One of the notable features of the images of the Milky Way circulating online is that the central part is particularly bright, appearing brighter than the overall brightness of other stars at the edges. This is not artistic processing, in fact, whether it is in the visible light band, or in the infrared, X-ray, gamma ray and other bands, the central area is so bright!
What is there, what can emit such a bright light?
Let's get to know the Milky Way first. It is a spiral galaxy (barred galaxy in a spiral galaxy) that is oblate in shape, thick at the center (about 10,000 light-years thick) and thin at the edges (about 2,000 light-years thick). The raised area of the core, the area with the highest brightness, is called the silver core; the flat area around it is called the silver disk. The Milky Way contains about 100 billion to 400 billion stars, of which 90% of the material is distributed in silver nuclei and disks, and the outermost part is a silver halo.
The Milky Way has four main spiral arms, namely the centaur arm, the Orion arm, the Perseus arm and the swan arm, and the solar system where humans are located is located on the support wall (the main spiral arm) on the inside of the Orion arm.
There are many theories about the diameter of the Milky Way, but the values are in the range of 100,000 to 200,000 light years, and one of the more mainstream views is that the diameter of the Milky Way is about 160,000 light years. Our Sun is located about the middle zone of the Milky Way, 26,000 light-years from the galactic center.
The luminous objects in the universe are usually stars. In general, larger stars look brighter, but neither the most massive star in the universe, R136a1, nor the largest star, Stevenson 2-18, can emit such a dazzling light. If it's a star, obviously there can't be just one star at the center of the Milky Way.
In fact, the centers of all galaxies in the universe are very bright, because the central region has a large density and number of stars, which is the gravitational center of the entire galaxy. Observational data suggest that stars in the central region of the Milky Way are predominantly old red stars over the age of 10 billion.
Because of the density of stars and the high radiation at the center of the Milky Way, it is almost impossible to give birth to life here. If the Earth revolves around a star there, the night sky will be as bright as day.
After a long period of observation, scientists have found that the center of the Milky Way is so bright, not only because of the large number of stars there, but also because there is an extremely dangerous celestial body in the universe - black holes.
A black hole is a dangerous object that can swallow everything, and once anything falls into a black hole, it can never come out again. If you carry out interstellar voyage in the universe and encounter such a celestial body, you must adjust the course in advance to avoid it, and if you are captured by its gravity, it will be less fierce.
Black holes can be divided into miniature black holes, stellar black holes, intermediate mass black holes and supermassive black holes according to mass, and the current commonly found are stellar black holes and supermassive black holes. The black hole at the center of the Milky Way is a supermassive black hole called Sagittarius A, which scientists discovered in 1974.
The mass of the Sun is about 60 trillion tons, which is already ranked moderately among all the stars in the universe, but sagittarius A has a mass equivalent to more than 4 million times the mass of the Sun, which is really a super giant. A large part of the mass of the silver core is occupied by this black hole. It is its presence that attracts and pulls the many stars around it and becomes the center of the Milky Way, and it even plays a role in shaping the Milky Way to some extent.
Sagittarius A, although massive, is small in scale, equivalent to only a very large star. While it doesn't emit its own light like a star, there is a very large accretion disk around this super-black hole. One of the reasons the galactic center looks so bright is because of the accretion disk.
The accretion disk is a disk-like structure formed by the gravitational attraction of a black hole. Due to the gravitational pull of black holes, these substances collide and rub against each other at extremely high speeds, and they emit extremely dazzling light, sometimes even far exceeding the total luminosity of other stars in their galaxies.
How dangerous are black holes? Put it this way, a super black hole like the one above can even swallow a star in an instant.
In fact, almost all galaxies have a supermassive black hole in the center, and perhaps the formation of galaxies is inseparable from this supermassive black hole.
For example, the second largest known black hole is Ton618 in the direction of the northern celestial pole Orion, which is 10.4 billion light-years away from Earth and has a mass of about 66 billion times that of the Sun, which is much larger than Sagittarius A.
As for how such supermassive black holes are formed, scientists have not yet figured out, perhaps they really grew up by constantly devouring surrounding celestial bodies. If you think about it, will the Milky Way be completely swallowed up by black holes in the future?
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