R136a defies Laws of Stellar Evolution

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Discussion Overview

The discussion centers on the peculiar case of the star R136a, located in the R136 cluster, which appears to defy conventional models of stellar evolution. Participants explore the implications of its mass, age, and energy output, questioning the validity of existing stellar evolution theories and the mechanisms behind its continued existence despite expectations of an imminent explosion.

Discussion Character

  • Debate/contested
  • Exploratory
  • Technical explanation

Main Points Raised

  • Some participants express confusion over R136a's longevity given its mass and energy output, suggesting it should have exploded by now according to stellar evolution models.
  • One participant proposes that R136a may have formed from the merger of lighter stars, referencing the concept of blue stragglers.
  • Another participant mentions that R136a has shed a significant amount of its original mass, which could explain its continued existence, and suggests it may be part of a close binary system.
  • Concerns are raised about the validity of the mass and age estimates, with requests for clarification on the sources of these figures.
  • Some participants discuss the implications of Eddington luminosity, noting that while stars can exceed this limit, the structure of such stars is complex and not well understood.
  • There is a discussion on the mechanisms that could lead to a star's explosion, including the dynamics of mass loss and the role of gravitational forces during stellar mergers.
  • One participant argues that the solar wind does not significantly influence the dynamics of R136a, although this point is not fully elaborated.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the reasons behind R136a's unusual characteristics. Multiple competing views are presented regarding its formation, mass loss, and the implications of Eddington luminosity, indicating an ongoing debate.

Contextual Notes

There are unresolved questions regarding the assumptions behind the mass and age estimates of R136a, as well as the implications of stellar evolution models that may not fully account for the complexities observed in such massive stars.

AdamAutism1998
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At 265 SM, and age 1.7 Million years, at 163,000 Light Years Away in the R136 cluster, is R136a. But, it shouldn't be alive now. It should have exploded given the model of Solar Mass Evolution at 200,000-375,000 Years old of age. It's in it's Wolf-Rayet phrase, but it still shouldn't be alive. I'm confused by the dynamics in this scenario. It's larger than an average WR star (28.8 SR) but with it's energy output and luminosity of 8,700,000 Suns, it should have already died. I think we should study it more because this is a serious mystery for stellar evolution. Does anyone know anything more?
 
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This is almost certainly from a merger of lighter stars. Google "blue straggler".
 
R136a has already shed a significant amount of it original mass, so its continued existence is less a mystery. It may also be a close binary system, although that is arguable.
 
AdamAutism1998 said:
At 265 SM, and age 1.7 Million years, at 163,000 Light Years Away in the R136 cluster, is R136a. But, it shouldn't be alive now. It should have exploded given the model of Solar Mass Evolution at 200,000-375,000 Years old of age.
How do you get these numbers?
 
snorkack said:
How do you get these numbers?
Models based off Stellar Evolution. I studied that a lot.
 
Chronos said:
R136a has already shed a significant amount of it original mass, so its continued existence is less a mystery. It may also be a close binary system, although that is arguable.
True. Although it would be very hard to determine.
 
Vanadium 50 said:
This is almost certainly from a merger of lighter stars. Google "blue straggler".
I did. Although it should have exploded if that much mass was to merge. Plus it would be rotating fast.
 
AdamAutism1998 said:
Although it should have exploded if that much mass was to merge

Really? Are you an expert in stellar evolution? Or is this a guess? If it's not a guess, why? What would cause the explosion?
 
Vanadium 50 said:
Really? Are you an expert in stellar evolution? Or is this a guess? If it's not a guess, why? What would cause the explosion?
I'm not an "expert" on the subject nor do I consider myself one. But my reasoning is based off the total mass required to fuse. In the event such massive stars were to collide, they would merge at very high speeds due to the gravitational influence of approach. As the cores merge, it would leave a gap. Because the merging process makes both stars unstable for a certain period of time, the cores mass would make the orbital velocity very fast. If one core was more massive than the other by a certain level, the unbalance would be catastrophic. The rotation of the core would accelerate to the point of which breakup is inevitable. A pair instability supernova would obscure from the unbound core. Plus, there has been no evidence of extreme rotation, which in Blue Stragglers, is extremely fast, almost to breakup velocity.
 
  • #10
If RS-136a was part of a close companion binary system it would be expected to be an x ray variable. Since no variability has been detected in its x ray spectrum, it is argueably unlikely to be a member of a close binary system.
 
