History Of The Milky Way

By: Eshani Sharma

Deep in the universe sits the extraordinary spiral of over 100 billion stars, surrounded by 5,500 confirmed planets that rotate inside 4,000 solar systems, all spread across a width of 100,000 light years. The cosmic wonder known as the Milky Way has long perplexed astronomers, physicists, and researchers alike, as decades have been spent trying to determine a proper image of the dense disk of gas and stars. Yet, through meticulous techniques and remarkable technologies, scientists have been able to conjure explanations and theories as to the formation and structure of our home galaxy.

The name of the Milky Way lends itself to a creative story where the Greek goddess Hera poured milk all across the galaxy, creating streaks of white and gray in the cosmos (“The Milky Way Galaxy | AMNH”). The actual history, however, is less imaginative, beginning 14 billion years ago, when the Milky Way was created as a shapeless cloud of gas and dust (Finkbeiner). During the first couple of billion years, it is assumed that small clouds and galaxies began crashing into the Milky Way before it started to rotate coherently into a circular disk. Then, around 10 billion years ago, the Enceladus galaxy collided with the Milky Way, causing the formation of more stars and shapes, and for the next two billion years, the stars began to settle on the thin disk outside the galaxy. But it wasn’t until just 15 million years ago that massive stars, such as the Sun, started to form in the Milky Way (Pultarova et al.). 

Though the Milky Way has been around for billions of years, deep study of the formation didn’t begin until around 50 years ago by scholars Olin Eggen, Donald Lyndel-Bell, and Alan Sandage (Boyle). Since then, the agreed-upon structure of the Milky Way galaxy consists of a bulge of knotted stars in a peanut shape that churn in the center. Encompassing this is a thin disk of spiral arms, where the majority of stars reside. A thicker disk lays just outside, with flared edges and older stars, ultimately encircled by a spherical halo consisting of dark matter and gas.

 The creation of these theories is largely due to star mapping, an ancient technique transformed with new, invigorating tools that created an illustrative image of the galaxy. Star mapping has its roots in the Mesopotamians, who, over 4,000 years ago, would watch the movement of the sun, moon, and planets against a specific cluster of stars called the Normal stars. With their fingers, they would measure the distance between the Normal stars and the different planets, tracking these motions daily. Then, around 120 BC, the astronomer Hipparchus developed a more precise way of tracking stars. By creating a series of longitude and latitude coordinates in the sky, Hipparchus laid the foundation of modern star mapping. And now, with the advent of additional technologies, such as cameras and spectrographs, scientists have been able to map structures in meticulous detail. One such example of revolutionary technology would be the European space agency known as Gaia. Gaia, which was created in 2013, has recorded the age, 3D location, chemical composition, and signature of over 1.8 billion stars. It has helped form the basis of our knowledge of the Milky Way, disproving old myths of stability and order in the galaxy while also providing evidence for new conjectures. One such idea is that the Milky Way is actually heading toward a state of disequilibrium, departing from solidity and steadiness, soon to enter disarray. 

The wealth of information has allowed astronomers to delve deep into the makeup of our galaxy. Furthermore, with new, advancing telescopes and launch missions, the knowledge of our galaxy is only expected to grow. By continuing to study and enrich our understanding of the Milky Way, we can also appreciate the bewildering forces that keep our earth spinning and our home galaxy intact.