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.

482 Questions
Stellar Evolution

What is stellar evolution?

Stellar Evolution [See Link] - or Life of a Star.

Stellar evolution is the process by which a star undergoes a sequence of radical changes during its lifetime. Depending on the mass of the star, this lifetime ranges from only a few million years (for the most massive) to trillions of years (for the less massive), considerably more than the age of the universe.

Birth:


Star formation begins with the gravitational collapse of a giant molecular cloud. As the gases coalesce, heat and pressure increase until they condense into a rotating sphere of superhot gases. This is known as a protostar.

Protostars with masses less than roughly 1.6×1029 kg never reach temperatures high enough for nuclear fusion and become brown dwarfs.

For larger protostars, the core temperature will eventually reach 10 megakelvins, and nuclear fusion will begin.. The onset of nuclear fusion leads relatively quickly to a hydrostatic equilibrium in which energy released by the core exerts a "radiation pressure" balancing the weight of the star's matter, preventing further gravitational collapse.

The star thus evolves rapidly to a stable state.

Main Sequence.


Small, relatively cold, low mass red dwarfs burn hydrogen slowly and will burn for hundreds of billions of years

Massive hot supergiants will live for just a few million years.

A mid-sized star like the Sun will remain on the main sequence for about 10 billion years.

Maturity:


After millions to billions of years, depending on the initial mass of the star, the continuous fusion of hydrogen into helium causes a build-up of helium in the core. Eventually, the core exhausts its supply of hydrogen. Depending on the mass of the star, the outcome can vary.

Low Mass will become red dwarfs, such as Proxima Centauri, some of which will live thousands of times longer than the Sun.

Mid Sized will become red giants, such as Aldebaran and Arcturus .

Massive Stars will become red supergiants, such as VY Canis Majoris, Betelguise and Antares.

Stellar Remnants
(The End)

After a star has burned out its fuel supply, depending on its mass, one of three things can happen.

For a star with a mass similar to the Sun, it will turn into a white dwarf and radiate the remaining heat into space for billions of years. Finally ending it's life as a black dwarf. (Though none exist at the moment, as the universe is not old enough).

For larger stars, depending on the chemical composition and temperature, the star explodes as a supernova. and either collapses into a neutron star or, if the remaining mass is large enough, the pressure will be insufficient to stop the total collapse and the star will become a black hole.

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Stellar Evolution

Stellar evolution is the life cycle of a star A cycle suggests that upon death of a star another star is born How is this possible?

Although at the end of a stars life - another "type" of star is born, they are different to the "normal" type of star and are "star" in name only. Most "remnants" of stars should be classed as degenerate stars.

Our Sun (a star) will first turn into a red giant star [See related question] and then a white dwarf star [See related question]

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Astronomy
Stars
Stellar Evolution

What is the life cycle of a star determined by?

The life cycle of a star is simply determined by what element said star is currently fusing. Our sun is currently burning through its vast supply of Hydrogen, and when that runs out it will switch to Helium, and so forth. Every time the mass of the element it's fusing increases, the energy given off by the fusion process also increases. This causes a star to swell, forming its red giant phase. Unfortunately any given star will eventually reach the point where the temperature and pressure within its core are not sufficient to fuse the element it's left with, and the star will die by either going supernova or shedding off it's gaseous outer layers and leaving behind a white dwarf.

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Astronomy
Stars
Stellar Evolution

What is the life cycle of a star?

The life cycle of a star can follow a few different paths depending on the mass it starts out with. Really massive stars may live for only a few million years before going supernova, while low mass stars such as the Sun may take billions of years to use up their fuel and then die relatively quietly.

In star life cycles, a highmass star means a star with at least about 8 times the mass of our Sun

