3 ms·

A non-interacting boson star would be transparent, but it still has gravity, so it would probably pick up baryonic matter. Should look like an ordinary star tha

A non-interacting boson star would be transparent, but it still has gravity, so it would probably pick up baryonic matter. Should look like an ordinary star that has too much mass for its diameter and burns more brightly due to the additional gravity compression. Dropping straight through a clean solar-mass boson star, though, would be uneventful. A little bit of blueshift on starlight, but probably not enough to detect by eye. Avoid a slingshot orbit. If it has the mass of the Sun and the same density, then it would have a "surface" gravity of 28g one million kilometers out. With that sharp of a gradient, a close orbit will want to pull your spacecraft apart as each atom tries to take a different trajectory, tidal forces. https://en.wikipedia.org/wiki/Roche_limit https://en.wikipedia.org/wiki/Roche_limit (A plot point in many a Larry Niven story)

raattgift 3y ago
Depends very much on the boson and its interaction with the (extended) Standard Model that includes it. Axions, if they exist, take part in nuclear interactions. You can expect to have a bad day when encountering them at high density (e.g. expect fissions from neutron disruptions). In the preprint at the top, the Action (eqn (1)) and Lagrangian densities (eqn (2)) are non-interacting (except for self-interaction and gravitation) for tractability reasons, so the scalar boson version is only sorta like the axion. The paper's setting only considers each type of boson in isolation from any other type of matter in the universe. However any infalling body which has any nonzero distribution of these proposed vector or scalar bosons in them would expect the self-interaction term to be important, so you could still have a bad day for non-gravitational reasons. I don't think a non-relativistic analysis of a manifestly relativistic compact object is particularly enlightening. Boson stars can be more compact than neutron stars (see Figure 2 on p. 7 of the preprint). Qualitatively though, you'd have a bad day if you got too close; you are right that tidal stresses are probably what will get you in the case of only-self-interacting bosons. The Roche limit, developed well before even special relativity, matters for slowly-orbiting (hyperbolic orbits count) self-gravitating bodies (so big asteroids and comets count). Your parent commentator's flight would presumably be in a spacecraft (or suit) that is held together by intermolecular forces instead of its own gravity. Those forces are typically much stronger than gravity; gravity only overcomes them in relativistic systems.
- NoMoreNicksLeft 3y ago
  Wait. So there's not even a model of which bosons we're talking about? I'd seen the wikipedia a few years back, and I assumed it was just light on details because it's wikipedia.
  - raattgift 3y ago
    There are dozens, scores, and likely hundreds of different (hypothetical) bosons described as the sole (or at least dominant) matter in a boson star (cf. link at the end of this comment). In the preprint linked at the top I count at least sixteen different specific (hypothetical) bosons in their References section, and the preprint discusses two very broad families (in §2). The authors' claim is that a wide variety of (massive) boson theories can in bulk behaviour produce the important characteristics of a boson star constrained by what they know of this particular binary (see end of 1st paragraph of §6). > assumed it was just light on details because it's wikipedia An encyclopedic overview should probably not point to every paper one would get from a search of the literature, let alone to a search of preprints. Wikipedia is likely light on details because the topic is niche because it's an idea which is nowhere near as convincing as perturbations of black hole solutions of the Einstein Field Equations ("standard black holes"), and not even more persuasive than e.g. fuzzballs, gravastars, and other relativistic dark star hypotheses also aiming to overthrow standard black holes for various reasons. Even the list of reasons for studying just boson stars gets long: because the compact object may be dominated by a particle that might solve problems in particle physics (but which would be hard to prove/disprove in an Earthbound lab soon); or that might also describe dark matter and/or dark energy; or that (if observed) would support a broader theory like M-theory; or that might put to bed any questioning of unitarity; ... And because some types of boson stars (if found in nature) might support one of these broader aims to the exclusion of the other aims, it's a somewhat busy field with papers and anti-papers. Here's a couple hundred: <https://arxiv.org/search/?query=%22boson+star%22&searchtype=all&abstracts=show&order=-announced_date_first&size=50 https://arxiv.org/search/?query=%22boson+star%22&searchtype=...>
mr_toad 3y ago
> Dropping straight through a clean solar-mass boson star, though, would be uneventful. If you find being crushed into degenerate matter uneventful.
- antonvs 3y ago
  Crushed by what? Weakly-interacting bosons can't crush you with pressure. As far as gravity goes, as long as you're on a direct trajectory towards the center, you'll be free-falling so won't experience a gravitational "force" in your own reference frame.
  - mr_toad 3y ago
    The literature I’ve read all talks about Boson stars as extremely dense objects, comparable to neutron stars.
    - antonvs 3y ago
      The comment you originally replied to was talking about "a non-interacting boson star," i.e. a boson star made up one of the hypothetical types of boson that makes up dark matter. In that case, the only significant interaction between those bosons and you would be gravity which, when in free-fall, affects the path you follow but won't in itself crush you. This assumes that (a) that there's not much normal matter in the star to crash into, and (b) that the mass is not large enough to generate deadly tidal forces. That's why the OP specified "a clean solar-mass boson star". But it's worth noting that a "clean" non-interacting boson star can't really form in the normal way, since the bosons in question don't interact with each other in any way that would allow them to form dense clumps. You'd need some normal matter to provide a kind of anchor. In that case you'd see a more normal-looking object that just happens to be heavier than it should be given its visible composition, and you wouldn't be able to "drop through it."
antonvs 3y ago
> Dropping straight through a clean solar-mass boson star, though, would be uneventful. How would you figure out the safe trajectory to avoid tidal forces?
- sbierwagen 3y ago
  If you know the mass and radius of the object, you can calculate the tidal force. (You can map this with a gravity sensor on a probe or just throwing a bunch of rocks through the system and watching how it bends their trajectories) Then it depends on the spacecraft. If your ship is 1 km long and made of cotton candy, then it won't take much force at all to destroy it. If it's 10 m long (dramatically reducing the tidal effect) and made of solid diamond then it can fly much closer. Not that there would be anything to see. Read Neutron Star by Larry Niven (1966) for a dramatic description of a close flyby of a compact stellar mass object.
  - antonvs 3y ago
    > If you know the mass and radius of the object, you can calculate the tidal force. The issue is more the position of the object. Good luck doing trajectory correction for an object you can't see. The "throw a bunch of rocks" technique might help, but since they'd be unpowered they're not going to be following a trajectory that minimizes tidal force. It's still going to be enormously difficult to thread the needle through an invisible object that's going to tear you apart if you're not on the right trajectory. Perhaps the technique Beowulf Shaeffer used could work if it were done with instruments - measure the tidal forces aboard the ship and navigate accordingly to minimize them.

