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Thread: Could very small "non-solar-systems" exist?

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    Could very small "non-solar-systems" exist?

    I was going to comment in the "Is Earth a failed star" thread with this idea, but then thought it might be worth a separate question of its own.

    As I understand current theories, stellar systems are formed as rotating clouds, or rather disks, of dust and gas accrete and accumulate, with the large mass in the centre eventually reaching a temperature and pressure where fusion starts. Smaller accumulations of mass in the disk grow to become planets of various sizes.

    Now, would it be possible for the same sequence to happen on a smaller scale, where the central mass is very much below stellar size, even less than a brown dwarf? You'd end up, I think, with a Jupiter-like system of a planet sized primary, and a range of smaller "moon-ish" companions. At first glance there doesn't seem to be any reason this couldn't happen, although detecting such a system would be likely be impossible, even with the best instruments we currently have.

    Does anyone know if perhaps there's a lower mass limit in the dynamics of gas and dust clouds which would mean it would never be stable enough to get as far as forming something like this?
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    Quote Originally Posted by molesworth View Post
    ... Does anyone know if perhaps there's a lower mass limit in the dynamics of gas and dust clouds which would mean it would never be stable enough to get as far as forming something like this?
    If you somehow got a small dense cloud of cold gas with low turbulence out in a void between clusters, so there were few perturbations over billions of years, the lower limit might be quite small, but in a star-forming region of a galaxy, it looks like the lower limit might be somewhere between 5 and 15 Jupiter masses. ... this is from empirical data of observed object sizes, and not from modeling or dynamics studies.
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    Jupiter, Saturn and Neptune are all emitting infrared more than they get from Sun.

    At which distance could Jupiter be detected from its internal infrared?

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    Quote Originally Posted by chornedsnorkack View Post
    Jupiter, Saturn and Neptune are all emitting infrared more than they get from Sun.

    At which distance could Jupiter be detected from its internal infrared?
    Is that on topic? If you want a discussion of this, perhaps start a new thread.
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    Quote Originally Posted by antoniseb View Post
    If you somehow got a small dense cloud of cold gas with low turbulence out in a void between clusters, so there were few perturbations over billions of years, the lower limit might be quite small, but in a star-forming region of a galaxy, it looks like the lower limit might be somewhere between 5 and 15 Jupiter masses. ... this is from empirical data of observed object sizes, and not from modeling or dynamics studies.
    Thanks, that's useful information. It was kind of an idle speculation initially, based on the other thread, but now it's in my head I'm interested in the possibilities.

    Of course, with no central star, the whole system would be very cold indeed (low levels of IR from gas giants notwithstanding) but the fact that they could exist is an interesting thought. I have some contacts with people working on stellar and planetary system origins and evolution, so next time I get a chance I'll ask them about this. (Might even fire off a couple of emails...)
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    Quote Originally Posted by antoniseb View Post
    If you somehow got a small dense cloud of cold gas with low turbulence out in a void between clusters, so there were few perturbations over billions of years, the lower limit might be quite small, but in a star-forming region of a galaxy, it looks like the lower limit might be somewhere between 5 and 15 Jupiter masses. ... this is from empirical data of observed object sizes, and not from modeling or dynamics studies.
    I'm wondering if the star-forming size you're giving is for "spontaneous" star formation. Couldn't a smaller star be ignited by a high speed collision with another object?
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    Quote Originally Posted by DaCaptain View Post
    I'm wondering if the star-forming size you're giving is for "spontaneous" star formation. Couldn't a smaller star be ignited by a high speed collision with another object?
    I think there are people with much more expertise on this subject who may answer, but I would think that's a very, very (repeat to N) unlikely occurrence. Firstly, as far as I understand the process, protostars and star-forming regions are fairly far apart, even in "stellar nurseries", and secondly, the chances of a high speed collision, rather than a co-rotational merger, would be very low.

    It may be possible that low mass protostellar clouds could merge, and bring the total mass into the range for fusion ignition, but that would be a very different process from what you describe.
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    Quote Originally Posted by DaCaptain View Post
    I'm wondering if the star-forming size you're giving is for "spontaneous" star formation. Couldn't a smaller star be ignited by a high speed collision with another object?
    Ignited? what are you talking about? molesworth's question is about objects too low in mass to ever sustain fusion. There would be some heat from the formation process, but that would be purely thermodynamic ideal gas heat from collapse/compression.
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    Quote Originally Posted by antoniseb View Post
    Is that on topic?
    Neglected to quote the point of departure:
    although detecting such a system would be likely be impossible, even with the best instruments we currently have.
    I see two possible ways of detecting a Jupiter-sized or Neptune-sized object free floating in interstellar space away from luminous stars:
    1) Infrared (Jupiter, Saturn and Neptune all emit some)
    2) Observe them passing between Earth and a background star, either direct occultation or gravitational bending of light.
    Note that 1) depends on the age of the object - young objects would be hotter, brighter and easier to spot than old. 2) depends on mass, but not age.
    Now, if free floating planets are formed, how?
    Could a Saturn sized planet found in outer space have been ejected from a solar system by interaction with a Jupiter like planet? Or did it form alone?
    In case of an old planet, may be hard to tell.
    While a young planet may be observed forming in a gas cloud, alone, and verified to be forming there rather than ejected from some other system.

