Milky Way

Introduction

The Milky Way is the galaxy that contains our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. The term Milky Way is a translation of the Latin via lactea, from the Greek γαλαξίας κύκλος (galaxías kýklos, "milky circle").

A wide-angle view of the Milky Way as seen from a dark sky location.

Structure and Composition

The Milky Way is a barred spiral galaxy with an estimated visible diameter of 100,000–200,000 light-years. It is estimated to contain 100–400 billion stars and more than 100 billion planets. The dark matter halo around the Milky Way may span over a million light years. The Galactic Center is marked by an intense radio source named Sagittarius A*, which is likely to be a supermassive black hole.

Galactic Center

The Galactic Center contains a complex and dynamic environment. In addition to the black hole known as Sagittarius A*, the Galactic Center is home to multiple regions of intense star formation, including large clusters of massive stars. These regions are also rich in interstellar dust and gas, the raw materials for new star formation.

Spiral Arms

The Milky Way consists of a bar-shaped core region surrounded by a warped disk of gas, dust and stars. The disk of the Milky Way is made up of four main spiral arms, which are regions of stars and nebulae where star formation is occurring. These arms are named the Norma Arm, the Scutum-Centaurus Arm, the Sagittarius Arm, and the Perseus Arm.

Halo and Dark Matter

The Milky Way, like all galaxies, is enveloped in a vast halo of dark matter, which is detectable by its gravitational influence on visible matter. This dark matter is thought to make up about 90% of the mass of the Milky Way. The nature of this dark matter is still unknown, and its detection is one of the great challenges facing modern astrophysics.

Galactic Habitable Zone

The concept of the Galactic Habitable Zone (GHZ) is analogous to the circumstellar habitable zone (CHZ), where conditions might be right for life as we know it. The GHZ is defined by a variety of factors, including distance from the Galactic Center, the density of interstellar medium, the frequency of supernovae, and the presence of metal-rich stars like our Sun, which are more likely to host terrestrial planets.