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

On 05/04/2024 15:28, John Larkin wrote:

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

>
TBH I'd prefer there to be something wrong with the Type Ia supernovae
standard candles in the early universe (making them overly bright).
>
https://en.wikipedia.org/wiki/Type_Ia_supernova
>
I understand that possibility has been ruled out but I don't know any
more details. They are very handy since when they go off they can
outshine an entire galaxy and are visible over huge distances.

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

The safe distance for a supernova explosion is estimated to be around 25 ly by the optimists and 250 ly by the pessimists. The true value is probably somewhere in between those two and not all supernovae are type I other sorts can be even more potent.
https://www.skyatnightmagazine.com/space-science/how-close-supernova-affect-life-earth
I recall a famous researcher in this field who gave a somewhat whimsical popular science talk on type Ia supernovae entitled "Can a young blue giant find lasting happiness in the arms of a degenerate white dwarf?" (spoiler alert - no they can't the liasson won't last!)
Betelgeuse and eta Carina are both candidates for going pop in the not too distant future and are already bright stars in our night sky. They will be daylight objects when they go bang possibly even as bright as the moon but point sources.

Are those things the sources of our heavy elements?

Supernovae and ultra massive stars are. Very massive stars can endothermically make heavier elements than iron by slow neutron capture but they are doomed to implode as supernovae when they finally run out of fuel. They collapse on the free fall timescale due to gravity and the core collapse can go to either a neutron star or black hole depending on the total mass. The rebound shockwave distributes the remains of the star into a shell supernova remnant of which the brightest in the night sky is Cassiopiea A. It looks for all the world like a hand grenade went off with an expanding shell of material around it.
https://public.nrao.edu/gallery/cassiopeia-a/
It would be about 1/5 the size of the moon if we could see in 6cm waveband!
Ultra massive stars become red giants in their final stages and aren't too good at holding onto their atmospheres so there is a lot of material that doesn't end up in the implosion but gets spread out into space. Only the mostly iron core undergoes collapse and implosion and a proportion of that material rebounds due to shockwave reflections.
--
Martin Brown