Milky Way Galaxy

 

Introduction:

        Our Sun and all the planets around it are part of a galaxy known as the Milky Way Galaxy. A galaxy is a large group of stars, gas, and dust bound together by gravity. They come in a variety of shapes and sizes. The Milky Way is a large barred spiral galaxy. All the stars we see in the night sky are in our own Milky Way Galaxy. It is very difficult to count the number of stars in the Milky Way from our position inside the galaxy. Our best estimates tell us that the Milky Way is made up of approximately 100 billion stars. Our galaxy is called the Milky Way because it appears as a milky band of light in the sky when you see it in a really dark area. Our Solar System is located at a radius of about 25,000 light-years from the Galactic Center. Just as the Earth goes around the Sun, the Sun goes around the center of the Milky Way. It takes 250 million years for our Sun and the solar system to go all the way around the center of the Milky Way. The term Milky Way is a translation of the Latin via lactea, from the Greek γαλακτικός κύκλος (galaktikos kýklos), meaning "milky circle. The Milky Way is a spiral galaxy with an estimated visible diameter of 100,000–200,000 light-years. Milky Way galaxy is the Second largest galaxy in the group after the Andromeda Galaxy, which may or may not be the most massive galaxy of the group. The Milky Way has several satellite galaxies and Milky Way Galaxy is part of our Local Group of galaxies, which local group of galaxy is part of the Virgo Supercluster & Virgo Supercluster is itself a component of the Laniakea Supercluster. The estimated mass of our milky way galaxy is (1.54±0.1)×10¹² M_☉  (the Milky Way is approximately 890 billion to 1.54 trillion times the mass of the Sun).  In our galactic center there is a supermassive black hole which is known as Sagittarius A*. Sagittarius A * has an estimated mass of 4.100 (± 0.034) million solar masses.

Milky Way Galaxy

Location of Sun & Galactic Center:

        The Sun is 25,000–28,000 ly (7.7–8.6 kpc) from the Galactic Center. This value is estimated using geometric-based methods or by measuring selected astronomical objects that serve as standard candles, with different techniques yielding various values within this approximate range. In the inner few kiloparsecs (around 10,000 light-years radius) is a dense concentration of mostly old stars in a roughly spherical shape called the bulge. The Galactic Center is marked by an intense radio source named Sagittarius A* (pronounced Sagittarius A-star). The motion of the material around the center indicates that Sagittarius A * is a large, compact object. This concentration of mass is best explained as a supermassive black hole(SMBH) with an estimated mass of 4.1–4.5 million times the mass of the Sun. The rate of accretion of the supermassive black hole is consistent with an inactive galactic nucleus, being estimated at around 1×10−5 M☉ per year. Observations indicate that there are supermassive black hole located near the center of most normal galaxies.

Diagram of the Sun's location in the Milky Way

Spiral arms:

Outside the gravitational influence of the Galactic bar, the structure of the interstellar medium and stars in the disk of the Milky Way is organized into four spiral arms. But there has been some debate over the years as to whether the Milky Way has two spiral arms or four. Spiral arms typically contains a higher density of interstellar gas and dust.

Color	Arm(s)
turquoise	Near 3 kpc Arm and Perseus Arm
blue	Norma and Outer arm (Along with extension discovered in 2004
green	Scutum–Centaurus Arm
red	Carina-Sagittarius Arm
orange	Orion–Cygnus Arm (which contains the Sun and Solar System)