Lingering Chemical Traces Of Stars Most Ancient


The first generation of stars to blast their sparkling fires through the darkness of the primordial Universe were not like the stars we know today. Born directly from the very lightest of all gases–the hydrogen and helium that emerged in the Big Bang birth of the Universe itself, almost 14 billion years ago–many of these very ancient stars were probably extremely massive, dazzlingly luminous, and their existence was likely responsible for changing our Universe from what it once was to what it now is. Ancient first-generation stars are thought to be the probable precursors of the Universe’s structure and chemical enrichment–large stellar systems, or galaxies, are commonly thought to have emerged later. In August 2014, an international team of astronomers announced that they have discovered a low-mass star that shows the peculiar chemical abundance ratios associated with the process of forming new atomic nuclei (stellar nucleosynthesis) in a first generation, massive star. Until now, there has been no observational evidence adding credibility to numerical simulations of very massive, brilliant first generation stars that sparkled their way into existence after the Big Bang.

The team of astronomers who made this fascinating discovery are from the National Astronomical Observatory of Japan (NAOJ), the Konan University and the University of Hyogo in Japan, and the University of Notre Dame and New Mexico State University in the U.S. The astronomers used the 8.2 m Subaru Telescope’s High Dispersion Spectrograph (HDS) to spot this low-mass star, dubbed SDSS J0018-0939.

First-generation stars were born in the ancient Universe–within a few hundred million years after the Big Bang–from cradles composed of pristine clouds of primordial gases that contained only hydrogen, helium, and traces of lithium. First-generation stars–or Population III stars–are frequently thought to have dazzled their way into the previously dark and dismal Cosmos before the galaxies, which formed somewhat later. Nevertheless, little is known about the first stars because they lived for barely a cosmic wink–only a few million years.

Numerical simulations devised on supercomputers have made great progress in helping scientists to understand the mysterious birth process of Population III stars. More recent simulations indicate that a small fraction of these ancient, very massive “monster” stars, weighing-in at over one hundred times that of our Sun, could have been born in the ancient Universe–despite the fact that a great majority of the first stars formed with lighter masses of ten to a hundred times that of our Sun. 바카라사이트

Supernova blasts hurled the elements created in the nuclear-fusing hearts of the first massive stars screaming into space, dispersing these newly forged elements into the gas that later gave birth to the next generation of stars, called Population II stars. Smaller stars, like our own Sun–or even somewhat smaller–“live” for a very long time. They “live” so long, in fact, that many of them that were born in the early Universe are still shining. Our large, barred-spiral Milky Way Galaxy hosts such long-lived, low-mass stellar denizens that contain a low-metal content. In astronomical jargon, metals are all of the atomic elements that are heavier than hydrogen and helium–and all of these metals were formed in the searing-hot, nuclear-fusing cores of stars, or else in their fiery supernova death throes. Therefore, the first stars, the Population III stars, created the first heavy atomic elements from which galaxies and subsequent generations of stars were born.

Using a new technique termed stellar archaeology, Dr. Wako Aoki of the NAOJ in Tokyo and his team have discovered the very first tantalizing hint of the existence of one of the first stars, preserved like an ancient footprint captured in stone, lurking in the chemical composition of its ancient daughter–SDSS J0018-0939. This bewitching stellar fossil whispers hauntingly that it may have been born from an ancient cloud of gas that had been polluted with material formed in the explosive rage of a single, very massive Population III star when it went supernova.

“This is a much awaited discovery. It seems Aoki et al. have finally found an old relic that shows intriguing evidence that there really was such a monstrous star in the distant past,” Dr. Naoki Yoshida said in the August 21, 2014 online Nature.com News. Dr. Yoshida is an astrophysicist at the University of Tokyo who was not involved in the study. That such chemical fossils have never previously been found in the Universe, even though numerous theoretic studies predict their existence, has been a long-standing mystery.

Over the past three decades astronomers have conducted large-scale observational studies to hunt down low-mass, metal-poor stars that were born in the early Universe. Follow-up spectroscopic investigations, which measured their chemical abundances, have spotted stars that recorded the abundance patterns associated with the first stars that had several tens of solar masses and churned out immense quantities of carbon and other light atomic elements. However, no earlier research conducted of low-mass metal-poor stellar denizens of our Milky Way have detected the signature of supernova blasts of very massive stars with more than 100 solar masses–which synthesize large quantities of iron but little carbon.

Stars Pass The Torch From One Generation To The Next

The stellar Populations I, II, and III display increasing metal content with decreasing age. This means that Population I stars, like our own Sun, are the youngest stellar population in the Universe and contain the highest metal content. The first stars to ignite in the Universe–the Population III stars–were barren of metals. The “sandwich” generation of Population II stars are extremely ancient, but not nearly as ancient as the Population III stars, or as youthful as Population I stars–like our sparkling, bouncy Sun. Population II stars carry within them the precious metals manufactured by the first stars.

Because of the hefty masses of the “monster” Population III stars, today’s models of stellar evolution suggest that they would have speedily burned up their supply of pristine hydrogen fuel and blasted themselves to smithereens in extremely violent, raging supernova conflagrations. Those horrendous explosions would have hurled their material literally all over the Universe, blasting newly created metals throughout the once-pristine Cosmos to be swallowed up by subsequent generations of stars–the lovely stars that we see today. The “monster” Population III stars lived fast and died young, and blew themselves up in powerful supernova blasts in the very ancient Universe. Therefore, such Population III stars can only be observed inhabiting the most distant galaxies of the early Universe, and discovering such stars or establishing their non-existence presents quite a challenge. In astronomy, long ago has the same meaning as far away. The more distant a sparkling denizen of the Cosmos is, the more ancient it is.

As astronomer Dr. Volker Bromm of the University of Texas at Austin writes in the August 22, 2014 issue of the journal Science: “One of the key events in cosmic history was the onset of star formation in the hitherto dark and featureless Universe. Once the first stars, also called Population III stars, appeared, they began to transform the simple initial state of the primordial Universe into one of ever-increasing complexity, endowing it with growing bubbles of high-energy radiation and heavy chemical elements. The nature of this transition crucially depends on the mass of the first stars. Massive stars are efficient sources for both ionizing photons and heavy chemical elements, or ‘metals,’ comprising all species heavier than hydrogen and helium made in the Big Bang.”

 


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