According to a new study published in the May 2, 2019 issue of Nature, 4.6 billion years ago, two neutron stars collided near the early Solar System (actually about 1000 light-years from the gas cloud that eventually formed the Solar System). This violent collision has created heavy elements like silver, gold, platinum, cesium, and uranium. The study says 0.3% of the Earth’s heaviest elements have been created by this event.

Researchers concluded that 4.6 billion years ago, about 100 million years before the formation of Earth, two neutron stars collided about 1000 light-years away Since our galaxy, the Milky Way is at least 100,000 light-years in diameter, this distance can be easily treated as the “cosmic neighborhood”.

Scientists say “if a comparable event happened today at a similar distance from the Solar System, the ensuing radiation could outshine the entire night sky”.

Two neutron stars collided near the solar system 4.6 billion years ago
The merger of two neutron stars is an extremely powerful event. Gravitational waves (pale arcs) bleed away orbital energy, causing the stars to move closer together and merge. As the stars collide, some of the debris blasts away in particle jets moving at nearly the speed of light, producing a brief burst of gamma rays (magenta). In addition to the ultra-fast jets powering the gamma-rays, the merger also generates slower moving debris. An outflow driven by accretion onto the merger remnant emits rapidly fading ultraviolet light (violet). A dense cloud of hot debris stripped from the neutron stars just before the collision produces visible and infrared light (blue-white through red). The UV, optical, and near-infrared glow is collectively referred to as a kilonova. Later, once the remnants of the jet directed toward us had expanded into our line of sight, X-rays (blue) were detected.

To arrive at their conclusion, the authors of the study, astrophysicists Szabolcs Marka at Columbia University and Imre Bartos at the University of Florida, compared the composition of meteorites to numerical simulations of the Milky Way.

There is a process called “r-process” (rapid neutron-capture process) which is responsible for the creation (nucleosynthesis) of approximately half the abundances of the atomic nuclei heavier than iron.

Two Neutron Stars Collide - explosion

Related: LIGO detects gravitational waves from neutron star merger

As neutron-star mergers occur infrequently, their deposition of radioactive isotopes into the pre-solar nebula could have been dominated by a few nearby events. Although short-lived r-process isotopes (with half-lives shorter than 100 million years) are no longer present in the Solar System, their abundances in the early Solar System are known because their daughter products were preserved in high-temperature condensates found in meteorites.

Researchers assert that that abundances of short-lived r-process isotopes in the early Solar System point to their origin in neutron-star mergers, and indicate substantial deposition by a single nearby merger event.

By comparing numerical simulations with the early Solar System abundance ratios of actinides produced exclusively through the r-process, researchers constrain the rate of occurrence of their Galactic production sites to within about 1-100 per million years. This is consistent with observational estimates of neutron-star merger rates, but rules out supernovae and stellar sources, Marka ad Bartos say.

Origins of the elements

Related: Origins of the elements [amazing infographic by NASA]

Researchers further find that there was probably a single nearby merger that produced much of the curium and a substantial fraction of the plutonium present in the early Solar System. Such an event may have occurred about 300 parsecs (978 light-years) away from the pre-solar nebula (see notes 1), approximately 80 million years before the formation of the Solar System.

Since our current technology depends heavily on these rare elements, these findings will have interesting effects on the quest for extraterrestrial civilizations. If heavy elements are even more scarce, there could be no intelligent species in the Universe with the level of technological growth we have had.

This could be one possible explanation of why we haven’t heard from ET yet, or as Enrico Fermi put it: “Where is everybody?“.

https://www.youtube.com/watch?v=x_Akn8fUBeQ
Neutron star collision: two doomed neutron stars whirl toward their demise in this animation. Gravitational waves (pale arcs) bleed away orbital energy, causing the stars to move closer together and merge. As the stars collide, some of the debris blasts away in particle jets moving at nearly the speed of light, producing a brief burst of gamma rays (magenta). In addition to the ultra-fast jets powering the gamma rays, the merger also generates slower-moving debris. An outflow driven by accretion onto the merger remnant emits rapidly fading ultraviolet light (violet). A dense cloud of hot debris stripped from the neutron stars just before the collision produces visible and infrared light (blue-white through red). The UV, optical, and near-infrared glow are collectively referred to as a kilonova. Later, once the remnants of the jet directed toward us had expanded into our line of sight, X-rays (blue) were detected. This animation represents phenomena observed up to nine days after GW170817, a gravitational wave (GW) signal observed by the LIGO and Virgo detectors on 17 August 2017, originating from the shell elliptical galaxy NGC 4993. The GW was produced by the last minutes of two neutron stars spiraling closer to each other and finally merging and is the first GW observation that has been confirmed by non-gravitational means.

Notes

  1. The nebular hypothesis says that the Solar System formed from the gravitational collapse of a fragment of a giant molecular cloud.] The cloud was about 20 parsec (65 light-years) across, while the fragments were roughly 1 parsec (three and a quarter light-years) across. The further collapse of the fragments led to the formation of dense cores 0.01-0.1 pc (2,000-20,000 AU) in size. One of these collapsing fragments (known as the pre-solar nebula) formed what became the Solar System.

Sources

  • Study: “A nearby neutron-star merger explains the actinide abundances in the early Solar System” on Nature.com
  • “Two neutron stars collided near the solar system billions of years ago” on Phys.org
  • Discussion about the study on Reddit
  • r-process on Wikipedia
  • Formation and evolution of the Solar System on Wikipedia
M. Özgür Nevres
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