Simulations reveal an unusual death for ancient stars

Simulations reveal an unusual death for ancient stars
This image is a slice through the interior of a supermassive star of 55,500 solar masses along the axis of symmetry. It shows the inner helium core in which nuclear burning is converting helium to oxygen, powering various fluid instabilities (swirling lines). This "snapshot" from a CASTRO simulation shows one moment a day after the onset of the explosion, when the radius of the outer circle would be slightly larger than that of the orbit of the Earth around the sun. Visualizations were done in VisIT. Credit: Ken Chen, University of California at Santa Cruz
(Phys.org) —Certain primordial stars—those 55,000 and 56,000 times the mass of our Sun, or solar masses—may have died unusually. In death, these objects—among the Universe's first-generation of stars—would have exploded as supernovae and burned completely, leaving no remnant black hole behind.

Astrophysicists at the University of California, Santa Cruz (UCSC) and the University of Minnesota came to this conclusion after running a number of supercomputer simulations at the Department of Energy's (DOE's) National Energy Research Scientific Computing Center (NERSC) and Minnesota Supercomputing Institute at the University of Minnesota. They relied extensively on CASTRO, a compressible astrophysics code developed at DOE's Lawrence Berkeley National Laboratory's (Berkeley Lab's) Computational Research Division (CRD). Their findings were recently published in Astrophysical Journal (ApJ).

First-generation stars are especially interesting because they produced the first heavy elements, or chemical elements other than hydrogen and helium. In death, they sent their chemical creations into outer space, paving the way for subsequent generations of stars, solar systems and galaxies. With a greater understanding of how these first stars died, scientists hope to glean some insights about how the Universe, as we know it today, came to be.

"We found that there is a narrow window where supermassive stars could explode completely instead of becoming a supermassive black hole—no one has ever found this mechanism before," says Ke-Jung Chen, a postdoctoral researcher at UCSC and lead author of the ApJ paper. "Without NERSC resources, it would have taken us a lot longer to reach this result. From a user perspective, the facility is run very efficiently and it is an extremely convenient place to do science."

The Simulations: What's Going On?

To model the life of a primordial supermassive star, Chen and his colleagues used a one-dimensional stellar evolution code called KEPLER. This code takes into account key processes like nuclear burning and stellar convection. And relevant for massive stars, photo-disintegration of elements, electron-positron pair production and special . The team also included general relativistic effects, which are important for stars above 1,000 solar masses.

They found that primordial stars between 55,000 to 56,000 solar masses live about 1.69 million years before becoming unstable due to general relativistic effects and then start to collapse. As the star collapses, it begins to rapidly synthesize heavy elements like oxygen, neon, magnesium and silicon starting with helium in its core. This process releases more energy than the binding energy of the star, halting the collapse and causing a massive explosion: a supernova.

To model the death mechanisms of these stars, Chen and his colleagues used CASTRO—a multidimensional compressible astrophysics code developed at Berkeley Lab by scientists Ann Almgren and John Bell. These simulations show that once collapse is reversed, Rayleigh-Taylor instabilities mix produced in the star's final moments throughout the star itself. The researchers say that this mixing should create a distinct observational signature that could be detected by upcoming near-infrared experiments such as the European Space Agency's Euclid and NASA's Wide-Field Infrared Survey Telescope.

Depending on the intensity of the supernovae, some supermassive could, when they explode, enrich their entire host galaxy and even some nearby galaxies with elements ranging from carbon to silicon. In some cases, supernova may even trigger a burst of star formation in its host galaxy, which would make it visually distinct from other young galaxies.

"My work involves studying the supernovae of very with new physical processes beyond hydrodynamics, so I've collaborated with Ann Almgren to adapt CASTRO for many different projects over the years," says Chen. "Before I run my simulations, I typically think about the physics I need to solve a particular problem. I then work with Ann to develop some code and incorporate it into CASTRO. It is a very efficient system."

To visualize his data, Chen used an open source tool called VisIt, which was architected by Hank Childs, formerly a staff scientist at Berkeley Lab. "Most of the time I did my own visualizations, but when there were things that I needed to modify or customize I would shoot Hank an email and that was very helpful."

Chen completed much of this work while he was a graduate student at the University of Minnesota. He completed his Ph.D. in physics in 2013.


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Astrophysicists model the formation of the oldest-known star in our galaxy

More information: Astrophysical Journal , iopscience.iop.org/0004-637X/790/2/162
Journal information: Astrophysical Journal

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Sep 29, 2014
Computer simulations = unusual outcomes

Sep 29, 2014
This comment has been removed by a moderator.

Sep 29, 2014
No. The primordial black holes were certainly extant and have with the same certainly evaporated.

