Where is the solar system located in the galaxy?

The sun, the moon, and the stars were once proudly thought to be centered on the earth, but the emergence of the heliocentric theory has poured cold water on mankind, and now we all know that the sun's position in the universe is not special, it is just an ordinary star in the huge galaxy of the Milky Way. Where in the galaxy?

The figure above shows what the Milky Way looks like and where the solar system is located in the Milky Way based on known observations by scientists.

As a whole, the stars of the Milky Way are not uniformly distributed, as evidenced by the fact that the density of stars decreases exponentially with increasing distance from the center of the galaxy.

Observations show that the stellar density can reach 289,000 stars per cubic light year in the core region at a distance of 1 second from the center of the Milky Way (about 3.26 light-years), increasing to a distance of 40 seconds, the stellar density decreases to about 288 stars per cubic light year, and at a distance of 100 seconds, the stellar density is only about 2.9 stars per cubic light year, while the distance between the solar system and the center of the Milky Way is about The distance between the solar system and the center of the Milky Way is about 8000 seconds apart (about 26,000 light-years), and in this region, the stellar density has dropped to about 0.004 stars per cubic light-year.

In other words, the stellar density of the region where the solar system is located is only 1 in 72 million of the highest stellar density region in the Milky Way, which is completely called the remote and desolate part of the galaxy, so is this unfortunate or lucky for humans? It is lucky for human beings because it is difficult for life to survive for a long time in the "busy zone" of the galaxy.

First of all, there is excessive radiation, which is quite understandable, there are more stars and more radiation, and in excessive radiation, it is difficult for life to survive.

Then there is the catastrophic event, you know the stars are not always quietly "burning", in the process of stellar evolution, from time to time there will be some high-energy events, especially those massive stars evolved to the end of the main sequence star stage, usually will occur a surprisingly powerful supernova explosion, and in a short period released enough to rival the energy of the entire galaxy. galaxies.

At the end of the Ordovician period, about 445 million years ago, a biological extinction event occurred on Earth, which scientists speculate was probably caused by a gamma-ray burst that struck the Earth, and whose source was a supernova explosion about 6,000 light-years away.

Such catastrophic events have occurred in remote and inhospitable parts of the galaxy, not to mention the dense region of stars, although supernova explosions do not occur often, if the period is stretched to hundreds of millions of years, the number of occurrences should not be underestimated, in such an environment, life simply can not exist for a long time.

In addition, gravitational perturbation is also a big problem, for the solar system, the nearest star is 4.22 light years away, so the gravitational perturbation of other stars is completely negligible, and we know that the magnitude of gravity and the square of the distance is inversely proportional, so in a dense region of stars, the gravitational perturbation between the stars will affect the stability of the star system.

If the solar system is placed in the "busy zone" of the Milky Way, then the gravitational force of other stars will lightly disturb the orbits of comets, asteroids, and other small bodies in the solar system, making the risk of the Earth being hit by small bodies significantly higher, or directly affect the stable operation of the eight planets, or even trigger a collision between the planets. or throwing the Earth directly out of the solar system.

It is important to note that being too far from the center of the galaxy is also bad for life. The farther away from the center of the galaxy, the lower the density of the star, and this rule also applies to the past galaxy, so that the abundance of heavy elements in the region too far from the center of the galaxy is not sufficient to support the birth of life.

In other words, the region of the galaxy that is suitable for life should be neither too close to the center of the galaxy nor too far from it. According to scientists' estimates, this range should be between 13,000 light years and 35,000 light years from the center of the galaxy (as shown in the figure below).

As you can see, the solar system is located in this range, although this is considered a remote and desolate part of the galaxy, this is the luck of mankind, if not, the solar system will be difficult to breed life, of course, humans will not appear on Earth.

Of course, the above is only based on our carbon-based life, and if there are other forms of life in the universe (such as silicon-based life), then it is a different story.