Our spiral Milky Way Galaxy is a hazy band of light when seen in Earth’s clear, dark night-time sky. This glowing band of nebulous light, stretching from horizon to horizon, is formed from a host of fiery stars that cannot be seen individually with the unaided human eye. Our 4.56 billion-year-old Sun is one of billions of other brilliant stars that perform their fantastic, joyful dance within this large Galaxy that is our home. Our Star is situated in our Milky Way’s far suburbs, in one of its whirling spiral arms. But, the ancient history of the star-birth, that occurred deep within our Galaxy’s heart, has remained a long-standing mystery. In December 2019, astronomers at the Max Planck Institute-Gesellschaft in Germany, released their findings proposing that there were two intense bursts of activity that led to the birth of stars in the center of our Milky Way.
The new observations indicate that star-birth peaked in our Galaxy’s heart around eight billion years ago. However, the observations also suggest that there was a second round of stellar birth that occurred about one billion years ago. Many astronomers had previously proposed that the stars inhabiting our Milky Way’s relatively small central disk had been born continuously. This scenario will inspire new theoretical work explaining the origin and properties of the bar-shaped feature within our Galaxy’s disk.
According to the new observations, more than 90% of the disk stars formed during the first round of star-birth at least eight billion years ago. However, the second round of stellar-birth, that was responsible for the formation of approximately 5% of the disk stars, occurred much later–within a relatively brief span of time only about one billion years ago. Between the two episodes of intense stellar birth, there was a long period of celestial peace and quiet, when hardly any bright new baby stars were born.
The stars observed in this study populate a dense, disk-shaped region of our Galaxy, termed the nuclear disk. This disk encircles the Milky Way’s innermost cluster of stars and its central, resident supermassive black hole, dubbed Sagittarius A* (pronounced Sagittarius-a-star). Our Galaxy’s central black hole is a relative light-weight– at least as far as supermassive black holes go–and weighs in at mere millions of times solar-mass, as opposed to the billions of times solar-mass sported by many others of its bizarre kind.
With their observations of two intense episodes of star-birth, the astronomers have suggested a revision of part of our Galaxy’s mysterious ancient history. Many astronomers have assumed that the stars populating the heart of our Milky Way were born gradually over the past millions of years. However, the new findings suggest that there may be a different timeline. If so, this could have consequences for a number of other astronomical phenomena.
The new scenario is also particularly interesting because it sheds new light on the growth of Sagitarrius A*. Gas floating into the mysterious heart of our Galaxy results both in star-birth and an increase of our resident supermassive black hole’s hefty mass. This newly proposed revision of our Milky Way’s star-formation history suggests that Sagittarius A* probably attained most of its present mass before eight billion years ago.
A Brief History Of Our Galaxy
Our starlit, barred-spiral Milky Way is just one of billions of other galaxies inhabiting the observable Universe. Before 1920, astronomers thought that our Galaxy was unique–and that it was the entire Universe. 바카라사이트
Our Milky Way has an impressive diameter that is between 150,000 and 200,000 light-years, and it is estimated to be the home of 100-200 billion stars–as well as more than 100 billion planets. Our Solar System is situated at a radius of approximately 27,000 light-years from the Galactic center, on the inner edge of the Orion Arm, which is one of the spiral-shaped concentrations of gas and dust that make our Milky Way look like a twirling gigantic starlit pin-wheel in the vastness of Spacetime. The fiery, brilliant stars situated within the innermost 10,000 light-years form a bulge and one or more bars that radiate from the bulge.
Brilliant stars and clouds of gas, located at a wide range of distances from our Galaxy’s heart, all circle at approximately 220 kilometers per second. This constant speed of rotation contradicts the laws of Keplerian dynamics and indicates that about 90% of the mass of our Galaxy is invisible to our telescopes–and that it neither emits nor absorbs electromagnetic radiation. This invisible, ghostly material has been called the dark matter, and it is thought to be composed of exotic non-atomic particles. The mysterious dark matter plays the important role of the gravitational “glue” that holds galaxies together, and its existence explains why objects at varying distances all rotate at a constant speed around the Galactic center, thus defying Keplerian dynamics.
Our Milky Way, as a whole, is soaring through Spacetime at a velocity of approximately 600 kilometers per second with respect to extragalactic frames of reference. The most ancient stars inhabiting our Galaxy are almost as old as the 13.8 billion-year-old Universe itself, and therefore likely formed shortly after the cosmological dark ages following the Big Bang. The cosmological dark ages refer to a very ancient era before the birth of the first generation of stars.
When we use the term “Milky Way”, we are referring only to the band of glowing light that we see stretching from horizon to horizon in our sky at night. The dark areas within this nebulous and gently luminous band, such as the Great Rift and the Coalsack, are actually regions where interstellar dust is blocking the light emanating from distant stars. The part of the night sky that our Galaxy obscures is referred to as the Zone of Avoidance.
Our Milky Way has a low surface brightness, and its visibility can be signficantly reduced by background light flowing out from light pollution or moonlight. Our Galaxy is difficult to see from brightly lit cities, but it shows itself off very well when observed from rural areas when Earth’s Moon is below the horizon. Indeed, one third of the human population cannot see the Milky Way from their homes because of this background light.