A Trip Through The Universe (Episode 12)

by Carson
Milky Way. Space background with starry sky

Milky Way is a galaxy with a supermassive black hole in its centre. It is also surrounded by a lot of galaxies…

Our Home Galaxy — The Milky Way

The Milky Way is the galaxy the Solar System in. It is a barred spiral galaxy, 200,000 light years across. We are in the inner edge of the Orion arm, which is about 27,000 light years from the centre. Also, our galaxy has 4 spiral arms instead of 2, and its centre isn’t circular so it is barred.

The Milky Way seen in the night sky appears as a band of light. Those stars are very dim and they are invisible but they are bright altogether. That’s because the Milky Way has hundreds of billions, if not a trillion stars. Other than stars, there are also free-floating planets, asteroids and comets.

The Centre of the Galaxy

In the centre of the galaxy, there is a supermassive black hole called Sagittarius A*. It has a whopping 4,300,000 solar masses. Its diameter is also mind-boggling, it’s 18 Suns across, comparable to a blue supergiant star.

Although it seems huge, it is very small compared to the centre of other galaxies. The Andromeda Galaxy, has a supermassive black hole, having about 200 million times the mass of Sun.

Due to gravity, the centre of the galaxy is much denser than the outskirts. There are a lot of globulars and molecular clouds discovered near there. Also, their velocity is so fast because they are in tight orbits. Sometimes they could escape the galaxy entirely after a flyby of the supermassive black hole.

Like early explorers mapping the continents of our globe, astronomers are busy charting the spiral structure of our galaxy, the Milky Way. Using infrared images from NASA’s Spitzer Space Telescope, scientists have discovered that the Milky Way’s elegant spiral structure is dominated by just two arms wrapping off the ends of a central bar of stars. Previously, our galaxy was thought to possess four major arms. This annotated artist’s concept illustrates the new view of the Milky Way, along with other findings presented at the 212th American Astronomical Society meeting in St. Louis, Mo. The galaxy’s two major arms (Scutum-Centaurus and Perseus) can be seen attached to the ends of a thick central bar, while the two now-demoted minor arms (Norma and Sagittarius) are less distinct and located between the major arms. The major arms consist of the highest densities of both young and old stars; the minor arms are primarily filled with gas and pockets of star-forming activity. The artist’s concept also includes a new spiral arm, called the “Far-3 kiloparsec arm,” discovered via a radio-telescope survey of gas in the Milky Way. This arm is shorter than the two major arms and lies along the bar of the galaxy. Our sun lies near a small, partial arm called the Orion Arm, or Orion Spur, located between the Sagittarius and Perseus arms.

Our Galactic Neighbourhood

The Andromeda Galaxy is the closest galaxy to us, right? No! About 50 galaxies are orbiting the Milky Way!

The largest satellite galaxy of the Milky Way is the Large Magellanic Cloud. Tarantula Nebula, a huge nebula there has a lot of hot, luminous and massive stars. R136a1 there is the most luminous and the most massive star known! It is a barred spiral galaxy, just like the Milky Way.

Dwarf galaxies don’t only be spiral, there are also dwarf elliptical galaxies and dwarf irregular galaxies.

Our galaxy is located in the Local Group with galaxies mainly orbiting the Milky Way and the Andromeda Galaxy. The Local Group is about 10 million light years across. There is also the Triangulum Galaxy, which might be a companion of the Andromeda Galaxy.

The Andromeda Galaxy

The Andromeda Galaxy is also a barred spiral galaxy, the same size as the Milky Way. It has about a trillion stars, if not hundreds of billions, just like ours. It has the same mass as the Milky Way, or maybe lower.

The Andromeda Galaxy (Image Source: wikipedia.org)

The Andromeda Galaxy is moving towards us and therefore, they will eventually collide. This will happen 4 billion years later. At that time, we won’t be on Earth because it’ll be fried by Sun’s increased luminosity. When they collide, they will become irregular due to the tidal forces produced by each other. Neither of them will survive and they would form an elliptical galaxy.

A Galactic Collision (Image Source: wikipedia.org)

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