# Stellar Evolution

## Stellar evolution is the life cycle of a star. Stars start out as clouds of gas and dust. The composition of the gas and dust will determine the stages that the star may go through.

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Physics
Black Holes
Stellar Evolution

# How do scientists calculate the mass of a black hole?

Scientists calculated indirectly the mass of a black hole by the behavior of matter around it, from which its gravitational pull can be determined, and with an accurate measure of its distance, its mass can then be inferred. In some cases an upper limit can be calculated by the closest approach of a visible object observed near it; in this case, its size is a result of a direct relation to its mass since the radius of the event horizon is directly proportional to the black hole's mass.

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Stars
Stellar Evolution
Supernovae

# What is the Chandrasekhar limit?

It is named after the astrophysicist Subrahmanyan Chandrasekhar.

In Simple terms: If the remnant core of a dying star has a mass lower than the Chandrasekhar Limit, then it will become a white dwarf star. Above this limit, it will explode, as a Type II supernova.

More detailed: Stars produce energy through nuclear fusion. The heat generated from these reactions prevents the gravitational collapse of the star.

Over time, the star builds up a central core of elements for which the temperature at the center of the star is not sufficient to fuse. For stars with a mass less than 8 Suns, the mass of the core will remain below the Chandrasekhar limit, and they will eventually lose mass, as planetary nebulae, until only the core remains - as a white dwarf star.

Stars with a higher mass will eventually develop a core of iron. Iron cannot be used as fuel in fusion reactions and the star collapses onto the core. The mass of the core will soon exceed the Chandrasekhar mass.

At this point the star will explode in a "core collapse" Type II supernova, leaving either a neutron star or, if the core is massive enough, a black hole.

The "Chandrasekhar Limit" is normally associated with the supernovae

called Type Ia supernovae.

The "Chandrasekhar limit" was originally worked out, by Chandrasekhar, as the limiting mass for a white dwarf star.

It's about 1.4 times the mass of our Sun.

If a white dwarf star becomes more massive than that limit, it

should explode as a supernova (called a Type 1a supernova).

This happens when a white dwarf is in a binary star system.

The white dwarf pulls material from its larger, less dense companion. When this material is enough to take the white dwarf's mass beyond the Chandrasekhar limit, the supernova explosion occurs.

There is also the "Chandrasekhar mass", which is more or less the same thing.

The Chandrasekhar mass is important in the theory of Type II supernovae.

See the Link below: "Supernovae and the Chandrasekhar limit". There may be a bit too much detail. Just take from it what you need.

Also, see the Link below: "Type Ia Supernovae".

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Constellations
Stellar Evolution

# What type of star is beta herculis?

It is a G-type giant star.

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The Sun
Biggest, Strongest, Fastest and Other Extremes
Stellar Evolution

# How much bigger is a massive star than the sun?

The most massive known star is R136a1. You did ask about massive.

The largest star known is VY Canis Majoris.

R136a1 is about 35 times as large as our Sun.

VY Canis Majoris is about 2,100 times the size of the Sun.

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Stellar Evolution

# Which stage in stellar evolution is the longest?

The longest stage of stellar evolution is the main sequence phase.

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Nuclear Fusion
Stellar Evolution
Furnaces

# Why are stars called atomic furnaces?

Because stars burn lighter elements through fusion into heaver elements.

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Stellar Evolution

# Why is iron special in stellar evolution?

Energy is liberated through fusion reactions, producing heavier and heavier elements. There are two transient elements heavier than iron which are produced by standard stellar nucleosynthesis, but these are short lived and decay into lighter elements. Iron is the heaviest element forged in the heart of a star via standard stellar evolution.

All elements heavier than iron are the byproduct of a supernova, wherein atomic nuclei are smashed together with such force energy is consumed in the nuclear reaction. This is why there tends to be an abundance of stable isotopes as light as iron, but elements heavier than iron are much more rare. Lead is an exception to this general rule as it is the end product of a long radioisotope decay sequence.

