Results 1 to 12 of 12

Thread: properties of cloud surrounding a star

  1. #1
    Join Date
    Jul 2020
    Posts
    6

    properties of cloud surrounding a star

    Hi, All

    I have some assumptions about clouds surrounding, and produced by, a star - burning through fuel, say

    1) the cloud would spin with the star (same spin axis), with the velocity of the surface of the star surface (equator)
    2) cloud particles obtain this velocity by being projected from the surface
    3) the spin of the cloud is now inertial - as opposed to being continually spun up - by friction, say
    4) if the cloud expands, momentum is conserved - I1w1 = I2w2

    Does this sound right?

    Thanks, Mark

  2. #2
    Join Date
    Apr 2007
    Location
    Nowhere (middle)
    Posts
    39,870
    Quote Originally Posted by marksthespot View Post
    Hi, All

    I have some assumptions about clouds surrounding, and produced by, a star - burning through fuel, say

    1) the cloud would spin with the star (same spin axis), with the velocity of the surface of the star surface (equator)
    2) cloud particles obtain this velocity by being projected from the surface
    3) the spin of the cloud is now inertial - as opposed to being continually spun up - by friction, say
    4) if the cloud expands, momentum is conserved - I1w1 = I2w2

    Does this sound right?

    Thanks, Mark
    Hi, marksthespot.

    1) Since the star usually forms with or from the cloud, it will usually spin along the same axis and in the same direction. As for speeds, the nature of orbital mechanics says the cloud will not match the spin rate of the star's surface, and the further out from the star you go, the slower the spin.
    2) No. The stellar wind imparts its momentum outward from the surface or guided by magnetic fields, not in a rotation.
    3) The inertial spin is from the formation of the star, when the cloud fell inward from a dispersed state to a compact one, all that gravitational energy had to go somewhere. It got converted into orbital velocity in the cloud; in the star, to pressure and heat.
    4) Momentum from the cloud will be, not the star.

    So altogether, your premise is incorrect.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

  3. #3
    Join Date
    Jun 2005
    Posts
    15,016
    Quote Originally Posted by marksthespot View Post
    Hi, All

    I have some assumptions about clouds surrounding, and produced by, a star - burning through fuel, say
    I guess I’d like to ask what you are thinking about in your scenario. What do you mean by a star producing a cloud?


    Sent from my iPhone using Tapatalk
    As above, so below

  4. #4
    Join Date
    Jul 2020
    Posts
    6
    Hi. nothing serious...Just wondered how a cloud would react in a supernova. would it be projected out....how far....would it retain angular momentum
    For the cloud, think planetary nebula...produced near the end of star life. I don't know how....that's why I'm asking.....solar wind, maybe
    I got the idea from a picture of SN1987....looked like a smoke ring

    first post...I may have overdone it....but thanks for responding

  5. #5
    Join Date
    Apr 2007
    Location
    Nowhere (middle)
    Posts
    39,870
    As far as planetary nebulae, the rotational speed of the matter immediately starts to slow as the star sheds its outer layers and the momentum is distributed over a larger volume. Stellar wind would probably have little measurable effect on such a large mass of plasma, it would be lost in the natural variations of the huge effects of the nebular expulsion.

    The nebula retains its general torus (donut) shape because of its inertia, flung outwards from the rotating star. I don't know if other forces such as magnetic fields have significant effects, but angular momentum is the main reason for this shape.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

  6. #6
    Join Date
    Dec 2016
    Posts
    334
    Quote Originally Posted by marksthespot View Post
    Hi, All

    I have some assumptions about clouds surrounding, and produced by, a star - burning through fuel, say

    1) the cloud would spin with the star (same spin axis), with the velocity of the surface of the star surface (equator)
    2) cloud particles obtain this velocity by being projected from the surface
    3) the spin of the cloud is now inertial - as opposed to being continually spun up - by friction, say
    4) if the cloud expands, momentum is conserved - I1w1 = I2w2

    Does this sound right?

    Thanks, Mark
    This cloud would be more like a ring than a cloud. When the cloud would first forms there may initially be small amounts of cloudiness. But as it ages it will condense and in the end flatten into a ring.
    I know that I know nothing, so I question everything. - Socrates/Descartes

  7. #7
    Join Date
    Apr 2011
    Location
    Norfolk UK and some of me is in Northern France
    Posts
    10,062
    In a super nova the particles which were the star, explode. Angular momentum is lots of linear momentum tied together by forces. In a cloud of dust particles, there is gravity. So at first simplification a spinning star going supernova would eject particles in straight lines. Pressure acts as collisions between particles, introducing randomness, until they spread out , no longer colliding.

