The Milky Way is a system of gravitationally bounded stars, white dwarfs, neutrons stars, black holes, interstellar gas, dust and dark matter in our solar system.
From Earth Milky Way appears as a band of light 30 degrees wide arching across the sky because it’s disk-shaped structure.
In 1610, Galileo was the first one who discovered that the band of light has individual stars. Until 1920, astronomers thought that all the stars in the universe are contained in the Milky Way, but after a lot of debates, astronomer Edwin Hubble showed that the Milky Way is just one of the many Galaxies from the 200 billion galaxies in the Universe.
The Milky Way is a galaxy in shape of a spiral with the central bar-shaped that is a diameter between 100.000 to 180.000 light years ( 1 light year is about 6 trillion miles)
The disc is shaped as a warp because of 2 clouds, or dwarf galaxies. These are believed to have pulling dark matter in our galaxy. The warp extends across the entire diameter of the Milky Way.
The dark matter is considered to be 20 times more massive than all visible matters in the galaxy combined and 90% of our galaxy’s mass consists in dark matter. 10% or less of the mass that we can see with the naked eyes or with telescope in the luminous matter.
The motion of the clouds through the dark matter creates a warp that enhance their gravitational influence on the disk. When this dark matter is included, the 2 clouds in their orbit around the Milky Way reproduce the type of warp observed in the Galaxy very closely.
The Milky Way is estimated to contain around 200 to 400 billion stars and at least 100 billion planets. It’s located about 27.000 light years from his rotation center, on the inner edge of the spiral arm of the Milky Way, named the Orion Arm. The stars from the inner side form a tightly packed group. The center of it is considered to be a supermassive black hole named ” Sagittarius A.”
The studies shoe that the mass of Milky Way does not emit or absorb radiant energy. This mass is called dark matter because it can’t be seen with telescopes, but it does account for most of the matter of the universe.
The Oldest star in the Milky Way is considered to be as old as the Universe being formed shortly after the Big Bang.
The Milky Way has several smaller galaxies that orbit in larger galaxies due the gravitational attraction being par of a larger group of galaxies; and it’s considered to be the second largest galaxy in this group with his stellar disk of 100.000 ly in diameter. Most of the mass in the Milky Way is dark matter.
The galactic disc is surrounded by a galaxy of old stars and globular clusters. The extended spherical component of the galaxy that is beyond visible part is called halo. A halo has a few essential elements that can influence it: the stars, the hot gas, and the dark matter.
The Milky Way is at the center of an enormous halo of gas extending for hundreds of thousands of light years.
The mass of this gas is estimated to be similar to the mass of all stars in the Milky Way combined.
This discovery was made by Nasa’s Chandra X-ray Observatory. The Chandra Observatory is a space observatory in outer space launched on a partially reusable low Earth orbital spacecraft, on July 23, 1999
Chandra is sensitive to x-ray sources 100 times more sensible than any other X-ray telescope.
Since the Earth atmosphere absorbs the majority of x-rays, they can’t be detected by Earth based telescopes only by space based telescopes.
The data used from Chandra by a group of 5 astronomers showed that there are eight bright X-ray sources located far beyond the Galaxy, at a distance of hundreeds of millions of light years. The oxygen ions absorb the x-rays from this distant sources in the vicinity of the Galaxy.
The temperature of the absorbed halo is between 1 million and 2,5 million.
This proves that the Milky Way is embedded in a hot gas with temperatures over 100.000 to 1.000.000 degrees Celcius.
The gas cloud contains 2 types of gas: 10 million degrees Celcius gas and 100 million degrees gas.