Have you ever held a piece of gold? Not a small piece of jewelry, but an ounce or more? If you have, you can understand what makes people want to possess it and where it comes from.
We know that gold comes from the stars. The stars are made of hydrogen and helium. They contain elements that are referred to as a star's metallicity. Our Sun has a high metallicity and contains 2.5 trillion tons of gold.
Astronomers have found a distant star that contains 65 elements, the most ever found in another star. Among them is gold.
HD 222925 is a bright star in our neighbourhood. It is close to the southern sky. Astronomers call it the gold standard because it is their best chance to study how stars create heavy elements in the Universe. The r-process is a rapid neutron capture process.
There is a chemical inventory for HD 222925 of the elements produced by the r-process. The paper is called The R-Process Alliance: A Nearly Complete R-Process template Derived from Ultraviolet Spectroscopy of the R-Process-Enhanced Metal-Poor Star HD 222925. Ian is an astronomer at the University of Michigan.
HD 222 295 is a metal-poor star. It has high metallicity, meaning it has many elements other than hydrogen and helium, but not much of those elements by mass. It is not the first one discovered. The scientist who first identified 53 chemical elements in it is the one who earned that distinction. HD 222295 is brighter in the UV than the star, making it easier to observe. The researchers were able to identify 65 elements.
To the best of my knowledge, that is a record for any object beyond our Solar System. This star has a very high relative proportion of elements listed along the bottom two-thirds of the periodic table. The elements were made by the rapid neutron capture process. We are trying to understand the physics of how, where and when those elements were made.
There are two types of capture, the slow and the r-process. Scientists still have questions about the r-process, despite the fact that the s-process is well-understood. Astrophysicists have a good theoretical understanding of the r-process, but it wasn't observed until the year 2019.
The r-process begins with elements lighter than iron. Lighter elements can capture neutrons in an environment with a lot of energy. An electron is emitted when an atom captures a neutron. The lighter element becomes a heavier element when the atomic number is raised.
The astrophysical sites that foster the r-process are rare and so are heavier elements.
The r-process is difficult to study and the heavier elements, like gold, are rare. HD 222295 is the gold standard.
The r-process is fostered by environments such as nova star mergers. Massive stars are the other. Understanding the r-process is dependent on understanding the astrophysical environments that allow it. astrophysicists want to study the process in more detail.
It's an important step forward to recognize where the r-process can occur. What did that event do? What was produced there?
The heavy elements it contains were not produced by HD 222 295. They were produced earlier in the Universe and then spread into space. They were taken up in another generation of star formation.
The detailed element-by-element output of some r-process event that happened early in the universe is now known. She said that any model that tries to understand what is happening with the r-process has to be able to reproduce that.
The r-process is one of the main ways stars and their remnants produce heavier elements with atomic numbers greater than 30. Recent observations show that the r-process occurs in star mergers. There are still some questions that have persisted for a long time, like which elements it produces and what abundances.
The R-Process Alliance is a group of scientists trying to find answers. The authors of this study are members of the Alliance. This is the second paper published by members of the Alliance. HD 222 295 is thought to be one of the stars that formed in an environment enriched by the r-process. The metallicity of the star is higher than most known stars. Multiple supernovae enriched it. HD 222295 was captured by our galaxy at some point in the past, but it didn't form as part of the Milky Way.
The authors write that HD 222925 exhibits no remarkable characteristics in its chemical abundance pattern, other than the overall enhancement of r-process elements.
A bright star containing elements from the r-process can be used as a proxy for what will happen in the future. The models of the r-process inside these events must have the same signature as HD 222295. It is the gold standard.
There is a certain mystique to gold. It is unique among the elements and has appeared in myths. In ancient Greece, the Gods dressed in gold and golden apples killed those who ate them if they could get past the dragon that guarded them. The source of power in Hindu mythology is gold. It is also the soul of the world.
Those beliefs have been lost to time. The science that replaces them is even more fascinating. The myths of the ancients were never imagined to be replaced by science and stars could explode and create gold and other elements. They couldn't have imagined giant telescopes that peer into space. They couldn't have imagined that we could cut up a star's light and determine if it held gold.
They couldn't have known that our own Sun has 2.5 trillion tons of gold.