Sep 29, 2014
Shootist, I believe the term primordial black hole refers to an object that was created from a quantum density fluctuation right after the big bang that would create a black hole, because the universe was so hot and dense the random positioning of particles would create a black hole, it doesn't have anything to do with stars. Plus the background radiation of the universe is still too high for any black hole with a mass greater than that of the moon from evaporating.
No black hole of a meaningful mass will begin to lose mass for trillions of years

Sep 30, 2014
among the Universe's first-generation of stars..... more bs! no way to prove that.

Sep 30, 2014
This comment has been removed by a moderator.

Sep 30, 2014
He's right about one thing, stars are the slaves to creation within a galaxy.

Sep 30, 2014
Please tell me that picture is not some kind of rorshach test, 'cause I'm seeing all kinds of stuff in there. Should have been an album cover for some late sixties acid rock band...

Sep 30, 2014
"55,000 and 56,000 times the mass of our Sun, or solar masses" -should be "55 and 56"

Sep 30, 2014
"55,000 and 56,000 times the mass of our Sun, or solar masses" -should be "55 and 56"


Are you sure?

Sep 30, 2014
"55,000 and 56,000 times the mass of our Sun, or solar masses" -should be "55 and 56"
@birger
where are you getting your information from?
the study linked has, in the abstract
However, we have now discovered that non-rotating primordial stars with masses close to 55,000 M ☉ can instead die as highly energetic thermonuclear supernovae powered by explosive helium burning, releasing up to 1055 erg, or about 10,000 times the energy of a Type Ia supernova. The explosion is triggered by the general relativistic contribution of thermal photons to gravity in the core of the star, which causes the core to contract and explosively burn.
So, no, it is NOT "55 and 56"... unless you are reading something that we are not...????

Sep 30, 2014
I think Birger's concerns follow my own. The most massive known star is R136a1, estimated at only 256x Msolar http://arxiv.org/abs/1007.3284 55-56,000 is several orders of magnitude larger.

Oct 01, 2014
This may just be a case of taking computer modelling to absurd limits, but this IS the universe we're talking about.

Still, I'd expect some sort of signature from a past explosion this big.

This star would be as bright as a million modern galaxies at peak luminosity, like a Quasar, which is simply unfathomable.

Oct 01, 2014
55-56,000 is several orders of magnitude larger
@barakn
how to reconcile the difference?
The link you posted suggests
Comparisons with stellar models calculated for the main-sequence evolution of 85-500 Msun suggest ages of ~1.5 Myr
Which is also what the above is claiming, except that it is claiming a far higher mass (as you state, orders of magnitude higher)

we should contact the author and request clarification... I have already put in a request to the author, so I am hoping for something explaining soon


Oct 01, 2014
@barakn
how to reconcile the difference?
The link you posted suggests
Comparisons with stellar models calculated for the main-sequence evolution of 85-500 Msun suggest ages of ~1.5 Myr
Which is also what the above is claiming, except that it is claiming a far higher mass (as you state, orders of magnitude higher)

we should contact the author and request clarification... I have already put in a request to the author, so I am hoping for something explaining soon


I forget his name now but their was the astrophysics-Skippy who wrote the paper awhile back about the stars that got made without the polluted gases in the beginning could have been 1000s of times bigger than the stars beginning today. He said they would only be around 1 million years or less before exploding.

I can not for the life of ol Ira remember what his name is to ask the google but I will keep trying to remember. I do remember he was a normal-Skippy from the famous school not the crankpot Skippy

Oct 01, 2014
Hooyeei, I am getting better with stuffs. I found him. Not the one I read, I found one about the one I read. The astrophysical-Skippy who's name I could not remember is in these article. His name is Abraham Leob from the Harvard science school.

http://www.scient...-the-un/

Oct 02, 2014
Ooh, this must be controversial. They are outside of Eddingtons mass limit:

"The limit on mass arises because stars of greater mass have a higher rate of core energy generation, their luminosity increasing far out of proportion to their mass. For a sufficiently massive star the outward pressure of radiant energy generated by nuclear fusion in the star's core exceeds the inward pull of its own gravity. This is called the Eddington limit. ... Although the limit can be stretched for very early Population III stars, and the exact value is uncertain, if any stars still exist above 150-200 M☉, they would challenge current theories of stellar evolution."

[ http://en.wikiped...wn_stars ]

Oct 02, 2014
Relativity crackpot warning on mentioning loop[y] theorists Rovelli & Mersini. (The later the one that claims black holes doesn't exists while they are observed.)

@Shootist: Primordial black holes are primordial, from before the Hot Big Bang - stars come after the HBB.

@Rustybolts: Cosmology means we must have a first generation. And yes, they have been observed now. http://www.astron...ve-stars

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