The “Little Lion” Galaxy Sheds Light On The Universe’s Birth

Mysterious, vast, and blasted with the distant flames of countless stars, our night sky has long been a source of wonder for those who seek to understand its well-kept secrets. How did the Universe come to be, emerging and then evolving from the featureless, incredible expanse of primeval blackness that it was soon after its birth in the Big Bang almost 14 billion years ago? In physical cosmology, Big Bang nucleosynthesis–also alternatively termed primordial nucleosynthesis–refers to the manufacture of all of the atomic nuclei formed in the Big Bang fireball itself, long before the first stars had been born. Essentially, all of the atomic elements heavier than hydrogen, helium, and traces of beryllium were born much later in the searing-hot, roiling furnaces of the stars (stellar nucleosynthesis), and the quantities of these heavier elements reveal strange secrets about the nature of the Cosmos soon after its birth. In May 2016, astronomers announced that a faint blue galaxy, nicknamed the “little lion”, that is located approximately 30 million light-years from our planet and situated in the constellation Leo Minor, could shed some light on the mystery surrounding the birth of the Universe.

The team of astronomers announced that the little lion galaxy–or Leoncino–contains the scantiest quantity of heavy atomic elements ever observed in a gravitationally bound system of stars. In the terminology that astronomers use, all atomic elements heavier than hydrogen and helium are called metals. Therefore, the term metal carries a different meaning for astronomers than it does for chemists.

The new research study appears in the May 12, 2016 issue of The Astrophysical Journal. The lead author on the paper is Alec S. Hirschauer, a graduate student in astronomy at Indiana University in Bloomington.

“Finding the most metal-poor galaxy ever is exciting since it could help contribute to a quantitative test of the Big Bang. There are relatively few ways to explore the condition at the birth of the Universe, but low-metal galaxies are the most promising,” Dr. John J. Salzer noted in a May 12, 2016 Indiana University Press Release. Dr. Salzer is a professor of astronomy at Indiana University.

This discovery is important because the current favored model of the Universe’s mysterious birth billions of years ago makes certain clear predictions concerning the quantity of helium and hydrogen present during the Big Bang–and the ratio of these atoms in metal-poor galaxies provides a direct test of the model. This is because the elemental composition of metal-poor galaxies–like the little lion–is very close to that of the primordial Universe soon after its birth.

In order to detect these low-metal galaxies, however, astronomers must search far, far from home. Our own barred-spiral Milky Way Galaxy is a poor source of information because it harbors a high level of heavier atomic elements, formed by the process of stellar nucleosynthesis, in which stars churn out heavier atomic elements. Stellar nucleosynthesis involves the nuclear fusion of the atoms of lighter elements into the atoms of heavier elements. Ultimately, the stars hurl these freshly forged atoms back out into the Galaxy when they perish in the fatal, fiery tantrum of supernovae blasts.

“Low metal abundance is essentially a sign that very little stellar activity has taken place compared to most galaxies,” Hirschauer explained in the May 12, 2016 Indiana University Press Release.

All of the atomic elements heavier than helium, listed in the familiar Periodic Table, were manufactured in the nuclear-fusing furnaces of main-sequence stars–or else in the supernova explosions that marked the death of the most massive stars in our Universe. This means that the very first generation of stars in the Cosmos were pristine objects that contained only the atomic elements formed in the Big Bang. This is because there had been no earlier generations of stars to produce the heavy metals.

The Three Stellar Generations

The first generation of stars to light up the Cosmos were not like the familiar stars we see today. The earliest stars were formed directly from the lightest of all gases–hydrogen and helium–that were born in the Big Bang. Generally thought to have been dazzling, fiery giants, the very first stars changed our Universe from what it once was, to what it now is. These very ancient first stars are termed Population III.

Later stellar generations are roughly classified into two stellar populations: Population I (metal-rich) or Population II (metal-poor). However, even the most metal-poor Population II stars contain a relatively small quantity of metals. This indicates that Population II stars are composed of more than merely the pristine gas formed in the Big Bang. An earlier generation of stars must have existed in order for these heavier atomic elements to have formed–the Population III stars.

The gas from which the primordial Population III stars formed had not been “polluted” by the metals manufactured in the nuclear-fusing furnaces of earlier generations of stars. The most ancient stars to populate the Universe, Population III stars, were born in pristine cradles composed only of the gases produced in the Big Bang. Numerical supercomputer simulations suggest that Population III stars lived very brief stellar “lives”–they lived fast and died young. In fact, the first stellar generation went raging into that good night when they perished in the noisy, brilliant, and fierce fireworks of supernovae conflagrations. These very dramatic and violent stellar grand finales hurled the heavier atomic elements, formed in the nuclear-fusing ovens of the first stars, screaming like banshees into space. In this way, the newly formed metals were incorporated into the numerous frigid, dark, and eerily beautiful giant molecular clouds that ultimately became the nurseries of the next generation of stars–the Population II stars. Small stars, like our Sun, can continue to shine throughout the Cosmos for a very long time before they must at last meet their inevitable deadly doom. Very ancient small stars, that were born when our Universe was still quite young, may still be hanging around today, illuminating space with their sparkling stellar fires. Our Milky Way Galaxy contains a population of these very elderly, low-mass, long-lived tiny stars, that contain only trace amounts of metals.