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Astronomy
Stars
Stellar Evolution

# What is the order of evolution of stars?

The details are a bit complicated, and vary depending on the star's mass, mainly. I recommend you read the Wikipedia article on "stellar evolution" to get a general overview; then ask back here if you have any additional questions.

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Science
Astronomy
Stars
Stellar Evolution

# What stage in its evolution is the star the hottest?

i would say its supernova

(red giant is not hotter than the sun)

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Stars
The Sun
Stellar Evolution

# How much longer should the sun remain stable?

roughly 6 billion years

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Stellar Evolution

# How was carbon first formed in stars?

by the big bang. the big bang happened and caused different gasses floating everywhere and combining to form different gasses like atom

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Stellar Evolution

# What are the 6 steps to stellar evolution?

1. A nebula, an immense cloud of hydrogen gas and dust, condenses into smaller regions of matter.
2. On occasion, one of these regions collapses under the force of its own gravitational attraction, often triggered by an outside force, like a nearby supernova-an explosion of a star.
3. After the collapse of a cloud, atoms begin gravitating together to form a condensed center. The condensed center is a protostar. As gravity pulls in more gas and dust, pressure builds, causing the protostar core to heat up.
4. Clouds and matter begin to rotate around the protostar and flatten due to their rotation. They surround the protostar like a rotating disk.
5. The protostar continues to grow and its core continues to heat. When the core is hot enough, nuclear fusion begins. The start of nuclear fusion is technically the beginning of a star's life.
6. Eventually, when the nuclear energy runs out, the star dies. Depending on the size and mass of the star, it can go through many stages and die in different ways-one of those ways being a supernova.
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Stellar Evolution

# How can you describe the life cycle of a star?

size and diameter

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Stellar Evolution

# What current stage of stellar evolution is altair?

Main Sequence

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Stellar Evolution
Supernovae

# What is the last stage in an intermediate-mass star's life cycle?

White dwarf

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Planetary Science
Astronomy
Stellar Evolution

# What is a large cool star formed when a star runs out of hydrogen?

A supergiant or red giant. They are normally around 3,500 degrees C and are very bright, near -5 on the Hertzsprung-Russell Diagram. These are the largest stars in the galaxy and universe.

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Planetary Science
Definitions
Stellar Evolution

# What is a star whose brightness changes?

A variable star is one whose brightness changes.

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The Sun
Stellar Evolution

# Will the sun ever blow up?

In Brief:

In about 5 billion years, the Sun will dramatically expand and become a red giant, but it won't explode. It won't ever become a supernova.

An Explanation:

It is true that the Sun is very slowly expanding and getting brighter right now. The reason for this is that as it is burning hydrogen to helium in the core the amount of hydrogen there gradually decreases. In order to keep the energy generation rate the same, the temperature and density in the core must rise. This has the effect that the energy can flow to the surface a little faster and it puffs up the outer layers (as well slightly brightening the Sun). When the Sun runs out of hydrogen in its core completely (which won't be for another 5 billion years or so) nuclear reactions will stop there, but they will continue in a shell around the core. The core will contract (since it is not generating energy) and as it contracts it will heat up. Eventually it will get hot enough to start burning helium into carbon (a different nuclear reaction). While the core is contracting the hydrogen burning around it heats will heat up the outer layers which will expand, and while they do that they will cool. The Sun will then become what is called a Red Giant and its radius will be large enough to envelop the Earth! Eventually the Sun will also run out of helium in its core. When this happens the core will contract again, but it will never be able to get hot enough to start burning any other elements into anything else. There will still be nuclear reactions of helium and hydrogen in shells around the core though, and these will continue to heat up the outer layers and cause them to move outwards. The core will eventually turn into what we call a white dwarf star, which is an extremely small (roughly Earth sized) dense star. A white dwarf does not generate energy so it will just slowly cool as it shines. The outer layers of the Sun will turn into what we call a "planetary nebula" (although it has nothing to do with planets) and gradually drift out into the interstellar medium. Planetary nebulae are some of the most beautiful objects you can see in the night sky. So the Sun will never explode (even though more massive stars can and do). The difference is that the Sun isn't massive enough to ignite anything past helium in its core. More massive stars continue nuclear burning until they start making iron. This creates an unstable core which will then explode in a supernova explosion.