Birth
  • All stars are formed when a giant cloud of gas and dust, called a molecular cloud or nebula, begins to collapse under the influence of its own gravity
  • This may be triggered by a collision with another molecular cloud, the shockwave from a nearby supernova, or even the collision of galaxies
  • As the cloud contracts, it breaks apart. An individual fragment will condense into a hot, dense sphere known as a protostar
  • A new star is born when the protostar becomes hot enough to begin fusing hydrogen into helium. Now, the star will enter the main sequence, or adult, phase
  • If a star is too low in mass to initiate nuclear fusion it will become a brown dwarf
Main sequence
  • A star will remain in this state for most of its lifetime, fusing hydrogen to make helium and releasing energy in the process
  • A star may fall on different points on the main sequence depending on its mass. In general, the more massive the star the shorter its lifespan on the main sequence
  • Red dwarfs are small, dim stars that fuse hydrogen at a slow rate, and may remain on the main sequence for hundreds of billions of years.
  • Low massstars such as our Sun will be on the main sequence for several billion years
  • High massstars may only stay on the main sequence for a few million years
Maturity
  • Eventually a star will run out of its hydrogen fuel, and begin fusing helium and other elements instead. At that point it will leave the main sequence phase
  • Red dwarf stars will use up all their hydrogen and collapse directly into white dwarfs
  • Low mass stars like our Sun will expand and become red giants.
  • This happens when a star runs out of hydrogen at its core. The core will collapse and begin fusing helium while hydrogen fusion is transferred to the outer layers
  • This causes the star to swell to many times its original size and become cooler as the heat is distributed over a larger area
  • More massive stars will grow into supergiants, which are among the largest stars in the Universe
  • In this stage a star will maintain hydrostatic equilibrium by fusing heavier and heavier elements as the lighter ones run out. The largest stars can produce elements up to iron
Death and stellar remnants
  • Low mass stars like our Sun will eventually die by shedding their outer layers as a planetary nebula
  • The core will collapse into a white dwarf,which will eventually cool into a black dwarf
  • More massive stars will die in a tremendous explosion called a supernova
  • This happens when a massive stars begins to fuse iron. This absorbs energy and caused the core to violently collapse while the outer layers are ejected
  • The extreme heat produced by supernovae is responsible for the nucleosynthesis of elements heavier than iron, up to uranium
  • After a supernova, the core may compress into a neutron star or a black hole.
  • Neutron stars are much denser than white dwarfs, to the point where protons and electrons combine to form neutrons (hence the name)
  • Black holes are denser still, so much so that they produce an extremely strong gravitational force that even light cannot escape.

For more information see "Sources and related links", below.
The life of a star varies from one star to another depending on the mass of the star ranging from a few million years to trillions of years.
The explanation varies depending on the type of star we're discussing.

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Astronomy
Stars
Stellar Evolution

How is a star's color related to its temperature?

The color of a star's visible light indicates its surface temperature: a relatively cool star glows red (longer wavelength), and very hot ones glow bluish-white or even blue (shorter wavelengths).

* Blue more than 30,000 °Kelvin * Blue to blue white 10,000 to 30,000 °Kelvin * White 7,500 to 10,000 °Kelvin * Yellowish White 6,000 to 7,500 °Kelvin * Yellow 5,200 to 6,000 °Kelvin * Orange 3,700 to 5,200 °Kelvin * Red 1,000 to 3,700 °Kelvin * Brown less than 1,000 °Kelvin

* Black close to 0 °Kelvin The relationship is λmax*T=2.898*10^-3m°K Where λmax is the wavelength at which the star emits the maximum amount. So, for example for the Sun λmax = 5.1 nm Therefore T=(2.898*10^-3m°K)/(5.1*10^-9m) T=568,000 °C So as an object increases in temperature, its colour will slowly change, starting at red and progressing into blue and beyond.





A stars temperature is generally worked out by the average temperature of the photosphere.

This is not typical through out the star however.

The Solar Corona which is above the photoshere is very hot indeed, several million degrees. We normally cant see this because it does not shine in visible light. We only see this during an eclipse. It the bright band that is visible that seems to surround the moon during a solar eclipse. It is caused when matter is excited by the solar magnetic field.

Hotter still is the core. In the sun this is thought to be 10 - 20 million degrees. These temperatures are due to the pressure caused by gravity trying to compress the star. It has to be this temperature for fusion of hydrogen to take place. Once fusion starts in a young star this adds to the temperature to ensure that fusion continues.
The star's temperature is depended on the color of the star, blue is the hottest ,and red is the coolest.
the red stars are at under 3,500 K

the white and yellow stars are at 5,000 - 6,000 K

the blue and white stars are at 6,000 - 7,500 K

the blue stars are at over 25,000 K

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Astrophysics
The Sun
Stellar Evolution

Why is the center of the sun hotter than the surface?

The nuclear reactions creating our Sun's energy all take place in the core. This energy then radiates outward to the surface. If you do some simple geometry, you'll see that the intensity of the energy from these nuclear reactions must be lower at the surface than at the core, where that energy starts. Lower energy intensity, lower temperature.

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Astronomy
Stellar Evolution

The earliest stage of a stars life is called?

A Protostar.

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Astronomy
Black Holes
Stellar Evolution

If there are black holes does that also mean that there are white holes scientifically?

No. White holes were a hypothesis which has never been shown to be correct.

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Astronomy
Stars
Stellar Evolution

How many elements from the sun make up starch?

Three*: Hydrogen, Carbon, and Oxygen.

* However, these components probably came from a sun other than our own.

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Astronomy
Astrophysics
The Sun
Stellar Evolution

Why is the corona hotter than the surface of the sun?

The ions leaving the sun are accelerated prior to entering the corona. The accelerated ions have a higher velocity and this higher velocity creates a higher temperature through collisions.

The corona is hotter than the photosphere because the sun's magnetic field carries energy upward from the surface and into the chromosphere and corona. The opposite effect is observed when the magnetic fields cause sunspots to form, resulting in cooler surfaces.

313233
Stars
Novas
Neutron Stars
Stellar Evolution

What causes the collapse of a star?

