Current theory holds that the solar system formed from an interstellar gas cloud. Current theory also holds that heavy elements are formed in supernovae.
How do you get from the supernova to the gas cloud?
This site gives a good basic outline of the evolution of the universe.
In escence at around 300k years after the matter dominated the universe and coalesced into gas clouds which over time collapsed due to gravity to form the first stars and then galaxies. These were known as Population III stars and were massive and had very short lifespans, these stars exploded in supervovae.
A star is basically a big ball of mainly hydrogen gas which when it explodes as a supernova (which not all stars do, only the very heavy ones) leaves a dense remnant, which may be either a neutron star or black hole and is surrounded by a rapidly expanding dust cloud, such as the Crab Nebula .
Lots of early supernovae seeded the galaxy with dust clouds such as this which lead to the formation of type II stars, which are low in metals and eventually type 1 stars, which is what our sun is.
Hope this makes sense. Will happily provide more detail if you want.
Yes, I’m comfortable with that side, but how do you go from the stuff ejected by a supernova to the cloud which then contracts to form a new star? How do you get from the Crab Nebula to the Pillars of Creation?
Objects with mass (such as particles of gas and dust) tend to be attracted to one another - gravity, isn’t it?
Eventually the gas cloud will slow due to loss of energy, or interaction with other expanding gas clouds. Either way the gas clouds of the early universe combined into super sized gas clouds,combined with interstellar gas left over form the BB. Also because pop III stars were supermasive they contain enough material to make many sun size stars, so it is possible for a single supermassive star to produce a cluster of smaller stars.
The most likely reason for causing new collapses is perturbations caused by nearby suns or other heavy objects, these will disturb the gas clouds and over time a dynamic collapse may occur.
If a collapse occurs in a large (> Lys across)cloud then the ignition of the new sun will cause further perturbations due to the heat/radiation pressure exerted on the gas cloud by the new sun, this in turn may lead to the formation of other proto stars by collapse of the gas cloud.
I always hear the “perturbations caused by nearby stars” theory, but I never hear a Seed Hypothesis, in which extra-solar planets, large comets, asteroids and even existing brown dwarves travel into or through the gas clouds and form new stars, much like dust motes collect water vapor to form rain droplets.
Another source of large gas clouds is the outgassing of Quasars (at one extreme) and of stars (at the other extreme). Look at the immense jets of matter streaming from those things. Eventually, it gets collected by something.
And then I think that “gas clouds” are fairly common in the first place. Look at the halo around any galaxy. Look at the arms of any galaxy. I’d bet that there’s more matter hanging around in unseen gas clouds than there is in all the stars that we can see.
But IANAA and someone will be along to tell me I’m wrong.
Fair point about the perturbation theory, but it was the one I was taught at Uni. As a certain pointy eared fictional character said “there are always possibilities”.
As for the gas clouds, it’s true that there is a lot of gas (relatively speaking) distributed throughout the galaxy, can’t remember the exact figure off the top of my head, but it’s of the order of a 100-1000 particles per centimetre cubed in gas clouds. It’s not true that it is “unseen”, while it may not be seen at visible wavelengths, it will be visible at some wavelength (depending upon the atoms/molecules involved). Scientists have done a fairly reasonable job of estimating the amount of matter in the universe based upon the luminosity of matter. The problem is there’s not enough of it, but that takes us to the topic of dark matter, which is a different topic.
The problem with your “seed hypothesis” is that any two random masses (of bodies or dust clouds) you pick in the galaxy are very likely moving at a relative velocity in excess of escape speed. A brown dwaft flying through a gas or dust cloud at tens of km/s isn’t (by itself) going to cause the dust to nucleate; it’ll just strew it about in its wake. However, the complex influence of a system of bodies on a cloud (including itself and other massive clouds) and on each other can cause perturbations which can result in condensation of the cloud into discrete bodies, and once that starts more of the material in the cloud (which is moving at a much slower relative speed) will condense, until you have an accretion disk that forms a star and the protoplanetary medium.
For the most part quasars don’t eject matter; rather, they are thought to be supermassive black holes that consume matter in enormous quantites and produce jets of very high energy radiation via synchrotron emission as well as radio frequency emissions from the lobes. Heavy elements (and in particular pretty much all elements heavier than silicon) are formed via explosive nucleosynthesis processes in supernovae, and are ejected following core collapse.
Gas and dust are very common forms of matter in the galaxy (and presumably the universe), far moreso than stars and solid objects by about an order of magnitude, though it is hard to tell just how much of galactic mass is comprised of dust (which makes up 1% of the observable stellar medium) and gas (which makes up 99%), since a large portion of the mass making up the galactic disk is unobservable, i.e. dark matter. As I last read on the subject, about 85% of the matter in our galaxy is unaccounted for, either very dark baryonic (normal) matter, or some kind of mass that interacts only weakly or not at all with the electromagnetic spectrum.
