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Long lived supernova ?

supernova iPTF14hls pulsation pair instability magnetar

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#1 Mee_n_Mac

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Posted 08 November 2017 - 06:03 PM

https://www.space.co...erstanding.html

The appearance of a years-long supernova explosion challenges scientist's current understanding of star formation and death, and work is underway to explain the bizarre phenomenon.

 

Stars more than eight times the mass of the sun end their lives in fantastic explosions called supernovas. These are among the most energetic phenomena in the universe. The brightness of a single dying star can briefly rival that of an entire galaxy. Supernovas that form from supermassive stars typically rise quickly to a peak brightness and then fade over the course of around 100 days as the shock wave loses energy.

 

In contrast, the newly analyzed supernova iPTF14hls grew dimmer and brighter over the span of more than two years, according to a statement by Las Cumbres Observatory in Goleta, California, which tracked the object. Details of the discovery appeared on Nov. 8 in the journal Nature.

 

Supernova iPTF14hls was unremarkable when first detected by a partner telescope in San Diego on Sept. 22, 2014. The light spectrum was a textbook example of a Type II-P supernova, the most common type astronomers see, lead author Iair Arcavi, an astronomer at the University of California, Santa Barbara, told Space.com. And the supernova looked like it was already fading, he said.

 

The observatory was in the middle of a 7.5-year collaborative survey, so Arcavi focused on more-promising objects. But in February, 2015, Zheng Chuen Wong, a student working for Arcavi that winter, noticed the object had become brighter over the past five months.

 

iPTF14hls_brightness_600px.jpg

 

"He showed me the data," Arcavi said, "and he [asked], 'Is this normal?' and I said, 'Absolutely not. That is very strange. Supernovae don't do that,'" Arcavi said.

 

At first, Arcavi thought it might be a local star in our galaxy, which would appear brighter because it was closer, he said. Many stars are also known to have variable brightness. But the light signature revealed that the object was indeed located in a small, irregular galaxy about 500 million light-years from Earth.

 

And the object only got weirder. After 100 days, the supernova looked just 30 days old. Two years later, the supernova's spectrum still looked the way it would if the explosion were only 60 days old. The supernova recently emerged from behind Earth's sun, and Arcavi said it's still bright, after roughly three years. But at one one-hundredth of its peak brightness, the object appears to finally be fading out.

 

"Just to be clear, though, there is no existing model or theory that explains all of the observations we have," said Arcavi. The supernova may fade out; it may grow brighter, or it may suddenly disappear.

 

One reason for Arcavi's uncertainty is that a supernova was seen in the same location in 1954. This means that the event Acavi has been observing, whatever it is, may actually be 60 years running. There's a 1 to 5 percent chance the two events are unrelated, but that would be even more surprising, said Arcavi. Astronomers have never observed unrelated supernova in the same place decades apart.

 

iPTF14hls_diptych_LCO_600px.jpg

 

"We are beyond the cutting-edge of models," Arcavi said.

 

"I'm not sure, and I don't think anyone else is sure, just what the hell is happening," astrophysicist Stanford Woosley, at University of California, Santa Cruz, told Space.com. "And yet it happened, and so it begs explanation."

 

Woosley is not affiliated with the study, but he is among the theoreticians working to understand the event. Two hypotheses show promise in explaining it, he said.

 

Much more at the link above.

 


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#2 owlhoot

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Posted 08 November 2017 - 07:17 PM

Mystery indeed. So far outside the norm, they can't even postulate a theory...
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#3 XZG 1138

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Posted 08 November 2017 - 11:18 PM

Aliens are using the star as a bombing range, antimatter bombs and photon torpedoes. The natives are not happy about it, terrible sunburns.


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#4 MzSnowleopard

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Posted 15 November 2017 - 02:07 AM

As I read the article, I was reminded of something, someone once told me. I'm paraphrasing here but you get the idea.

 

On discoveries and breakthroughs- scientists don't cry 'Eureka'- they whisper "hmm, that's funny" 

 

This would seem to be one of those times.