The collapse of a star is based on its age. When it runs out of "Fuel" its inside contracts as the outside expands. it can then super nova or collapse into a tiny star.

313233
Astronomy
Cosmology
Stellar Evolution

What is thought to be the physical mechanism that was responsible for the present mix of chemical elements in the universe?

1) Hydrogen and some helium and a fairly small amount of lithium were formed very shortly after the start of the Universe, when matter cooled down enough for quarks to join into nucleons, and for some nucleons to join into heavier elements. There wasn't enough time to form any of the heavier elements.

2) The heavier elements - the so-called metals - were formed inside of stars, by nuclear fusion. In some cases, significant amounts of this matter went back into space, in supernova explosions.

For additional information, I suggest searching Wikipedia or Google for the following topics:

  • Nucleosynthesis
  • Supernova
  • Metallicity
  • Nuclear fusion
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Stellar Evolution

The helium flash occurs at what stage in stellar evolution?

When the star becomes a "Red giant" is when the helium flash occurs.

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Planet Earth
The Sun
Stellar Evolution

Is the earth and the sun nonrenewable?

The answer is yes . Its only a matter of time before the Earth and the Sun both run out of energy but not in our lifetime.

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Stellar Evolution

What stage of stellar evolution follows the fusion of heavy elements in iron?

s

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Atoms and Atomic Structure
Particle Physics
Stellar Evolution

What is a neutron star?

A neutron star is the remnant of a supernova explosion. Such stars are composed almost entirely of neutrons.

A typical neutron star has a mass between 1.35 and about 2.1 solar masses, with a corresponding radius of about 12 km

A neutron star is so dense that one teaspoon (5 millilitres) of its material would have a mass over 5 trillion kg. The force of gravity is so strong that an object falling from just one meter high would take a microsecond to hit the surface but at around 2,000 kilometres per second, or 4.3 million miles per hour.

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Astronomy
Stars
Stellar Evolution

Is eta carinae bigger then vy canis majoris?

No, you don't have to confuse "more massive" with "bigger". The most massive star in the eta Carinae system may have 100 times the mass of the Sun and be dozens of times bigger than our star but it is far smaller than VY CMa.

VY CMa is a red supergiant that has swollen to an extremely large size due to shell burning of different layers on its last stages of life. VY CMa is a cool star. On the other hand eta Carinae is very hot and it is in a different evolutionary state.

It is so massive that it will never reach the red supergiant state because it is losing mass at a fast rate. Also the companion play a role and alters the evolution.

Eventually eta Car will become a WR star (a naked core) and explode as a supernova. The same fate is expected for VY CMa but since it has already become a rec supergiant it is very likely that it won't become a WR star. This shows that VY CMa is far less massive than eta Car.

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Nuclear Energy
Nuclear Fusion
Stellar Evolution

What two elements are involved in nuclear fusion reaction?

Various isotopes of Hydrogen are fusible into Helium.

Helium is fusible into Carbon.

Carbon, various isotopes of Hydrogen, and Helium are fusible into Nitrogen and Oxygen.

After this the reactions get complex, but the final results are Nickel and Iron.

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Stellar Evolution

What is the life cycle of a yellow star?

Nebula

protostar

mid sized star

red giant

nova

white dwarf

black dwarf:)

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Stars
Elements and Compounds
Stellar Evolution

What are the most common elements in most stars?

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Stars
Stellar Evolution
Dwarf Stars

Why are dwarf plants are hot but dim?

They are not hot.

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Stars
Black Holes
Stellar Evolution

In How Much Years The Stars Near To Supermassive Black Hole will Orbit?

Just as the orbital period of the planets in the Solar System depend on the planets' distances from the sun, the answer to this question depends on how close to the black hole the star is.

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Astronomy
Stars
Stellar Evolution

What is the majority of stars?

One item of note is that fairly recent studies indicate that the majority of stars in the galaxy are the faint and small red dwarfs; estimates of the population in our Milky Way galaxy say they constitute something between three quarters to over 85%, although most are too dim to see. Observations of nearby elliptical galaxies showed their abundance to be around twenty times that of our own galaxy. This changed some ideas about the universe and their abundance even tripled some estimates of the total number of stars.

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Nuclear Fusion
Stellar Evolution

How do stars fuse elements together to make the heavier elements?

The most important reactions in stellar nucleosynthesis:

Elements heavier than Iron and Nickle are only produced in supernova explosions.
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Stars
Black Holes
Stellar Evolution

What controls galaxies without supermassive black holes?

For galaxies without the gravitational underpinning of a central supermassive black hole, the mutual gravitational attraction of the stars plays a lead role in determining its general shape, rotation, and other characteristics. Recently, low-luminosity stars such as red dwarfs have been found to contribute a significant quantity of mass to galaxies; there is also gas, dust, and non-visible matter ("dark matter") adding to the gravitational pull.

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