Voyage of the Stars

As early as the Earth era, humans have mastered several methods of observing black holes, which are also the main methods of observing black holes, which are "invisible" stars.

Because they cannot be seen directly like stars, black holes can only be observed indirectly. One of them is the star observation method. By observing the abnormal movement of stars in a certain star field for many years, it is found that there is a black hole in this area that binds these stars.

This method does not work here, because there are no stars around this black hole.

Another way is to determine the existence of a black hole by observing the accretion disk of the black hole. According to the principle of conservation of angular momentum, as matter gradually approaches and is sucked into the black hole, a rotating accretion disk will form outside the black hole's event horizon. Humans can indirectly discover the existence of black holes through the temperature radiation and high-intensity X-rays generated by the collision of gases in the center of the accretion disk.

Unfortunately, this method does not work here either, because the matter around this black hole has long been swallowed up by it. It has no accretion disk and is a silent black hole.

The third method is actually related to stars. It is a combination of the first two methods. It is to determine the existence of black holes based on the celestial system formed by black holes and visible stars. In this case, there will generally be an accretion disk, but unfortunately it is not applicable to this black hole now.

The fourth method is the well-known gravitational waves, which are used to determine the existence of black holes through gravitational waves generated by the merger of two black holes. Obviously, this black hole has completed the merger long ago, and now it has become a quiet black hole again, so this method does not work.

Speaking of which, the reason why the civilization exploration team of the Star Alliance members sent by humans was able to discover this black hole was not because of these four observation methods, but because they discovered the gravitational lens effect at the location of this black hole.

In astrophysics, everyone is familiar with the gravitational lens effect. Simply put, a strong gravitational field distorts the path of passing light, so that observers on the other side of the strong gravitational field see a false light source.

It is worth mentioning that if the observer keeps observing at a fixed position, he cannot find out whether the position of the light source he sees is real or false. However, humans are sailing, and it is not difficult to find changes by careful observation and comparison, so the black hole is discovered.

However, at a close distance now, humans cannot use these indirect methods to observe black holes, because there is another way to directly observe black holes in theory, that is, Hawking radiation.

Also called black hole radiation.

Hawking radiation does not obey the area law, but the larger the black hole, the smaller the Hawking radiation, and the smaller the black hole, the larger the Hawking radiation, so that a micro black hole created by a particle collider in a laboratory will disappear instantly as soon as it appears. This is also the reason why scientists are not worried about the danger of black holes created in the laboratory.

The essence of Hawking radiation is related to quantum field theory, which is related to virtual particle pairs spontaneously generated in the void due to vacuum quantum fluctuations.

Human scientific theories describe such a possibility. When virtual particle pairs are generated by quantum fluctuations near the event horizon of a black hole, negative energy particles will be sucked into the black hole, while positive energy particles will escape from the black hole. From the outside of the black hole, these escaped positive energy particles are Hawking radiation emitted by the black hole.

In this process, the black hole absorbs negative energy particles, which reduces its internal energy and causes black hole evaporation. Hawking believes that since the ordinary space-time of a black hole does not allow negative energy particles to exist stably, the phenomenon of positive energy particles entering a black hole and negative energy particles escaping is impossible, so Hawking radiation can only radiate positive energy particles.

Humans predicted the existence of Hawking radiation in the Earth era, and of course verified the existence of this phenomenon from other physical facts, but never directly observed black holes from astronomy through Hawking radiation.

The reason is simple. The Hawking radiation of a black hole is too low. Looking up at the stars from the solar system and observing black holes tens of thousands or even millions of light years away, it is impossible to directly observe the Hawking radiation of a black hole. Let's put it this way. For a black hole with the mass of the sun, its Hawking radiation is only about 0.0000001~600 millionths of a Kelvin. The mass of this black hole is 130 times the mass of the sun, so the Hawking radiation is even smaller.

It is far below the temperature of the cosmic background radiation.

So it is definitely impossible to detect Hawking radiation from a distance. Even with the current technology of human beings, it can only be discovered by launching detectors closer.

Now human scientists do this. After the research ship stops until it is safe, they launch detectors one by one to the black hole. In order to facilitate the real-time transmission of observation information, they also dispatch several spacecraft for relay communication.

As the detector gets closer and closer, the black hole's imperceptible Hawking radiation is finally captured by the detector, and humans finally "see" the black hole directly for the first time. From the moment when the black hole is truly observed from this angle, every piece of data transmitted to the human research ship is precious.

Human detectors keep approaching and reach the Roche limit radius of the black hole. Macroscopic celestial bodies exceeding this radius will be directly torn apart by the black hole and then turned into matter. These materials will continue to collide before falling to the event horizon, thus emitting a large amount of radiation outward. This is what people usually know as the black hole accretion disk.

Black holes are different from ordinary celestial bodies because extreme celestial bodies such as black holes have a place called the innermost stable circular orbit inside the Roche limit orbit.

The innermost stable circular orbit refers to the closest distance that an object can get to a black hole. No matter what object is ahead, it will fall into the black hole at a speed close to the speed of light. This is the plunge zone of the black hole. This radius position is calculated according to the general theory of relativity and is an area three times the radius of the black hole.

Human detectors cannot reach the boundary of the plunge zone to observe this black hole, because if it exceeds the Roche limit, the detector will be decomposed. Of course, this Roche limit radius cannot only look at the mass of the black hole, but also depends on the level of human detector creation.

It is difficult for human detectors to reach the innermost stable circular orbit, let alone the Schwarzschild radius, because no matter how powerful the material of human detectors is, once it exceeds three times the Schwarzschild radius, the detectors that are not torn apart by the tidal force of the black hole will fall into the black hole and fall to the event horizon and never return.

Well. The so-called black hole radius is not the real black hole singularity radius, but its Schwarzschild radius, which is where the event horizon is.

After calculating the Roche limit radius, the human detector entered a stable orbit, and while circling to stabilize its orbit, it then observed the black hole.

However, scientists want to do more than just observe. They also want to throw something into the black hole to observe the process of accretion disk formation. They plan to use thrusters to push a rocky planet here and let it fall into the black hole for observation.

However, this experiment will inevitably take a lot of time. Obviously, humans don’t have so much time to spend here, so these scientists who are interested in exploration can only settle for the second best, launch several detectors into the black hole, do the falling experiment, and throw some space junk or the minerals carried by the planetary spacecraft into it, and then observe.

If you don’t want to waste time to transport asteroids to nearby star systems, you can only do this.

They also want to test whether the detectors made of alloy No. 2 can reach the innermost stable circular orbit area of ​​the black hole, so as to observe the black hole at a closer distance and accumulate more data for the quantitative change of science.