Scientists calculate age of massive neutron star crash that helped form our solar system

rod

Oct 22, 2019
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Impressive calculation supporting the r-process to explain elements found on Earth today using the solar nebula. I note from the article, "When neutron stars merge, they spew a wealth of short-lived elements into their surroundings, and these materials become part of later-forming solar systems. Now scientists are trying to close in on the merger that seeded our solar system by tracing the elements produced by the original decaying material. From that work, they believe the responsible merger occurred 100 million years before and 1,000 light-years away from the birth of our solar system. "It was close," the project's lead scientist, Szabolcs Marka, who is a physicist at Columbia University, told Space.com. "If you look up at the sky and you see a neutron-star merger 1,000 light-years away, it would outshine the entire night sky."

The calculated age for the neutron stars merger suggest it took place about 4.7 billion years ago, the precise location of the merger is not known because the location of the solar nebula or proto-sun at that time is not known in the Milky Way as the report indicates. However, the model does use an assumed mass for the solar nebula to explain the r-process elements, using meteorite studies too. Today we have a variety of stars documented with dust disks around them, many in the mass range of 1-3 earth masses, some quite large, more than 40,000 earth masses, quite a variety it appears. Is there spectra evidence for neutron star merger elements in those disks and gas like gold and uranium? For example, DH Tau system with DH Tau b, FU Orionis disk < =22 earth masses. There are *baby stars* forming documented in Orion nebula with <=26 earth masses.

The report provides an interesting, r-process calculation for our solar system to explain gold on Earth as an example.
 
Jan 4, 2020
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The neutron-star merger that showered the solar system with its precious metals was fairly close and fairly recent.

Scientists calculate age of massive neutron star crash that helped form our solar system : Read more
It's hard to find solar sister stars birthed from the same molecular cloud region, with 4.5 billion years and 200 million years orbit for Sun it has done 20+ orbits. Meanwhile the RMS velocity spread of the orbit speed is something like 50/220 on average or 20 %. So the spread is more than an orbit, and the sisters could be anywhere.

The single neutron star event simplifies things. From last year's article:

"Neutron star mergers are thought to be pretty rare in our galaxy, occurring only a few times every million years, the researchers wrote. Supernovas, on the other hand, are much more common; according to a 2006 study from the European Space Agency, a massive star explodes in our galaxy once every 50 years or so.

That supernova rate is much too high to account for the levels of heavy elements observed in early solar system meteors, Bartos and Marka concluded, ruling them out as the likely source of those elements. A single nearby neutron star merger, however, fits the story perfectly."
 
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Jan 4, 2020
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However, the model does use an assumed mass for the solar nebula to explain the r-process elements, using meteorite studies too.
Good catch!

But the proof is in the pudding.

First I note that the meeting proceedings are likely not yet published in peer review, but the older paper gets an 80 +/- 40 Myrs period and 300 +/- 100 pc distance between merger and our system birth so essentially the same. The one event dominance they get from the rarity of mergers and dispersion in between.

Second, the cloud process that birthed our system is complicated. In the canonical model, a vast molecular cloud self attracts. Eventually it births a first generation of very massive, shortlived stars that go supernova and both seed and compress the cloud parts. That sets of a second generation of massive, active stars whose solar winds blow up spherical shells of compressed gas. Such shells break up into solar nebula and eventually form disks that birth on average some five hundred star "sisters" of more common mass, among them our Sun.

The difference here is that the model timing has the neutron binary merger seed the cloud, before or at the same time as the nebula formation (perhaps before, since massive stars mature and die within 10s of milions of years). The paper show it seeding the individual nebula in Fig. 1, but I think that is just the illustration of the model run, not an entire model of a merger interacting with a molecular cloud. I wouldn't take the extent of the model too seriously - it works either way.

They rule out more frequent processes being dominant contributors since our system has a low abundance of radioactive isotopes, which is a funny constraint since the metal level is average (IIRC GAIA results - it used to be labeled "high"). But that is the beauty of the merger, since it produces a lot of such isotopes!
 
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rod

Oct 22, 2019
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Torbjorn, hopefully the gold and uranium is in the accretion disks documented now around other stars too :) There are plenty of assumptions and non-observables in the model, like the neutron star merger and location that did this seeding for the solar nebula, in whatever form it was 4.7 billion years ago as well as the mass at that time vs. many stars today with very low mass dust disks documented.
 

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