Mass Below Jeans Mass: Implications for Systems

In summary: IN that case AFAIK the collapse process doesn't involve pulsation so much as jet formation and the intense early stellar wind, both of which throw off excess angular momentum that stars need to be rid of to collapse. But there's all sorts of complicated opacity effects too which slow down the escape of heat from the star.
  • #1
Ranku
410
18
What happens when the mass of a system is below Jeans mass? Will the system dissipate mass? Are all gravitationally bound systems required to be precisely the Jeans mass, to avoid gravitational collapse or dissipation of mass?
 
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  • #2
In the early universe, when a system is below the Jeans mass, it undergoes oscillations. When it is greater than the Jeans mass, it becomes gravitationally unstable.
 
  • #3
bapowell said:
In the early universe, when a system is below the Jeans mass, it undergoes oscillations. When it is greater than the Jeans mass, it becomes gravitationally unstable.

Ok, and what about in the present universe? And what does oscillations mean?
 
  • #4
Ranku said:
What happens when the mass of a system is below Jeans mass? Will the system dissipate mass? Are all gravitationally bound systems required to be precisely the Jeans mass, to avoid gravitational collapse or dissipation of mass?

It doesn't have to be precisely at the Jeans mass for part of the mass in a volume to gravitationally collapse into a denser state. Down to about half the Jeans mass a system can collapse, but more matter is thrown off the lower the initial mass. That's due to the "oscillations" the other poster mentioned, which is a series of radial pulsations (if the system is spherical) that lose mass as the system collapses. Remember that the Jeans mass is achieved when gravitational self-attraction of a system causes it to collapse faster than pressure changes can smooth out over-dense regions i.e. sound/pressure waves can't smooth it out quick enough.
 
  • #5
qraal said:
It doesn't have to be precisely at the Jeans mass for part of the mass in a volume to gravitationally collapse into a denser state. Down to about half the Jeans mass a system can collapse, but more matter is thrown off the lower the initial mass. That's due to the "oscillations" the other poster mentioned, which is a series of radial pulsations (if the system is spherical) that lose mass as the system collapses. Remember that the Jeans mass is achieved when gravitational self-attraction of a system causes it to collapse faster than pressure changes can smooth out over-dense regions i.e. sound/pressure waves can't smooth it out quick enough.

Is this the same oscillation seen in stellar evolution, where a star collapses alternately contracting and expanding, radiating away half of the released gravitational energy in accordance to the virial theorem?
 
  • #6
Ranku said:
Is this the same oscillation seen in stellar evolution, where a star collapses alternately contracting and expanding, radiating away half of the released gravitational energy in accordance to the virial theorem?

Which bit of stellar evolution do you mean?
 
  • #7
qraal said:
Which bit of stellar evolution do you mean?

I guess when a star is gravitationally collapsing.
 
  • #8
Ranku said:
I guess when a star is gravitationally collapsing.

IN that case AFAIK the collapse process doesn't involve pulsation so much as jet formation and the intense early stellar wind, both of which throw off excess angular momentum that stars need to be rid of to collapse. But there's all sorts of complicated opacity effects too which slow down the escape of heat from the star. It's complicated.
 

1. What is the concept of "mass below Jeans mass"?

The concept of "mass below Jeans mass" refers to the minimum amount of mass required for a cloud of gas or dust to collapse and form a star or planet. This is known as the Jeans mass, and any amount of mass below this threshold will not have enough gravitational force to overcome the pressure and hold the object together.

2. How does the concept of "mass below Jeans mass" impact systems?

The concept of "mass below Jeans mass" has significant implications for the formation and evolution of systems, such as galaxies, stars, and planets. It determines which objects will form and which ones will not, as well as the size and characteristics of these objects.

3. What factors determine the Jeans mass of a system?

The Jeans mass of a system is primarily determined by two factors: the temperature and density of the gas or dust cloud. Higher temperatures and densities will result in a smaller Jeans mass, while lower temperatures and densities will result in a larger Jeans mass.

4. How does the mass below Jeans mass affect the stability of a system?

The mass below Jeans mass plays a crucial role in determining the stability of a system. Objects with mass below the Jeans mass will not be able to hold themselves together and will disperse, while objects with mass above the Jeans mass will continue to collapse and form more massive objects. This balance between gravity and pressure is essential for the stability of a system.

5. Are there any observational or experimental evidence for the concept of "mass below Jeans mass"?

Yes, there is extensive observational and experimental evidence for the concept of "mass below Jeans mass". Observations of star-forming regions and simulations of gas clouds have shown that objects with mass below the Jeans mass do not form stars or planets. Additionally, laboratory experiments have demonstrated the formation of objects with mass above the Jeans mass under specific conditions.

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