Voyage of the Stars.

Chapter 711: Initial Exploration of Black Hole

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" celestial bodies.

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

This approach doesn't work here because there are no stars orbiting this black hole.

Another way is to confirm the existence of a black hole by observing its accretion disk. According to the principle of conservation of angular momentum, as matter gradually approaches and is sucked into a black hole, a rotating accretion disk will form outside the black hole's event horizon. Humans can indirectly discover the existence of a black hole 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, because the matter around the black hole has long been swallowed up by it. It has no accretion disk and is a quiet black hole.

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

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

Speaking of it, the reason why the Star Alliance member civilization exploration team 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 where the black hole was located.

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 always stays at a fixed position to observe, he will not be able to find out whether the position of the light source he sees is real or false. However, humans are in the process of sailing, and it is not difficult to find the changes by careful observation and comparison, and thus the black hole was discovered.

However, at today's close distances, humans naturally cannot use these indirect methods to observe black holes, because in theory there is another way to directly observe black holes, and that is Hawking radiation.

Also called black hole radiation.

Hawking radiation does not obey the area law. Instead, the larger the black hole, the smaller the Hawking radiation, and the smaller the black hole, the greater the Hawking radiation. As a result, a micro black hole created by a particle collider in a laboratory will disappear instantly as soon as it appears. This is why scientists are not worried that black holes created in the laboratory are dangerous.

The essence of Hawking radiation is related to quantum field theory, and is related to the 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, the negative energy particles will be sucked into the black hole, while the positive energy particles will escape from the black hole. From the outside of the black hole, these escaping positive energy particles are the Hawking radiation emitted by the black hole.

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

Humans predicted the existence of Hawking radiation in the Earth era, and of course have verified the existence of this phenomenon from other physical facts, but have never directly observed a black hole through Hawking radiation from an astronomical perspective.

The reason is very simple. The Hawking radiation of a black hole is too low. If we look up at the stars from the solar system and observe black holes tens of thousands or even millions of light years away, we cannot directly observe the Hawking radiation of a black hole. Let's put it this way. The Hawking radiation of a black hole with the mass of the sun is only about 0.0000001~6 millionths of a Kelvin. The mass of this black hole is times the mass of the sun, so the Hawking radiation is even smaller. It is far lower than the temperature of the cosmic background radiation.

Therefore, it is definitely impossible to detect Hawking radiation from a distance. Even with today's human technology, it can only be discovered by launching detectors closer.

This is what human scientists do now. After they stop the research ship until it is safe, they launch detectors towards the black hole. In order to facilitate the real-time transmission of observation information, they also dispatch several spacecraft for relay communications.

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

Human detectors are getting closer and closer, and reaching the Roche limit radius of a black hole. Macroscopic celestial bodies that exceed this radius will be directly torn apart by the black hole and then turned into matter, which will continue to collide before falling to the event horizon, thus emitting a large amount of radiation. This is what people usually know as a black hole accretion disk.

Black holes are different from ordinary celestial bodies because for extreme celestial bodies such as black holes, there is a place called the innermost stable circular orbit within the Roche limit orbit.

The innermost stable circular orbit is the closest distance an object can get to a black hole. Any object beyond that 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 is calculated according to general relativity and is three times the radius of the black hole.

Human probes cannot reach the boundary of the crash zone to observe the black hole, because if it exceeds the Roche limit, the probe will be disintegrated. Of course, the Roche limit radius cannot only be determined by the mass of the black hole, but also by the level of human probe creation.

It is difficult for human probes to reach the innermost stable circular orbit, let alone the Schwarzschild radius. This is because no matter how strong the material of human probes is, once they exceed three times the Schwarzschild radius, the probes that are not torn apart by the tidal force of the black hole will fall into the black hole and fall onto the event horizon, never to 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 in orbit.

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, let it fall into the black hole and then observe.

However, this kind of experiment will inevitably take up a lot of time, and humans obviously do not have so much time to waste on this. Therefore, these scientists with a strong interest in exploration can only settle for the second best, which is to launch a few probes into the black hole, conduct a fall-in experiment, and throw some space junk or the minerals carried by the planetary spacecraft into it, and then conduct observations.

This is the only way to do it if we don't want to waste time transporting asteroids from nearby star systems.

They also want to test whether the detectors built by humans with Alloy No. 2 can reach the innermost stable circular orbit region of the black hole, so as to observe the black hole at a closer distance and accumulate more data for scientific quantitative changes.

(End of this chapter)