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How is Gold Made? - Neutron Star Mergers!

10/17/2017 11:13 AM

The accuracy of the theorists' predictions compared to the observed merger is remarkable! Here is an article talking about it...

https://www.sciencedaily.com/releases/2017/10/171016102822.htm

Where and how this process of heavy element production occurs has been one of the longest-standing questions in astrophysics. Recent attention has turned to neutron star mergers, where the collision of the two stars flings out clouds of neutron-rich matter into space, where they could assemble into heavy elements.

Speculation that astronomers might see light from such heavy elements traces back to the 1990s, but the idea had mostly been gathering dust until 2010, when Brian Metzger, then a freshly minted graduate student at UC Berkeley, now a professor of astrophysics at Columbia University, co-authored a paper with Quataert and Kasen in which they calculated the radioactivity of the neutron star debris and estimated its brightness for the first time.

"As the debris cloud expands into space," Metzger said, "the decay of radioactive elements keeps it hot, causing it to glow."

Metzger, Quataert, Kasen and collaborators showed that this light from neutron star mergers was roughly one thousand times brighter than normal nova explosions in our galaxy, motivating them to name these exotic flashes "kilonovae."

Still, basic questions remained as to what a kilonova would actually look like.

"Neutron star merger debris is weird stuff -- a mixture of precious metals and radioactive waste," Kasen said.

Astronomers know of no comparable phenomena, so Kasen and collaborators had to turn to fundamental physics and solve mathematical equations describing how the quantum structure of heavy atoms determines how they emit and absorb light.

Jennifer Barnes, an Einstein postdoctoral fellow at Columbia, worked as a Berkeley graduate student with Kasen to make some of the first detailed predictions of what a kilonova should look like.

"When we calculated the opacities of the elements formed in a neutron star merger, we found a lot of variation. The lighter elements were optically similar to elements found in supernovae, but the heavier atoms were more than a hundred times more opaque than what we're used to seeing in astrophysical explosions," said Barnes. "If heavy elements are present in the debris from the merger, their high opacity should give kilonovae a reddish hue."

"I think we bummed out the entire astrophysics community when we first announced that," Kasen said. "We were predicting that a kilonova should be relatively faint and redder than red, meaning it would be an incredibly difficult thing to find. On the plus side, we had defined a smoking-gun -- you can tell that you are seeing freshly produced heavy elements by their distinctive red color."

That is just what astronomers observed.

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#1

Re: How is Gold Made? - Neutron Star Mergers!

10/17/2017 1:29 PM

Nice article and a great triumph for LIGO, VIRGO and the optical telescopes (Hubbel?) that witnessed this neutron star collision into a kilonova.

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#2

Re: How is Gold Made? - Neutron Star Mergers!

10/17/2017 1:46 PM

That last point is the key, and may even tell us the timeline of heavy metals formation.

The reddest light was not until the latter part of the event.

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#3

Re: How is Gold Made? - Neutron Star Mergers!

10/17/2017 2:06 PM

$10 Octillion worth.

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#6
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Re: How is Gold Made? - Neutron Star Mergers!

10/17/2017 11:01 PM

.

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#10
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Re: How is Gold Made? - Neutron Star Mergers!

10/18/2017 10:50 AM

Is that the last point?

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#11
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Re: How is Gold Made? - Neutron Star Mergers!

10/18/2017 7:29 PM

Sorry, no! Rethought posting.

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#12
In reply to #11

Re: How is Gold Made? - Neutron Star Mergers!

10/20/2017 9:14 AM

Rethought posting?

Is that like reposting a thought?

(Sorry if I'm going off on weird(er) tangents today, I think I'm under-caffeinated. Or over-caffeinated. In any case, I'm not caffeinated the right amount.)

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#4

Re: How is Gold Made? - Neutron Star Mergers!

10/17/2017 2:57 PM

I understood the theory was that heavy elements (heavier than iron, that is) were formed and spread around, by supernova explosions, without reference to neutron star collisions. Is that theory now disbanded?

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#5
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Re: How is Gold Made? - Neutron Star Mergers!

10/17/2017 4:32 PM

There might be some of the heavier elements than iron from supernovae, but to get the preponderance of heavy metals, I think it does take this more energetic kilonova.

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#7
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Re: How is Gold Made? - Neutron Star Mergers!

10/18/2017 4:46 AM

Could be. I believe elements up to iron are made in the cores of "ordinary" stars, but to spread these elements around the galaxy to benefit the likes of you and me they would need to explode as (super)novas at the end of their life.

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#8
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Re: How is Gold Made? - Neutron Star Mergers!

10/18/2017 6:46 AM

The article said these kilonovas were 1000 times more powerful than a regular nova.

In a regular nova, a star blows off an outer shell of gas, but the star mostly remains.

A supernova is a much more powerful explosion in which a late-stage star collapses and then completely explodes. Supernova are visible in distant galaxies near the edge of the observable universe.

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#9
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Re: How is Gold Made? - Neutron Star Mergers!

10/18/2017 9:38 AM

Yes, this reaction is the now observed fourth type of nova; nova, supernova, hypernova and now a kilonova. With the exception of a "simple" nova (which reminds me of stellar indigestion) one should expect some amount of heavier element formation to happen from the shock wave propagating into the star and possibly adjacent material that may or may not be part of that stellar system.

In a nova, a white dwarf star of a binary system with an expanding red giant star significantly brightens from time to time from the material stripped from its partner but both stars remain after a burst. (Reminds me of some marriages.) In all three other types of novas the end of a star happens.

I suspect that the linguistic differentiation of hypernovas and kilonovas will fade in time when more gravity wave detection coincide with other hypernovas. IMHO a kilonova will become a subset of hypernovas (aka superluminous supernova).

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