Star formation

[Andrew*]

How I understand it is that from a star-forming area, such as M42, stars are formed from the hot gas, and a large patch of stuff becomes a star cluster (such as M45), but how about individual stars? If it is in the same way, where is the rest of the gas that went into producing our own sun?

Cheers

Andrew

[thing]

The sun most probably was part of an open cluster some 5 biilion years ago when it was formed, they disperse with time. Open clusters are groups of very young stars, in the millions of years old rather than the billions.

The gas you mention in M42 only becomes hot as it begins to collapse around a common gravitational point. This takes millions of years as the gas cloud that makes up a star may be around 10 light years across. It carries on collapsing, turning into a protostar until the temperature at it's centre gets to around 15 million degrees when nuclear fusion can take place. The star then enters the 'main sequence', ie it's considered to have been 'born.' By the way when we talk about the gas clouds, they are actually thinner than the best vacuums we can create on earth, they're not some thick swirly mist type stuff. The reason M42 is 'lit up' is not that the gas is particularly hot, it's because it is an emission nebula, the gas atoms are excited by the radiation from the newly formed stars within it.

[Andrew*]

Sounds a sensible explanation... do we then know which stars were part of "our" cluster?

Andrew

[algol]

alpha centauri? random sci fi fan guess lol

[thing]

Dunno, the ones that are near us I suppose.

[lunator]

Andrew

Most of the Sun's siblings have dispersed into the galaxy as the Sun has travelled around the galaxy several times.

The only way we might find some of the Sun's siblings is to llok at the abundance of metals and how closely they match with Sun.

The gas of the nebula has long since dispersed.

Cheers

Ian

[acey]

I recall reading something in Sky and Telescope a few years ago about a star with a composition similar to our Sun's (ie the percentages of "metals" were about the same), from which it was guessed that it might have formed in the same cluster. Can't offer any link for that, but here's an interesting one, on what might have made the Sun's cluster disperse:

http://www.space.com/scienceastronomy/061024_sun_sisters.html

[lunator]

I know that 18 scorpii is seen as a close analgue to the Sun and there is another star that has a HD number that is even closer.

I will try to track the info down.

Cheers

Ian

[lunator]

Here's one link

http://space.newscientist.com/article/dn12725-suns-twin-an-ideal-hunting-ground-for-alien-life.html

[gurney]

It does rather rest on the premise that similar metal content means it formed from the same original gas cloud. But that original gas cloud would never have really been that unique in a galaxy system. The galaxy itself would have it's own properties, meaning that generally wide spread gas clouds would be somewhat interconnected, even thinly, and they would be somewhat similar (not wholly, but in the general scheme of things).

So it is possible that similar stars, in similar locations, started from different clouds.

I think I'd be more interested in looking at velocity distributions to try and track back and look at physical origins, rather than checmical. But I'm not sure where we're up to with that. Even with galactic orbits being taken into account, I'd have thought that local velocity would remain fairly intact, and should allow some measure of discovering the origins.

[barkis]

I join in here knowing my knowledge is sketchy to say the least. Are the heavier metals which are necessary in order for a system to form, such as the solar system.

A type 1 Supernova spewing out material that has fused into these metals, and precursers to the formation of the next generation of star and planets. such as ours.

Ron.

[lunator]

Hi Gurney

The velocity method could be interesting but will be tough to calculate as the Sun has completed several orbits around the galaxy so its space velocity may have been changed in the process.

The metals content is only a very rough guide but as the metals content of stars increases significantly towards the galaxtic centre you can say that stars with similar metals contents probably formed at roughly the samr distance from the centre.

The one element that seems to be focussed on is Lithium as I understand it (and I could be wrong) is that lithium levels in the Sun are quite low in comparison to many other similar stars.

Cheers

Ian

[InvaderXan]

How I understand it is that from a star-forming area, such as M42, stars are formed from the hot gas, and a large patch of stuff becomes a star cluster (such as M45), but how about individual stars? If it is in the same way, where is the rest of the gas that went into producing our own sun?

