Shulou(Shulou.com)11/24 Report--

Pigeons and white dielectric pigeons are creatures not only blamed for being "late" in both Eastern and Western cultures, but also for a period of time in the history of astronomy. As a result, the pigeons were expelled by engineers and driven out of their nests. After being expelled, the pigeon concerned tried to return to the scene to argue with the engineers and was killed.

The tragedy occurred in the 1960s, when two radio engineers at Bell Labs, Arnold Penzias and Robert Wilson, were allowed to experiment with a radio telescope about 6m in diameter, and the first step in the experiment was to adjust the antenna.

Arnold and Robert and Holmdel trumpet antenna NASA during debugging, they found that no matter which direction the antenna was pointed at the sky, it would receive a stable noise signal with a strength equal to the energy emitted by an ideal blackbody of 3K. Because the signal came uniformly from the sky in every direction, the possibility that "noise is a man-made signal" was ruled out, and then they turned their attention to the observation equipment itself, suspected that the noise carried by the observation equipment affected the observation results. so they began to check the observation equipment.

They found that two pigeons built nests in the trumpet antenna, and the pigeons produced a large amount of "white dielectric" (pigeon droppings) in the antenna, which once made them think they had found the source of the noise. So they sent the pigeons dozens of kilometers away, cleaned the "white dielectric" in the antenna and re-adjusted the antenna.

But just when they thought they had eliminated the interference and victory was in sight, they already regarded it as a pigeon at home, flew back across dozens of kilometers and got into the antenna. So the two engineers had to shoot the two pigeons.

As we all know later, the interference did not come from pigeons, but from the famous cosmic microwave background radiation. The two men who competed with pigeons won half the Nobel Prize:

Arnold and Robert nobelprize-org are not unique to horn antennas. Even modern radio telescopes, which use paraboloid antennas more often, cannot escape the fate of birds building nests. In particular, the truss structure on the back of the parabolic antenna not only attracts birds to build nests, but also attracts swarms of wasps to build hornet nests. (as shown below)

ASKAP antenna | Image Source Ann Johns Radio Telescope inevitably invades the wilderness while avoiding human interference sources, making a close contact with wild animals.

Tickle and grind your teeth if Hawaiian residents refuse to build a 30-meter telescope on Mount Mauna Kea because they are afraid of affecting the local environment, then the most environmentally friendly, ecologically friendly and harmonious radio telescope should be LOFAR.

LOFAR, whose full name is Low Frequency Array, is the largest radio telescope array at present, and its working frequency is as low as the lowest frequency that can be observed on Earth. Different from the single parabolic radio telescope, LOFAR is a huge array, each antenna has an independent sensor, which will produce a large amount of observation data in the process of observation. There are two kinds of antennas for LOFAR: low-frequency LBA (Low Band Array) and high-frequency HBA (High Band Array) (as shown in the following figure).

LBA | Image source: photo by Zhang Peijin

HBA | Image Source: Zhang Peijin photographed this is why LOFAR uses a linear oscillator as an antenna instead of the paraboloid antenna commonly seen in people's minds. Because the wavelength of the low-frequency electromagnetic wave is longer, it is necessary to use the linear oscillator as the antenna in order to obtain better gain. At the same time, the ultra-long baseline brought by the huge array can also improve the observation resolution of the low-frequency sky.

LOFAR super-terp | Image source astron.nl

The moat of LOFAR super-terp | the area protected by the moat in Zhang Peijin's photo is called "Super-Terp", while Terp is meant to be a man-made hill built of cow dung to protect against sea erosion, which is almost indestructible by this special building material.

LOFAR inherited the name, creating a "Super-Terp" to place antennas for radio observations. Some people even say that the moat next to "Super-Terp" is used to protect the antenna from nearby cattle and sheep.

The moat can defend against geo-carbon-based organisms (such as cattle and sheep), but it is still unable to defend against air raids. "White dielectric" can also be seen at the top of the LOFAR antenna in Super-Terp.

White dielectric Orige on LOFAR-LBA | Source: Zhang Peijin, but we now know that this white dielectric Origin is a transparent body, so it has no effect on low-frequency radio observation, even with Ollie's antenna can get excellent observation results:

The imaging results of solar radio storms obtained by LOFAR instantaneous interference imaging did not affect the observation results. The observation equipment not only did not damage the local ecological environment, but also provided the animals with an excellent living environment. For example, the local sheep often go to the observation station to grind their teeth, scratch and play games with the wire vibrator of the antenna, and the picture is very warm, reflecting the harmonious coexistence of technology and ecology, that is, the engineer in charge of repairing the antenna may be a little uncomfortable.

