Milky Way’s oldest star

Andromeda Galaxy, Milky Way, Collision

As we gaze up at the night sky, while standing far from the interfering glare of bright city lights, we could see our Milky Way Galaxy extending from horizon to horizon like a sparkling starlit grin –telling us that we are only a tiny part of something vast, historical, and mysterious. Astronomers have long thought that our Galaxy is extremely old. Indeed, scientists have proposed that it could be almost as old as the Universe itself. In November 2018, astronomers using the Gemini Observatory announced that they have discovered a tiny tattle-tale star that is likely the earliest known star dwelling in the disk of our Milky Way. Despite its unimpressive size, this diminutive star could play a significant role in our scientific understanding of the real age and history of our Galaxy. The ancient star also sheds new light on the mysterious conditions which existed in the newborn Universe soon after its arrival in the Big Bang nearly 14 billion years ago.

The Gemini Observatory is composed of twin 8.1-meter diameter optical/infrared telescopes that can together scan the entire sky. Gemini North and Gemini South are located at two separate locations in Hawaii and Chile, respectively.

The tiny tattle-tale star has a very interesting story to tell. It’s old, small, and most significantly composed of elements very similar to those that formed from the Big Bang. So as to host a star like this, the disk of our Milky Way might well be up to three billion years older than previously believed. Our Galaxy’s age has been calculated to be approximately 13.51 billion decades, while our Universe is believed to be roughly 13.8 billion years old.

“Our Sun likely descended from thousands of generations of short-lived massive stars which have lived and died since the Big Bang. However, what is most interesting about this star is that it’d perhaps only one ancestor separating it and the beginnings of everything,” commented Dr. Kevin Schlaufman at a November 5, 2018 Gemini Observatory Press Release. Dr. Schlaufman is of Johns Hopkins University in Maryland, and lead author of this study published in the November 5, 2018 issue of The Astrophysical Journal.

The Big Bang birth of the Universe formed just the lightest of nuclear elements–hydrogen, helium, and smaller amounts of lithium (Big Bang Nucleosynthesis). All atomic elements heavier than helium–termed metals by astronomers–were made by the stars in their nuclear-fusing furnaces (Stellar Nucleosynthesis). Alternatively, in the case of the heaviest atomic components of all–such as gold and uranium–at the powerful and fiery supernovae blasts that heralded the explosive passing of massive stars (Supernova Nucleosynthess).

When celebrities perish, their stellar material is recycled to be utilised in the formation of new baby stars. Newborn stars get –as their legacy from earlier generations of stars–all the elder stars newly forged heavier nuclear elements. The oxygen you breathe, the iron in your blood, the calcium in your bones, the sand beneath your feet, the water that you drink, were all formed in the nuclear-fusing hearts of the Universe’s myriad stars.

Astronomers refer to stars that are depleted of atomic elements heavier than helium as low metallicity stars. “But this one has such low metallicity it is called an ultra metal poor star–this celebrity may be one in ten million,” Dr. Schlaufman continued to describe in the Gemini Observatory Press Release.

The arrival of the first generation of stars is among the most fascinating mysteries haunting cosmologists. The most ancient stars are thought to have ignited as early as 100 million years after the Big Bang. However, the very first stars to form in the Universe were unlike the stars we know today. These primordial gases were primarily hydrogen and helium, and both of these lightest of atomic components are thought to have gravitationally pulled themselves together to form tighter and tighter knots. The cores of the first generation of protostars to emerge from our ancient Universe caught fire within the mysterious dark and frigid hearts of those exceptionally cold dense knots of pristine historical gases–which finally collapsed under their own relentless, heavy gravitational pull. The very first stars didn’t form the same manner or even from the same elements as celebrities do now. The first stars are referred to as Population III stars. Our own Sun is a part of the youngest stellar generation, and is categorized as a Population I star. Sandwiched between the youngest and oldest stellar generations are the Population II stars.

It’s been proposed that the massive primordial Population III stars were brilliant, and their presence is regarded as responsible for causing the Universe to change from what it was to what it now is. These cryptic, dazzling first stars altered the dynamics of the Universe by heating it up and ionizing the present gases.

The metallicity of a star refers to the fraction of its substance that is composed of atomic components –metals–that are heavier than hydrogen and helium. Stars account for nearly all of the nuclear (visible) matter in the Cosmos, being composed primarily of hydrogen and helium. A star, no matter which of the three leading generations it belongs to, will be a gigantic roiling, searing-hot sphere composed mostly of hydrogen gas. The term metallic in astronomical jargon doesn’t mean the same thing that it will in chemistry. Metallic bonds cannot exist in the extremely hot cores of stars, and the very strongest of chemical bonds are only possible from the outer layers of cool”failed stars” called brown dwarfs. Brown dwarfs may be born the same way as true stars, but they never quite manage to attain the necessary mass to light their nuclear-fusing stellar fires.

The metallicity of a celebrity offers an important tool which astronomers use to ascertain a particular star’s true age. When the Universe was born, its”ordinary” atomic matter was mostly hydrogen that, by way of the practice of primordial nucleosynthesis, proceeded to make lots of helium along with much smaller quantities of beryllium and lithium–but nothing thicker. The expression nucleosynthesis itself is described as the process by which heavier atomic components are made from lighter ones, as the result of atomic fusion (the fusion of atomic nuclei.

As a result, the leading Populations I, II, and III, exhibit an increasing metallic content with decreasing age. Population I stars, such as our Sun, have the maximum metal content, while Population III stars are depleted of metals. Population II stars have only trace amounts of metals.

