<p>The start of it all is usually something called a Giant Molecular Cloud, a particular kind of nebula which is denser than usual and cooler than usual.  A GMC will typically be 10x to 1000x the mass of the Sun.</p>

<p>That mass is enough to cause the outer layers to fall in on the inner parts and the GMC starts to collapse and shrink. (Diffuse though it is, the mass exerts the same force on the outer edges as it would if the entire mass was concentrated at the center.)</p>

<p>The cloud collapses and frequently fragments into a bunch of smaller collapsing blobs centered on especially dense sections of the cloud. At this point it looks a lot like the Oriion Nebula. The young stars light up and blow away the remaining bits of the GMC, and in the end, you have a cluster of young stars with planetary disks looking something like the Pleiades. </p>

<p>There never was a central mass -- none is needed.  The GMC collapses under its own self-attraction.</p>

CC BY-SA 4.0
2019-04-23T05:48:44.680Z
The start of it *all* is where you should've started. Photons colliding to make protons and neutrons, and somehow electrons show up (???), and now there's hydrogen in the universe. Which coalesced itself (because everything except photons have mass), became the first stars, and then the first (type I) supernovas happened, during which heaver elements can form, from which stars that will go type II supernova can form. Then type III. .... And then the dinosaurs came.
Mazura
CC BY-SA 4.0
2019-04-23T06:50:52.620Z
@Mazura Protons and neutrons are *not* made by colliding photons.  They're made up of quarks and result from from the big bang when it became cool enough for quarks to bond.
StephenG - Help Ukraine
CC BY-SA 4.0
2019-04-23T09:40:44.567Z
The one (over) simplification in the "collaps under gravity" explanations is that orbiting dust and debris, eventually forming a protoplanetary disk, does not simply "collapse" under its own gravity. Not any more than our solar system collapses: All parts are in orbits and there is conservation of energy, after all. Objects accelerate on the way in and thus have exactly the necessary kinetic energy to get out again. What's needed is collision, friction and shedding of kinetic energy by radiation, allowing the orbits to become smaller. At a certain density there must be a runaway effect.
Peter - Reinstate Monica
CC BY-SA 4.0
2019-04-23T10:15:15.177Z
@StephenG -sorry, wrong particles; electrons and positrons. *Where did the mass come from that caused gravity?* - apparently, quarks.
Mazura
CC BY-SA 4.0
2019-04-25T05:49:53.713Z
@Mazura You said *"Then type III"*. It's not clear what you're talking about, but whatever it is, I suspect you're wrong. ;) Population III stars formed *before* population II stars, and although Zwicky devised a [type III supernova](https://en.wikipedia.org/wiki/Supernova#Types_III,_IV,_and_V) class, only one object (SN 1961i) was assigned to it, and in modern treatments it would be classed as type II.
PM 2Ring
CC BY-SA 4.0
2019-04-25T05:54:43.890Z
@PM2Ring - that's why I'm not even trying to answer. I just want someone write the history of the universe in a single paragraph.
Mazura
CC BY-SA 4.0
2019-04-25T12:20:41.830Z
@Mazura Bang! Time passes. Whimper.
Mark Olson
CC BY-SA 4.0
2019-04-23T00:03:43.907Z
2019-04-23T00:03:43.907Z
Mark Olson
<p>In my class we are studying objects in our solar system and this question seemed to just pop up. And since I cannot answer this, I've been really frustrated for quite a while now and would like some help on understanding this.</p>

CC BY-SA 4.0
2019-04-22T23:47:50.623Z
It's not clear what you're asking. What was the actual statement that caused your question? What's the context?
Florin Andrei
<solar-system>
If gravity precedes the formation of a solar system, where did the mass come from that caused the gravity?
Lusy
# If gravity precedes the formation of a solar system, where did the mass come from that caused the gravity?

(Asked by: username_0 on 2019-04-22)

In my class we are studying objects in our solar system and this question seemed to just pop up. And since I cannot answer this, I've been really frustrated for quite a while now and would like some help on understanding this.

**Tags:** solar-system
> **Comments:**
> **username_1**: It's not clear what you're asking. What was the actual statement that caused your question? What's the context?  

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## 1 answers

### Answer by username_2 on 2019-04-23. Score: 15

The start of it all is usually something called a Giant Molecular Cloud, a particular kind of nebula which is denser than usual and cooler than usual. A GMC will typically be 10x to 1000x the mass of the Sun.

That mass is enough to cause the outer layers to fall in on the inner parts and the GMC starts to collapse and shrink. (Diffuse though it is, the mass exerts the same force on the outer edges as it would if the entire mass was concentrated at the center.)

The cloud collapses and frequently fragments into a bunch of smaller collapsing blobs centered on especially dense sections of the cloud. At this point it looks a lot like the Oriion Nebula. The young stars light up and blow away the remaining bits of the GMC, and in the end, you have a cluster of young stars with planetary disks looking something like the Pleiades.

There never was a central mass -- none is needed. The GMC collapses under its own self-attraction.

> **Comments:**
> **username_3**: The start of it *all* is where you should've started. Photons colliding to make protons and neutrons, and somehow electrons show up (???), and now there's hydrogen in the universe. Which coalesced itself (because everything except photons have mass), became the first stars, and then the first (type I) supernovas happened, during which heaver elements can form, from which stars that will go type II supernova can form. Then type III. .... And then the dinosaurs came.  
> **username_4**: @Mazura Protons and neutrons are *not* made by colliding photons.  They're made up of quarks and result from from the big bang when it became cool enough for quarks to bond.  
> **username_5**: The one (over) simplification in the "collaps under gravity" explanations is that orbiting dust and debris, eventually forming a protoplanetary disk, does not simply "collapse" under its own gravity. Not any more than our solar system collapses: All parts are in orbits and there is conservation of energy, after all. Objects accelerate on the way in and thus have exactly the necessary kinetic energy to get out again. What's needed is collision, friction and shedding of kinetic energy by radiation, allowing the orbits to become smaller. At a certain density there must be a runaway effect.  
> **username_3**: @StephenG -sorry, wrong particles; electrons and positrons. *Where did the mass come from that caused gravity?* - apparently, quarks.  
> **username_6**: @Mazura You said *"Then type III"*. It's not clear what you're talking about, but whatever it is, I suspect you're wrong. ;) Population III stars formed *before* population II stars, and although Zwicky devised a [type III supernova](https://en.wikipedia.org/wiki/Supernova#Types_III,_IV,_and_V) class, only one object (SN 1961i) was assigned to it, and in modern treatments it would be classed as type II.  
> **username_3**: @PM2Ring - that's why I'm not even trying to answer. I just want someone write the history of the universe in a single paragraph.  
> **username_2**: @Mazura Bang! Time passes. Whimper.  

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