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This paper doesn't seem to agree: > the scenario of a central black hole requires unreasonable amount of fine-tuning within the usual evolutionary channels. In

by spuz 3y ago

This paper doesn't seem to agree: > the scenario of a central black hole requires unreasonable amount of fine-tuning within the usual evolutionary channels. In particular, if the system is expected to have formed as a binary in isolation, a common envelope formation scenario is rather unlikely, given the system’s arrangement. This requires an extreme, and possibly unphysical, tuning of the relevant parameters of the evolutionary channel under consideration. Moreover, formation within a globular cluster is also improbable given the geometrical characteristics of the observed orbit. Other evolutionary channels such as formation without a common envelope or via a hierarchical triple also seem unlikely for similar reasons. What makes you think their proposal isn't more likely than a black hole?

daniel-thompson 3y ago
More likely != confirmed
nawgz 3y ago
Is a "boson star" even a confirmed physical construct? I can see confirmed neutron stars like RXJ1856 that they think might be a strange star, but... Just based on what is a confirmed physical construct in the universe, a black hole seems far likelier. Obviously they address this in a way I'm not knowledgeable enough to argue against. Regardless, it will be an interesting scenario to watch evolve!
- pja 3y ago
  > Is a "boson star" even a confirmed physical construct? No. We don’t even have evidence of a candidate boson you could use to make one.
  - dboreham 3y ago
    First catch your boson.
jwuphysics 3y ago
> What makes you think their proposal isn't more likely than a black hole? Because a boson star is purely theoretical and I have a much stronger observational prior that the object is a black hole.
- bookofjoe 3y ago
  Once upon a time black holes were purely theoretical. See, for example: >The Country Parson Who Conceived of Black Holes [in 1783] https://www.amnh.org/learn-teach/curriculum-collections/cosmic-horizons-book/john-michell-black-holes#:~:text=A%20black%20hole%20is%20a,Michell%2C%20an%20English%20country%20parson https://www.amnh.org/learn-teach/curriculum-collections/cosm.... >A Brief History of Black Holes https://www.amnh.org/learn-teach/curriculum-collections/cosmic-horizons-book/john-michell-black-holes#:~:text=A%20black%20hole%20is%20a,Michell%2C%20an%20English%20country%20parson https://www.amnh.org/learn-teach/curriculum-collections/cosm.... >At a conference in New York in 1967, Dr. Wheeler, seizing on a suggestion shouted from the audience, hit on the name “black hole” to dramatize this dire possibility for a star and for physics. https://www.nytimes.com/2008/04/14/science/14wheeler.html#:~:text=At%20a%20conference%20in%20New,a%20star%20and%20for%20physics https://www.nytimes.com/2008/04/14/science/14wheeler.html#:~....
  - The_Colonel 3y ago
    Survivorship bias. Aether was once also a theory which "just" needed an experimental evidence.
jiggawatts 3y ago
P-hacking. The universe is big and has lots of stars. Even “very unlikely” things ought to turn up. E.g.: one in a billion chance ought to occur hundreds of times… in our galaxy alone!
- burnte 3y ago
  This is one of the hardest things to grasp about the size of the universe; it's so damn big pretty much anything is possible somewhere.
  - vlovich123 3y ago
    Conversely, anything we do manage to observe is more likely to lay within most common probability space simply because we’re similarly observing such a tiny portion of what’s happening in the universe. Think about if you sample uniformly 0.01% of 1B requests / second coming into your system - you’re going to see all the common scenarios and none of the uncommon ones. Sure space isn’t quite the same thing since we don’t observe uniformly, but similarly we’re observing an infinitely smaller part of the overall space anyway.
  - vinaypai 3y ago
    The universe is big, but we're only observing a miniscule fraction of it, especially at the level of individual star systems.
    - burnte 3y ago
      That doesn't really have any relevance, though. Every single possibility is as likely as the others, it's just there are many more situations in which a system will look "normal", but we still shouldn't be overly surprised by the occasional outlier, we're bound to stumble on them even if rarely.
metalliqaz 3y ago
that's what I mean by "unusual circumstances". As you point out, the "usual evolutionary channels" don't really fit.
- spuz 3y ago
  This is why I included this part of the quote: > Other evolutionary channels such as formation without a common envelope or via a hierarchical triple also seem unlikely for similar reasons. Maybe it's hard to say without getting into specifics but it seems that the paper has considered the "unusual circumstances" in your statement.
  - raattgift 3y ago
