Stellar Evolution: A Quick Overview of Star Types

[Labguy]

Seems that not much gets posted here lately. The link is to a simple chart that answers (in advance) some of the questions asked here. Note in particular the abundance label at the bottom of each class, with M Class stars being 80% !

See how few of the biggies (Class O, B and A) are either (1) left from original formation or (2) forming in current H2 clouds of starbirth. That same,short lifespan carries down to the very small abundance of the Supergiants.

http://anzwers.org/free/universe/startype.html

 

[wolram]

LABGUY.
See how few of the biggies (Class O, B and A) are either (1) left from original formation or (2) forming in current H2 clouds of starbirth. That same,short lifespan carries down to the very small abundance of the Supergiants.
----------------------------------------------------------------------------------
the class o stars seem more of an oddity, only 15 known? what is the
secret to these survivors?

 

[Labguy]

LABGUY.
See how few of the biggies (Class O, B and A) are either (1) left from original formation or (2) forming in current H2 clouds of starbirth. That same,short lifespan carries down to the very small abundance of the Supergiants.
----------------------------------------------------------------------------------
the class o stars seem more of an oddity, only 15 known? what is the
secret to these survivors?

Actually, at a ~10 million year life, there wouldn't be any original "survivors". Any Class O, and B I would think, that we can see (detect) today would have to be new 2nd or 3rd generation stars. Some Type A could be 1st generation if they formed late from the original BB material, very late.

 

[wolram]

i think i worded that badly LABGUY, i meant is it the short life span or
the rarity of these stars forming that is the reason only 15 have been
observed

 

[marcus]

i think i worded that badly LABGUY, i meant is it the short life span or
the rarity of these stars forming that is the reason only 15 have been
observed

it's a good basic arithmetic question
lets say that in our galaxy (the part we can see, not obscured by dust etc)
these biggies form at the rate of X per year

so if they lasted 10 years then on average we would see 10X in the sky.

(that is easy to check, if X = 1 that is if one formed per year, and it lasted ten years, then we would see around 10 in the sky at anyone time)

And if X form per year and they last ten million (10^7) years then we would
see
10^7 X
in the sky

and in fact we see 15 of them

therefore X = 15 divided by ten million = 1.5 x 10^-6
that is the rate they form in the Milkyway Galaxy
0.0000015 per year

one of those suckers forms every 2/3 of a million years

so in a billion years only 1500 of them would form, in the whole galaxy

so from this arithmetic I want to get a sense of how to explain the rarity
and I have to say BOTH reasons
because not only does one of those things have a lifetime that is only
a thousandth of the Sun's (say 10 billion years)

but they also form extremely rarely, only 1500 in a galaxy in a billion years.

----------

this discussion is simplified because we can probably see these things
in neighbor galaxies and I was assuming all 15 are in Milkyway
but it is just a rough calculation anyway

 

[wolram]

wow, the pure, blue diamond of the heavens.

 

[marcus]

blue is right
Labguy's table says O type surface is 6 or 7 times hotter than sun
so the mix of wavelengths will be 6 or 7 times shorter
that is a lot of UV as well as blue

since we may have Labguy's attention let's keep asking questions
(he knows lots of answers)

I have been interested by the fact that there seems to be an upper limit on the size of stars

O-types are only about 10 times size of sun in diameter

I don't know the mass ratio but probably O-types never get more than
100 times solar mass

why should there be this limit?
why cannot nature put together a star bigger than that, in situations
where conditions accidentally happen to be right for it?

I think I read somewhere that the upper bound on size of star which can
condense out of dust and gas
is because of the LIGHT PRESSURE which tends to drive the condensing star apart
if you try to make too big a star, then its own light pushes it apart
so it can't fall together and be born

Labguy will know if this is the correct explanation or not
Labguy?

 

[wolram]

with all the action just pre BB its almost as if our U
was pre ordained, "im an athiest",but how many
possible outcomes could materialise out of that
mayhem? why an upper mass for stars, planets, why did
only 0.5% matter evolve into "solid bodies", if the BB
was more damp squid, why not several super super massive
stars?

 

[Labguy]

blue is right
Labguy's table says O type surface is 6 or 7 times hotter than sun
so the mix of wavelengths will be 6 or 7 times shorter
that is a lot of UV as well as blue

since we may have Labguy's attention let's keep asking questions
(he knows lots of answers)

I have been interested by the fact that there seems to be an upper limit on the size of stars

O-types are only about 10 times size of sun in diameter

I don't know the mass ratio but probably O-types never get more than
100 times solar mass

why should there be this limit?
why cannot nature put together a star bigger than that, in situations
where conditions accidentally happen to be right for it?

I think I read somewhere that the upper bound on size of star which can
condense out of dust and gas
is because of the LIGHT PRESSURE which tends to drive the condensing star apart
if you try to make too big a star, then its own light pushes it apart
so it can't fall together and be born

Labguy will know if this is the correct explanation or not
Labguy?

Correct on the reason(s) of "light pressure" (high temp. = high radiation pressure = high stellar winds), but there is a candidate for 200 solar masses:

http://praxis.pha.jhu.edu/astro2/astro2_science/nolan.html and:
http://resource2.ca.jhu.edu/pipermail/jhu_science_and_medicine_news/2002-January/000070.html

Same pages explain what Marcus said.

 

[marcus]

with all the action just pre BB its almost as if our U
was pre ordained, "im an athiest",but how many
possible outcomes could materialise out of that
mayhem?...

real questions
i am an atheist too but
it does look at least a little bit planned
(conditions for life almost seem contrived, when looked at
in a certain light)
i try not to think about this since for me at least it tends
to be a waste of time, but i must acknowledge there are real and deep questions people can ask in that department

 

[selfAdjoint]

ALways remember that evolution is a soulless process that with enough time can produce the illusion of purpose and design.

 

[wolram]

SELFADJOINT
ALways remember that evolution is a soulless process that with enough time can produce the illusion of purpose and design.
----------------------------------------------------
i agree, but 500MYs ish, is not a long time when you consider
the age of our earth. our U did seem to sort itself out quickly.

 

[selfAdjoint]

But in the unknown time before our U initiated, we can suppose time enough to evolve. At least we are not limited to the age of the universe. Your statement is like saying 250 ky is not enough time for humans to evolve, when that's the time they have existed as a species.