3 ms·

Pretty good summary of what he’s getting at: https://www.explainxkcd.com/wiki/index.php/1758:_Astrophysics https://www.explainxkcd.com/wiki/index.php/1758:_Ast

• sillysaurusx 4y ago
  Whoa. Dark matter = possibly an unknown type of star too dim to see. https://en.m.wikipedia.org/wiki/Massive_compact_halo_object https://en.m.wikipedia.org/wiki/Massive_compact_halo_object Never thought about that. I always heard that dark matter was a particle that interacts gravitationally but not electromagnetically. The dim star theory seems at least worth considering. But that raises all kinds of questions, like how is it a star if it’s not emitting light? I like how some salty physicist added “Therefore, the missing mass problem is not solved by MACHOs” a few paragraphs in. :)
  • at_a_remove 4y ago
    I have been, rather annoyingly, been downvoted quite often in the past for being really clear on "dark matter," which is to say that astronomers study --broadly-- stars and their assemblages, things that emit light. Dark matter can encompass anything that doesn't shine like a star, be it exotic particles or just cold interstellar gas, little black holes, whatever. It isn't necessarily some Star Trek shit. It is just stuff we can tell exists by its gravitational signature on things that do shine -- light matter, aka stars.
    • nisegami 4y ago
      It's not just that it doesn't emit light, it doesn't appear to reflect or absorb light either. If it did, we should be able to pick it up through spectral analysis.
  • wiml 4y ago
    I think the usual place MACHO theories struggle to match observation is lensing events. If there were enough dark stars / planets / whatever out there to be the missing mass, we'd see characteristic blips in the light curves of stars when they wander between us and the star.