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From: Martin Brown <'''newspam'''@nonad.co.uk>
Newsgroups: sci.electronics.design
Subject: Re: OT: Dark energy might not be constant at all
Date: Sat, 6 Apr 2024 14:48:59 +0100
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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