To be all technical for a minute...

Molecular clouds (or dark nebulae, depending what youlike to call them) are gravitationally bound -- in other words, they're massive enough to hold themselves together by their own gravity). A molecular cloud starts to collapse when a critical mass (known as the Jeans Mass) becomes enclosed within a critical radius (the Jeans Radius). This gives rise to a "Jeans Instability", leading to the fragmentation and inevitable gravitational collapse of a molecular cloud. Once fragmented, little cloudlets (often referred to as Bok globules) form which then collapse into one or more stars. The exact mechanics aren't well known, but essentially the mass and density of a cloud will govern the mass of the stars formed.

Protostars start out as dense knots of molecular gas and dust which become heated by gravitational contraction. The gravitational energy released is eventually high enough that the object shines like a star even though it isn't yet fusing hydrogen. These are known as T Tauri stars (or Herbig Ae/Be stars -- if their mass is high enough). These young stars are puffy compared to main sequence stars, as they are still contracting. They also emit a lot of radiation. Their spectra show strong emission lines, and they exert a lot of radiation pressure.

This radiation pressure drives a powerful stellar wind (known as a T Tauri wind) which serves to disperse remnant gas that didn't fall into the star originally. The star continues to accrete material onto it's surface from a circumstellar disk, while simultaneously blowing away any excess. This disk eventually goes on to (presumably) accrete planets, and the star's wind blows a big bubble in the interstellar medium, effectively isolating the star from it's surroundings. That radiation also generates a lot of UV, ionising hydrogen and creating the red blotches (HII regions) you see in lots of pictures of galaxies. The Triangulum Galaxy has an impressive number of these if you want to see for yourself.

By the time the star initiates fusion in it's core, the dense cloud material that originally collapsed has become diffuse. Diffuse clouds are not bound by gravity, so they eventually disperse completely. Of course, when the original cloud fragmented, some vast patches of cloud might remain untouched, but over the course of a few billion years, any remaining stars will drift away from their parent cloud.

...So to answer your question, the rest of the gas that the Sun formed from was blown away as the Sun formed.

Hope that was of interest...

[MikeP]

Thank you InvaderXan - very informative. I look forward to reading more such posts.

Mike

[dogfish]

I enjoyed that too. I knew the general process but lacked the detail you've added.

Thanks, Martin

[InvaderXan]

Anytime!

[phillc]

Thanks for taking the time to explain the process in greater depth.

phillc :wave:

[InvaderXan]

In fact, there's rather a nice YouTube video of a star formation simulation...

http://uk.youtube.com/watch?v=GoQ08ONholQ

It's not perfectly accurate -- but it's quite pretty!

[Talitha]

Thank you InvaderXan (Markus, isn't it?), you explained everything so well even I understood it. You're a wonderful teacher.. glad to have you with us! :notworthy:

Are the HII regions those the little pink 'knots' in the images? I loved the youtube presentation.. very nicely done.

[InvaderXan]

Thank you InvaderXan (Markus, isn't it?), you explained everything so well even I understood it. You're a wonderful teacher.. glad to have you with us! :notworthy:

Are the HII regions those the little pink 'knots' in the images? I loved the youtube presentation.. very nicely done.

Wow... I'm flattered. You're very welcome!

And yes it is. Have we met before someplace...?

Yes, those pink knots are HII regions. Hydrogen gives off balmer emission lines at specific wavelengths. The strongest (called H-alpha emission) is in the red part of the spectrum, making hydrogen give off pink/red light. You can see the same colour in solar flares during a total eclipse.

I can't really take credit for that YouTube video though...

[Talitha]

And yes it is. Have we met before someplace...?

No, I never had the pleasure. It's listed in the right hand side-bar of your livejournal page. Very interesting collection of entries you've got there, btw!