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#5 silylene

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Posted 15 November 2017 - 04:45 PM

I have a serious speculative explanation.  (Yes, you read it hear first, but like usual, I expect some noted astronomer will publish this explanation about 5 years from now in a nice paper)

 

Maybe we are not looking at one star in that photo, or in that graph, but rather we are observing the core of a dense globular cluster of stars and misinterpreting the result as a single star which is a fluctuating serial supernova.

 

In my serious speculative explanation, this far away star globular cluster is full of young similar-aged hot short-lived stars in close proximity to one another.

 

And simply, this far away globular star cluster has a supernova popping off every 10-30 years within it.  So the supernova, to the limit of our resolution, always looks to be in the same location in that far away galaxy.

 

Since the galaxy at best resolves like a distant fuzzball, we cannot resolve this hot vigorous globular star cluster.

 

picture of galaxy:

iPTF14hls_diptych_LCO_600px.jpg

 

picture of an example of a dense globular star cluster in our Milky Way, Messier 80.  M80 today consists mostly of old stars, and so we don't see supernovas:

300px-A_Swarm_of_Ancient_Stars_-_GPN-200

 

In fact the core of a dense globular cluster has about 5 stars per ly3.  Often stars are only a light month apart from one another.

 

I would not be surprised if a supernova in the dense core of a globular cluster sends ejected material into adjacent stars, and the mass input plus the the radiation pushes them much more rapidly into supernova.  In this manner, one may even get a catalytic chain-supernova event, where they keep popping off one every 20-50 years until the core large young star density is consumed and more sparse.

 

Maybe this is what we are seeing.


Edited by silylene, 15 November 2017 - 04:48 PM.

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#6 owlhoot

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Posted 15 November 2017 - 07:05 PM

Nice idea but the mass doesn't work out, nor does the consistent spectra. Different stars, no matter how close together would vary enough in their spectral signatures to differentiate easily enough.
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#7 silylene

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Posted 15 November 2017 - 07:55 PM

Stars in a core of a globular cluster are remarkably similar in spectrum, since they were all formed the same time from the same gas cloud collapse.  Generally low metal stars.

 

The only stars that would trigger would be those of similar large size.  Smaller stars wouldn't trigger.   I would expect only that similar aged stars would go supernova.  So yes, they would look the same, since it is a selective propensity.



#8 Bill Slugg

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Posted 15 November 2017 - 08:53 PM

I read a theory that the star was very low metallicity and on the order of 200 solar masses and thus in a stage of repeating pair-production instabilities.


Edited by Bill Slugg, 15 November 2017 - 08:54 PM.


#9 Mee_n_Mac

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Posted 15 November 2017 - 10:10 PM

I have a serious speculative explanation. 

...

I would not be surprised if a supernova in the dense core of a globular cluster sends ejected material into adjacent stars, and the mass input plus the the radiation pushes them much more rapidly into supernova.  In this manner, one may even get a catalytic chain-supernova event, where they keep popping off one every 20-50 years until the core large young star density is consumed and more sparse.

 

Maybe this is what we are seeing.

Could the above match the increases in luminosity seen in the data ? By that I mean the curve posted in the OP looks pretty continuous. Now I know we're not seeing the raw data and so I can't say how much of the curve (posted in the OP) is interpolated and/or smoothed, but I'd expect multiple SN to show rapid jumps in the aggregate luminosity curve followed by sharp roll-offs.  Can you take a number of light curves from a typical Type II-P supernova, time splice them and come up with the curve posted ?


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#10 silylene

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Posted Yesterday, 10:44 AM

What is being measured in the curve shown (I haven't read the journal article)?  Is it the luminosity of that tiny distant smudge of a galaxy?  Is it the luminosity of that corner of the tiny smudge of a galaxy?

 

Assuming the latter (most likely), what is being measured is the sum light output of millions of stars in that corner of a distant galaxy that looks like a smudge to me.  Of course there is a continuous baseline output of those millions of stars.  I simply suggest that there is a globular cluster of hot young stars read to pop, embedded in that corner of that distant galaxy.

 

I suggest that each of the peaks in that light curve are the aggregate luminosity of one or more surpernova popping off in the scenario I suggested earlier (probably each peak could be a sequence of several supernova, since the stars are light months apart in the core of a globular cluster).  Remember that the stars in the core are not uniformlly distributed.  There would a delay each time for the expelled matter and energy to reaches anpther clusterlet of hot young stars within the core ready to pop


Edited by silylene, Yesterday, 10:45 AM.


