Source: qubit
Ming Min from Wafei Temple
Quantum bit report | Official account QbitAI
When it comes to black holes, our first thought must be Light can't escape Properties of.
So a black hole is really just a hole?
The answer is not so simple.
Previously, scientists found that black holes, while devouring everything with strong gravity, also emit a very high energy plasma jet, that is Black hole jet 。
Take M87 galaxy black hole as an example, these jets can extend at least 5000 light-years from the center of the black hole, and the speed is close to the speed of light.
This is a big head. Scientists had a hard time figuring out why a black hole can capture light, and then it ejects itself?
However, this cosmic problem has received good news recently.
The Event Horizon Telescope (EHT) released an image of a black hole under polarized light, which provides strong evidence for the study of black hole jets.
This photo provides a new perspective for studying black holes.
Scientists synthesized images of M87 black hole in polarized light.
Different from the first black hole photo released in 2019, the black hole under polarized light has a circle of cool Spiral striation 。
Scientists introduce that these spiral light streaks are caused by the strong magnetic field around the black hole.
This result has been popular for 44 years Black hole jet principle ——The Blandford – Znajek process provides strong evidence.
Spin up and escape from the black hole
However, why can the principle of black hole jet be verified by seeing a circle of light streaks around the black hole?
To understand the relationship, we need to find out what the black hole jet is.
As early as 1918, the scientist Heber Curtis observed the jet of the black hole of M87 galaxy, which he described as "a very strange direct light" emitted from the center of a fuzzy spot.
But at that time, scientists did not know that the light came from a black hole.
Everyone is puzzled: why does the spot emitting this direct light come from both sides of a galaxy?
△ The jets in the Cygnus A galaxy produce huge interstellar patches Roger Blandford and Roman Znajek speculate that this may be related to black holes.
Later physicists also proved that the black hole is the "anchor" of a galaxy, and these patches are generated by the jet from a large black hole in the center of the galaxy in the opposite direction.
On the basis of mathematician Roy Kerr calculating the black hole spin equation and Roger Penrose proving that the black hole spin can decelerate and convert the generated energy into other things, they formally put forward Brandford – Zenaj process 。
△ Roger Branford (left) and Rome Genaje (right) First, they know that a black hole can attract a large amount of interstellar gas around it, which will form an "accretion disk" when rotating with the black hole.
At the same time, the gas is heated to a very high temperature.
This will lead to the loss of electrons in the gas, becoming a carrier magnetic field Plasma.
Blanford and Zhinajie believe that the spin of the black hole will distort the magnetic field generated by the accretion disk into a spiral shape.
When the magnetic field moves, a strong voltage will be generated. This voltage will attract energy from the black hole along the spiral upward and outward, thus forming Jet 。
Since the 1980s, scientists have tried to simulate this process on computers.
At first, the researchers only magnetized the accretion disk slightly, and obtained SANE model 。
In this model, when the plasma rotates around the black hole, it is like water flowing to the drain unable And the direction is random.
This will cause particles to collide with each other, lose energy and angular kinetic energy and fall into the black hole.
As more and more particles fall into the black hole, a magnetic field is formed around the black hole, and the spin of the black hole will twist the magnetic field into a spiral shape, and then generate jet.
In the late 1990s, researchers such as Ramesh Narayan of Harvard University began to try to improve the magnetic field intensity around the black hole in the model.
They found that when the magnetic field is strong enough, the plasma will become very orderly and can control the accretion disk instead of being controlled by it.
The magnetic field line can form a force field around the black hole as the sleeve of the jet, which can also prevent the plasma from falling into the black hole.
This is it. MAD model 。
For a long time, people believed that the SANE model was more reasonable.
But the current observation results show that the magnetic field near the black hole is very strong and the magnetic field lines are very orderly, which is obviously closer to the MAD model.
move on
In order to further explore the strong magnetic field around the black hole of M87 galaxy, scientists must first crack the "code" of the spiral magnetic field line.
At present, they are trying to deduce the shape of the magnetic field in reverse.
At the same time, some researchers are simulating the larger area around the black hole to study how stars generate central magnetic fields.
In addition, they also raised some questions:
For example, How does the jet glow?
It can produce about 3 trillion megajoules of energy per second. How can such a small particle do that?
This also made Blanford sigh: "It's amazing that nature can construct these things."
Reference link:
[1] https://www.quantamagazine.org/physicists-identify-the-engine-powering-black-hole-energy-beams-20210520/
[2] https://eventhorizontelescope.org/blog/astronomers-image-magnetic-fields-edge-m87s-black-hole
(Statement: This article only represents the author's view, not Sina.com's position.)
