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What is a Dwarf Star?



As far as suns go, ours is pretty small, but we never think of it as such. It’s fairly average in size when you consider how big other stars are, though. There are, of course, larger stars out there. Much larger, in fact. The largest we’ve discovered up to now makes our Sun look like a dot of light. But stars can go the other way, too. These are called dwarf stars, and they’re pretty interesting.



1. By definition, our sun is a dwarf star.
Yes, our huge and all-powerful star is actually a dwarf star. It’s a main sequence star, and most main sequence stars are dwarf stars. Main sequence stars can be between 1/10th the mass of our Sun all the way up to 200 times the mass. Indeed, something 200 times the mass of our Sun is considered a dwarf. What does that tell you about the supergiants?



2. There are about three main types.
Dwarf stars come in three main types, namely red dwarfs, white dwarfs, and yellow dwarfs. Our Sun is a yellow dwarf, as are most main sequence stars. Red dwarfs are faint and cool, and they are the most common type of star. White dwarfs are rather special because they’re essentially dead stars, or almost dead. They’re the remnants of red giants that have shed their outer layer.

3. Brown dwarfs are the odd ones out.
There might be three main types, but there’s also a fourth that’s a little different from the others. Brown dwarfs are basically failed stars. They’re too small for nuclear fusion like most stars, and that means they’re not very luminous.
 
Jul 4, 2021
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Prediction: When the JWST is finally deployed, it's infrared range will allow it to detect copious amounts of brown dwarf stars. More significantly, we'll be able to identify brown dwarf solar systems. There very easily could be brown dwarf solar systems right in our back yard, and we wouldn't be able to detect them with our current technology. The JWST will open that door for us. Can't wait.
 
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Jun 1, 2020
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Hi Sara,

You're presentations are always elegant and enjoyable. I offer some more pedantic views that may be worth considering....

There, formally, is no such thing as a star that qualifies as a white dwarf. A white dwarf is the final remains of a burnt-out star. It certainly would qualify as a star under the old Greek definition of a point of light in space, but a star today requires hydrostatic fusion processes. White dwarfs have no normal fusion process at work.

As far as suns go, ours is pretty small, but we never think of it as such. It’s fairly average in size when you consider how big other stars are, though.
Yes, if you are only considering the range of sizes. But our Sun is a much larger star (size and mass) than the average star since so many more stars are small (ie red dwarfs).

But stars can go the other way, too. These are called dwarf stars, and they’re pretty interesting.
Yes, "dwarf star" is a term that was put into use to distinguish them from the only other class of stars -- giants. :)

Indeed, something 200 times the mass of our Sun is considered a dwarf. What does that tell you about the supergiants?
Wow, is this possible? Any examples?


2. There are about three main types.
Dwarf stars come in three main types, namely red dwarfs, white dwarfs, and yellow dwarfs. Our Sun is a yellow dwarf, as are most main sequence stars.
Yes, but interestingly, our Sun is a white star (in true color). It was originally thought to actually be yellow in color, but its spectral properties matched that of other stars that do appear yellow (e.g. Capella), hence it fell into the yellow type of stars. So this is, especially today, a spectral classification, though misleading, IMO.

White dwarfs are rather special because they’re essentially dead stars, or almost dead. They’re the remnants of red giants that have shed their outer layer.
Yes. This is why they no longer qualify as being an actual star, which require a balanced (hydrostatic) fusion system.

$5. ;)
 

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