How a star is born

[Eclogite]

Is star formation on the decline?

Yes: If our current theories on the evolution of the Universe are correct. As stars form and process the primordial hydrogen into heavier elements the total volume of gas clouds dimimishes. The more massive stars replenish these to an extent when they go supernova; the smaller stars drag out a long slow life, followed an even longer slow death. Overall, the quantity of gas available to form new stars decreases over time.

[Tormod]

From Space.com (2003 article):

 

It's Universal: The Lights are Going Out

Not enough stars are being born to replace those that are dying across the cosmos, according to a new study supporting previous claims that the universe is headed into darker times.

 

http://www.space.com/scienceastronomy/lights_out_030807.html

[geokker]

So nothing lasts forever then, not even everything!

[Chacmool]

:) And it was always somehow such a comforting thought to me that the universe would be eternal!

[rynaldo]

That was a good article about not enough stars being formed to replace the ones that are dying out. I noticed it was saying how the universe may well end up being completely dark as not enough stars are forming. As its from the stars that black holes are formed when they collapse, black holes will not be forming aswell then?

 

With the supermassive black holes which... its believed that there may be one in every galaxy, they are supposed to change colour when they feed. Would this therefore affect there light and would this be the only light that would be being created in the universe?

[Chaos]

just think, we're all probably going to be in the sun someday. :)

[C1ay]

From Space.com (2003 article):

 

It's Universal: The Lights are Going Out

Not enough stars are being born to replace those that are dying across the cosmos, according to a new study supporting previous claims that the universe is headed into darker times.

 

http://www.space.com/scienceastronomy/lights_out_030807.html

It really stands to reason that if the universe is finite it can only have a finite quantity of hydrogen and helium to form stars with. As stars are formed it uses up a portion of that finite quantity leaving leass and less over time. To free the hydrogen and helium that is fused in a star's normal process so that it could be recycled would require some natural fission process. I'm not aware of any such natural mechanism. These means that it is inevitable that all star building material will eventually be used up.

[Southtown]

Not a problem. Spontaneous collapse arising out of random motion was perfectly able to create the first stars. However, once they were formed and then went supernova that readily triggered further collapse and star formation.

I have a big problem with the word "spontaneous". It usually implies that a reasonable mechanism is not needed for the poetically described "arising out of random[ness]", which isn't scientific at all and actually treads in the realm of faith.

 

To my knowledge, a gaseous "cloud" does not exhibit a collective center of mass. Gaseous particles don't "condense" in a vacuum, they expand. They only influence each other's flight paths and collide occasionally. Collision hasn't been shown as an adequate mechanism for accretion. Particles that bump into each other simply scatter back out again, causing further expansion.

 

Gravitational spheres of influence do alter paths of nearby particles that don't collide, but they don't get sucked into orbit or absorbed by gravity. Effected particles take parabolic paths through the sphere of influence in which the particle increases speed toward its minimum distance from the effecting particle then slows again to its speed at the time of entry before exiting the sphere of influence.

 

Only the presence of external forces that reduce the speed of the effected particle while inside the sphere of influence allows it to be captured. Solar wind would be a candidate if the two particles are extremely similar in direction and velocity, but solar wind would require the accretion of the first star. Multiple particles effecting each other in such a way is a possibility, but the ratio of captured particles to free particles would be rediculously low.

 

Additionally, any system of particles that happen to accumulate will more likely be torn apart by further influences from rogue particles, and the chances of acquiring more particles decrease astronomically with the number of particles already in that system since the complexity of orbital balances increases exponentially with each particle acquisition.

[TeleMad]

Southtown: I have a big problem with the word "spontaneous". It usually implies that a reasonable mechanism is not needed for the poetically described "arising out of random[ness]", which isn't scientific at all and actually treads in the realm of faith.

 

Huh? That's not what spontaneous means in science. Spontaneous refers to the allowed, energetically 'downhill' direction of a reaction or process. Water falls down a waterfall spontaneously, accumulating at the bottom; water does not fall up a waterfall spontaneously to accumulate at the top. Plop a drop of food color into a glass full of water and the individual molecules of the food color will spontaneously disperse, diffusing into the most random arrangement they can obtain; once in that random, disordered arrangement they won't spontaneously reassemble themselves into a single drop. These statement of spontaneity don't leave science nor do they tread in the realm of faith.

 

Southtown: To my knowledge, a gaseous "cloud" does not exhibit a collective center of mass.

 

Why not?

 

Let's use Newton's Universal Law of Gravitation. Consider an isolated, roughly spherical cloud of gas, and look at a given particle on the surface of the sphere at the 12 O'clock position. Now, in what direction will that particle be tugged? Inward, towards the center of the cloud. It has no particles above it to counterbalance the inward force exerted by the massive number of particles below it. This applies to all particles on the surface of the sphere: they feel an inward force exerted by all of the particles "below" them, which is not counterbalanced by any particles "above" them.

 

This logic applies to the rest of the sphere. Consider a shell just a bit below the outer surface. The particles in it have a huge number of particles "below" them and only a few "above" them; they too will experience a net inward force. Continue looking at a smaller and smaller shell and the trend continues; each shell has particles that experience a net inward tug because there are more particles lying "below" that shell than "above" it.

 

So an isolated gas cloud does have a tendency to gravitationally collapse. Other factors enter into the equation so the behavior of a cloud does not have to coincide with this tendency.

[Southtown]

Ah, I see, thanks. I guess I'm confusing it with orbital capturing. It makes sense, then. Non-uniform density would produce spinning, warming clusters. 'Scuze me, I'm self-educating. :)