitational field strength become stronger?

I've seen in a documentary that when a star collapses and becomes a black hole, it starts to eat the planets around. But it has the same mass, so how does its gravitational field strength increase?
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1answer
728 views

What is the percentage of stars that are massive enough to end their lives in a supernova?

I have been searching for the percentage of stars that are massive enough to end their lives as a supernova but couldn't get any result. As far as I know, a star has to be at least 8 times more ...
8
votes
1answer
167 views

Will a black hole eventually turn into a neutron star?

As far as i understand, black holes radiate away energy in form of Hawking Radiation. Thus, they lose mass, i suppose. Is there a point where the mass becomes too small for the object to still be a ...
6
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4answers
351 views

How does the formation of a solar system not break the second law of thermodynamics?

Please forgive: I am a layman when it comes to physics and cosmology, and have tried finding an answer to this that I can understand, with no luck. As I understand it, the solar system evolved from a ...
6
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1answer
191 views

Lifetime of a horizontal branch star

I'm trying to determine what the lifetime of a star on the horizontal branch of the Hertzsprung-Russell diagram would be. Some websites say $10^8$ while others said $10^7,$ so I don't know which one ...
6
votes
3answers
437 views

Neutron stars and black holes

The official limits for a neutron star is $1.4 - 3.2\;M_\odot$. But I read that the limit depends on the particular structure of a star to estimate which mass it must have. I also read that neutron ...
8
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3answers
407 views

Why does gravitational collapse occur suddenly in a supernova progenitor?

I was reading the Wikipedia article on Supernovae, and it says that one of the reasons why a supernova occurs is due to sudden gravitational collapse when the core of the star has little fusable ...
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3answers
210 views

When a star turns into a red giant what stops its core contracting

I recently asked this question When do stars become red giants? and am now wondering when the star's core is contracting after it has fused $H$ to $He$ what force stops the contraction just before it ...
2
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2answers
109 views

When do stars become red giants?

I am a bit confused when do stars become red giants? Is it just after they have finished core H burning and the core contracts creating high temperatures which result in core He burning to occur which ...
6
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1answer
98 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 ...
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5answers
4k views

Why does a star collapse under its own gravity when the gravity at its centre is zero?

The gravity at the centre of a star is zero as in the case of any uniform solid sphere with some mass. When a massive star dies, why does it give rise to a black hole at it's centre? I know how to ...
7
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2answers
265 views

What causes the dimensions of a star increase when its hydrogen fuel is exhausted?

What causes the dimensions of a star increase when its hydrogen fuel is exhausted? For example, the Sun is expected to increase its radius 250 times. What causes this if its temperature is expected to ...
7
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4answers
366 views

Can a planet form before the parent star ignites?

I'm unable to find an answer to my questions via my searches. This questions pertains to the timeline of a star system creation. My question: During the creation of a star system, can satellite ...
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1answer
150 views

Surface Area Relative to Element Distribution

We tend to find heavier elements like iron and others toward the center of celestial bodies. Lighter elements like carbon, hydrogen, and oxygen are almost always towards the surface. That makes ...
5
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1answer
428 views

Red Giant branch and Asymptotic Giant branch

What's the difference between the RGB and the AGB? I can't seem to find an clear distinction anywhere. Thanks.
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2answers
176 views

Speed of birth of a star

A star forms when enough material gets close enough. But how fast does the star start to shine? Is it gradually heating up (similar to an oven) slowly shining more and more? Or is it more like an ...
3
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1answer
100 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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2answers
129 views

Gas giant evolution over lifetime

In various types of stars, one can learn how they evolve differently, depending on factors such as their size and chemistry. Some stars have a short lifetime and others much longer. But, what is ...
3
votes
1answer
155 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 ...
6
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2answers
393 views

How do interstellar hydrogen atoms form stars?

I would like to learn the basics about how interstellar matter contracts into stars under the influence of gravity. Some of my questions: Let's assume an ideal and infinite large cloud of equally ...
-2
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1answer
69 views

Conversion of a star

I need to know what would happen to a star that has size 2 times the solar mass. I guess it would either be a neutron or red giant. Is that right?
6
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2answers
725 views

What is the frequency of occurrence of stellar classifications off the HR main-sequence?

An alternative version of this question would be: "if was to pick a star from the $10^{11}$ or so in our galaxy at random, what are the probabilities of it being various kinds of star?" (and I do mean ...
2
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2answers
146 views

How accurate are our calculations about distant stars keeping in mind their enormous distances?

Since many stars are hundreds of light years away from the Earth and therefore, what we observe of them today is really their distant past, how can we say anything with certainty about their ...