A great merger between two galaxies is a sight to see. If only we could live longer, we would have seen this beautiful marriage between our galaxy, the Milky Way, and our neighbor galaxy, Andromeda Galaxy. The neighboring galaxy is moving towards us, relatively slowly if we consider the distance between. The only problem is that by the time it happens, half of our solar system will be gone. Including Earth.
Where is Andromeda.
If you look at a starlit night sky in a specific direction, you can see the Andromeda galaxy with the naked eye. It stands apart from the normal stars as it looks like a smudge, a bright smudge in the dark sky. We have known the presence of the Andromeda galaxy for centuries. In the mid 17th century, Immanuel Kant hypothesized the galaxy as a vast sea of stars distant to our own. The Andromeda galaxy has always had our attention. That fuzzy blob on the sky is two and a half million light-years away with a trillion of stars. The galaxy is massive too, with a diameter of 220 thousand light-years.
Is it coming towards us?
Edwin Hubble, by calculating the intensity of the stars’ brightness in the Andromeda galaxy, confirmed that this blob of stars is indeed a separate galaxy, far from our own. By Doppler shift measurements, scientists saw an anomaly. While most of the other galaxies were drifting away from us, due to the expansion of the universe, Andromeda was coming towards us. Since the galaxy is the closest to us, the gravitational attraction overcame the expanding universe’s effects. Now it was confirmed that our neighbor was coming towards us, at a speed of 110 km/s. But the question of whether there will be a collision or not was still prevailing. Although the linear velocity was towards us, we had to take into account the transverse velocity, which moves Andromeda sideways.
Is Andromeda going to hit us?
For eight years, from 2002-2010, a team of scientists mapped the location of the stars in the Andromeda galaxy using the Hubble space telescope. After the years-long collection of data and processing it, the team determined that the transverse velocity of the Andromeda galaxy and was 17 Km/s. This was much lower than the linear velocity and hence indicated that the galaxy will definitely hit ours. Just to be even more sure, the team ran computer simulations by making the two galaxies and putting in the values of speed and gravitational pull. The collision happened. The event was confirmed.
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The Milkdromeda galaxy.
So in about 4 billion years, the event of merging will commence, forming the new Milkdromeda galaxy, which will be an elliptical galaxy. The cores of both the galaxies, the black holes will dance around each other, losing their orbital energy slowly and circling to collide. This cosmic dance will result in some of the stars getting thrown in the periphery of the galaxy. Some even will be thrown out and wander the space. Finally the merger will be completed when both the black holes will merge, giving off gravitational waves as a sign of completion. There will be a series of star formation in the sky, making the ‘fireworks’ in celebration. Andromeda and Milky Way will be one.
What happens after the collison> The universe is huge and the distance between stars is much larger than the stars themselves. So in the merger, hardly any star will collide with any other star. Although they will be affected by the gravitational pull of the nearby stars. But the solar system and Earth? That’s a different story.
What about us?
In the midst of all this clash and collision, what would happen to us? The humans and the Earth given that we haven’t already nuked ourselves or destroyed the Earth. The team also ran simulations to see what would happen to our solar system. It made stars that are similar to the sun and tracked their motions. Multiple results were seen, each with a different consequence for the solar system family.
The Solar System will be sucked inside, in the center of the newly formed galaxy. Although it is highly unlikely that any damage will occur in this scenario, there is a possibility that the gravitational pull of the supermassive blackhole will fling us out of the galaxy, making us an orphan wondering star system.
The most likely scenario will be that our system will be thrown at the periphery of the new galaxy, unharmed. The orbit of Neptune is speculated to change, thereby affecting the orbit of other planets too. But the chances of that happening is extremely low.
It doesn’t matter.
If our race would live that long to see that day, it won’t matter what happens to Earth or the Sun. In 2-3 billion years, the sun will swell up and become a red giant. It will engulf the rocky planets so there will be no Earth to care for. We would probably be on some other galaxy or some other planet by that time. Maybe we’ll have robots to record the events so that it can be live-streamed where put civilization has settled. All that can be said surely is everything about us in the future is speculated.