<<The galaxy itself wasn't destroyed by Surtur. The comic doesn't say anything about that, and Surtur doesn't wield that kind of power.>>
apologies, cube, you are correct about that. not sure how i misread it . . .
last bit of physics - a white dwarf forms when low and medium mass stars collapse in on themselves. the limit for a white dwarf (called chandrasekar's limit) is about 1.5 solar masses. if our sun became a white dwarf, all of its mass (almost no mass is lost in the compression process) would be compressed into an area about the size of the earth and a single sugar cube sized amount would weigh several tons. the larger the collapsing star's mass (up to the limit) the greater the density of the white dwarf. if a star has mass greater than about 1.5 (1.4 i think) solar masses, nuclear compression can't stop its collapse and it becomes a black hole. there would be no 'molten material' left.
anyhow, how strong is supes? good question, actually. i've been trying to figure out how much stronger i think he is myself. i'm really not sure. not a 'LOT' stronger, i don't think (both have done impressive things) but strong enough that it would make a difference. in straight h2h (without thor's hammer) i'd say supes (without superspeed or heat vision) would win 9/10. thor has been almost killed by hulk without his hammer, and that showing really was disappointing. supe's invulnerability is i think much better than thor's as well.
not sure that answers your question, but them's my thoughts.