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Wally
2002-Jul-03, 02:51 PM
This from the following webpage:

http://www.cnn.com/2002/TECH/space/07/03/hubble.supernova.reut/index.html

"With their fuel exhausted, the stars' cores collapse, releasing an enormous amount of gravitational energy that in turn flings most of a star's mass into space at speeds up to 45 million miles (72 million km) per hour."

Is "gravitational energy" acceptable here? I'd think something like "incredible heat generated" or some such thing might work better.

Jim
2002-Jul-03, 05:34 PM
Since gravity holds things together, it seems illogical that excessive gravity would "fling" anything.

I think what they mean to say is that the gravitational energy leads to higher temp and press which causes a massive production of neutrinos which leads to the explosion of the collapsing core which flings stuff into space.

So they left out the middle part.

g99
2002-Jul-03, 05:36 PM
just ask yourself one question. What does it take to be the science advisor to a news agency? Poplarity. They can care less about the facts, all they care about it viewers, and what gets viewers is scary stuff. It is a hell of alot scaryer if you start spewing out a stream of nonsense scientific sounding words than saying that "the suns energy finally looses the tug-a-war with the inward gravitational pull of the star and thus collapses and explodes." What soends better "gravitational energy" or "the sun runs out of gas"?

Hale_Bopp
2002-Jul-03, 06:55 PM
Imagine you have a ball on a table. The ball rolls off the table. What happens when it hits the floor? It bounces! The energy for the bounce was gravitational potential energy that was converted.

A supernova is similar. Infalling matter "bounces" off a superdense core. So in that sense, the energy did, at least partly, come from gravity.

Of course this is a pretty big simplification. Much of the matter in the outer layers of stars heats up and undergo a series of complex nuclear reactions...some of which give off energy, some of which absorb energy.

I will have to do some reading on supernova now...you have me curious /phpBB/images/smiles/icon_smile.gif

Rob

roidspop
2002-Jul-05, 01:41 AM
...some of which give off energy, some of which absorb energy.

Without the 'absorbing' part, elements past iron would be vanishingly rare. So that gold ring I'm wearing is condensed gravitational energy. Who woulda thunk it?

g99
2002-Jul-05, 02:31 AM
you can't have any more elements past iron., Iron is the limit in a stars fusion., the other heavier elements are coused by nova and supernovas.

roidspop
2002-Jul-05, 04:44 PM
Iron is the limit in a stars fusion.,

With respect to the core, yes. When nucleosynthesis reaches iron in the core, the core is fated to collapse because no more energy is being released to support it.


the other heavier elements are coused by nova and supernovas.

The elements past iron are produced by fusion in the outer layers during the rebound phase.

g99
2002-Jul-05, 04:50 PM
Thanks, I thought differently. See even college students like me can learn something every once in a while.

Donnie B.
2002-Jul-05, 07:52 PM
On 2002-07-05 12:50, g99 wrote:
Thanks, I thought differently. See even college students like me can learn something every once in a while.


Even college students can learn? Er, isn't that what college students are supposed to do?
/phpBB/images/smiles/icon_biggrin.gif

nebularain
2002-Jul-05, 10:09 PM
On 2002-07-05 15:52, Donnie B. wrote:
Even college students can learn? Er, isn't that what college students are supposed to do?


Does he really want us to answer that?

(Note: I iz a colaje stoodent. /phpBB/images/smiles/icon_biggrin.gif)

Wiley
2002-Jul-05, 11:43 PM
On 2002-07-05 15:52, Donnie B. wrote:
Even college students can learn? Er, isn't that what college students are supposed to do?
/phpBB/images/smiles/icon_biggrin.gif



Donnie, remember at that age we already knew everything. /phpBB/images/smiles/icon_smile.gif

<font size=-1>[ This Message was edited by: Wiley on 2002-07-05 19:44 ]</font>

jaydeehess
2002-Jul-07, 05:02 AM
With their fuel exhausted, the stars' cores collapse, releasing an enormous amount of gravitational energy that in turn flings ...

How about; With the fuel down to a level at which thermonuclear pressures can no longer overcome gravity, the star collapses quickly upon itself creating an enormous impulse on the core. Fusion reactions creating elements above iron can then take place which creates a really, really (I ran out of superlatives) big explosion.

The journalism school at Carleton University in Ottawa , Canada offers specific science journalism courses. One of the few schools to do so.

I was yelling at the TV one time during a press conference about the crash of a jetliner. The NTSB official was giving a briefing about the accelerations (in three dimensions) that the plane underwent as revealed by the "black boxes". She was asked no less than 4 times to explain "acceleration" and "g-forces". Why would an editor send someone who could not understand acceleration to an aircraft crash briefing? Because the editor doesn't understand it either!
The briefer was reduced to using her hands to illustrate what the plane was doing.

<font size=-1>[ This Message was edited by: jaydeehess on 2002-07-07 01:03 ]</font>