Hi All

Lithium and deuterium burning need a mass ~ 13 times Jupiter. Core temp ~ 500,000 K

Main sequence ~ 80 times Jupiter : Core temp ~ 4,000,000 K

[NB: Jupiter: Core temp ~ 50,000 K... way too low]

...Ignition is due to the overall gravitational collapse of the body getting the core up to fusion temperatures and then containing those temperatures via pressure so convection doesn't cool the core off too much.

Drop some quark nuggests or neutronium into the core and you might create a local hot-spot that will heat up the core via fusion being "catalysed" around the ultra-dense mass, perhaps then igniting the whole core. But convection would "quickly" puff up Jupiter - I'm not sure what the equilibrium radius would then be.

For Europa to melt (T eff ~ 400 K) then Jupiter at its current radius will be ~ 1225 K... which wouldn't be that bright in the visible. To make 5775 K light like the Sun the final radius would need to be ~ 3200 km and the density ~ 14,000 times that of water... which would imply that stellifying Jupiter would most of it to collapse into degenerate matter. But collapsing the core too quick might cause a mini-Supernova rebound.

Collapsing Jupiter from R~ 71,500 km to R~ 3,200 km would release ~ 3 x 10^37 Joules - about 2,500 years worth of the Sun's output. To remain life-friendly on Europa that would need to be dragged out over ~ 116 million years. If we just wanted to illuminate Callisto then Jupiter would need to be ~ 9,600 km, and the collapse would need just 8 million years.

To conserve angular momentum stellar-Jupiter ("Lucifer" aka Clarke) would rotate once every 1.2 minutes. In which case it would be more lenticular than spherical. Overall stellifying Jupiter would be quite a feat...

Adam