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Sun Feb 18, 2018, 12:15 PM

A question for my fellow DUers interested in the stars...

A question that perhaps someone can answer for me. I do read quite a bit and so forth, but 1 thing still escapes me. We all (most of us) know that stars form by hydrogen / helium gases (in clouds scattered throughout the universe) collapsing under the weight of so much gas, and eventually, after a certain point, enough gases and pressure has built up that nuclear fusion starts, and you have 'liftoff' or a brand new star.

I am assuming that this process occurs once a certain threshold of gases and pressure is achieved.

However, there are massive stars that from 10 to a 1000 times the size of our sun.

Why didn't these massive stars start burning as stars when they already had enough pressure and material after 1 solar mass of material available, e.g., like our own sun? Or put in another way, how did these super-sized stars manage to gather so much material before igniting into a star? If it ignited at 1 solar mass (like our own sun), then all other incoming gases etc. would have been pushed away by the solar winds.

So, how does a star gather up so much more material than our own sun before igniting?

Thanks for any thoughts and light you may shed on this (pun was not intended, purely accidental)!?

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Response to SWBTATTReg (Original post)

Sun Feb 18, 2018, 12:18 PM

1. Good question.

I don't know the answer, but am wondering if the large stars form when a very large amount of mass gathers before compressing, so that by the time fusion starts it is already really massive.

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Response to SWBTATTReg (Original post)

Sun Feb 18, 2018, 12:19 PM

2. I'm not an expert but I believe those massive stars aren't as dense as some smaller ones.

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Response to SWBTATTReg (Original post)

Sun Feb 18, 2018, 12:32 PM

3. Maybe this?

"As the dusty gas collapsed, onto the star's growing core, instabilities developed that resulted in channels where radiation blew out through the cloud into interstellar space, while gas continued falling inward through other channels."

"You can see fingers of gas falling in and radiation leaking out between those fingers of gas," Krumholz said. "This shows that you don't need any exotic mechanisms; massive stars can form through accretion processes just like low-mass stars."

The entire article with pictures here: https://www.space.com/6328-massive-stars-form-simple-solution.html

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Response to Ferrets are Cool (Reply #3)

Sun Feb 18, 2018, 12:53 PM

6. Very interesting. I'll read your link. Like they say, ...

the simplest solution is the most likely. Seems like it's not really a star yet, 100%, but well on its way to being one.

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Response to SWBTATTReg (Original post)

Sun Feb 18, 2018, 12:36 PM

4. not a complete answer.

 

as gravity crushes a cloud of interstellar gas into a smaller volume, it will create its own gravitational well which will pull in more gas, it will also heat up, if the temperature rise is too large, the pressure generated will halt the collapse of the gas mass until more material falls into the previously created well, which eventually overcomes the heat pressure, and becomes dense enough to initiate fusion.

if WATER is present in the interstellar gas, then the heat created by compression will be radiated away as IR and microwaves, (pure H and He cannot emit IR), the collapse will not stop and the density needed for fusion will occur before any additional mass can fall in.

astrophysicists theorize that only massive stars were formed in the immediate post big bang environment ( which was only H and He)

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Response to Terminally_Chill (Reply #4)

Sun Feb 18, 2018, 01:02 PM

7. Being built up in cycles, eh? Makes sense too...

cycle 1, initial burst of star building occurs, then slows to a halt, as radiating off excess heat from 1st wave of compression, and then resumes after 1st wave is radiated away as heat ... then the process starts anew, w/
cycle 2, another wave of star building resumes, excess heat pushed away, cycle 3, cycle 4, etc. until finally, the pressure of the solar winds are so powerful that they finally are able/strong enough to push the incoming weight of all of the gases flowing inwards back. Seems very doable/likely.

I assume that the astrophysicists are theorizing that massive stars were created initially after the 'big bang' because only then was large amounts of gas available then?

Just curious, since life cycles of big stars are so short, then obviously there is a mechanism still in play here that allows big stars to still be created, even billions of years after the 'big bang'?

Take care and thanks!

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Response to SWBTATTReg (Reply #7)

Sun Feb 18, 2018, 02:24 PM

12. oxygen, and therefore water were only available after the first gen of massive stars supernova'd

 

supernovae also create violent concentrated gravity waves which can compress the interstellar medium, they have in important role in star formation.