A Big Starlit Smile

Galaxies like our Milky Way, are gravitationally bound systems composed of stars, interstellar gas, dust, leading relics, and dark thing. Dark matter is regarded as composed of exotic non-atomic particles that do not interact with light or another form of electromagnetic radiation, making it invisible. However, most astronomers think that it actually exists in the Universe since it does interact gravitationally with items which can be observed. Dark matter is a much more abundant form of matter than the”ordinary” atomic matter that composes the Universe which we are most familiar with.

Galaxies can range in size from dwarfs that host just a few hundred million stars to galactic behemoths that contain an astounding one hundred trillion stellar inhabitants, each orbiting around its galaxy’s center of mass.

Relatively small, spherical, and closely bound collections of celebrities termed globular clusters are one of the most ancient objects in our Milky Way. The ages of individual stars in our Galaxy could be estimated by measuring the abundance of long-lived radioactive elements such as thorium-232 and uranium-238. Astronomers can then compare the results to estimates of the original abundance, by way of a technique termed nucleocosmochronology.

Several individual stars are discovered in our Galaxy’s halo with ages measured very near the 13.80-billion-year-old Universe. As the most ancient known item inhabiting our Milky Way at the time, this dimension put a lower limit on our Galaxy’s age.

The era of stars dwelling in the Galactic thin disk was also estimated by astronomers using nucleocosmochronology. Measurements of stars inhabiting the thin disk indicate they were born roughly 8.8 billion years ago–give or take about 1.7 billion years. More recent studies of the chemical signatures of thousands of stars indicate that starbirth may have plummeted by an order of magnitude at the time of disc formation, 8 to 10 billion years back, when interstellar gas was much too hot to give birth to new baby celebrities at the same rate as before. Although it seems counterintuitive, things need to get really cold for a fiery new leading baby to be born.

Satellite galaxies surrounding our Milky Way are not dispersed randomly. Indeed, they seem to be the consequence of an ancient break-up of a larger system that produced a ring structure about 500,000 light-years in diameter and 50,000 light-years broad. Close and catastrophic encounters between galaxies tear off enormous tails of gas that, over time, can coalesce to create dwarf galaxies.

In November 2018, astronomers reported the discovery of that small tattle-tale star that is one of the oldest inhabiting the Universe. This tiny star may also be among the very first stars to be born in the Cosmos, and it is categorized as an ultra-metal-poor (UMP) star composed almost entirely of matter formed in the Big Bang. Astronomers refer to such stars that are depleted of heavy metals as low metallicity stars. “However, this one has such low metallicity, its known as an ultra metal poor star–this star may be one in ten million,” Dr. Schlaufman commented at the November 5, 2018 Gemini Observatory Press Release.

Indeed, this star’s location within our Milky Way’s disc –which is usually equally crowded and extremely active–is a surprise.

2MASS J18082002-5104378 B is a part of a binary stellar system. It’s the smaller companion of a low-metallicity celebrity observed in 2014 and 2015 from the European Southern Observatory’s (ESO’s) Very Large Telescope UT2. Prior to the discovery of the tiny tattle-tale star, astronomers had mistakenly assumed that the binary system could host a stellar mass black hole or a neutron star. Stellar mass black holes and neutron stars are the relics that massive stars leave behind after they’ve gone supernova. From April 2016 to July 2017, Dr. Schlaufman and his colleagues used the Gemini Multi Object Spectrograph (GMOS) on the Gemini South telescope in Chile and the Magellan Clay Telescope located at Las Campanas Observatory, so as to study the leading system’s light and measure its relative motions, like this discovering the small UMP by spotting its gravitational pull on its leading partner.

“Gemini was critical to this discovery, as the elastic observing modes enabled weekly check-ins on the machine over six months,” Dr. Schlaufman commented at the November 5, 2018 Gemini Observatory Press Release.

“Understanding the history of our own Galaxy is crucial for humanity to understand the wider history of the entire Universe,” noted Dr. Chris Davis at the same Press Release. NSF provides financing for the Gemini Observatory on behalf of the USA.

2MASS J18082002-5104378 B comprises approximately a mere 14 percent of the mass of our Sun which makes it a red dwarf star. Tiny red dwarf stars are both the smallest and longest-lived of true stars who have gained sufficient mass to light their nuclear-fusing fires. Red dwarfs are also the most numerous stars inhabiting our Galaxy. That is because, while average-sized stars like our Sun”live” for approximately 10 billion years on the hydrogen-burning main-sequence of their Hertzsprung-Russell Diagram of Stellar Evolution–before finally consuming their whole necessary supply of nuclear-fusing fuel–smaller red dwarf stars take”life” easy, and burn brightly for trillions of years.

“Diminutive stars like these are inclined to shine for a lengthy time. This star has aged nicely. It looks exactly the same now as it did when it formed 13.5 billion years ago,” Dr. Schlaufman said in the November 5, 2018 Gemini Observatory Press Release.

The discovery of 2MASS J18082002-5104378 B is important since it provides astronomers with new hope for detecting more of those ancient stars which shed new light on what occurred in the primordial Universe. Only about 30 UMPs have been identified so far. But, as Dr. Schlaufman reasoned,”Observations such as these are paving the way to perhaps one day finding that ever elusive first generation star.”

Judith E. Braffman-Miller is a writer and astronomer whose articles have been published since 1981 in various magazines, journals, and papers. Although she has written on a variety of topics, she particularly loves writing about astronomy as it gives her the chance to communicate with others some of the many wonders of her area. Her first book,”Wisps, Ashes, and Smoke,” will be released soon.

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