# properties of cloud surrounding a star

• 2021-Apr-27, 12:58 AM
marksthespot
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
• 2021-Apr-27, 01:29 PM
Noclevername
Quote:

Originally Posted by marksthespot
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.
• 2021-Apr-27, 11:05 PM
Jens
Quote:

Originally Posted by marksthespot
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
• 2021-Apr-28, 02:26 AM
marksthespot
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
• 2021-Apr-30, 01:18 PM
Noclevername
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.
• 2021-May-03, 03:28 AM
DaCaptain
Quote:

Originally Posted by marksthespot
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.
• 2021-May-03, 08:15 AM
profloater
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.
• 2021-May-03, 07:36 PM
DaCaptain
Quote:

Originally Posted by profloater
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.
• 2021-May-04, 03:39 PM
marksthespot
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.
• 2021-May-04, 11:10 PM
Noclevername
Quote:

Originally Posted by marksthespot
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.
• 2021-May-05, 11:20 AM
profloater
Quote:

Originally Posted by Noclevername
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
• 2021-May-05, 01:54 PM
DaCaptain
Quote:

Originally Posted by profloater
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.