Only a Very Narrow Range of Star Sizes Suitable for Life?

The following suggests that only a very narrow range of star sizes is
suitable for life and is exerpted from
http://www.godandscience.org/love/sld019.html :

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The size of the parent star is crucial for the ability of that star to
support life. Large stars undergo rapid and unstable burning (extreme
temperature variations over millions of years), which cannot support life.
Stars increase in luminosity as they age. For example, our star, the Sun,
has increased its energy output by 35% since its beginning. Fortunately for
the Earth, this change has been compensated by a decrease in the levels of
greenhouse gases (another design parameter), which lowered the ability of
the Earth to hold onto the increased heat produced by our more luminous Sun.
For stars larger than our Sun, the increase in luminosity is much greater,
which could not be compensated. In addition, large stars have very short
lifespans (as short as a few million years).

Stars smaller than our Sun are not suitable to support life on planets.
Although these stars are able to undergo quite stable burning for billions
of years, their small mass requires that life-containing planets be much
closer to the star. Planets within the life zone have to be so close to the
star that the gravitational interaction (which increases with the fourth
power as the distance decreases) causes the planet's rotational period to be
increased significantly. For example, both Mercury and Venus have rotational
periods that are as long or longer than their revolutionary period. These 88
and 243 Earth-day rotational periods (for Mercury and Venus, respectively)
result in extremes of temperatures on the surface of these planets, which
prohibits the survival of lifeforms.
************************

Would the people knowledgeable in this area in a.a respond Yes to the
Subject Line heading? And is the text generally valid? (And no (sigh),
It's not homework.) TIA Regards, Brett.

"Brett Aubrey" wrote in message
news:qtZHd.133718$Xk.51181@pd7tw3no...
The following suggests that only a very narrow range of star sizes is
suitable for life and is exerpted from
http://www.godandscience.org/love/sld019.html :

************************
The size of the parent star is crucial for the ability of that star to
support life. Large stars undergo rapid and unstable burning (extreme
temperature variations over millions of years), which cannot support life.

The following, from http://www.stardate.org/resources/stars/bash.html seems
to conflict somewhat with the above statement, vis-a-vis stability:

For long periods of a star's life, between its birth and death, it
changes
very slowly. The changes are so slow that astronomers who study stars
consider a star's mass, size, temperature, and luminosity to be constant.

I would be interested in comments on this apparent conflict. TIA. Brett.

Stars increase in luminosity as they age. For example, our star, the Sun,
has increased its energy output by 35% since its beginning. Fortunately
for
the Earth, this change has been compensated by a decrease in the levels of
greenhouse gases (another design parameter), which lowered the ability of
the Earth to hold onto the increased heat produced by our more luminous
Sun. For stars larger than our Sun, the increase in luminosity is much
greater, which could not be compensated. In addition, large stars
have very short lifespans (as short as a few million years).

Stars smaller than our Sun are not suitable to support life on planets.
Although these stars are able to undergo quite stable burning for billions
of years, their small mass requires that life-containing planets be much
closer to the star. Planets within the life zone have to be so close to
the
star that the gravitational interaction (which increases with the fourth
power as the distance decreases) causes the planet's rotational period
to be increased significantly. For example, both Mercury and Venus
have rotational periods that are as long or longer than their
revolutionary
period. These 88 and 243 Earth-day rotational periods (for Mercury
and Venus, respectively) result in extremes of temperatures on the
surface of these planets, which prohibits the survival of lifeforms.
************************

Would the people knowledgeable in this area in a.a respond Yes to the
Subject Line heading? And is the text generally valid? (And no (sigh),
It's not homework.) TIA Regards, Brett.

In message qtZHd.133718$Xk.51181@pd7tw3no, Brett Aubrey
writes
The following suggests that only a very narrow range of star sizes is
suitable for life and is exerpted from
http://www.godandscience.org/love/sld019.html :

Would the people knowledgeable in this area in a.a respond Yes to the
Subject Line heading? And is the text generally valid? (And no (sigh),
It's not homework.) TIA Regards, Brett.


No.
I don't trust your source simply because of its agenda, and while it's
right about large stars having too short a life span it isn't right
about dwarf stars.
Planets have already been detected around red dwarfs, and theoretical
studies have shown that they can retain an atmosphere, and that flares
from the star aren't necessarily lethal.
More, water maser radiation has been detected from the star Lalande
21185, which is known to have planets
http://members.nova.org/~sol/solcom/stars/la21185.htm. There's a
warning that the radiation could come from the star itself, but I wonder
if Hal Clement's Dhrawn is waiting for us :-)
--
Support the DEC Tsunami Appeal http://www.dec.org.uk/.
Remove spam and invalid from address to reply.

Brett Aubrey wrote:

"Brett Aubrey" wrote in message
news:qtZHd.133718$Xk.51181@pd7tw3no...
The following suggests that only a very narrow range of star sizes is
suitable for life and is exerpted from
http://www.godandscience.org/love/sld019.html :

************************
The size of the parent star is crucial for the ability of that star to
support life. Large stars undergo rapid and unstable burning (extreme
temperature variations over millions of years), which cannot support life.

The following, from http://www.stardate.org/resources/stars/bash.html seems
to conflict somewhat with the above statement, vis-a-vis stability:

For long periods of a star's life, between its birth and death, it
changes
very slowly. The changes are so slow that astronomers who study stars
consider a star's mass, size, temperature, and luminosity to be constant.

I would be interested in comments on this apparent conflict. TIA. Brett.


Something like 95% stars are smaller than the Sun, aging so slowly
that their characteristics remain constant over any conceivable
observing programme. Even the 'short-lived' blue supergiants spend
most of their lifespans in the main sequence, changing only gradually
and fairly little overall for a period comparable to the age of our
species -- the difference between millions and billions of years is
pretty meaningless from a human POV! That's not to say, though, that
variability sufficient to make life difficult is uncommon; a great
many stars are also in binary or multiple systems, which would often
limit or eliminate the 'habitable zone', beside that close stellar
companionship is frequently associated with erratic variability in
one or more of the stars, the most dramatic examples being novae.

At any rate, the first quote seems to come from a context of the very
long time-scales involved in evolution (based on the history of
terrestrial life), while the second appears to concern the amount of
change that can be observed in a span of decades or centuries.

--
Odysseus