Romance from deep space! Details of "Laser" and ultra-high energy photons revealed

In 1054 AD, an astronomer in the Northern Song Dynasty witnessed the most stunning sight in the universe: a supernova explosion. Nearly a thousand years later, on May 17, 2021, the National High Altitude Cosmic Ray Observatory (LHAASO), a major national scientific and technological infrastructure, recorded a gamma photon of 1.4 PeV, the highest energy photon ever observed by humans.

For the first time, humans have discovered gamma photons with energies exceeding quadrillion electron volts in the Cygnus region (Photo courtesy of the Institute of High Energy Physics, Chinese Academy of Sciences)

Cosmic rays are high-energy particle streams from outer space, and their origin is a cutting-edge scientific issue. Previous observations have not found any celestial bodies in the Milky Way that can accelerate cosmic rays to more than 1PeV.

He also shared many details about ultra-high-energy photons and "Lasso" with Cao Zhen, chief scientist of "Lasso" and researcher at the Institute of High Energy Physics of the Chinese Academy of Sciences.

Aerial photo of "Laso" in August 2021 (Photo provided by the Institute of High Energy Physics, Chinese Academy of Sciences)

Are ultra-high-energy photons and the "photons" in the high-tech beauty technology "photorejuvenation" the same type?

Cao Zhen: These two types of photons are essentially the same, but the photons used to irradiate the skin are actually very low in energy, while what we discovered are ultra-high-energy photons.

For example, visible light is photons with relatively low energy. Using such photons to illuminate the skin may not cause any harm. However, if the energy is a little higher, visible light will become ultraviolet light, which will cause damage to the skin. Therefore, if high-energy photons are used to illuminate the skin, it will not cause skin rejuvenation but damage.

In addition, if the ultra-high-energy photon we discovered hits your skin, you will not have any reaction at all, but if many high-energy photons keep hitting your skin, you will not be able to bear it.

Where do these ultra-high-energy photons come from?

Cao Zhen: The article we published in Nature magazine actually reported the sources we saw in 12 directions. We judged that they are basically evenly distributed within the Milky Way. That is to say, there is an equal probability that some ultra-high-energy photon sources may appear almost everywhere in the Milky Way. So we believe that ultra-high-energy photons are everywhere in the Milky Way.

But among these photons, the one with the highest energy comes from the direction of Cygnus.

How do scientists know that the highest energy photons come from the constellation Cygnus?

Cao Zhen: "Lasso" receives signals from the sky every moment. Some of the signals are photons and some are cosmic ray particles. We will record the cosmic ray events and then find a way to select out the ultra-high-energy photons.

The biggest difference between these photons and cosmic rays is that the photons come from a certain direction and will not be deflected by the magnetic field during their flight.

After we pick out these photons, we can match their directions to the celestial coordinate system, and then we will know that the photon comes from Cygnus.

Nebula in the Cygnus constellation in North America.

Image source: Tuchong Creative

"The Three-Body Problem" mentioned that photons are one of the aliens' relatively low-end weapons. So, is it possible that the ultra-high-energy photons seen by scientists are weapons fired by aliens at the earth?

Cao Zhen: First of all, it is very difficult to artificially generate a high-energy photon.

We found that among the photons of various energies we have now recorded, the number of photons with higher energy is smaller.

How much less? For every 10-fold increase in energy, the number of photons decreases by 1,000 times. This means that it takes much more effort to produce a high-energy particle than a low-energy particle. In addition, our Earth has a very good protective layer - the atmosphere. The atmosphere is thick enough at low altitudes to absorb all these particles.

Therefore, if we were to produce such high-energy particles to attack us, it would actually be more trouble than it would take.

Using this kind of photon as a weapon to attack the earth is a very stupid idea, and they (aliens) will never do that.

Does this ultra-high energy photon contain any unusual information? Why do scientists look for this type of photon?