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Response to Terminally_Chill (Reply #12)

Sun Feb 18, 2018, 02:42 PM

13. Good point, perhaps then ...

a primary, massive wave of massive superstars at first rapidly went off, and then all compressed the gases again (2nd initial wave) leading to tens of thousands of smaller stars (as well as secondary massive superstars where material is available in the conditions needed), and so forth, in a rapid cascade until it slowed down a bit, after it 'sputtered' out. Then gravity starts its long dance, into what we see today.

These initial waves then shaped the universe as it now appears.

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Response to SWBTATTReg (Original post)

Sun Feb 18, 2018, 12:43 PM

5. Great question! Answer seems to be they did start on the main sequence with what,was it a .6 solar..

...mass to start fusing hydrogen? But their lives as Supergiants begins when they have fused all the hydrogen in their cores and start fusing heavier elements in their shells, helium, C-N-O cycle and on up, IIRC:


Sorry to quote wikipedia, I'm on the run:

[link:https://en.wikipedia.org/wiki/Blue_supergiant_star|]

Supergiants are evolved high-mass stars, larger and more luminous than main-sequence stars. O class and early B class stars with initial masses around 10-100 M☉ evolve away from the main sequence in just a few million years as their hydrogen is consumed and heavy elements start to appear near the surface of the star. These stars usually become blue supergiants, although it is possible that some of them evolve directly to Wolf–Rayet stars.[2] Expansion into the supergiant stage occurs when hydrogen in the core of the star is depleted and hydrogen shell burning starts, but it may also be caused as heavy elements are dredged up to the surface by convection and mass loss due to radiation pressure increase.[3]

Blue supergiants are newly evolved from the main sequence, have extremely high luminosities, high mass loss rates, and are generally unstable. Many of them become luminous blue variables (LBVs) with episodes of extreme mass loss. Lower mass blue supergiants continue to expand until they become red supergiants. In the process they obviously must spend some time as yellow supergiants or yellow hypergiants, but this expansion occurs in just a few thousand years and so these stars are rare. Higher mass red supergiants blow away their outer atmospheres and evolve back to blue supergiants, and possibly onwards to Wolf–Rayet stars.[4][5] Depending on the exact mass and composition of a red supergiant, it can execute a number of blue loops before either exploding as a type II supernova or finally dumping enough of its outer layers to become a blue supergiant again, less luminous than the first time but more unstable.[6] If such a star can pass through the yellow evolutionary void it is expected that it becomes one of the lower luminosity LBVs.[7]

The most massive blue supergiants are too luminous to retain an extensive atmosphere and they never expand into a red supergiant. The dividing line is approximately 40 M☉, although the coolest and largest red supergiants develop from stars with initial masses of 15-25 M☉.



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Response to Anon-C (Reply #5)

Sun Feb 18, 2018, 01:06 PM

8. Look no further than this comment for the answer. Thanks.

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Response to Anon-C (Reply #5)

Sun Feb 18, 2018, 01:14 PM

9. Makes sense as far more massive stars (w/ the higher temps) undergoes different processes...

of development apart from that of our own sun. Perhaps because of the higher temps, material is ejected more often, causing a delay in the actual star making process? Like a fine tuned steam engine, too much heat, and you'll blow up the train/delay the star formation/fusion?

Maybe another analogy is cooking bread at a higher altitude vs. a lower altitude?

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Response to SWBTATTReg (Reply #9)

Sun Feb 18, 2018, 01:40 PM

10. I did want to add, with respect to the gist of your question...

...we have a tendency to look at this "taxonomically". It used to be phrased "settling unto the main sesequence" to be more descriptive of the stars process. So this mass is collapsing usually out of a larger cloud of stuff. at the point this protostar is massive enough to be what we call a brown dwarf, its already giving off some light and heat , but not enough to fuse hydrogen to helium and not enough "push away" more gas still collapsing in.

Then Boom it gets enough mass to fuse but IIRC its far from stable, often partially blows itself up and subsequently recollapses to ignite its fusion core again, and again until it does stabilize. I believe this stage of settling on is what Cephied Variable stars are.

Ok, thats it. Can you tell I enjoyed your question?

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Response to Anon-C (Reply #10)

Sun Feb 18, 2018, 01:47 PM

11. And I enjoyed your great answer...it does go a long long way to answering my ?. Thanks so much!! nt

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Response to Anon-C (Reply #10)

Mon Feb 19, 2018, 05:15 PM

14. Well answered.

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