  • #11
AdamAutism1998 said:
Models based off Stellar Evolution. I studied that a lot.
Where precisely do they quote your 200 000-375 000 years?
 
  • #12
snorkack said:
Where precisely do they quote your 200 000-375 000 years?
It's a stellar evolution chart. It's on Wikipedia, but I used the variables to follow it down further.
 
  • #13
AdamAutism1998 said:
It's a stellar evolution chart. It's on Wikipedia, but I used the variables to follow it down further.
The thing is, you cannot. Care for an explanation why?
 
  • #14
snorkack said:
The thing is, you cannot. Care for an explanation why?
Yes, Please. I would like to understand more.
 
  • #15
It's impossible for a star to explode appreciably sooner than about 2 million years, no matter how massive. Do you spot the reason?
 
  • #16
snorkack said:
It's impossible for a star to explode appreciably sooner than about 2 million years, no matter how massive. Do you spot the reason?
Energy vs Pressure. Although Massive, and having a very prominent gravitational field, there's a counterbalance in the core caused by the intense energy it radiates. This prevents the star from collapsing until it has lost enough mass to be able to counteract the force of gravity forcing it to collapse. Since the star was so massive, it was able to hold it's own for a while against this immense pressure. But, in the process this force is causing a powerful stellar wind, making the star lose the mass of the sun every 50,000 years, but the rate is decreasing as it loses more mass, from a possible Solar Mass every 10,000 at birth in recent studies.

However, (This was last year, and I don't remember the source so don't ask please) Inside the massive star, there is a barrier between the two forces. Although the collision should be too intense and violent for atoms to fuse, there's a limit. The core is generally unpredictable. However, unlike the Earth, which has gravitational fields that vary notably, Stars can have this too, but in much, much, smaller differences. However, in massive stars, this is critical. The weight of the barrier will increase in certain areas, slowing down the effects of energy causing the atoms to be unable to fuse. If you shoot a bullet through a series of walls, it will slow down with each wall it passes through, until it stops. In a key area of this layer, the force of energy is no longer strong enough to effect fusion. The heat allows fusion of heavier elements very quickly. Iron is fused in a few thousand years, and as this mass grows greater, energy is suppressed more. However, a star this massive cannot form a black hole or neutron star due to the unstable pressure and heat now at the core. It explodes as a Pair-Instability Supernova.
 
  • #17
The reason is that the luminosity of a star is limited by Eddington luminosity.
 
  • #18
snorkack said:
The reason is that the luminosity of a star is limited by Eddington luminosity.
Okay.
 
  • #19
And Eddington luminosity is proportional to the mass of star.
 
  • #20
snorkack said:
And Eddington luminosity is proportional to the mass of star.
Okay.

I thought it had surpassed that limit according to recent studies.
 
  • #21
Certainly the structure of stars very close to the Eddington limit, or beyond it, is complicated and not well known. You are right that stars can exceed the Eddington limit, because they go convective over most of the interior, and then the Eddington limit does not apply. In the outer layers, where the density is too low for convection to be effective, the star can exceed the Eddington limit because the light can escape through gaps in the clumps of gas, and can also drive a dense wind where the force is allowed to exceed gravity. But it shouldn't exceed that limit by too much, so it's still true that extrapolating a table is only going to work if the table already goes up to where the Eddington limit is reached. That also means snorkack is right that the lifetime cannot get too short, perhaps not too much less than a milllion years.
 
  • #22
Ken G said:
Certainly the structure of stars very close to the Eddington limit, or beyond it, is complicated and not well known. You are right that stars can exceed the Eddington limit, because they go convective over most of the interior, and then the Eddington limit does not apply. In the outer layers, where the density is too low for convection to be effective, the star can exceed the Eddington limit because the light can escape through gaps in the clumps of gas, and can also drive a dense wind where the force is allowed to exceed gravity. But it shouldn't exceed that limit by too much, so it's still true that extrapolating a table is only going to work if the table already goes up to where the Eddington limit is reached. That also means snorkack is right that the lifetime cannot get too short, perhaps not too much less than a milllion years.
Okay.

How does the Solar Wind apply as well?
 
  • #23
The solar wind plays no role-- the rest of the star is almost completely ambivalent to it, its mass and energy fluxes are so pathetic.
 

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