raattgift 3y ago

Depends very much on the boson and its interaction with the (extended) Standard Model that includes it. Axions, if they exist, take part in nuclear interactions. You can expect to have a bad day when encountering them at high density (e.g. expect fissions from neutron disruptions). In the preprint at the top, the Action (eqn (1)) and Lagrangian densities (eqn (2)) are non-interacting (except for self-interaction and gravitation) for tractability reasons, so the scalar boson version is only sorta like the axion. The paper's setting only considers each type of boson in isolation from any other type of matter in the universe. However any infalling body which has any nonzero distribution of these proposed vector or scalar bosons in them would expect the self-interaction term to be important, so you could still have a bad day for non-gravitational reasons. I don't think a non-relativistic analysis of a manifestly relativistic compact object is particularly enlightening. Boson stars can be more compact than neutron stars (see Figure 2 on p. 7 of the preprint). Qualitatively though, you'd have a bad day if you got too close; you are right that tidal stresses are probably what will get you in the case of only-self-interacting bosons. The Roche limit, developed well before even special relativity, matters for slowly-orbiting (hyperbolic orbits count) self-gravitating bodies (so big asteroids and comets count). Your parent commentator's flight would presumably be in a spacecraft (or suit) that is held together by intermolecular forces instead of its own gravity. Those forces are typically much stronger than gravity; gravity only overcomes them in relativistic systems.

