How do we know Nemesis is not a black hole (or neutron star)?

  • Nemesis, the hypothetical "death star", is supposed to be a massive body that orbits the Sun at long distances and periodically sends comets from the Oort Cloud into the inner solar system. These comets impact the Earth and cause extinction events. It hasn't been found, and the theoretical case for it is not compelling anyway.

    My question here is about this curious line from Richard Muller's page at LBL.

    Fortunately, several all-sky surveys are underway that should find Nemesis in the next few years, if it is there, and rule out Nemesis if they don't. (Nemesis could hide if it were a black hole, but that is not very plausible.) These surveys include Pan-Starrs and the LSST.

    How do we know it's not plausible for Nemesis to be a black hole? For that matter, how do we know it's not a neutron star?

    Answering this question might require divining what the author means by "rule out" and "not very plausible". If you need a dark, quiet object of almost any mass, you can propose a primordial black hole and explore the consequences, as in the paper Keith links to above. But perhaps "not very plausible" is intended to mean that a stellar black hole isn't very plausible, and when Muller said "rule out Nemesis", he meant "rule out any Nemesis belonging to any class of object we actually know about, as opposed to classes of object we can speculate".

  • ProfRob

    ProfRob Correct answer

    2 years ago

    If the Sun had been born in a relatively wide binary system with a star that was to become a black hole or neutron star via a supernova, then (a) it is quite likely that such a system would be disrupted by that supernova and we would not be in a binary system now; (b) there should be evidence of the supernova in the form of very high abundances of the daughters of certain short-lived radionuclides incorporated into solar system material. There is some evidence of the latter, but not I think enough for the Sun to have been in a binary system with such a star (though I might be checking this).

    An alternative argument is that the Sun is captured in orbit by the stellar remnant at a later date. This avoids the supernova problems, but the capture process is inherently unlikely in our Galaxy once stars have left their birth environments, especially capture which is tuned rather precisely to yield just less than zero for the resultant system potential energy of a very wide binary. Capture by a "normal" star would in any case be much more likely than capture by a relatively rare compact object.

    The sun is what would be captured not the other way around.

    Nemesis would be the more massive object; put the embryonic sun on a much more energetic orbit and have it be the captured body rather than the capturing body and it looks a little more sane.

    @Joshua "An alternative argument is that the Sun is captured..." I can't see which bit of that sentence implies that it is the Sun doing the capturing?

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