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Ramon Rozas
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  		   Posted 6/10/2008 8:15 PM (GMT -5)    Quote This PostAlert An Admin About This Post.
Imagine a scenario where a MacGuffin lowered the strength of gravity by 50% in a star.  Would fusion stop because of the drop in pressure?  Would there be an explosion due to the rebound?  Can anyone point me to a layperson's resource where I might try to answer these questions for the purposes of my story de jour?  :-)
 
Thank you very much in advance!
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Anthony G Williams
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  		   Posted 6/12/2008 3:20 AM (GMT -5)    Quote This PostAlert An Admin About This Post.
I'm not a physicist but, at an uninformed guess, a sudden halving of the gravitational force holding a sun together would cause it to expand rapidly, and to cool down quite sharply. Whether the remaining gravity would be strong enough to maintain fusion I don't know, but I would at least expect ordinary stars to become more like red giants, blue-whites to become huge ordinary stars, etc.
 
If you're thinking of putting it in a story, though, best to check on an appropriate site. Possibly this one: http://www.mkaku.org/forums/
 

Tony Williams
Scales (2007), The Foresight War (2004)
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SFF Blog: http://sciencefictionfantasy.blogspot.com/


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Rob Santa
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  		   Posted 6/12/2008 8:03 AM (GMT -5)    Quote This PostAlert An Admin About This Post.
While I realize the most informed experts do not have a full understanding of how gravity works, isn't it tied to mass? If the gravity fell apart, wouldn't it be due to a sudden dropping in the sun's mass as well?


Rob Santa
Hopelessly Addicted Writer of Speculative Fiction
and CEO of Ricasso Press

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tchernabyelo
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  		   Posted 6/12/2008 9:03 AM (GMT -5)    Quote This PostAlert An Admin About This Post.
I'm assuming the question involves the laws of physics being changed locally, which is not an unusual bit of handwavium in SF circles... there are various universal "constants" which could be tinkered with to have interesting effects.

I'm m with Tony - it will definitely be dependent on the mass and type of the star in question. The weaker the star, the less chance it has of carrying on functioning.

One should note that if you DO reduce gravity locally for a star, you have to look at the effect that has on anything orbiting the star, as well. Some orbits will surely result in things flying off into space, freed from the confines of their local frame of reference.... all in all, you are looking at something majorly cataclysmic for anyone and anything in the immediate vicinity, though it would be irrelevant to stuff beyond the local orbit.

Brian Dolton
 
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"The Box Of Beautiful Things" - IGMS#3
"The Man Who Was Never Afraid" - Abyss and Apex #20
"At Blue Crane Falls" - Abyss and Apex #25
"Where No Wind Blows" - Staffs & Starships #2
"The Gray World" - Every Day Fiction (June 1st 2008) 
"What The Sea Refuses" - Black Gate (forthcoming)
"What The Heart Bears" - Black Gate (forthcoming)
"Above The Clouds" - Paper Blossoms, Sharpened Steel (forthcoming)
"Three Out Of Four" - Sorcerous Signals Feb-Apr 08 
"The Dragon Path" - Fictitious Force #5
"The Last Arrow Of Liang Xi" - Darwin's Evolutions (forthcoming)
 
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"The Unicorn Hunter" - OG's Speculative Fiction #8
"Call Centre" - Necrotic Tissue #1
"When Winter Came" - ASIM #32
"Cold Fire" - Flashing Swords #9, The Age Of Blood And Snow (forthcoming) 
"St. Saviour And The Devil's Dandy" - Flashing Swords (forthcoming)
"In This City" - Fantasy Magazine (forthcoming)

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Ramon Rozas
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  		   Posted 6/12/2008 10:37 AM (GMT -5)    Quote This PostAlert An Admin About This Post.
Oh, I hope its cataclysmic! In a 1-sol mass star, I was guessing that the left-over fusion pressure would cause the star to "puffball", exactly as Tony suggested, although what I've read suggests that fusion would then stop because a stellar mass with only 1/2 the gravitational pressure of Sol would likely not be able to sustain fusion (if I'm understanding it correctly).

