This is something I read a while ago that completely blew me away. I wrote about this before. As an amateur astronomer who has been watching the stars since childhood, this fact was a surprise to me.
My sister and I once spotted the Andromeda Galaxy directly above the constellation Andromeda. We were thrilled to see a faint, blurry, tiny patch of light that we thought might represent the entire Andromeda Galaxy, located 2.5 million light-years from our Milky Way. We thought it was the entire Andromeda Galaxy, 2.5 million light-years away from our Milky Way. But we were wrong. We weren't seeing the entire Andromeda Galaxy.
What we were seeing was only the bright central part of the galaxy. It's bright because the stars are most densely packed in the center of the galaxy. It has the cute name "galactic bulge."
If your eyes could collect light like a time-lapse camera, making faint stars appear much brighter than they actually are, the Andromeda Galaxy would look like this in the night sky near the moon. My sister and I were actually only seeing the central part; the rest was too dim to see.
Can you imagine seeing this scene in the night sky? It's just that the stars aren't bright enough to see it.
Another amazing thing is that the Andromeda galaxy and the Milky Way are traveling towards each other at a speed of 250,000 MPH (402,336 KPH). In 4.5 billion years, these two galaxies will collide. Catastrophic? Not quite. The stars in the galaxies are so far apart that there will be very few stars that collide. The galaxies will pass each other, but will be pulled back by gravity, and the two galaxies will form a giant elliptical galaxy.
If two galaxies collide, the solar system will be pushed to three times its current distance from the galaxy's core. Furthermore, there is a 12% chance that the solar system will be ejected from the new galaxy during the collision. Even if such an event occurs, it is unlikely to have a negative impact on the system, and it may be unlikely that the sun or planets themselves will suffer any damage.
However, by then the sun will have entered its red giant phase and will have already swallowed Mercury and Venus. Earth will be just around the corner, the water will have boiled long ago, and by then all life will have vanished from Earth. At that time, Earth will be devoid of all life, and all that will remain in the once magnificent world full of life will be vivid ashes.
Hold on tight to your hat. Located in the Orion Arm of the Milky Way galaxy, 100,000 light-years away, our solar system spirals like a giant frisbee, moving at an average speed of 515,000 miles per hour (828,000 kilometers per hour). Even at this speed, it would take approximately 230 million years for our solar system to complete one orbit around the Milky Way. It's like riding an enormous carousel.
In the photo above, on a dark night far from city lights, we can see a part of our Milky Way galaxy. We are looking at the galactic center, where the stars are most densely packed.
Where you are – the Milky Way galaxy, indicating the location of the solar system.
Now, here's another surprising fact: the Andromeda galaxy and the Milky Way galaxy are actually touching right now. Each galaxy has something called a "galactic halo," which consists of gas, dust, and stray stars. It has been discovered that the galactic halos of our galaxy and the Andromeda galaxy extend much further than previously thought.
In other words, the faint halos of the galaxies appear to be clearly beginning to touch each other. You could say the collision of the two galaxies has already begun.
The Andromeda galaxy and the Milky Way collide.
When these two galaxies collide, it will be a truly beautiful sight from Earth. As the Andromeda Galaxy approaches, the Milky Way galaxy's belt will appear distorted. And eventually, the galactic centers will merge. However, at that time, no one on Earth will be able to witness this spectacle.
It's already happened. Ten billion years ago, another small galaxy collided with the Milky Way. Again, no stars collided; the galaxies passed each other like ghosts. Eventually, the small galaxy was pulled in and joined the Milky Way along with new alien stars and gas. And that's what happened with a dwarf galaxy 4 billion years ago. Andromeda won't be the first galaxy to collide with our galaxy, but it will be the largest. Andromeda is 50% larger than our Milky Way.