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    Quote Originally Posted by chornedsnorkack View Post
    ... I see two possible ways of detecting a Jupiter-sized or Neptune-sized object free floating in interstellar space away from luminous stars:
    1) Infrared (Jupiter, Saturn and Neptune all emit some)
    2) Observe them passing between Earth and a background star, either direct occultation or gravitational bending of light. ...
    Concerning method 1, it is estimated that our most recent infrared survey missions would have caught Jupiter at about 1 light year (give or take a factor of two) as long as it wasn't passing in front of a dense area of the Milky Way where it would have been missed, but that's a 4.6 billion year old Jupiter. at a few million years old it would have been much hotter and obvious from perhaps 100 light years. If it were 10 billion years old, it could have been somewhat closer than a light year and still not have been noticed. Future, yet unplanned infrared survey missions might be more sensitive, and extend the range of detection.
    Concerning method 2, the OGLE, MACHO, and similar surveys have turned up some interesting results concerning free-floating objects and their mass ranges.
    Concerning your final point, yes, today it would be impossible to tell if an old free-floating Saturn-mass object was formed as a planet and then ejected, or was formed as an isolated object from an interrupted star-forming process.
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    I suspect that there is a large lower limit on such a system.

    One of the reasons why star systems are stable is because the central gravitational body is far, far more massive than its children. Sol is 1000 times more massive than Jupiter and all the other bodies in the system put together.

    Not sure how well that scales down.

    Not sure a Jupiter could form without being in the maelstrom of material that surrounds a normal-sized star. I suspect you need a sun-sized mass to keep the gas and dust whirling around until it can collect into a planet such as Jupiter.

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    Large masses are not required for a "stellar" system to be stable. Individual brown dwarfs have been detected with masses as small as about 10 x Jupiter, i.e. about 1% of the mass of our sun. Brown dwarfs orbiting one another have been observed, too. See, for example, https://en.wikipedia.org/wiki/Luhman_16 and https://en.wikipedia.org/wiki/List_of_brown_dwarfs
    Selden

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    Quote Originally Posted by selden View Post
    Large masses are not required for a "stellar" system to be stable. Individual brown dwarfs have been detected with masses as small as about 10 x Jupiter, i.e. about 1% of the mass of our sun. Brown dwarfs orbiting one another have been observed, too. See, for example, https://en.wikipedia.org/wiki/Luhman_16 and https://en.wikipedia.org/wiki/List_of_brown_dwarfs
    There's been several articles about planetary-mass objects in star forming regions. When PMOs are recently formed they are easier to detect.

    They usually find the number of PMOs is a few per cent of the number of stars in the cluster. I recall a figure of 14% in one paper.

    It is not certain if these are formed as stars, or as planets which then get ejected from their home systems.

    But anyway, theory says that Jupiter mass objects and above can form independently, by the star formation process. When formed like this it seems fairly reasonable to me they would have a small planetary system of their own. Smaller stars have smaller planet forming discs which don't last as long, but even so.

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    This paper addresses Brown Dwarf formation as part of the IMF (Initial Mass Function). There is a steep decline in their production, apparently, relative to the less massive stars.
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    Quote Originally Posted by George View Post
    This paper addresses Brown Dwarf formation as part of the IMF (Initial Mass Function). There is a steep decline in their production, apparently, relative to the less massive stars.
    Yes but there is still a substantial number produced. In fact your article says there have to be several formation mechanisms to account for their surprisingly large number.

    It also says that PMOs formed in circumstellar disks and ejected carry their accretion disks with them, i.e. they could form planets later on. So this formation mechanism does not disallow them from having planets.

    The article below finds

    <<We estimate that objects below the deuterium-burning limit contribute of the order 5 - 15% to the total number of Cha-I members.>>

    This is in one cluster, but you can find other articles that come out with figures of the same order of magnitude.

    https://arxiv.org/abs/1507.07780

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    Quote Originally Posted by kzb View Post
    Yes but there is still a substantial number produced. In fact your article says there have to be several formation mechanisms to account for their surprisingly large number.

    It also says that PMOs formed in circumstellar disks and ejected carry their accretion disks with them, i.e. they could form planets later on. So this formation mechanism does not disallow them from having planets.

    The article below finds

    <<We estimate that objects below the deuterium-burning limit contribute of the order 5 - 15% to the total number of Cha-I members.>>

    This is in one cluster, but you can find other articles that come out with figures of the same order of magnitude.

    https://arxiv.org/abs/1507.07780
    Well, I originally thought the chances of these kinds of systems existing was pretty small, but it appears they may be not at all unusual. Thanks for all the interesting information, and the leads for further investigations...
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    Quote Originally Posted by kzb View Post
    Yes but there is still a substantial number produced. In fact your article says there have to be several formation mechanisms to account for their surprisingly large number.

    It also says that PMOs formed in circumstellar disks and ejected carry their accretion disks with them, i.e. they could form planets later on. So this formation mechanism does not disallow them from having planets.
    Yes, that's interesting and I hope to read it more thoroughly on the plane tomorrow, along with this more recent work on Planet-to-star mass ratios using microlensing, which may be of some value. I was only injecting the IMF into the discussion. No doubt ALMA and other sources, in time, will be able to give us a much better idea on PMOs and small stellar systems.
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