Re: OT: Dark energy might not be constant at all

On 6/04/2024 1:28 am, John Larkin wrote:

On Fri, 5 Apr 2024 09:17:23 +0100, Martin Brown <'''newspam'''@nonad.co.uk> wrote:

On 05/04/2024 06:17, Jan Panteltje wrote:

10^44 joules could fry a thousand civilizations. We're lucky to live
in a boring suburb of the universe.

Supernova pop up all over - just not all that often. There's nothing unique about our suburb of the universe - corner of the galaxy might be a better way of referring to our immediate vicinity

Are those things the sources of our heavy elements?

That seems to be the current working hypothesis. Anything up to iron - 26 protons and 30 neutrons in the most common isotope Fe-56 (91.754%)
<https://en.wikipedia.org/wiki/Isotopes_of_iron>
can be synthesised in mainstream star, but it has the largest mass defect of any element. Fe-54, Fe-57 and Fe-58 are the other stable isotopes.
Getting anything heavier takes a supernova - gravitational pressure exceeds nuclear repulsion and all the matter at the core of the star collapses into neutron soup, but if the star isn't heavy enough to become a black hole the collapsing soup that was moving inward very fast until it hit it's density limit mostly bounced back out again and reverted from neutron soup to regular matter that included a lot of elements heavier than iron. The heaviest ones fissioned rapidly, but rest provide all the elements from iron upwards to uranium and the like.
They weren't there in the very early universe, and the second generation stars don't have all that much of them.
--
Bill Sloman, Sydney