This record-breaking “Gold Standard” star is different from anything we’ve seen in the past

This record-breaking “Gold Standard” star is different from anything we’ve seen in the past

What does a star have? Well, if you’re a highly sophisticated end-of-life specimen called HD 222925, that’s probably a lot.

Scientists analyzed this dim object and identified 65 individual elements. These are the most elements ever found in a single object outside the Solar System, and most of them are heavy elements from the bottom of the periodic table, rarely found in stars.

Since these elements can only be formed at extremely active events, such as supernovae or neutron star mergers, through a mechanism called the fast neutron capture process, the composition of this star could be a means of learning more about how they are formed. heavy items.

“As far as I know, this is a record for any object beyond our Solar System. And what makes this star so unique is that it has a very high relative proportion of the elements listed along two thirds below the magazine. “We even found gold,” said Ian Roederer, an astronomer at the University of Michigan.

“These elements were created by the process of rapid neutron capture. This is really what we are trying to study: physics in understanding how, where and when these elements were created.”

Stars are the factories that produce most of the elements in the Universe. In the early Universe, hydrogen and the sun – still the two most abundant elements in the universe – made up almost all matter.

The first stars formed as gravity gathered clusters of this hydrogen and helium. In the fusion furnaces of their nuclei, these stars forged hydrogen in the sun. then sun on coal; and so on, fusing heavier and heavier elements as they end up being lighter until iron is produced.

Iron can fuse, but it consumes huge amounts of energy – more than that produced by such a fusion – so the iron core is the end point. The nucleus, no longer supported by external fusion pressure, collapses under gravity and the star explodes.

To generate elements heavier than iron, the fast neutron capture process or the r process is required. Really energetic explosions trigger a series of nuclear reactions in which atomic nuclei collide with neutrons to synthesize elements heavier than iron.

“You need a lot of neutrons that are free and a set of very high energy conditions to release them and add them to the nuclei of atoms,” Roederer said. “There are not many environments in which this can happen.”

This brings us back to HD 222925, which is about 1,460 light-years away, which is definitely a bit strange. He has passed the stage of the red giant of his life, having run out of hydrogen to fuse, and now fuses sun in his core. It is also what is known as a “metal-poor” star, low in heavier elements… but extremely enriched in elements that can only be produced by the r process.

As a result, the elements of process r were somehow distributed throughout the hydrogen and helium molecular cloud that formed HD 222925, about 8.2 billion years ago. This “somewhat” must have been an explosion that sprayed the elements of the r process into space.

The next question is: what data? And there HD 222925 is useful. We already knew that the star was rich in r-process elements. Roederer and his team used spectral analysis to determine exactly what it contained. This is a technique based on dividing the wavelength of light from a star into a range of wavelengths.

Some elements can either amplify or reduce specific wavelengths of light as atoms absorb and re-emit photons. These emission and absorption characteristics in the spectrum can then be analyzed and identified in the elements that produced them and determine their abundance. Of the 65 items the team identified in this way, 42 – almost two-thirds – were r-process items.

These include gallium, selenium, cadmium, tungsten, platinum, gold, lead and uranium. Since HD 222925 does not show any other strange composition in its chemical composition, this means that we can consider it representative of the yields produced by the source of process r.

Although we do not know if the r processes that produced these elements took place in a neutron star collision or in a violent supernova, the level of detail we have now means that the star can be used as a kind of blueprint for understanding process production. r.

“We now know the exact output item by item of an r-process event that occurred early in the universe,” said MIT physicist Anna Frebel.

“Any model trying to figure out what happens to process r must be able to reproduce it.”

The survey was accepted on The Astrophysical Journal Supplement Seriesand is available on arXiv.

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