The heaviest natural elements on the periodic table such as gold, platinum, and uranium were forged during the mergers of binary neutron stars. Astronomers have previously estimated that tens of thousands of such binary neutron star mergers must have occurred throughout our Milky Way Galaxy during the past 10 billion years, sprinkling neutron-rich elements throughout the gas that eventually formed the next generation of stars and planets. By studying the composition of meteorites, astronomers now conclude that a single collision of neutron stars occurred shortly before and near to the formation of our solar system, producing a measurable fraction of the heavy elements here on Earth.
“How invigorating it was to glimpse a cosmic puzzle touching us all! How thrilling is the expanding global quest investigating all flavors of dead and exploding stars to probe our shared origins,” Columbia University astrophysicist Szabolcs Marka wrote in an email to The Daily Galaxy. In 2019, Marka and collaborators determined that a violent collision of two neutron stars 4.6 billion years ago, approximately 80 million years before the formation of the Solar System, was the likely source of some of the most coveted matter on Earth. “So many open questions emerged since,” he added, “providing opportunities for scientists worldwide.”
“Our results address a fundamental quest of humanity: Where did we come from and where are we going? It is very difficult to describe the tremendous emotions we felt when realized what we had found and what it means for the future as we search for an explanation of our place in the universe,” said Marka
The Milky Way galaxy itself is 100,000 light years in diameter, or 100 times the distance of this cosmic event from the birthplace of Earth. “If a comparable event happened today at a similar distance from the Solar System, the ensuing radiation could outshine the entire night sky,” Marka added.
This single cosmic event, close to our solar system, gave birth to 0.3 percent of the Earth’s heaviest elements, including gold, platinum and uranium, according to a paper appearing in the journal Nature.
“This means that in each of us we would find an eyelash worth of these elements, mostly in the form of iodine, which is essential to life,” said Imre Bartos at the University of Florida. “A wedding ring, which expresses a deep human connection, is also a connection to our cosmic past predating humanity and the formation of Earth itself, with about 10 milligrams of it likely having formed 4.6 billion years ago.”
One of the intriguing points about this finding is the demonstration of how much our immediate cosmic neighborhood is dependent on random cosmic events”
“Meteorites forged in the early solar system carry the traces of radioactive isotopes,” said Bartos, who received his Ph.D. at Columbia. “As these isotopes decay they act as clocks that can be used to reconstruct the time they were created,” Marka said.
To arrive at their conclusion, Bartos and Marka compared the composition of meteorites to numerical simulations of the Milky Way. They found that a single neutron-star collision could have occurred about 100 million years before the formation of Earth, in our own neighborhood, about 1,000 light years from the gas cloud that eventually formed the Solar System.
The Last Word –Imre Bartos
The “Last Word’ is from co-author, astrophysicist Imre Bartos with the Institute for High Energy Physics and Astrophysics at the University of Florida, His research focuses on multi-messenger astrophysics: the exploration of the Universe through combining information from a multitude of cosmic messengers, including gravitational waves, electromagnetic radiation, neutrinos, and atomic nuclei. Bartos wrote in an email to The Daily Galaxy:
“One of the intriguing points about this finding is the demonstration of how much our immediate cosmic neighborhood is dependent on random cosmic events. For example, the rate of neutron star mergers varies over time and over location in the Milky Way, so where the Solar System formed in space and time affected how much heavy elements we have now here on Earth. When we are looking for other, extrasolar planets one may need to take into consideration the respective histories of neutron star mergers associated with these Worlds.
“We are also poised to learn a lot more about neutron star mergers in the next years. The LIGO gravitational wave detector is turning back on at the end of this year with vastly increased sensitivity, and we anticipate the detection of multiple neutron star mergers. This in turn can be used to better characterize how much heavy elements each of these mergers produces, or how much variation there is between mergers. This in turn will give us a better picture of what ended up making our Earth the way it is.
“A third point I would mention is that there is an ongoing scientific debate about the contribution of not just neutron star mergers but also a rare type of stellar death, called collapsars, to the heavy elements we find. Meteoritic heavy elements also carry information about this, and as we find in another 2019 paper, they suggest that the origin of these heavy elements is probably as common as neutron star mergers, pointing to them as the major contributor to what we observe.
“And finally, as a fourth point, neutron star mergers similar to the one we found in the 2019 paper should occur near Earth every several tens of millions of years. While this is not likely to happen during the existence of humanity, let alone our lifetime, it is interesting to think about what such a nearby merger would look like if we just see it in the night sky with our naked eye. We explored this question with a student of mine and showed what we would actually see, it is quite interesting, one could easily spot such a merger even during the daytime.
The researchers believe that their study provides insight into a uniquely consequential event in our history. “It sheds bright light on the processes involved in the origin and composition of our solar system, and will initiate a new type of quest within disciplines, such as chemistry, biology and geology, to solve the cosmic puzzle,” Bartos said.
Image credit: Hubble Space Telescope