Stranger
The problem with this explanation is that it is unproven at this point. Space may well be littered with debris and we wouldn’t know it. Masses of rocks, comets and extra-solar planets could be drifting aimlessly at less than escape speeds all over the place.
And if we’re talking about a cloud created by an exploding star, then we also have the leftover planetary and cometary debris from said system, which is left floating through the expanding gas cloud.
That’s only true assuming that they weren’t blown into dust by the force of the supernova. How likely is that?
How likely is it that they’ll be blown “to dust”? Would the force of a supernova, or a regular nova for that matter, completely obliterate even remote Oort cloud objects?
A regular nova, no. But nobody is talking about a regular nova, which is a completely different phenomenon than a supernova.
There’s no question that if the sun magically were to go supernova, the earth would be converted eight minutes later into a fast-moving stream of particles. That’s one parameter. The other end is represented by this article, which states that a supernova 26 light years away would be sufficient to strip away the ozone layer.
The Oort cloud is in between, about 1 ly from the sun. That means it would be subject to a blast 26[sup]3[/sup] times as strong, or 17,576 times as much force as that distant supernova. Not much is going to survive that whole.
Supernovas are powerful beyond most of our imaginations. Comets are just icy snowballs, without the integrity of an iron core like the earth’s. Any major blast will rip them to shreds. That applies to the bodies in the Oort cloud. And before anyone asks, the Kuiper Belt bodies are also icy masses and will be subject to an even greater force.
The odds are extremely high that nothing in a solar system like ours would survive a supernova at any distance.
It is true that it is very difficult to detect small dense objects at interstellar distances; unlike clouds of gas (which absorbs radiation and then re-emits it, leaving behind a distinct fingerprint in the spectral pattern) or dust (which just obscures or reflects radiation), dense objects barely effect the transmission of light and radio waves at all except via the weak lensing effect, observable only from the most massive objects and only when transited by another bright source. However, the mechanics of celestial bodies and the interstellar medium have been and continue to be well studied and simulated by models, and this “nucleation” that you suggest does not occur, or at least via the mechanism you describe ("…extra-solar planets, large comets, asteroids and even existing brown dwarves travel into or through the gas clouds and form new stars, much like dust motes collect water vapor to form rain droplets.")
For the sake of discussion, let’s take the Earth and fling it out of the Solar system to use as a typical condensed “dark” i.e. non-radiating (we’ll make everybody shut off their radio transmitters for the duration of the discussion) object; the proverbial large hunk of rock. The Earth is moving through the averaged local interstellar medium at about 20 km/s (not accounting for orbital speed), which means that in order to capture some dust or an object much smaller than its own mass it will have to pass withing 2000 km of the Earth’s center; that is to say, material would actually have to impact the Earth. The situation gets even worse as you go to smaller objects, and even if you go with much larger objects, like brown dwarves, just capturing some material in orbit doesn’t do a lot of good, as things in orbit tend to stay in orbit unless otherwise influenced. Collect enough loose material together and some of it will very slowly condense as some of the dust or gas loses momentum from impacts, but other mass is then flung away, or at least further outward, which ends up creating a balance that tends to starve out an aspiring star. It is not a good scenario for star formation even if you can get some material to stick around.
On the other hand, a large cloud of gas and/or dust tends to have a kind of internal inertia, acting like a self-damping fluid, especially in rotation. This tends to help keep the mass together, and an “impact” with another cloud, or a large shockwave from a supernova, or some other impact creates large areas of greater density, when then tend to form more graduated structure than you would get with a small condensed mass, which then permits larger structures to form without tearing themselves apart. The real trick of star formation is, like making pie crust, to put everything together without overworking it or getting too stretched out.
As others have noted, the residues from a supernova, if not completely pulverized, are certainly reduced. Meanwhile , the ball of material emitted from the explosion will be moving at several percent of the speed of light, much too fast to be influenced by planetary or smaller masses, pushing interplanetary gas and dust out in front of it, and in fact not slowing down much until it hits the interplanetary medium where it forms a shell called a supernova remnant. This, like the planetary nebulae emitted by smaller and less intense stellar deaths, is eventually swept into the interstellar medium where it does eventually contribute to the birth of metal-rich Population I type stars. Supernova remnants don’t condense back down into their original systems, however; they have too much radial momentum to return from whence they came. Or as Thomas Wolfe wrote, you can’t go home again.
Stranger
It seems to me the assumptions are;
a> High relative speed of objects, and
b> That the cloud consists only of gas, nothing larger, and
c> Short time frame.
However, if you’re allowing millions, or hundreds of millions of years for that gas cloud to expand, slow and begin moving in the same relative frame of reference as the objects around it, then we’re not simply talking about an object moving at 20km/s in relationship to everything around it (since those other objects are themselves moving). The gravitational attraction of the gas cloud will have an influence on the smaller objects around and within it, slowly moving them into sympathetic (probably the wrong word, but whatever) movement within the same relative framework.
