Where does the gold come from?

For decades, gold and other heavy metals have been considered supernova eruption, but many researchers have recently questioned this.

Historically, there is a lot of bizarre absurd interpretation of the question of how “gold is on earth” or “how to get more gold?”. For example, the people of the Inca Empire (the ancient empire of the South American continent from the 11th century to the 16th century) believed that gold came from the tears and sweat of the sun gods; Aristotle thought that gold was a hardened water Solar water penetrates into the depths of the surface when the change; Isaac Newton also wrote with the Holy stone preparation of gold formula; even, Green fairy tale dwarf demon can be rotated by straw to get gold.

Modern astronomers also have their own theory, the result is relatively clear: about four billion years ago, in a known as the “late veneer” (late veneer) period, embedded in a small amount of precious metals (including gold) meteorite fall to Earth on. But the most essential question is, where is the gold in the universe coming from? , This is still an unsolved mystery.

For decades, more and more people have begun to believe that the supernova eruption has produced gold and elements in the periodic table after several lines of heavy elements. However, with the simulation of the supernova model to enhance the level of the majority of the gold outbreak simulation process performance more like the ancient alchemist set. Perhaps new discoveries (which are considered very difficult by traditional research) can answer this puzzle!

In the past few years, the new theory quickly detonated the research circle. Now, many astronomers believe that neutron stars have collapsed and collapsed to forge the heavy metals in the universe. There are also some people think that although many supernova bursts can not produce these heavy metals, but still some special supernova can do. In order to resolve the controversy, astrophysicists began to spare no effort to collect evidence from the computer simulation of the model to the deep sea manganese nodule gamma ray detection. They want to observe a very rare universe of metal to end this argument

Supernova problem

In 1957, the physicists Margaret, Geoffrey Burbidge, William Fowler and Fred Hoyle presented a set of Theory, can explain how stars produce and destroy almost every element of the periodic table [1]. This means that humans (at least the elements that make up our body) were stardust and, of course, gold elements.

Anna Fribbel, an astronomer at the Massachusetts Institute of Technology, said: “The problem has been a long time, and the secret of Stardust has been around for a long time.

The Big Bang produced hydrogen, helium and lithium. Then, the stars use these elements to gradually synthesize the heavier elements. But this process to iron after the stagnation, because the iron element is the most stable element, the nucleus than the iron element charge is very large, it is difficult to gather together, so that the synthesis process of energy input is greater than the energy output.

In order to make the heavy element more stable, you can use neutral neutrons to bombard the iron nuclei. Newly added neutrons tend to cause nuclei to be unstable, in which case the neutrons will decay into protons (which also release an electron and an anti-neutrino), and the net increase in protons leads to new Heavy elements appear.

If the neutron velocity captured by the nucleus is slower than its decay rate, the process is called slow neutron capture, or is called the S process, such as the formation of strontium (Sr), barium (Ba) and lead (Pb); if the neutrons are captured by the nucleus faster than its decay speed, the process is called fast neutron capture, or called the R process, such as uranium (U) and gold (Au) and other heavy element.

In order to get the elements of the R process, Bobby and his team realized that you need to meet the following conditions: First, you need a fairly pure neutron source; then, you also need a heavier ” (Such as iron nucleus) to capture these neutrons; finally, you have to put them in a hot, dense environment (density can be too high). Of course, you will hope that everything will happen in the explosion, so that the product will be scattered out, and can be detected by.

For many astronomers, a special kind of material to meet the above conditions, that is supernova.

The mechanism of the supernova is like this: when the high-quality stars of their own nuclear slowly synthesize the heavier elements to the iron element, the synthesis will stop, the stars of the ball rolling, about a sun-quality stars will collapse Shrink the radius of only a dozen kilometers of the sphere, followed by the core collapsed into a very high density of stars, it will produce super planets outbreak, it produces and radiant energy up to billions of light years away.

