A black hole is an extremely powerful object in the universe, and theoretically the entity of a black hole is just a singularity of infinite density and infinite small size, but because the region within the event horizon of a black hole is completely invisible, we may never be able to verify this inference.
Why is it completely invisible within the event horizon of a black hole? To get rid of the shackles of a gravitational field, it is necessary to have a certain initial velocity, for example, to get rid of the earth's gravitational pull and enter low Earth orbit, it is necessary to reach the first cosmic speed, that is, 7.9 kilometers per second. To completely get rid of Earth's gravitational pull and travel to other planets, it is necessary to reach a second cosmic speed, which is 11.2 kilometers per second. If you want to get rid of the gravitational constraints of the entire solar system and go to the deep space of the universe, you must reach the third cosmic speed, which is 16.7 kilometers per second.
The gravitational intensity of a black hole is far from comparable to that of the Earth and the Sun, so within a certain range, even if it reaches the speed of light, it cannot escape, so the area within this range becomes a completely invisible world, and the boundary of this invisible world is called the "event horizon".
Within the event horizon, light cannot escape, but this does not mean that it is safe outside the event horizon, in fact, the gravitational force of a black hole can affect a very wide range, but this is not unusual, even if it is the sun, gravity can also act 2 light years away. Affected by the strong gravitational pull of a black hole, a wide range of celestial bodies will orbit it, thus forming a more powerful gravitational core, which can dominate the operation of a galaxy.
Like all galaxies in the universe, there is a stellar black hole at the center of the Milky Way, with a mass of about 4 million times the mass of the Sun.
The black hole, named "Sagittarius a*," drives the dense movement of the surrounding celestial bodies and forms a gravitational core, the silver core, under the action of the silver core, the Milky Way with a radius of hundreds of thousands of light years rotates. The celestial bodies around the black hole orbit the black hole due to its gravitational pull, but if a celestial body is too close to the black hole, it will undoubtedly be torn apart and swallowed up by the black hole's gravitational pull. Are there exceptions? Yes, in 2011, astronomers discovered such an object. The spectral type of this object is G, so it is named G2, and when it was discovered, its trajectory was showing a tendency to move closer to the black hole.
At first, astronomers predicted that G2's ultimate fate would be to be torn apart and swallowed by the gravitational pull of the black hole, so they waited with great anticipation, after all, the scene of black holes devouring stars is not often seen, but the results are surprising.
After 3 years of waiting, in 2014, G2 finally came to the closest place to the black hole event horizon, due to the strong gravitational pull of the black hole, its shape began to change, it was stretched longer and longer, but it was not torn in the end, but escaped from the side of the black hole, and as the distance became farther and farther away from the black hole, its elongated body gradually returned to its original form. Astronomers didn't wait for the spectacle of black holes devouring stars, but they waited for the stars to escape from black holes, which is even more rare. So how can G2 escape from the black hole's powerful gravitational pull?
In fact, it is a bit far-fetched to say that G2 is a star, strictly speaking, it should be a cloud of dust, and through observation, we can only determine that its surface is a large amount of gas and dust.
But this dust cloud is not the same as the ordinary dust cloud, its own temperature is very high, where does the temperature come from? From this, it can be inferred that there are stars in the middle of the dust cloud. So why is there so much gas and dust attached to the outer periphery of a star? Because this is not a separate star, but the product of the collision of two stars, due to the collision, a large amount of gas and dust is released, so that such a special dust cloud will be formed. Of course, this is only speculation, and in response to this speculation, scientists at the University of Cologne in Germany have put forward a different view.
Such a dust cloud, the inside is not necessarily a new star created by the collision of two stars, but it may also be three stars moving on each other, and the age of these three stars may only be about 1 million years old.
Since the stars themselves are produced from nebulae, and the three stars are just forming, there is still a lot of gas and dust around them that have not been absorbed. The only problem with the claim, though, is that, as far as is known, there are no conditions for star formation near Sagittarius a*. Whether G2 is the product of a collision of two stars or three new stars, it can't explain why it was able to escape from the edge of the black hole. In fact, human beings have a very limited understanding of the extreme environment around the black hole and the gravitational interaction between celestial bodies, and this puzzle still needs to be slowly solved.