So yes, while the supernova might have blasted the original systems components off at high speed, there are other objects in space that may well be trapped or ‘caught up’ within the movement of the gas cloud through space and the long-term formation of star forming regions.
At the very bottom of it, what I’m saying is that I think it’s foolish to assume that there is nothing in the cloud other than gas and that any larger object is merely passing through it at a speed high enough to prevent accumulation of mass. This would seem to be an overly broad, simplistic and dismissive assumption to make.
(No, I’m not making that as any form of personal attack or directing it at you or anyone else in this thread. I’m stating that as a general (and personal to me) concern about this kind of theory response.)
Do you have any mathematical support for your notion? I can’t see any way to make the physics of what you describe work.
Unfortunately, just saying “I think it should work like this” is never sufficient in science.
So you can see gas being perturbed by external forces and collapsing into large stellar masses, but you can’t see it condensing around a pre-existing nucleus? :dubious:
Or you can’t imagine any larger object NOT hurling through the gas clouds at escape velocity?
Or maybe there’s another pattern emerging in your responses.
Although if we are just limiting the conversation to Pop III stars, then there would probably be no planetary systems due to the scarcity of heavy elements in the early universe. By heavy I mean anything heavier than Hydrogen, Helium and Lithium.
Why ? Couldn’t planets have formed out of those three elements ? They wouldn’t have rocky or metallic cores, of course, and they’d have to be big enough to hold on to such light elements, but a planet sized mass of just those three elements would still be a planet, I’d think. Rather like a modern gas giant. Is it theorized that planet sized masses just wouldn’t form or be stable under those conditions ?
This month’s Scientific American covers one of the theories on planetary formation. It’s more complex than you’d think. One of the ingredients necessary is “dust” which would seem to preclude Population III and probably the majority of Population II stars.
The problem here is that you are trying to reason a mechanism by analogy, which is a dubious methodology at best. Analogy–the comparison of unlike subjects–is suitable for illustration, but often gives false impressions when used as a means of reasoning. Specifically, you are assuming that the formation of stellar-sized masses occurs by accumulating around a solid nucleus as raindrops for around dust nuclei. There are, however, very different basic mechanics going on. When water accumulates around a dust or existing water drop, it is attracted by electrostatic forces produced by the charge on the dust and polarity in the water. This creates a bond that is not energy conservative; that is, the kinetic energy of the incoming drop is absorbed and distributed through the mass, and typically lost to drag by the atmosphere, giving a balance of forces that encourages stability. With gravitational attraction to a large mass, however, energy is conserved–the sum of kinetic and gravitational potential energy are a constant–unless the incoming particle actually collides with the body. This isn’t to say that existing collections of masses don’t attract other masses of gas and dust, but they do so by forming accretion disks in which internal hysteresis (drag from collisions or attraction inside the disk) causes some of the mass to lose momentum to other areas of mass.
This leads to the second problem; that the size of the accretion disk is limited by the scale over which the central body acts. A small, dense body will have a much higher graviational gradient (the curve of gravitational attractive as you move outward) than a large, diffuse one, while at the same time, the rotational speed of the entire system increases as matter falls inward, required to maintain rotational momentum of the system. As the disk spins faster, material (especially low atomic weight matter) on the outer edge spreads outward and eventually escapes the influence of the central body entirely. This relationship between density and rotational speed governs just how massive an accretion disk, and thus the resulting celestial body can be. It isn’t as if there is just matter that falls directly into the body like water droplets merging on a plastic sheet; everything that comes in increases the rotational speed, and the higher the gradient the more it increases. To borrow your water drop analogy for a minute, it is as if every bit of water that is subsumed by the attracting drop makes it spin faster, until water tension will not allow any more water to accumulate, spinning it off on a tangent course instead.
Using a solid core as a basis, you can form rocky planets but nothing the size of a star; the amount of material it can maintain a hold on is too small. In order to construct something of stellar-sized mass, you need to start with a relatively diffuse core that more gradually coelesces over a large volume. For something the size of the supermassive black hole in the center of our galaxy, your mass is actually so diffuse that it is less dense than the air around us, and fails to consume the galaxy in one extended gulp because of the balance between graviational attraction and rotational momentum.
It is true that we can’t just put on spandex uniformas and go out to survey the interstellar medium directly, and it is also true that, due to the duration involved, we can’t watch a system conceive a star from initial accretion to the initiation of fusion. We can, however, make observations of systems in various stages of star formation, and we can model the process using the rules of basic mechanical and fluid dynamics. Because the process is perturbative–very sensitive to small changes in conditions–we cannot just write it up in a couple pages of equations and call it a solved or trivial problem, and indeed, it is an area of active research, but the mechanism you suggest has been researched and long dismissed as a means of stellar formation.
Here is a IPAC site on star formation, and here is the “A Ten Step Program for Star and Planet Formation” from the Harvard-Smithsonian Center for Astrophysics.
:dubious: What the frass is that supposed to mean?
Stranger