    The paper rests on the MNRAS published version of <https://arxiv.org/abs/2209.06833 https://arxiv.org/abs/2209.06833> (ref. [EBRQ+22] in the preprint at the top, cited at the end of the paragraph you quote upthread). [EBRQ+22] itself proposes a triple as a possibility: "The system's evolution may be better-explained in models in which the G star was initially a wide tertiary companion to a close binary containing two massive stars. In this case, interactions between the two stars could have prevented either one from expanding to become a red supergiant, such that the G star could have formed in an orbit similar to its current orbit (but somewhat tighter) and remained there ever since. High-precision RV follow-up offers the tantalizing possibility of testing this scenario." RV there is "radial velocity measurements". Moreover, the part you quote and in particular "Moreover, formation within a globular cluster is also improbable" does not touch on their reference's "... dynamical formation in an open cluster that has since dissolved is more plausible." Disruptions of open clusters are well known. <https://en.wikipedia.org/wiki/Open_cluster#Eventual_fate https://en.wikipedia.org/wiki/Open_cluster#Eventual_fate>.
raattgift 3y ago
First see footnote 1 of the first page of the preprint linked at the top. The authors are jumping the gun. That's fine for theorists, but bear in mind that they are literally in the dark on a number of telescopic observables, any of which would shoot down the idea in the preprint. Some of these are achievable by EHT. See e.g. Olivares et al. "How to tell an accreting boson star from a black hole" (2020) <https://discovery.ucl.ac.uk/id/eprint/10112389/1/staa1878.pdf https://discovery.ucl.ac.uk/id/eprint/10112389/1/staa1878.pd...> [pdf]. The exotic bosons available in a 3+1 spacetime have never been detected at energy levels low enough that one might expect them to be reasonably bound by the weak (yes, weak) gravitation required by the boson star's internal repulsive forces. If the internal repulsive forces are too weak (or their self-gravitation isn't weak enough), the bosons cannot support the star against ultimate gravitational collapse (into a black hole). If the internal repulsive forces are too strong, the bosons all escape rather than stick around in the neighbourhood of the star. The latter is especially acute since the boson masses considered by the paper may be smaller than that of neutrinos. Until a suitable slightly self-repelling exotic boson is discovered, achieving and maintaining equilibrium between it and gravitation is pretty fatal to the boson star idea. Cold massive bosons are an idea for particle dark matter, incidentally. An example dark matter candidate is the axion. Axions have not been convincingly observed, and might not exist. A compact object made of essentially only axions could plausibly meet the criteria in the preprint linked at the top (cf their axion-motivated scalar field equation at eqn (9)), depending on details of heating during gravitational compaction. Also see e.g. Mohapatra et al., "Dense Axion Stars" (2016) <https://arxiv.org/abs/1512.00108 https://arxiv.org/abs/1512.00108> which is the preprint version of the PRL letter <https://doi.org/10.1103/PhysRevLett.117.121801 https://doi.org/10.1103/PhysRevLett.117.121801>. There is as far as I know no clear mechanism to have anything like the axion density required for self-gravitation except in the very early universe, a long time before the first galaxies. So then why would small primordial axion stars be in galaxies, as the binary in the article at the top appears to be? How do you keep them small, rather than coalescing into supermassive compact objects? The preprint at the top discusses other Beyond The Standard Model (of particle physics; BTSM) possibilities, but they are less convincing than the axion (for starters, such BTSM extensions need to have some non-physical degrees of freedom strongly suppressed, since such BTSM theories are almost always "haunted" by <https://en.wikipedia.org/wiki/Ghost_(physics) https://en.wikipedia.org/wiki/Ghost_(physics)>s.). Additionally, the axion is motivated by the strong CP problem in the Standard Model, and if there is a lot of them they become gravitationally relevant. The non-axion options in the preprint at the top are afaik only motivated by a lack of knowledge about the microscopic details of gravitational physics. (See Koberlein's 2021 blog entry on Proca Stars <https://briankoberlein.com/blog/proca-stars/ https://briankoberlein.com/blog/proca-stars/> for a brief intro to (light) massive vector boson stars).
jheriko 3y ago
runaway stars suggest that interactions occur leaving binaries behind in these kinds of configurations. i see no need for unphysical fine-tuning. looking at the paper they cite as reference for this claim, those authors thought exactly the same... https://academic.oup.com/mnras/article-abstract/518/1/1057/6794289 https://academic.oup.com/mnras/article-abstract/518/1/1057/6...

