When we observe a galaxy in the universe, if it is approaching us, then it emits light that is bluer than normal (blue shift), and if it is moving away from us, then the light it emits will be redder than normal (redshift), which is called the "Doppler effect", and through observations of this phenomenon, astronomers can infer the state of motion of a galaxy relative to us.
As early as the 20th century, astronomers found through this method that the Andromeda galaxy is approaching our Milky Way, because only the longitudinal velocity can be observed through the "Doppler effect", but not the lateral velocity, so astronomers are hesitant to determine whether the Andromeda Galaxy will "rub shoulders" with the Milky Way or collide with the Milky Way.
It wasn't until 2012 that astronomers determined the lateral velocity of the Andromeda galaxy through massive observations provided by the Hubble Space Telescope and came to the conclusion that the Andromeda galaxy was "rushing" straight toward our Milky Way, expecting a collision with the Milky Way in the future and eventually merging with the Milky Way.
To know that the Andromeda Galaxy is much larger than the Milky Way, with a diameter of about 220,000 light-years and a star population of up to 1 trillion stars, it is surprising that such a huge galaxy will merge with the Milky Way in the future.
A common answer to this question is that about 3.75 billion years later, which is also in line with our understanding, after all, the Andromeda galaxy is as far away as 2.54 million light-years away from us. However, there is a view that the merger of the Milky Way and the Andromeda galaxy has begun.
In fact, this view is based on a research project called "amiga", which is mainly dedicated to observing the absorption map of ionized gas in andromeda, and its results show that the Andromeda galaxy has a huge "halo".
The so-called "halo" refers to a spherical structure scattered around the outer periphery of the galaxy, the vast majority of which is ionized gas, because these materials are very sparse and extremely low radiation, it is difficult to observe directly, so researchers can only use the 43 quasars located "behind" the Andromeda galaxy for indirect observation.
Quasars are the brightest objects in the known universe, and their ultra-high brightness allows them to be observed by us tens of billions of light-years away, and when the light they emit passes through the "halo" of the galaxy, it may be partially absorbed by the material in the "halo".
By observing this change in light from quasars, the researchers were able to estimate how large the galaxy's "halo" really was, and the observations showed that the "halo" of the Andromeda galaxy was much larger than previously expected, and its extension could be as high as 2 million light-years. On the other hand, the Milky Way also has a "halo", according to researchers' estimates, the "halo" diameter of the Milky Way can reach 50 times the diameter of the flat body of the Milky Way.
It can be seen that the so-called "merger of the Milky Way and the Andromeda galaxy has begun", which actually means that the "halo" located on the outer periphery of the Milky Way and and andromeda galaxy has begun to merge, and in fact, the main body of the two galaxies has merged, and it is still about 3.75 billion years later.
To know the fate of the solar system, we need to first understand the merger process of the Milky Way and the Andromeda galaxy, and the following is a simulated scenario (with the Earth as the observation point) depicted by astronomers based on observation data.
The current scene.
2 billion years later, the Andromeda galaxy has become very large in the sky.
3.75 billion years later, the bulk of the Andromeda galaxy arrived in the Milky Way.
After 3.85 billion years, the Milky Way and the Andromeda galaxy began to pass through each other, and in the process, the nebula material in the two galaxies that had been in gravitational equilibrium began to form new stars after being disturbed.
After 3.9 billion years, star formation peaks and a very spectacular starry sky can be seen on Earth.
4 billion years later, the Milky Way and andromeda galaxies completed their first "passage through each other," with both galaxies being "stretched" by massive tidal forces distorted and deformed.
5.1 billion years later, the Milky Way and the Andromeda galaxy have passed through each other many times, the former galaxy structure has disappeared, and two bright giant structures will appear in the sky, which are the core structures of the Milky Way and the Andromeda galaxy (also known as the "nuclear ball").
7 billion years later, the Milky Way and the Andromeda Galaxy merged into a giant elliptical galaxy, and everything returned to calm, and the night sky seen on Earth at this time would be occupied by the bright core structure of the galaxy.
We can see that although the above process is shocking as a whole, it has actually gone through more than 3 billion years, that is, it is a very slow and gradual process, and the solar system will not be violently impacted, of course, this does not mean that the solar system can definitely survive this period.
During the merger of the Milky Way and the Andromeda galaxy, there will be galactic-level gravitational perturbations, and basically all stars will deviate from their original orbits, and the Sun is no exception.
So the biggest risk the solar system may face is a direct collision with other stars (or massive objects), but the density of stars in galaxies is actually very low, in the Milky Way, there is only one star per 260 cubic light years on average, and the density of stars in the Andromeda galaxy is similar, so it can be said that the probability of such an event is almost zero.
If there are still humans in the solar system by then, there are three more likely risks for them: one is that the sun and other stars are close to each other under the influence of each other's gravity, eventually forming a binary (or multi-star) system, so that the solar system may no longer be habitable.
Second, when other stars pass through the solar system at close range, their gravitational pull will affect the orbits of various celestial bodies in the solar system, which may cause frequent celestial impact events in the solar system, which will threaten the survival of human beings.
The third risk is that the solar system may enter the core region of the galaxy along a new orbit, and we all know that the core region of the galaxy is not suitable for life.
Of course, if human beings can really develop for another 3.75 billion years, then the level of human science and technology should be so high that we can't imagine it now, and I believe that they are fully capable of controlling the future fate of the solar system and can calmly deal with the risks that the solar system may face.
Well, today we will talk about this first, welcome to pay attention to us, we will see you next time.
(Some of the pictures in this article are from the Internet, if there is infringement, please contact the author to delete)