The stellar Populations I, II, and III show increasing metal content with decreasing age. Population I stars, like our Sun, have the greatest metal content. In contrast, pristine Population III stars were born completely devoid of metals. The intermediate Population II stars, the stellar sandwich generation, contain the small quantities of metals formed by the earlier Population III stars.

The first stars were extremely massive, and for this reason it is generally thought that they would have quickly burned up their necessary supply of “unpolluted” hydrogen gas–and then blasted themselves into oblivion in extraordinarily powerful, ferocious supernova blasts. These fierce stellar explosions would have sent the erstwhile massive stars’ material flying all over their host galaxies. In this way, the fresh new batch of metals were formed, and then scattered, throughout what had once been a barren expanse. These newly formed metals found their way into future populations of sparkling stars.

The ancient existence of the very massive first generation of stars was largely responsible for causing a sea-change in our Universe. These gigantic sparklers altered the dynamics of the Universe by heating things up and, as a result, ionizing the ambient gases.

Low metallicty Population II stars are the most ancient stars to be directly observed by astronomers. However, even so-called metal-rich Population I stars contain only relatively small quantities of any atomic element heavier than hydrogen and helium. All stars are mostly composed of hydrogen.

The Little Lion Galaxy Sheds Light On The Universe’s Birth

The Little Lion galaxy is considered to be a denizen of the “local Universe”, a region of space within approximately 1 billion light years of our Solar System. The “local Universe” is estimated to harbor several million galaxies, of which only a small percentage have been cataloged. A galaxy that was earlier recognized to contain the lowest metal abundance was detected in 2005; however, the Little Lion has an estimated 29 percent lower metal abundance.

The abundance of elements within a galaxy is calculated based upon spectroscopic observations. Spectroscopic observations capture waves of light that are being emitted by the galactic structure. These observations enable astronomers to observe the light being emitted by galaxies, and this light looks like the rainbow of colors that are formed when a prism disperses rays of sunlight.

Star-birthing areas of space send forth light that contains specific types of brights lines. Each of the bright lines identify the atoms from differing gases: hydrogen, helium, oxygen, nitrogen, and so forth. In the light of the star-birthing region of the Little Lion galaxy, astronomers spotted lines from these elements, after which they used the laws of atomic physics to determine the abundance of the specific atomic elements.

“A picture is worth a thousand words, but a spectrum is worth a thousand pictures. It’s astonishing the amount of information we can gather about places millions of light years away,” Dr. Salzer noted in the May 12, 2016 Indiana University Press Release.

The new observations were conducted by spectrographs sported by two telescopes in Arizona: the Mayall 4-meter telescope at Kitt Peak National Observatory and the Multiple Mirror Telescope poised at the summit of Mount Hopkins outside of Tucson. The little blue galaxy was first discovered by Cornell University’s Arecibo Legacy Fast ALFA–or ALFALFA–radio telescope survey project. Cornell University is in Ithaca, New York.

The Little Lion goes by the official name of AGC 198691. The astronomers who took part in the metal abundance analysis playfully dubbed it Leoncino to honor both its location in the Leo Constellation and the Italian radio astronomer, Dr. Riccardo Giovanelli, who headed the team that first spotted the little galaxy.

The Little Lion galaxy is also unique in other ways–in addition to its display of low levels of metals. Leoncino is a “dwarf galaxy,” only approximately 1,000 light years in diameter, and it is populated by several million stars. By comparison, our own large spiral Milky Way Galaxy hosts an estimated 200 to 400 billion stellar inhabitants. Also, the Little Lion’s blue hue is the result of the presence of newborn searing-hot baby stars. Nonetheless, the blue galaxy is very faint. Indeed, the Little Lion shows the lowest luminosity level ever observed in a system of its class.

Dr. Salzer continued to comment to the press that “We’re eager to continue to explore this mysterious galaxy. Low-metal-abundance galaxies are extremely rare, so we want to learn everything we can.”

Dr. Salzer is in the process of pursuing observing time on other telescopes, including the Hubble Space Telescope, in order to search deeper into the mysterious, hidden depths of the fascinating faint blue Leoncino.

https://youtu.be/7KzPDdo4pRs