by spuz 3y ago

daniel-thompson 3y ago

More likely != confirmed

nawgz 3y ago

Is a "boson star" even a confirmed physical construct? I can see confirmed neutron stars like RXJ1856 that they think might be a strange star, but... Just based on what is a confirmed physical construct in the universe, a black hole seems far likelier. Obviously they address this in a way I'm not knowledgeable enough to argue against. Regardless, it will be an interesting scenario to watch evolve!

pja 3y ago
> Is a "boson star" even a confirmed physical construct? No. We don’t even have evidence of a candidate boson you could use to make one.
- dboreham 3y ago
  First catch your boson.

jwuphysics 3y ago

> What makes you think their proposal isn't more likely than a black hole? Because a boson star is purely theoretical and I have a much stronger observational prior that the object is a black hole.

bookofjoe 3y ago
Once upon a time black holes were purely theoretical. See, for example: >The Country Parson Who Conceived of Black Holes [in 1783] https://www.amnh.org/learn-teach/curriculum-collections/cosmic-horizons-book/john-michell-black-holes#:~:text=A%20black%20hole%20is%20a,Michell%2C%20an%20English%20country%20parson https://www.amnh.org/learn-teach/curriculum-collections/cosm.... >A Brief History of Black Holes https://www.amnh.org/learn-teach/curriculum-collections/cosmic-horizons-book/john-michell-black-holes#:~:text=A%20black%20hole%20is%20a,Michell%2C%20an%20English%20country%20parson https://www.amnh.org/learn-teach/curriculum-collections/cosm.... >At a conference in New York in 1967, Dr. Wheeler, seizing on a suggestion shouted from the audience, hit on the name “black hole” to dramatize this dire possibility for a star and for physics. https://www.nytimes.com/2008/04/14/science/14wheeler.html#:~:text=At%20a%20conference%20in%20New,a%20star%20and%20for%20physics https://www.nytimes.com/2008/04/14/science/14wheeler.html#:~....
- The_Colonel 3y ago
  Survivorship bias. Aether was once also a theory which "just" needed an experimental evidence.

jiggawatts 3y ago

P-hacking. The universe is big and has lots of stars. Even “very unlikely” things ought to turn up. E.g.: one in a billion chance ought to occur hundreds of times… in our galaxy alone!

burnte 3y ago
This is one of the hardest things to grasp about the size of the universe; it's so damn big pretty much anything is possible somewhere.
- vlovich123 3y ago
  Conversely, anything we do manage to observe is more likely to lay within most common probability space simply because we’re similarly observing such a tiny portion of what’s happening in the universe. Think about if you sample uniformly 0.01% of 1B requests / second coming into your system - you’re going to see all the common scenarios and none of the uncommon ones. Sure space isn’t quite the same thing since we don’t observe uniformly, but similarly we’re observing an infinitely smaller part of the overall space anyway.
- vinaypai 3y ago
  The universe is big, but we're only observing a miniscule fraction of it, especially at the level of individual star systems.
  - burnte 3y ago
    That doesn't really have any relevance, though. Every single possibility is as likely as the others, it's just there are many more situations in which a system will look "normal", but we still shouldn't be overly surprised by the occasional outlier, we're bound to stumble on them even if rarely.

metalliqaz 3y ago

that's what I mean by "unusual circumstances". As you point out, the "usual evolutionary channels" don't really fit.