NoMoreNicksLeft 3y ago
Wait. So there's not even a model of which bosons we're talking about? I'd seen the wikipedia a few years back, and I assumed it was just light on details because it's wikipedia.
- raattgift 3y ago
  There are dozens, scores, and likely hundreds of different (hypothetical) bosons described as the sole (or at least dominant) matter in a boson star (cf. link at the end of this comment). In the preprint linked at the top I count at least sixteen different specific (hypothetical) bosons in their References section, and the preprint discusses two very broad families (in §2). The authors' claim is that a wide variety of (massive) boson theories can in bulk behaviour produce the important characteristics of a boson star constrained by what they know of this particular binary (see end of 1st paragraph of §6). > assumed it was just light on details because it's wikipedia An encyclopedic overview should probably not point to every paper one would get from a search of the literature, let alone to a search of preprints. Wikipedia is likely light on details because the topic is niche because it's an idea which is nowhere near as convincing as perturbations of black hole solutions of the Einstein Field Equations ("standard black holes"), and not even more persuasive than e.g. fuzzballs, gravastars, and other relativistic dark star hypotheses also aiming to overthrow standard black holes for various reasons. Even the list of reasons for studying just boson stars gets long: because the compact object may be dominated by a particle that might solve problems in particle physics (but which would be hard to prove/disprove in an Earthbound lab soon); or that might also describe dark matter and/or dark energy; or that (if observed) would support a broader theory like M-theory; or that might put to bed any questioning of unitarity; ... And because some types of boson stars (if found in nature) might support one of these broader aims to the exclusion of the other aims, it's a somewhat busy field with papers and anti-papers. Here's a couple hundred: <https://arxiv.org/search/?query=%22boson+star%22&searchtype=all&abstracts=show&order=-announced_date_first&size=50 https://arxiv.org/search/?query=%22boson+star%22&searchtype=...>

mr_toad 3y ago

> Dropping straight through a clean solar-mass boson star, though, would be uneventful. If you find being crushed into degenerate matter uneventful.

antonvs 3y ago
Crushed by what? Weakly-interacting bosons can't crush you with pressure. As far as gravity goes, as long as you're on a direct trajectory towards the center, you'll be free-falling so won't experience a gravitational "force" in your own reference frame.
- mr_toad 3y ago
  The literature I’ve read all talks about Boson stars as extremely dense objects, comparable to neutron stars.
  - antonvs 3y ago
    The comment you originally replied to was talking about "a non-interacting boson star," i.e. a boson star made up one of the hypothetical types of boson that makes up dark matter. In that case, the only significant interaction between those bosons and you would be gravity which, when in free-fall, affects the path you follow but won't in itself crush you. This assumes that (a) that there's not much normal matter in the star to crash into, and (b) that the mass is not large enough to generate deadly tidal forces. That's why the OP specified "a clean solar-mass boson star". But it's worth noting that a "clean" non-interacting boson star can't really form in the normal way, since the bosons in question don't interact with each other in any way that would allow them to form dense clumps. You'd need some normal matter to provide a kind of anchor. In that case you'd see a more normal-looking object that just happens to be heavier than it should be given its visible composition, and you wouldn't be able to "drop through it."

antonvs 3y ago

> Dropping straight through a clean solar-mass boson star, though, would be uneventful. How would you figure out the safe trajectory to avoid tidal forces?

sbierwagen 3y ago
If you know the mass and radius of the object, you can calculate the tidal force. (You can map this with a gravity sensor on a probe or just throwing a bunch of rocks through the system and watching how it bends their trajectories) Then it depends on the spacecraft. If your ship is 1 km long and made of cotton candy, then it won't take much force at all to destroy it. If it's 10 m long (dramatically reducing the tidal effect) and made of solid diamond then it can fly much closer. Not that there would be anything to see. Read Neutron Star by Larry Niven (1966) for a dramatic description of a close flyby of a compact stellar mass object.
- antonvs 3y ago
  > If you know the mass and radius of the object, you can calculate the tidal force. The issue is more the position of the object. Good luck doing trajectory correction for an object you can't see. The "throw a bunch of rocks" technique might help, but since they'd be unpowered they're not going to be following a trajectory that minimizes tidal force. It's still going to be enormously difficult to thread the needle through an invisible object that's going to tear you apart if you're not on the right trajectory. Perhaps the technique Beowulf Shaeffer used could work if it were done with instruments - measure the tidal forces aboard the ship and navigate accordingly to minimize them.