#11 owlhoot

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Posted Yesterday, 08:31 PM

It can't just be the aggregate luminosity of the cluster. They have historical data to show the event is a supernova.
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#12 Mee_n_Mac

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Posted Yesterday, 09:04 PM

I suggest that each of the peaks in that light curve are the aggregate luminosity of one or more surpernova popping off in the scenario I suggested earlier (probably each peak could be a sequence of several supernova, since the stars are light months apart in the core of a globular cluster).  Remember that the stars in the core are not uniformlly distributed.  There would a delay each time for the expelled matter and energy to reaches anpther clusterlet of hot young stars within the core ready to pop

Right, I understood that. As each SN pops off, the aggregate luminosity increases. And then should decrease according to a fairly predictable timeline. This is how we judge the distance to galaxies via type 1A SN even when we don't catch the first moments of the "pop". Type II-P SN also have a typical light curve. What I'm saying is that if your hypothesis is correct then you should be able to take a type II-P light curve, duplicate and time shift it N times, add the resulting curves and come up with an amplitude (only) scaled version of the light curve presented above in the OP. The rise and fall times of the composite curve should match the observed data. The assumption is that all the stars going SN in this case are of the same size and composition and therefore have the same spectrum and (also) characteristic light curve.

 

SNIIcurva.png

This graph of the luminosity as a function of time shows the characteristic shapes of the light curves for a Type II-L and II-P supernova. -  from the prior Wiki link.

 

Using the data posted in the OP (reproduced below), there's a rapid rise and fall at about the 250 day mark that seems to me to defy any such attempt to add'n'shift curves, it falls off too quickly.

 

iPTF14hls_brightness_600px.jpg


Edited by Mee_n_Mac, Yesterday, 09:09 PM.

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#13 silylene

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Posted Yesterday, 10:04 PM

Well I am assuming an irregular ensemble of novas and supernovas popping off.  I don't know how well the data would fit.  A Monte Carlo model might be a nice start.  But I think my speculation deserves some simulations!



#14 Anvel

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Posted Yesterday, 11:43 PM

I don't think Silylene's hypothesis even requires a globular cluster. A star forming large nebula in the same spot will do. The light curves would be distorted by gases in the nebula. The Pleides is an open cluster containing a half dozen or so blue giants all formed at about the same time. They'll all eventually go SN. Maybe one right after another. At any rate, the cluster hypothesis fits very well with the observation from a half century ago in the same spot as this latest observation. Maybe it's a nebula that for some reason formed a bunch of hypergiant stars with extremely short lives with the other gas in the nebula making interpretation of the light curve problematic.



#15 Mee_n_Mac

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Posted Today, 12:16 AM

I don't think Silylene's hypothesis even requires a globular cluster. A star forming large nebula in the same spot will do. The light curves would be distorted by gases in the nebula.

I take your last sentence to mean that the individual SN luminosities won't all be the same. That some SN may be blocked or decreased in amplitude by intervening gas/dust/etc. I agree but the timeline of those individual SNs won't be so affected. If one has a plateau of 100 days, the others will as well (give or take). Can you take as many as needed type II-P SN light curves, scale each one as you desire, time shift each one as you desire and then add them all up to get something resembling the observations ? I agree that the general concept of multiple SN is intriguing and reasonable and so have proposed one method to test it.

 

At a glance I'm not sure the simplest answer, multiple SN, all of the same type (due to coming from the same type progenitor stars) can be made to fit the observations. Perhaps someone can do it and I'm just not seeing it. At some point people who do this for a living thought the SN was a single event of common type. Only later did extended observations over the next year prove it otherwise, but the initial observation remains.

 

Now it may be that not all the SN are of the same type and that the spectral analysis has missed this because it was ... done once and not since ... or ??? But let's start with the simplest concept (AIUI from sily's post) and see if it "has wings".

 

I'd like to know what data is available from the 1954 observations. Those details were not in the article referenced in the OP.


Edited by Mee_n_Mac, Today, 12:20 AM.

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