spuz 3y ago
This is why I included this part of the quote: > Other evolutionary channels such as formation without a common envelope or via a hierarchical triple also seem unlikely for similar reasons. Maybe it's hard to say without getting into specifics but it seems that the paper has considered the "unusual circumstances" in your statement.
- raattgift 3y ago
  The paper rests on the MNRAS published version of <https://arxiv.org/abs/2209.06833 https://arxiv.org/abs/2209.06833> (ref. [EBRQ+22] in the preprint at the top, cited at the end of the paragraph you quote upthread). [EBRQ+22] itself proposes a triple as a possibility: "The system's evolution may be better-explained in models in which the G star was initially a wide tertiary companion to a close binary containing two massive stars. In this case, interactions between the two stars could have prevented either one from expanding to become a red supergiant, such that the G star could have formed in an orbit similar to its current orbit (but somewhat tighter) and remained there ever since. High-precision RV follow-up offers the tantalizing possibility of testing this scenario." RV there is "radial velocity measurements". Moreover, the part you quote and in particular "Moreover, formation within a globular cluster is also improbable" does not touch on their reference's "... dynamical formation in an open cluster that has since dissolved is more plausible." Disruptions of open clusters are well known. <https://en.wikipedia.org/wiki/Open_cluster#Eventual_fate https://en.wikipedia.org/wiki/Open_cluster#Eventual_fate>.

raattgift 3y ago

First see footnote 1 of the first page of the preprint linked at the top. The authors are jumping the gun. That's fine for theorists, but bear in mind that they are literally in the dark on a number of telescopic observables, any of which would shoot down the idea in the preprint. Some of these are achievable by EHT. See e.g. Olivares et al. "How to tell an accreting boson star from a black hole" (2020) <https://discovery.ucl.ac.uk/id/eprint/10112389/1/staa1878.pdf https://discovery.ucl.ac.uk/id/eprint/10112389/1/staa1878.pd...> [pdf]. The exotic bosons available in a 3+1 spacetime have never been detected at energy levels low enough that one might expect them to be reasonably bound by the weak (yes, weak) gravitation required by the boson star's internal repulsive forces. If the internal repulsive forces are too weak (or their self-gravitation isn't weak enough), the bosons cannot support the star against ultimate gravitational collapse (into a black hole). If the internal repulsive forces are too strong, the bosons all escape rather than stick around in the neighbourhood of the star. The latter is especially acute since the boson masses considered by the paper may be smaller than that of neutrinos. Until a suitable slightly self-repelling exotic boson is discovered, achieving and maintaining equilibrium between it and gravitation is pretty fatal to the boson star idea. Cold massive bosons are an idea for particle dark matter, incidentally. An example dark matter candidate is the axion. Axions have not been convincingly observed, and might not exist. A compact object made of essentially only axions could plausibly meet the criteria in the preprint linked at the top (cf their axion-motivated scalar field equation at eqn (9)), depending on details of heating during gravitational compaction. Also see e.g. Mohapatra et al., "Dense Axion Stars" (2016) <https://arxiv.org/abs/1512.00108 https://arxiv.org/abs/1512.00108> which is the preprint version of the PRL letter <https://doi.org/10.1103/PhysRevLett.117.121801 https://doi.org/10.1103/PhysRevLett.117.121801>. There is as far as I know no clear mechanism to have anything like the axion density required for self-gravitation except in the very early universe, a long time before the first galaxies. So then why would small primordial axion stars be in galaxies, as the binary in the article at the top appears to be? How do you keep them small, rather than coalescing into supermassive compact objects? The preprint at the top discusses other Beyond The Standard Model (of particle physics; BTSM) possibilities, but they are less convincing than the axion (for starters, such BTSM extensions need to have some non-physical degrees of freedom strongly suppressed, since such BTSM theories are almost always "haunted" by <https://en.wikipedia.org/wiki/Ghost_(physics) https://en.wikipedia.org/wiki/Ghost_(physics)>s.). Additionally, the axion is motivated by the strong CP problem in the Standard Model, and if there is a lot of them they become gravitationally relevant. The non-axion options in the preprint at the top are afaik only motivated by a lack of knowledge about the microscopic details of gravitational physics. (See Koberlein's 2021 blog entry on Proca Stars <https://briankoberlein.com/blog/proca-stars/ https://briankoberlein.com/blog/proca-stars/> for a brief intro to (light) massive vector boson stars).

jheriko 3y ago

runaway stars suggest that interactions occur leaving binaries behind in these kinds of configurations. i see no need for unphysical fine-tuning. looking at the paper they cite as reference for this claim, those authors thought exactly the same... https://academic.oup.com/mnras/article-abstract/518/1/1057/6794289 https://academic.oup.com/mnras/article-abstract/518/1/1057/6...