astronomy

clearedtoland, 10 miesięcy temu w Neptune and Uranus seen in true colours for first time

First they take away Pluto and now they’ve come for Neptune! My childhood was a lie.

Xariphon, 10 miesięcy temu w A Bizarre State of Matter Exists Deep Inside Large Neutron Stars

Would it be a yes-or-no thing, or more of a continuum?

At stellar mass x there's Some quark soup but it's mostly ordinary neutronium, at 50x there's More, at 10,000x there's Pretty Much All Of It, etc?

Or is it a critical mass kind of thing where at stellar mass x there's No Soup For You and at x+3 it's a veritable soup buffet?

MartianSands, 10 miesięcy temu

The latter, I suspect. That’s certainly how forming a neutron star works in the first place, because if a star gets so dense that it can form neutronium then the neutronium (which is far more dense than the core was before) can easily keep making more.

It’s a similar story with black holes. Get past the threshold at which it forms, and the process runs away and swallows the whole star.

If a quark soup is more dense than neutronium, then it would be fairly all-or-nothing

elucubra, 10 miesięcy temu w ESA's tiny pinhole thruster is ready for production

Nobody expects the Spanish propulsion

Artyom, rok temu w Are we living in a baby universe that looks like a black hole to outsiders?

I used to think this idea was kinda silly and based on flimsy and handwavey justification, but then I saw a colloquium by a famous black hole physicist on it. Now I REALLY think this idea is silly and made up!

TauZero, rok temu w Black holes could come in 'perfect pairs' in an ever expanding universe

Oh! They don’t mean that black holes must come in perfect pairs! The headline makes it sound like it’s about wormholes across vast distances. No! What they’ve found is a stable “orbit” solution for the two-body problem. Normally when you place two bodies anywhere in an empty universe, they will gravitate towards each other until they collide. But in a universe with dark energy, there is some perfect distance between them, where the accelerating expansion perfectly counterbalances the accelerating attraction. They’ve used general relativity math to actually calculate such an arrangement.

The “stable” orbit in this case is the same kind of stable as a pencil balanced on its sharp tip - if it tilts even slightly one way it will fall out of control. Although they tantalize the idea that they might be able to make it truly stable against small perturbations once they finish their spinning black hole solution.

I would like to have known some specific numbers examples! Like if you have as much dark energy as our universe, and two 10-solar-masses stellar black holes, how far apart would that be? Is it like 1Ly or 1MLy? How far for two 10-million-solar masses supermassive black holes? The formulas they created should give the exact answer but I am not skilled enough to substitute the correct numbers for the letters.