Even when scientists write notes on relevant experimental activities, they will propose additional protection for the antenna to deal with attacks on the antenna by cattle and sheep in the wild.

The blackbody radiation of carbon-based flying objects, "early in the morning, open the curtains, birds standing on the windowsill singing", may be a very beautiful picture. But "early in the morning, start the telescope and the bird gets hot standing on the antenna" must be something that increases blood pressure and the noise temperature of the receiver.

We know that in order to avoid the influence of man-made electromagnetic interference, radio telescopes are usually built in an open area around them (if there is no such place, then blow it up with explosives). So the birds with nowhere to stay chose to stand in a circle on the edge of the paraboloid antenna. The more naughty may also fly to the feed to defecate, or peck the waterproof film with the beak to test whether the waterproof film is strong, and then leisurely leave after ensuring that the waterproof film is no longer waterproof after pecking.

Can these birds really damage radio telescopes? The answer is yes.

The largest part of a radio telescope with paraboloid antenna is its antenna and feed, the former is used to converge electromagnetic waves, and the latter is used to induce electromagnetic waves. And any object has the property of constantly radiating, absorbing and reflecting electromagnetic waves, and these birds with a body temperature of about 40 ℃ are no exception, they emit blackbody radiation all the time.

In addition to the above-mentioned "birds destroy waterproof membranes with their claws and beaks", their blackbody radiation alone, as well as large amounts, can interfere with highly sensitive radio telescopes. At the same time, once their excrement is covered on the reflector or feed, it will also cause corrosion to the telescope body and affect the performance.

When birds attack telescopes with both energy weapons (fever) and kinetic weapons (pecking waterproof membranes) and biochemical weapons (excreting to feeds), some unbearable astronomers choose to fight and set up bird driving devices. Use modern "scarecrows" to fight birds in a vain attempt to drive away these enemies of radio astronomy. Some astronomers choose to endure in silence, turn on the antenna, make a cup of coffee and wait for the birds to change places and stop interfering with the antenna before starting to work.

At the end of the day, astronomers have always been a group of people who rely on highly developed modern technology. They need high-speed sampling equipment, powerful computers, and super-wide-bandwidth networks. But at the same time they want to escape from the crowd, to "live alone" with their observation equipment, to set up optical telescopes in the most desolate deserts, radio telescopes in the quietest valleys, and high-energy particle detectors on the highest plateau. This is even a bit of a poet's contradiction. On the one hand, if you want to escape from all the people who interfere with the observation, on the other hand, you must be close to the crowd in order to take advantage of the convenience of water, electricity and power grid brought by modern industry.

These wild animals, which are curious about observation equipment, seem to have the same properties. Their lives do not need human existence at all, but in fact, it is impossible to avoid the influence of human beings on their lives. They see humans suddenly come to the place where they live and build huge or dense instruments. The birds soon found that although the huge iron frame was bluffing, it was not very dangerous to step on it. The sheep also found that there were more stakes and wire on the lawn where they lived, which was not only less aggressive, but tickled much better than trees.

Astronomers can only clean up the stains on the antenna, re-tie the broken vibrators, and think angrily that they must eat pigeons / sheep / cattle tonight.

# Thank you #

Thanks to Qian Mengxuan, Zhu Biyun and Li Peiru for their comments on the revision of this article.

references

[1] "they used to compete with pigeons, but they won the Nobel Prize." https://www.thepaper.cn/newsDetail_forward_5041967

[2] Discovery of cosmic microwave background radiation https://en.wikipedia.org/wiki/Discovery_of_cosmic_microwave_background_radiation

[3] Low Frequency Array https://www.astron.nl/telescopes/lofar/

[4] Zhang, PeiJin, et al. "Interferometric imaging with LOFAR remote baselines of the fine structures of a solar type-IIIb radio burst." Astronomy & Astrophysics 639 (2020): A115.

[5] "Radio detection of Cosmic-Ray Air Showers and High-Energy Neutrinos"

This article comes from the official account of Wechat: stone Science Popularization Studio (ID:Dr__Stone), written by Astropond, Zhang Peijin, American editor: Liu Yuling

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