What is in a star? HD 222925 is a highly evolved specimen that is nearing the end of its life.
Scientists identified 65 separate elements after analyzing this dim object. Most of the elements found in that object are heavy elements from the bottom of the periodic table, which is rare in stars.
The star's composition could be used to learn more about how heavy elements form, since these elements can only form in extremely energetic events.
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. astronomer Ian Roederer of the University of Michigan said that they detected gold.
The elements were made using the rapid neutron capture process. The physics in understanding how, where and when those elements were made is what we are trying to study.
Most of the elements in the Universe are produced by stars. The two most abundant elements in the universe were hydrogen and helium.
The first stars formed when clumps of hydrogen and helium were pulled together. The stars formed hydrogen into helium, then helium into carbon, and so on, as they run out of lighter elements until iron is produced.
An iron core is the end point because it consumes huge amounts of energy. The star explodes when the core is no longer supported by fusion's outward pressure.
The r-process is needed to create elements heavier than iron. Nuclear reactions occur when atomic nuclei collide with neutrons to make elements heavier than iron.
There aren't very many environments in which that can happen.
HD 222925 is located around 1,460 light-years away, which is a bit odd. It has run out of hydrogen and is now fusing helium in its core. It is a star that is low in heavier elements but enriched in elements that can only be produced by the r-process.
The cloud of hydrogen and helium was formed around 8.2 billion years ago. It has to have been an explosion that sprayed the r-process elements out into space.
What elements? HD 222925 is useful there. The star was rich in r-process elements. The team used analysis to narrow it down. The technique involves splitting the wavelength of light from a star into a spectrum of wavelengths.
The atoms absorb and re-emit light, either enhancing or diming the specific wavelength. Emission and absorption features in the spectrum can be traced back to elements that produced them. Almost two thirds of the elements identified were r-process elements.
They include gold, lead, and uranium. HD 222925 shows no other oddness in its chemical composition, so we can consider it a representation of the yields produced by the r-process source.
The star can be used as a model for understanding the output of the r-process because of the level of detail that we now have.
We now know the detailed element-by-element output of some r-process event that happened early in the universe.
Any model that tries to understand what is happening with the r-process has to be able to reproduce that.
The research is available on arXiv.