Confetti turned into dust

Interstellar dust prevented the main scientific sensation of 2014

In March 2014, at a specially organized press conference, a group of scientists presented the results of the analysis of observations of the Bicep2 research astronomical station in Antarctica. The data obtained could be not only the most vivid discovery of the year, but also the main scientific breakthrough of the still young XXI century.

Studying the relict background-the radiation of a very young universe that came to us-scientists found in it (or rather, in its polarization) special signals, the so-called B-mods that could be imprints of gravitational waves that arose at the early stage of development of the Universe. Leaving aside technical details, it is enough to say that this observation could be the first direct experimental confirmation of the theory of inflation, according to which the newly born world, which was not yet 10 in the minus 35th degree of seconds, expanded very quickly.

Why is it important?

One of the creators of the theory of inflation, Alan Gut

Our ideas about the evolution and origin of the Universe developed rapidly throughout the twentieth century and led to a rather harmonious theory, the bulk of which is known as a model of a hot universe (or the theory of a large explosion). This model in some aspects was confirmed by observations - in particular, it just predicted the presence of relict radiation, which was really discovered. However, she caused scientists more and more doubts. Roughly speaking, if the theory of a large explosion is correct, then in order for the modern world to look the way we see it, the conditions of its existence at the earliest stages should be very whimsical, as if artificially selected. The new model, originally proposed by the Moscow astrophysicist Alexei Starobinsky in 1979, was able to resolve most of the accumulated issues, and a little later, in 1980, in a more complete and apparent form, the American Alan Gutu. The new theory, which Gut called the model of the inflationary expansion of the universe, a year later, was developed by another Soviet astronomer, Andrei Linde.

The theory of inflation was not the last piece of the puzzle of the cosmological picture. There are many features and phenomena in the universe that are still waiting for their scientific explanation. But competing theories that would cope with the problems of a model of a hot universe better than an inflationary model (however, quite a lot of different options for this model were invented), also did not arise. The problem is that so far the inflation theory has not had any direct observation evidence (indirect, by measuring the spectrum of fluctuations, appeared recently) - it describes the process that practically did not leave behind traces that we could see today. Almost, but not quite: if the inflationary stage of the expansion of the universe was really, it was accompanied by the emergence of gravitational waves, which were supposed to leave the imprint in relic radiation. And it was precisely the search for this mark that the Bicep2 astronomical station was engaged in Antarctica.

Confetti

In the video published on YouTube on behalf of Stanford University on March 17, 2014, the young physicist Chao-Lin Kuo stands on the threshold of the house. The door opens, behind her - Professor Stanford Andrei Linde and his wife.

- I have a surprise for you. The data showed five sigm. R is 0.2

- What did you say? Repeat again!

The R indicator characterizes the force of the BICEP2 of the B-mod signal discovered by the collaboration, and its value, by the way, immediately aroused suspicions-according to some estimates, R cannot exceed 0.1. And five SIGM speaks of statistical reliability: the probability of observation error is 1 by 3.5 million. Kuo makes Linda understand that B-mods have been discovered, which means that the theory of inflation has received experimental confirmation: this is not the fruit of the imagination of the scientist, but the law of nature predicted by him. It is not surprising that in the next frames a video that received almost 3 million views on YouTube, Linda and Coo open champagne.

Another of the authors of the theory of inflation - Alan Gut told Radio Liberty in early April about his own impressions of the declared result:

- In fact, eight days before the official announcement of the results, on Sunday, March 9, John Kovak (the head of the research group BICEP2. - RS ) wrote to me that we need to talk about something urgently. Of course, I knew that he was working on the search for b-mods, which means that his letter could hint at important news, but was not too excited, because he expected a result at the level of the error of 2.5 sigma (that is, the probability of an error is slightly less than 2 percent.- RS ) , which then may well not be confirmed.

- Did you not expect 5 SIGM?