And, yes, it is handwavium!

Thank you for the suggestions!
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Ramon Rozas
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  		   Posted 6/12/2008 10:46 AM (GMT -5)    Quote This PostAlert An Admin About This Post.
Handwavium! I really like that term, Mr. Dalton!
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Rob Santa
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  		   Posted 6/12/2008 1:34 PM (GMT -5)    Quote This PostAlert An Admin About This Post.
Me too. Gonna,ahem, appropriate it.


Rob Santa
Hopelessly Addicted Writer of Speculative Fiction
and CEO of Ricasso Press

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Jordan Lapp
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  		   Posted 6/12/2008 5:16 PM (GMT -5)    Quote This PostAlert An Admin About This Post.
Ramon Rozas said...
Oh, I hope its cataclysmic! In a 1-sol mass star, I was guessing that the left-over fusion pressure would cause the star to "puffball", exactly as Tony suggested, although what I've read suggests that fusion would then stop because a stellar mass with only 1/2 the gravitational pressure of Sol would likely not be able to sustain fusion (if I'm understanding it correctly).

And, yes, it is handwavium!

Thank you for the suggestions!
There are brown dwarfs all the way down to .3% of the sun's mass, so I believe it would still be able to sustain fusion.
 
I'm admittedly a lay person (though my cosmology kung-fu is strong), but I'm guessing there'd be a Nova, not the gentle swelling that Tony describes. Super compressed gas suddenly uncompressing? That sounds like a boom.

Jordan Lapp
Managing Editor
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Ramon Rozas
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  		   Posted 6/12/2008 5:28 PM (GMT -5)    Quote This PostAlert An Admin About This Post.
Jordan - good point with the brown dwarves. However, wouldn't a nova require that more of the mass of the star remain inside the dense core? The decompression of the gas would be dramatic, but I wonder whether it would be as dramatic as the sudden fusion of a whole stellar layer of hydrogen, which is what I understand a nova to be.

For the purposes of my story, it would wreck that solar system, but would it send out an interstellar blast wave like a Type 1a supernova?

Interesting stuff!
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Jordan Lapp
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  		   Posted 6/12/2008 5:37 PM (GMT -5)    Quote This PostAlert An Admin About This Post.
I think you're confusing a nova and a supernova... but I didn't get it right either. Novae are caused when a white dwarf in a binary system accretes enough material from its companion to cause an explosion. Supernovae are the stellar explosions that you describe. And here I said my cosmology was strong :P

Pretend I said, "A nova-type explosion".

Jordan Lapp
Managing Editor
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Ramon Rozas
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  		   Posted 6/12/2008 8:23 PM (GMT -5)    Quote This PostAlert An Admin About This Post.
Yes, they are different. However, a nova occurs (as I understand it) when a layer of hydrogen has accumulated on a white dwarf (sucked off of its regular companion star) and is crushed down by the gravitational potential of the dwarf sufficiently to trigger an explosion of fusion.

A supernova is when the collapse of a star generates sufficient heat and pressure to trigger the sudden fusion of the remaning hydrogen and carbon ash of the star.

Both generate massive explosions (super obviously greater than nova, and a nova is repeatable). However, I'm not sure my thought-experiment would generate such a blast because there's no gravitational potential energy forcing fusion on the higher-atomic number byproducts (as in a supernova) or flash fusioning a layer of hydrogen (as a nova).

A blast, but not a nova-strength one (I think). Maybe more like the quick expansion of a red giant.
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Jordan Lapp
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  		   Posted 6/12/2008 8:36 PM (GMT -5)    Quote This PostAlert An Admin About This Post.
I'm not sure all that material would end up in a neat little (or big) ball. It would probably be flung way out into space (much like a nova), and not collapse back into anything recognizable as a "star" for millions of years, if at all.

But who knows? Good question for a PhD in astrophysics.

Jordan Lapp
Managing Editor
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