It seems that supernova has all the necessary conditions. In the process of star collapse, the protons and electrons at the core are very close, and then the neutrons are produced, and the nuclei are transformed into the embryos of neutron stars. Coupled with the rich iron content, heat is also sufficient, resulting in hot will last for nearly a thousand years, and continue to spray energy to the space until exhausted.

By about 1990, the computational model began to produce more specific images. Half a second after the collapse of the mass of the mass of the stars, the neutrino storm will last for nearly a minute, and some of the neutrino storms that contain a large number of neutrons will scratch the iron core that can be used as a “seed”.

Astronomer physician Thomas Janka (Thomas Janka, Germany plus Hing, Max Planck Institute) said: “find hope! I think it is nearly 20 years to explain the formation of R elements of the process, the most interesting and most The way forward. “And now there are still many people agree with this view. Astronomical physicist Enrico Ramirez-Ruiz, University of California, added: “If you now open a textbook, it will tell you that the R process will appear in the super planets Outbreak.

But with the supernova model more and more complex, but the situation has become more and more bad. For example, the temperature of the neutrino storm does not seem too high, the speed of the storm is too slow, so that too many species can not capture enough neutrons to form uranium-like elements, and neutrino can also Sub-conversion into protons – it means that the neutrons can participate in the less.

This makes theorists reexamine the most critical point in the supernova model – the super planetary outburion does not seem to depend on the neutron star’s R process.

StephanRosswog (University of Stockholm University) said: “This kind of nuclear synthesis is so incredible, at first you have other parts of the universe do not have a huge amount of neutron source, although the neutron star has a super Strong gravitational field, but the crux of the problem is – how can you determine that neutron stars can produce something?

Is there any way to let neutron stars crack? One way is to use supernova-level explosion, it seems that does not work If you think and then open a little, can you wait until a super planetary outbreak, and then use it to crack the neutron star?

Neutron star story

In 1974, radio astronomers first discovered [2] a double-pulse neutron star system. In each track, they consume energy, and one day there will be a collision. In the same year, astronomical physicists James Lattimer and David Schramm simulated [3] the case of neutron stars and black holes, but the collision between neutron stars in that era was too complicated As for the calculation can not be simulated.





Although the super-planetary outbreak can briefly illuminate the entire Milky Way galaxy, the neutron star is still difficult to observe. For example, as early as 1054, the supernova eruption produced by the crab nebula was recorded in many places, but until 1968, the neutron star was detected [4] to. Latimer and Schramm argue that although no one has ever seen the fusion of two neutron stars, it is not only difficult to find but also difficult to understand, but this extreme case can explain the generation of R elements.

Imagine the last scene of the combination of two neutron stars, when they become larger neutron stars or black holes, they will be destroyed by a huge gravitational tide, the collision process will also spray a lot of material.

Brian Metzger, a theoretical astronomer at Columbia University, said: “It’s kind of like you are squeezing toothpaste and it will eject something at the end.” Each neutron star will have a tail, The proportion of the child to the proton is close to 10: 1, the temperature is as high as several billion degrees Celsius, and the nucleus formation process is almost one second. Because they contain many unstable, activated neutrons, and finally they will decay into gold and platinum and the like elements.

At least, in the simulation process, they are carried out in this way.

Golden Star

Neutron star fusion and super-planetary outbursts will continue to produce R process elements, but the biggest difference between the two is the amount of production. Supernovae may have the size of the moon gold, and neutron star fusion can produce Jupiter-sized gold (thousands of times higher than the supernova produced), but the neutron star fusion probability is far less than the supernova outbreak. The distribution of elements of this R process can be used as a way for astronomers to explore their origins.

Ramirez Ruiz (RamirezRuiz) said: “R process elements like chocolate, the universe rich R process elements mainly from the supernova, this part is like a cookie evenly coated chocolate, compared to The fusion of neutron stars is like chocolate making cookies, and all of these chocolates or R processes are very intensive.