Cao Zhen: Our biggest confusion now is how it came about.

Because we have built many large accelerators on Earth, for example, the European Organization for Nuclear Research has built a 27-kilometer-long pipeline to accelerate particles. The highest energy they can accelerate to is only about one 100,000th of the energy of the ultra-high-energy photons we see.

Humans have built such a large accelerator, but they cannot add more energy to the particles. So how can this ultra-high-energy photon flying from outer space be accelerated to such a high energy?

Of course, we now prefer to think of it as a natural phenomenon rather than an alien weapon, so we have built various models to understand how nature's ultra-high-energy accelerators work.

Why did “Laso” have to run to an altitude of 4,410 meters to chase the light?

Cao Zhen: The atmosphere is a very important protective layer for humans. It can protect us from attacks by high-energy particles.

On the other hand, this is very unfavorable for our observation, so we have to place the detector at a very high place.

Image source: Tuchong Creative

Is it possible for "Lazo" to be open to the public?

Cao Zhen: Of course. This place will gradually become a popular science base open to the public, and we welcome everyone to visit.

We are also planning a viewing platform from which we can get a full view of the “Lazo”.

If the public is really interested in "Laso", they can also contact us and go deeper inside. There is a popular science introduction next to our detector.

How big is the "Lasso" team?

Cao Zhen: During the construction period, we had more than a dozen cooperative units and about 100 people, and young graduate students were a very important main force.

By making and installing the detector, they can understand how the detector works. In future data analysis, they can also understand which aspects of the detector will have what impact on the data analysis.

We have also established a scientific cooperation group of 275 people. They come from six countries, mostly Chinese scientists. This team is also a fairly young team. Of course, these young people are the ones who are doing the most effective work and producing the fastest results.

During the construction period, young people made great contributions. We would stay on the mountain for seven or eight months at most. I have a young colleague who often encountered troubles when he was in love. Once he went up the mountain, his girlfriend would "break up" with him. But when the mission came, he would still go.

What is Lasso doing now? What advice do you have for young people?

Cao Zhen: Now that the "cable" has been built, young people do not have to work on the mountain for a long time. They only need to go up the mountain occasionally to maintain the detector.

Now, our more important task is to do data analysis and concentrate on producing scientific results.

For young people, as long as they dare to think and can calm down to do it, "Laso" will definitely provide them with opportunities.

Further reading: The past and present of "Laso"

"Laso" is a major national scientific and technological infrastructure, located at an altitude of 4,410 meters on Haizi Mountain, Daocheng County, Ganzi Prefecture, Sichuan Province.

It is a major national scientific and technological infrastructure project launched during the "12th Five-Year Plan" period. It is also a magic weapon for capturing cosmic ray particles, which are "extraterrestrial visitors". It will also help to solve the "century-old mystery of scientific research in the new century."

Cosmic ray particles are high-energy particles from outer space. Protected by the atmosphere, most of the energy of high-energy particles will be absorbed when passing through the atmosphere, which is why humans cannot feel the arrival of cosmic ray particles.

Although they cannot be felt, they are very important. Cosmic ray particles are the only material samples from outer space. They carry the mysteries of celestial evolution and the early universe. They are considered by the academic community to be messengers of "big cosmic events" and probes for discovering "cosmic accelerators."

It has been more than 100 years since humans first started studying cosmic ray high-energy particles, and 5 Nobel Prize winners have been born during this period, but humans have never been able to explain the origin and acceleration mechanism of cosmic ray high-energy particles. The US National Science and Technology Council even listed it as one of the "11 century puzzles of new century scientific research."

In 2008, Chinese scientists started preliminary research on the construction of the "LaCe". Through extensive site selection and field surveys in China's high-altitude areas, Haizi Mountain in Daocheng County, with an average altitude of 4,410 meters, became the site of the observatory.

Comprehensive sources: Xinhuanet, China Science Daily, Science and Technology Daily, etc.