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Biology
Evolution
Stellar Evolution

# Is evolution correct?

The theory of evolution states that most living organisms share common ancestry. Charles Darwin proposed this theory 150 years ago to account for the remarkable diversity of life around the globe, and to explain apparent successions of fossils.

Since Darwin's time the theory of evolution has been modified to incorporate discoveries in genetics. We now know the source of the mutations that create change, for example. We have also learned a great deal about earlier stages of life. Multicellular organisms clearly originated in a marine environment. We have fossils of fish that predate any fossils of land plants or animals. Given that fact, evolution would predict the earliest terrestrial vertebrates should be amphibians.

It turns out this is what we find. Fossils of amphibious creatures like ichthyostega, eusthenopteron, acanthostega, and eogyrinus all bear remarkable resemblance to sarcopterygian lungfish of that era. One telling find was discovered by paleonotologists who predicted (on the basis of evolutionary theory) that there should be a creature with particular features in specific strata. When they searched that strata they found Tiktaalik roseae.

There are hundreds of scholarly papers published in peer reviewed journals on the subject of biological evolution each and every year, and this has been the case for decades. Research into this subject is ongoing and pervasive--it is of keen interest in numerous prestigious universities around the world. Essentially no research has been conducted that casts any serious or substantial doubt on the accuracy of Darwin's theory. On that basis I am led to the conclusion the theory is essentially correct.

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Astronomy
Stellar Evolution

# What causes a nebula to form a sun?

Gravitational instability of molecular nebulae causes formation of protostar, which evaluates to the star.

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Nuclear Fusion
Stellar Evolution

# What is the reaction for Nuclear fusion?

That depends on the temperature and pressure. Under different conditions different elements can fuse, starting at the lowest temperature and pressure deuterium and tritium fuse to make helium. In the end at the highest temperature and pressure a variety of reactants fuse to produce a mixture of nickel and iron, then fusion stops.

The full list of fusion reaction equations is several hundred equations long and is best found in a book on stellar evolution.

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Stellar Evolution

# What stage of the star cycle is Altair star in?

Altair is still in the main sequence stage of a stars life.

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Stellar Evolution

# What is the sequence for stellar evolution?

Stellar evolution states that stars are powered by a hydrogen fusion reaction. When a star has burned up its hydrogen, this reaction runs out, and its core will contract and heat up causing the hydrogen shell to ignite. This causes the star to expand into a giant star. Depending on the solar mass of the star, it will evolve into different objects. If its mass is in the 0.3 to 3 range, its core, now fusing helium will degenerate before the helium has a chance to ignite, and the explosion that results will be absorbed into the star itself. A star with a mass less than 0.4 will evolve into a white dwarf. If its mass is between 0.4 and 0.3, it will become a red giant and then burn out into a white dwarf. Stars that are more massive will collapse explosively as a super nova, and if it is larger than 25 stellar masses, it will be a neutron star.

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Stellar Evolution

# How do we study the stages of the star cycle?

We study star stages and cycles through teloscopes and time-lapse photography.

Generally in the same way we appreciate life-changes among a human population, which consists of babies, toddlers, children, teenagers... we notice that these reveal different traits. It's the same with stars. We see them born, evolve, age and die. Knowledge of nuclear processes enables us to piece this process together.

I don't think time-lapse photography will do it! Stellar evolution is far too slow a process. Most of what we know about stellar evolution is gained through spectroscopic analysis rather than 'looking through telescopes'.

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Stellar Evolution