Today we’re going to talk about our galactic home: the Milky Way. Although we’ve covered the matter partially by presenting the planets and Solar System which reside within the Milky Way, there’s so much more out there, and we’re going to focus on the most interesting facts.
In terms of size, the Milky Way is around 120,000 light years across, bulging out at its center about 12,000 light years, so it’s not exactly flat. The central bulge is surrounded by 4 large spirals that wrap around it. The Milky Way is a barred spiral, which means that it has a bar in its center and has two major arms. Our galaxy also had two smaller arms, and two smaller spurs. The one spur we should remember is the Orion Arm, which contains our Solar System, and it’s located between the two major arms, Perseus and Sagittarius. Although we’re not able to notice it, the Milky Way is not stationary, seeing as it’s constantly rotating. That means its arms are moving, and our Solar system is moving with them, at a speed of about 828,000 kilometers per hour.
Inside the center of the galaxy is a massive black hole, which is roughly billion times more massive than our Sun. The black hole might not have started off that massive, but because it had a huge supply of dust and gas inside the galaxy, it has grown so much that is now able to consume stars that find themselves in this path. Even though black holes are invisible and cannot be directly observed, scientists are able to determine their existence and location by observing the gravitational effect they have on the material around it. It is suspected that most galaxies have a black hole in their center. We are able to see only a small part of the Milky Way, such as the star, dust and gas, because 90% of the mass of our galaxy is dark matter. As is the case with black holes, we cannot detect this matter directly, but by observing it effect on the objects surrounding it.
We mentioned earlier that the Milky Way is spinning. In addition to that, it is also moving through space. As a consequence of that movement, in about 4 billion years, the Milky Way will crash into its closest neighbor, the Andromeda Galaxy. The two galaxies are moving towards each in each at a speed of 112 kilometers per second. The Andromeda Galaxy is showing the signs of crashing into another galaxy some time in the past, but we shouldn’t worry about the moment when the two crash, as our Sun will become a red giant by then, making the Earth inhabitable.
The Andromeda Galaxy
The red giants are the most commons stars in the Milky Way, cool stars about ten times less massive than the Sun. Although they were once unsuitable candidates for planets that could host life, as they would be have too be to close to meet the requirements. However, the red dwarfs are now considered the prime suspects for such possibility.