# colour progression of a star to the supernova.



## Asura Levi (Mar 22, 2015)

I was googling for it and besides a random image I really couldn't find the object of my enquire. I know it is out there somewhere, but I'm find oddly difficult to find, so here is the question:

Start colours are determined by size/temperature/what is actually being fused, right?
So I understand (more like 'guess') that as a supergiant grows and then collapse to end its life in a supernova, its colour would change, right?

It is this that I'm trying to find, what are the star's colours through its stages (if it does change, I mean).

The reason is, I have this 'fireball'-like spell, it is not a fireball threw at the foe, but a small globe of light that forms where the MC aims (given its limits). The sphere grows, then rapidly shrinks and ends in a flash of blinding light succeeded by a shockwave.

It is purely aesthetically, but I reckon is rather enriching to have the 'fireball' not only grow, shrink, explode; but also have its colour changed as its progress.
I know I could use any colour I liked, but I honestly prefer to have some real world reference.


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## X Equestris (Mar 22, 2015)

The sort of stars that go supernova don't, as far as I can remember, change color very much over their lifetime.  They usually burn white or bright blue.


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## Asura Levi (Mar 22, 2015)

X Equestris said:


> The sort of stars that go supernova don't, as far as I can remember, change color very much over their lifetime.  They usually burn white or bright blue.



When looking for it, I found Red Supergiant, Blue Supergiant, etc...

In the story, I ended up going from small blue sphere, growing into a big red ball and collapsing in bright white. But I would change it to reflect any real process.

If it doesn't happen that much, too bad then...


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## X Equestris (Mar 22, 2015)

Supergiants stay roughly the same color over their lifetime.  Orange to red or white to blue are the greatest changes they make.  So I would say a white to blue shift would work the best.  It doesn't really matter for your purposes, though.


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## ThinkerX (Mar 22, 2015)

This ties in (somewhat) with the boring science project that occupied much of my time this winter.  

Hmmm...a bit tricky, and oversimplified, but...

Most stars are part of what is called the 'main sequence.'  (Type V stars).  They retain the same spectral type for as long as they are on the main sequence - which lasts until their hydrogen fuel supply starts running low and they start burning other substances.  At this point they expand and swell, turning into first subgiants (Type IV stars) and then giants (Type III stars).  As they turn into giants, their luminosity increases along with their size, by a factor of 10...ish.  This is the case for stars of spectral class O, B, A, F, and G.  

Sun-like stars start at about F5 (main sequence version roughly 4 times brighter/hotter than our sun) and extend down to about M1 (about 1% of the sun's luminosity.  Start getting into tidal locking issues with earth like worlds in that range, but that's another story).  Stars brighter than F6 or so don't remain on the main sequence long enough to form habitable planets.  Planets, yes, but earth-like habitable, no - that takes billions of years, which is far longer than those stars last.  At the other end of the spectrum, though...

you have K and M stars.  These stars begin their lives as giants, and once they settle down, they have the potential to last dang near forever.  The age of the universe is usually put at about 13-15 billion years, depending on what source you go to.  Lifetime of a K8 or M0 star is thought to be something on the order of 100 billion years.  As yet - save maybe for a few flukes, none of these stars has evolved off the main sequence yet.

And...

most of the several thousand stars you can see with the unaided eye are distant giants and subgiants, or bright O, B, or A stars.  Very few are nearby (within a few dozen light years)

O stars are very scarce.  You can count the relatively nearby ones (within a few hundred light years) on the fingers of one hand - out of a total number of several hundred thousand.

For B stars within a few hundred light years, you would need both hands (and might have to take off your shoes - not sure, this gets into distance measuring issues).

A stars...probably a thousand or so within 300 light years.  Maybe 1% of the total.

F stars...several thousand, something on the order of another couple percent.  

G stars...hmmm...maybe ten thousand.

Something on the order of triple that number of K's.

But a good 70% of stars within 300 or so light years are very faint M dwarfs.


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## K.S. Crooks (Mar 29, 2015)

Star colour is based on temperature the hottest being blue and coolest red/red-brown. As a start ages its mass will change, as such so will its colour.


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## psychotick (Mar 30, 2015)

Hi,

As far as I can recall the end of our sun which is too small to go nova let alone supernova, will be that it will first gradually swell and cool as it starts burning the last of its fuel, becoming an orange giant. This will take millions / maybe even a billion years, and and wont happen for I understand five or six billion years. After that it will rapidly collapse becoming a red or brown dwarf.

As for stars that go nova, they are mostly large, very hot white stars. I don't think they change colour very much during their lives, and after you'll get either a burnt out dead star corpse or a black hole.

Cheers, Greg.


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## Asura Levi (Apr 1, 2015)

K.S. Crooks said:


> Star colour is based on temperature the hottest being blue and coolest red/red-brown. As a start ages its mass will change, as such so will its colour.



It is exactly what I was looking for. Many thanks @K.S. Crooks.

I might have not being very clear with my question though, (which may explain why I couldn't find the answer by googling it. So I apologize for it.) I should have focused on star colour by temperature and/or size, not on an unlikely change in the process that would create a supernova.

But the hottest being blue coloured? Wouldn't bet on it. (it was white for me).

Again, many thanks to all of you.


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