    The inner ones never catch up to the outer in that simplification. Gravity then works at all distances. If there was no initial spin the centre of gravity stays where the star was and slower particles would slow and fall back. Faster particles would escape. If spinning to start, the falling back would have net angular momentum as collisions and gravity fought it out, the momentum turning to heat again but with some oscillation.

    The cloud that escapes to form new stars, planets and so on, has particle spin and particle momentum and, presumably, a non uniform density so that clumps can form from gravity, before the particles reach another zone of gravity influence such as a preexisting star or planet.

    Since the star fuses all the elements together before exploding, it is the creation mechanism for making rocky planets like Earth. Net angular momentum is an interesting concept in the collapse of clouds, particles capturing each other by gravity and then by atomic forces, generate and accumulate spin randomly.

    But then...

    The role of the star magnetic forces within the plasma complicates the explosion simplification. The particles carry charge, so the movement of the particles will not be simple straight lines. The star is not like a uniform solid , its surface is complex. The question of net charge is like the question of net angular momentum.
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

  8. #8
    Join Date
    Dec 2016
    Posts
    334
    Quote Originally Posted by profloater View Post
    In a super nova the particles which were the star, explode. Angular momentum is lots of linear momentum tied together by forces. In a cloud of dust particles, there is gravity. So at first simplification a spinning star going supernova would eject particles in straight lines. Pressure acts as collisions between particles, introducing randomness, until they spread out , no longer colliding.

    The inner ones never catch up to the outer in that simplification. Gravity then works at all distances. If there was no initial spin the centre of gravity stays where the star was and slower particles would slow and fall back. Faster particles would escape. If spinning to start, the falling back would have net angular momentum as collisions and gravity fought it out, the momentum turning to heat again but with some oscillation.

    The cloud that escapes to form new stars, planets and so on, has particle spin and particle momentum and, presumably, a non uniform density so that clumps can form from gravity, before the particles reach another zone of gravity influence such as a preexisting star or planet.

    Since the star fuses all the elements together before exploding, it is the creation mechanism for making rocky planets like Earth. Net angular momentum is an interesting concept in the collapse of clouds, particles capturing each other by gravity and then by atomic forces, generate and accumulate spin randomly.

    But then...

    The role of the star magnetic forces within the plasma complicates the explosion simplification. The particles carry charge, so the movement of the particles will not be simple straight lines. The star is not like a uniform solid , its surface is complex. The question of net charge is like the question of net angular momentum.
    Here's a great example AG Carinae.
    I know that I know nothing, so I question everything. - Socrates/Descartes

  9. #9
    Join Date
    Jul 2020
    Posts
    6
    Yes. Wouldn't it be nice if the core was eliminated in a supernova explosion. Then this cloud could collapse to form a solar system.

  10. #10
    Join Date
    Apr 2007
    Location
    Nowhere (middle)
    Posts
    39,870
    Quote Originally Posted by marksthespot View Post
    Yes. Wouldn't it be nice if the core was eliminated in a supernova explosion. Then this cloud could collapse to form a solar system.
    Don't planetary nebulae generally keep on expanding and disperse? Most never collapse back into the core.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

  11. #11
    Join Date
    Apr 2011
    Location
    Norfolk UK and some of me is in Northern France
    Posts
    10,062
    Quote Originally Posted by Noclevername View Post
    Don't planetary nebulae generally keep on expanding and disperse? Most never collapse back into the core.
    Well I guess these things are big, bigger than any explosion I can imagine. The core is running through fusion reactions and “suddenly” that is not enough. The huge gravity compression starts to crush the core and that must avalanche, instead of a graceful gradual collapse, the compressed core goes wild and explodes. There is enough material there to form more, smaller stars or planets, and overall the centre of mass is mostly still there, less the energy converted, but exploded. I do not know how much of the original star mass is converted to energy in that explosion. There must be special fusion in that increased pressure at the centre or core. So a lot depends on what “suddenly “ actually means
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

  12. #12
    Join Date
    Dec 2016
    Posts
    334
    Quote Originally Posted by profloater View Post
    Well I guess these things are big, bigger than any explosion I can imagine. The core is running through fusion reactions and “suddenly” that is not enough. The huge gravity compression starts to crush the core and that must avalanche, instead of a graceful gradual collapse, the compressed core goes wild and explodes. There is enough material there to form more, smaller stars or planets, and overall the centre of mass is mostly still there, less the energy converted, but exploded. I do not know how much of the original star mass is converted to energy in that explosion. There must be special fusion in that increased pressure at the centre or core. So a lot depends on what “suddenly “ actually means
    Yet another super nova example. Makes you wonder how often they happen in the universe. They seem to be happening ALL the time. A constant redistribution of the elements.
    I know that I know nothing, so I question everything. - Socrates/Descartes

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •