A Dwarf Galaxy Reveals The Universe’s Secrets
By Judith E Braffman-Miller
The shining star-splattered galaxies of the observable Universe switched on long ago, and lit up the primordial Cosmos when it was less than a billion years old. The observable (visible) Universe is really only the relatively small region of the gigantic, unexplored, and unreachable Cosmos that we can see–we cannot see the rest of it because the light that travels towards us from those very remote and secretive regions beyond the horizon of our visibility has not had sufficient time to reach us since the Big Bang birth of the Universe 13.8 billion years ago. It is thought that large galaxies were uncommon inhabitants of the primordial Cosmos, and that they finally reached their majestic sizes as the result of ancient mergers of smaller protogalactic blobs. The most ancient galaxies were only one-tenth the size of our large spiral Milky Way, but they were set on fabulous fire with the brilliant flames of extremely hot, glaring baby stars. These ancient, amorphous galactic structures served as the “seeds” from which today’s mature galaxies emerged. In September 2017, astronomers announced that they had recently discovered a dwarf galaxy in the constellation Lynx that may serve the important function as a proxy that scientists can use to understand the evolving chemistry of the primordial Universe.
The new finding, published in the journal Monthly Notices of the Royal Astronomical Society (London), shows that the amount of oxygen within the dwarf galaxy is the lowest yet observed in any known star-birthing galaxy. This is the reason why the tiny galaxy is similar to the early nascent galaxies. These very ancient galaxies existed so long ago that nothing with eyes to see could bear witness to their mysterious birth in our Cosmic Wonderland.
Astronomers now think that the first galaxies to form in the Universe were chemically simple during their early formative stages. This means that they were composed of hydrogen and helium–the two lightest atomic elements. Hydrogen and helium–along with trace quantities of lithium and beryllium–formed in the Big Bang birth of the Universe, during its first three minutes of existence. All of the atomic elements heavier than helium were manufactured in the searing-hot, nuclear-fusing furnaces of the stars, their stellar fires fusing ever heavier and heavier atomic elements out of lighter ones. However, the heaviest atomic elements of all–such as gold and uranium–were produced in the furious supernova explosions that herald the demise of the most massive stars in the Cosmos.
Therefore, the atomic element oxygen came later, as massive stars were born. The stars formed heavier and more complex atomic elements in their cores by way of the process of nuclear fusion. The stars of the Universe are responsible for creating a Cosmos composed of countless oxygen-rich galaxies like our own large Milky Way.
The Beginning Of Spacetime
In the ancient Universe, clouds composed of opaque, pristine, and primarily hydrogen gas, merged together along massive and gigantic filaments of a mysterious, transparent structure called the Cosmic Web. Scientists think that the Cosmic Web is made up of a substance called dark matter that is composed of as-yet-unidentified exotic, non-atomic particles. According to this theory, the filaments of the Cosmic Web are not made of the so-called “ordinary” atomic matter that forms stars, planets, moons, and people–and all of the elements listed in the familiar Periodic Table.
Recent measurements indicate that the dark matter accounts for approximately 24% of the Universe, while the badly misnamed “ordinary” atomic matter accounts for only 4.6%. Most of the Universe–about 71.4%–is generally thought to be composed of a mysterious substance called the dark energy. Dark energy is thought to be responsible for making the Universe accelerate in its expansion, and it may be a property of Space itself.
There was a dark era that existed before the first stars were born to light up the Cosmos. But, gradually, opaque clouds–that were primarily composed of hydrogen–collected along the heavy, immense filaments of dark matter. The dense regions of the dark matter lured clouds of pristine, primordial gas with their powerful gravity. Dark matter does not dance with “ordinary” matter or electromagnetic radiation except through the pull of its gravity. However, because it does dance with “ordinary” matter gravitationally, and it distorts and bends light (gravitational lensing), scientists are almost certain that the ghostly, invisible substance really exists. Gravitational lensing is a phenomenon proposed by Albert Einstein when he came to the realization that gravity had the ability to warp and bend light–and, for this reason, can produce lens-like effects.
The powerful gravity of the Cosmic Web tugged on its atomic prey until these pools of gas became stellar nurseries for the first generation of stars to light up the ancient Universe, The powerful gravity of the Cosmic Web hoisted in its atomic prey until the captured gas clouds formed blobs as black as ebony within transparent halos composed of the exotic dark matter. The black blobs of pristine gas floated down into the hearts of these invisible halos, and strung themselves out along this mysterious Cosmic spider’s web.
The dark halos pulled in the first generation of sparkling baby stars, and the brilliantly shining newborn stars and hot, glaring gas lit up what was previously a Universe of blackness, devoid of light. Slowly, the writhing sea of pristine gases and the ghostly, invisible dark matter wandered their way throughout the ancient Cosmos, mixing themselves up together as they created the familiar structures that astronomers observe today.