By looking for the byproducts of R events on Earth and their distribution, they can be used as a means of assessment. After the supernova erupted to illuminate the Milky Way for a long time, the elements that it produced would enter the interstellar dust, and when the dust passed through the solar system, it would fall into the earth as a result of the geomagnetic field, At the office. In a 2016 issue of the journal Nature, it was found that [5] has radioactive Fe-60 elements in the deep-sea shells, which are considered to be traces of supernova outbreaks ten million years ago. However, these supernova bursts do not appear with the R process-related elements. They also found in this [6] a small amount of plutonium 244 (an unstable product of the R process). Metzjie argues that no matter how these overweight elements are produced, they will not be the most frequent in our galaxy.

Not everyone agrees with this conclusion. Such as the team led by Shawn Bishop (Munich University of Technology), who still want to find the radioactive plutonium left over by the supernova on Earth. Recently, their team is looking through the clues of the elements of the R process through substances such as microbial fossils that contain the metal elements they are ingested from the environment and used to prepare the magnetic crystals.

Of course, astronomers can also find from the depths of the universe, “chocolate cookies” footprint. For example, the europium element of the R process has a strong spectral line, and the astronomer can detect it through the gas layer of the star. In the aura of the Milky Way, the lines of these R process signals can be captured from some of the distant stars. Ramirez Ruiz said: “We can find almost two iron content, but the europium content is worse than two orders of magnitude stars.” Because of this, Ramirez Ruiz that the universe “chocolate Cookies “than” chocolate Weihua “more.

Astronomers also find an example that illustrates the problem, and many dwarf galaxies are experiencing the last period of death, and this process may be the process of R. Until 2016, no one observed that any star in the dwarf galaxy had frequent signs of R.

Suddenly one night, the Massachusetts Institute of Technology Freibel (Frebel) received a shock to him the phone. This phone call from her graduate student Alex Ji (Alex Ji), Alex Kyrgyzstan has been observed Reticulum II dwarf galaxy. Freibel recalls: “He called me at two in the morning and said, ‘Anna, I found the spectrum out of some problems, there is a star showing a strong europium line’, I thought he was joking, Say: ‘Oh, Alex, you may have found an R-process galaxy’. “In fact, he really found [7]. Reticulum II has seven stars that are synthesizing R elements of the process, very rare things.

New supernova

In order to support the neutron star fusion model [7], everything seems so right. Neutron star fusion is very rare, unlike the collapse of a single mass star, and finally become a supernova, it needs two neutron stars in the double track up to merge, perhaps one hundred million years only once. But the opponents point out that you can not deny its existence because it is rare.

In our galaxy, neutron star fusion may occur once a billion years, perhaps once a million years, a difference of nearly four orders of magnitude. Christopher Fryer (Christopher Fryer, Los Alamos National Laboratory) said: “Those who think that neutron star fusion can explain the elements of the R process used to be a million years to calculate, really surprised me.

When Fryr and his colleagues used the relative compromise frequencies to perform neutron fusion modeling and estimate the amount of R process material produced, they found that neutron fusion only explained 1% of the R elements of the universe [8]. If the real frequency is 100 million years, then the neutron star fusion contribution will be reduced by 100 times. “More people are starting to rethink the question – can the process still appear in other cases,” says Fryer.

So, the supernova burst into a focus. If 1% of the supernovae show nonstandard simulations, they may produce a significant number of R process elements in a “chocolate-prepared cookie pattern”. Nobuya Nishimura (Nobuya Nishimura, an astronomer at the University of Kiel) and his colleagues raised objections in the recent article [9], which, in addition to neutrino, could also explode through stars A large amount of magnetic spray produced, the latter will quickly generate a large number of neutrons, so that the nucleus into some of the R process elements. “It’s not like your tea party,” Fred said, “you just have to keep it for 100 milliseconds!”

Many astronomers believe that this answer will be in a compromise form ended. Moreover, that change may have begun to happen. Fryer also said: “The R process is no longer the previous R process, and perhaps it can be divided into two halves, than the barium light R process elements derived from supernova, and heavier elements such as gold, then from neutron stars The collision.