Dwarf Stars

The gas being used as a fuel source for white dwarfs is primarily hydrogen. During nuclear fusion reactions in the core of a white dwarf, hydrogen atoms are fused together to form helium, releasing energy in the process.

A white dwarf has approximately the mass of our Sun, in a volume that's about a million times smaller - so it has a very high density (some tonnes per cubic centimeter). It's also very hot. Since energy production has stopped, they will cool down over time, but not enough time has elapsed for that to happen yet - in other words, the existing white dwarves are still very hot.

Because a white dwarf star is the core leftover from a bigger star and the core is the densest part of the star so although the star is smaller than the sun it has a similar mass as it is more dense

Somewhat confusingly, there are no "medium" stars. Stars are either dwarfs or giants.

Dwarf stars (class V) come in all types: O, B, A, F, G, K, and M.

There are also class VII "white dwarfs", probably better called "degenerate dwarfs" which are distinct from AV stars. In the first place, they really are small (about the size of Earth); the smallest red dwarfs are much larger, and even the so-called "brown dwarfs" are around the size of Jupiter (though much more massive). Also, they're not part of the main sequence.

Dwarf stars are hard to find because they are small and faint compared to other types of stars, making them more challenging to detect with telescopes. Additionally, dwarf stars are abundant in the universe, but they are typically located far away from Earth, making them difficult to observe in detail.

1. Neutron stars are typically around 10-20 km in diameter.
2. White dwarfs are usually about the size of Earth, around 6,000-12,000 km in diameter.
3. Dwarf stars are generally similar in size to our Sun, around 1 million km in diameter.
4. Giants can vary in size but are typically larger than dwarf stars.
5. Supergiants are the largest stars with diameters that can be hundreds to thousands of times larger than our Sun.

They form the same way other stars form. Gas and dust in a nebular region collapse due to some sort of instability and coalesces onto a dense, spherical region which, upon receiving sufficient mass, starts nuclear fusion in its core. The star is now born. The major difference between red dwarfs and more massive stars is just that, mass. Red dwarfs has less mass to work with during their formation, and were thus left less massive than other stars. In truth, red dwarf stars represent the vast majority of stars in The Galaxy. Think of the larger, more massive stars, as "lucky to have a lot more mass than most other stars".

A white dwarf star starts out like a our sun and turns into a white dwarf at the end of the stars life cycle. They have used up all their nuclear energy. At the end of this nuclear burning stage the star expels most to all of its outer materials. This creates what is known as a planetary nebula. The hot core is the only part of the star that remains. Temperatures of the core can and will exceed 100,000 Celsius becoming a very hot white. From this point the star starts to cool down, but that takes a billion years or more.

• A Giant is a star up to 10 times larger than our Sun
• A Super giant is a star 10 times larger than our Sun
• A white dwarf is a stellar remnant about 100 times smaller than our Sun.

The spectral class of a star is dictated by its temperature. Hotter stars around 30,000K and higher tend to appear blue or bluish-white. At the other end of the spectrum, stars around 1,000-2,000K seem red. For more information see spectral classification, theory of stellar evolution, and the H-R diagram.

Simple answer:

It is a star that is not massive enough to initiate helium fusion, instead it just burns hydrogen at a very slow rate. Red dwarf's are the most common and longest lived stars known. [See related link for more information]

More complex answer:

According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type. They constitute the vast majority of stars and have a diameter and mass of less than one third that of the Sun (down to 0.08 solar masses, which are brown dwarfs) and a surface temperature of less than 3,500 K. They emit little light, sometimes as little as 1/10,000th that of the sun. Due to the slow rate at which they burn hydrogen, red dwarfs have an enormous estimated lifespan; estimates range from tens of billions up to trillions of years. Red dwarfs never initiate helium fusion and so cannot become red giants; the stars slowly contract and heat up until all the hydrogen is consumed. In any event, there has not been sufficient time since the Big Bang for red dwarfs to evolve off the main sequence.

The fact that red dwarfs remain on the main sequence while older stars have moved off the main sequence allows one to date star clusters by finding the mass at which the stars turn off the main sequence. In addition, the fact that no red dwarfs have evolved off the main sequence has been observed as evidence that the universe has a finite age.

One mystery which has not been solved as of 2004 is the lack of red dwarf stars with no metals (in astronomy a metal is any element other than hydrogen and helium). The Big Bang model predicts the first generation of stars should have only hydrogen, helium, and lithium. If such stars included red dwarfs, they should still be observable today, but are not. The conventional explanation is that without heavy elements, low mass stars cannot form. Since a low mass star fuses hydrogen in the presence of metals, then an early protostar of such a low mass devoid of metals would not 'go nuclear', it would simply sit around as a clump of gas until more material came along. This supports the theory that the first stars were extremely high mass population III stars which died quickly and produced the metals necessary for low mass stars to form later.

Red dwarf stars are believed to be the most common star type in the universe. Proxima Centauri, the nearest star to the Sun, is a red dwarf (Type M5, magnitude 11.0), as are twenty of the next thirty nearest. However, due to their low luminosity, few are known.

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Red dwarf is also a British sci fi TV series.

What happens to stars when they die depends on how massive they are. For instance stars the size of the Sun turn into white dwarfs that eventual cool, Stars about 8*thr size of the Sun explode to form Neutron Stars (Pulsars) and very very big stars explode and leave behind a black hole.

No. White dwarfs, neutron stars, and black holes are three different things. With the exception of some black holes, all are remnants of the cores of dead stars at various degrees of collapse.

A white dwarf is the remains of a low to medium mass star consisting of atomic nuclei surrounded by electrons from electron shells that were crushed by gravity. White dwarfs can be up to about two times the mass of the sun and are a few thousand miles across, some about the same size as Earth.

A neutron star is a remnant of a massive star that has collapsed even further. In a neutron star the atoms have been crushed so that neutrons are most of what remains. Neutron stars range from 2 to 3 times the mass of the sun and are roughly 12 to 25 miles across.

A black hole is the remains of a very massive star that has completely collapsed into, at least theoretically, an infinitely dense point. Around the black hole is an area where gravity is so strong that nothing can escape, not even light. Stellar mas black holes range from 3 to 30 times the mass of the sun. There are also supermassive black holes, which are millions to billions times the mass of the sun. It is not known how supermassive black holes form.

There are many types of Dwarf stars - all with different diameters. Our Sun is a dwarf star!

A typical neutron star has a diameter of about 24km our Sun has a diameter of 1.392×106 km

So our Sun is about 58,000 times bigger than a neutron star.

A yellow dwarf star, is a star on the main sequence that has a temperature range of between 5,200 to 6,000 Kelvin. It has a spectral class of G or possibly F.

Our Sun is a yellow dwarf - much as you may not believe it, it is a dwarf compared to other stars!!

See related question for a size comparison

About 0.5 AU, or about half the distance from Earth to the sun.

possibly

Yes, a brown dwarf is a star that failed to ignite hydrogen fusion because it did not have enough mass for a strong enough gravitational collapse.

Brown dwarf stars glow dimly with residual heat for a very short time.

Yes, red dwarfs burn their fuel slowly because they have small sizes.

No. A white dwarf is the remnant of a star in which fusion as stopped.

A white dwarf is a star that is dying and is in its final evolutionary stage.

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