Many astronomers think that the first stars to light up the Universe were not like the stars we see today. This is because they formed directly from primordial gases that were born in the Big Bang birth of the Universe itself almost 14 billion years ago. The pristine gases were mostly hydrogen and helium, and these two lightest of atomic elements are thought to have pulled themselves together, thus creating tighter and tighter knots. The cores of the first generation of protostars in the Universe first lit up within the mysterious dark, frigid hearts of these very dense knots composed mostly of hydrogen, with a smaller amount of helium. The knots went on to collapse under the power of their own relentless gravitational pull. Many scientists think that the first stars were huge (compared to the stars of today). This is because they did not form in the same way, or from the same elements, as stars do now. The first stars are designated as Population III stars, and they were true super stars. Our own Sun is a member of the youngest generation of stars, which are designated Population I stars. Wedged between the first and most recent generations of stars are the appropriately dubbed Population II stars.
The massive Population III stars were also brilliant spheres of gas, and their existence is responsible for triggering the sea-change of our Universe from what it once was to what it now is. These huge and dazzling stars changed the dynamics of our Cosmos by heating everything up and, in this way, ionizing the ancient gases.
The metallicity of a star refers to the percentage of its material that is composed of atomic elements heavier than helium. Because stars–which contain most of the atomic matter in the Universe–are nevertheless primarily composed of hydrogen and helium, astronomers use (for convenience) the general designation of metal to refer to all of the atomic elements that are heavier than hydrogen and helium. Therefore, the term metal, in the jargon of astronomers, is not the same as it is for chemists.
The metallicity of a star provides a precious tool that astronomers can use. This is because its determination can tattle on a star’s true age. The older stars (Populations II and III) display lower metallicities than more youthful stars, like our own Sun (Population I).
The three stellar Populations I, II, and III reveal to astronomers a decreasing metal content with increasing age. Population I stars show the largest metal content. The three stellar populations were designated in this rather confusing way because they were named in the order by which they were discovered–the reverse of the order in which they were born. The first stars to ignite in the Universe (Population III) were entirely depleted of metals. The stars having the highest metal content are the Population I stars. Population II stars are metal-poor, but nevertheless contain small quantities of the metals created in the hot nuclear-fusing hearts of the first stars.
A Dwarf Galaxy Reveals The Universe’s Secrets
The most ancient oxygen-deficient galaxies are so remote and faint that they are almost undetectable. However, relatively nearby star-birthing galaxies, that contain little oxygen (similar to early galaxies), may be easier to spot and also offer the same clues. Alas, these nearby small galaxies that contain little oxygen, which currently are forming a large number of massive blue stars, are extremely rare. But if discovered, they can provide precious insights into how the first galaxies were born, in the ancient Universe, about 13 billion years ago. In this way, astronomers can come to understand the evolution of the early Cosmos.
The star-birthing little galaxiy in the new study was discovered during an ongoing, large-scale inventory of the Universe, the Sloan Digital Sky Survey (SDSS), which revealed it as a potential object of interest. Astronomers then targeted it for additional observations using the Large Binocular Telescope in Arizona. Data derived from that powerful telescope showed that the small star-birthing galaxy, dubbed JO811+4730, is a record-breaking little object inhabiting the galactic zoo. This dwarf galaxy has 9 percent less oxygen–an indication of simplicity–than any other discovered so far.
“We found that a considerable fraction of the stellar mass of the galaxy was formed only a few million years ago, making this one of the best counterparts we’ve found of primordial galaxies. Because of its extremely low oxygen level, this galaxy serves as an accessible proxy for star-forming galaxies that came together within one to two billion years after the Big Bang, the early period of our nearly 14 billion year old Universe,” explained Dr Trinh Thuan in a September 22, 2017 University of Virginia Press Release. Dr. Thuan, an astronomer at the University of Virginia, is one of the study’s authors.
The tiny galaxy also is fascinating because it provides important clues to how the ancient, simple Universe became re-ionized by early intense star-birth–making it experience a sea-change from what is called the Cosmic Dark Ages of neutral gases to the development of the completely structured Universe that we live in today, where the gas in the space between galaxies is ionized.
Dr. Trinh continued to note that the observations indicate that the tiny galaxy is quickly producing bright new baby stars at a quarter of the rate of our own Milky Way Galaxy–yet its mass in stars is about 30,000 times smaller. Eighty percent of its stellar mass has formed in just the past few million years. This marks the dwarf galaxy as an exceptionally youthful structure, manufacturing enormous amounts of ionizing radiation.
Dr. Trinh’s colleagues on the study are astronomers Dr. Yuri Izotov and Dr. Natalia Guseva of the Ukrainian National Academy of Sciences, and graduate student Sandy Liss of the University of Virginia.
Judith E. Braffman-Miller is a writer and astronomer whose articles have been published since 1981 in various magazines, newspapers, and journals. Although she has written on a variety of topics, she particularly loves writing about astronomy because it gives her the opportunity to communicate to others the many wonders of her field. Her first book, “Wisps, Ashes, and Smoke,” will be published soon.
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