- No, I did not expect at all. But Kovak said that he wanted to immediately see me, and arrived at MIT (Massachusetts Technological Institute where Gut works. - RS ) for the next day. He gave me a copy of the article project and said about 5 SIGM. This, of course, completely stunned me: the first observations of the B-mods-and immediately with such a result. Amazing, incredible news.

Bicep2 telescope

The head of the Bicep2 scientific group, John Kovak, presented the results of the collaboration at a press conference specially convened on March 17. A rare, although not a unique case in science: the research results were presented to journalists even before the publication in the abstract scientific journal. It is difficult to say what pushed Kovak to this step, most likely, he himself was so stunned by the resulting data that he simply did not have the strength to keep them with him. During the day, I heard the whole world about the grand opening, everything was decisively informed of the detected traces of gravitational waves: from the Moscow Komsomolets to the New York Times . In almost every note (and Radio Freedom was no exception ), the Nobel Prize was mentioned: researchers with BisP2, Gut, Linde, and maybe Starobinsky automatically became the main applicants for it - if not in 2014, then in any case in one of the nearest.

However, with the Nobel Prize, it was necessary to wait a bit: the result announced by Bicep2 did not fully correspond to the expectations of some astrophysicists (in particular, this concerned the value of the mentioned parameter R) and in any case required additional verification. Astrophysicist Sergey Popov , a leading researcher at the State Astronomical Institute named after P.K. Sternberg, then said in an interview with Radio Liberty:

- Now you need to wait for the appropriate results of Planck [ the space telescope, during the period from 2009 to 2013, the relic radiation studied vonis ]. I note that there was a certain race, and the group working with BICEP was in a hurry to have time to present its results before the data of the satellite telescope. It is important that Planck will be able to present the results of observations on a larger scale than the ground bicep. In addition, you need to wait for other ground stations to process their similar observations. All this, judging by the existing pace of work, is a matter of several months.

But Alan Gut to the question of Radio Liberty, whether he believes that the results of Planck will confirm Bicep2 data, answered simply: "The chances are great."

Dust map

With the help of ground and orbital telescopes, we study the galaxies, look for black holes, we monitor the evolution of stars, but the most cited scientific articles on astrophysics are not talking about these amazing objects, but about banal interstellar dust. “Here the mission of the COBE spacecraft has ended, for some of its results they gave the Nobel Prize,” says Popov. “But scientists use it most of all by these data, but a galactic dust made by Cobe, because everyone looks into space through the same dust. The most wiped button in the elevator, even if the Nobel Laureate lives on the elevator. The same was the same with the next orbital mission, WMAP: after its end, the dust card made by this apparatus was again cited again.

Polarization of the Galactic dust of the Milky Way by a magnetic field. Image of the Planck telescope

Turning to the map of galactic dust, astrophysicists can, firstly, direct their telescopes to where there are the cleanest windows in the sky, where the signal from distant astronomical objects is the least polluted, and secondly, to subtract the component of dust from the receipt of the resulting awarded dust from the received signal. This is especially important when studying the relict background: "Dust shines at the same frequencies as relict radiation, signals are mixed, and dust in some regular way is very difficult to clean, except that if you looked at the whole sky at many frequencies." Popov compares the study of the relict background with the observation of the starry sky through a frozen window: you see not real stars, but their distorted image that has passed through dirt and frozen patterns. To “clean” the window, that is, to highlight the useful part of the signal, you need to understand well how the pollution works, where and how frosty patterns diverge on the surface of the glass. And for this, you need to have data about the state of the entire window at once, that is, as a more detailed map of galactic dust throughout the sky. Such a card, much more accurate than that of COBE and WMAP, for several years, from 2009 to October 2013, was the Planck space observatory.

Planck against Bicep2

The Planck orbital telescope stopped observation in October 2013, and the ground bicep2 finished work even earlier, in 2012. Since then, scientists have been processing the data obtained - titanic work, which has occupied years even when using supercomputers. John Kovak and colleagues were in a hurry and finished analysis in early 2014, while specialists working with Planck began to publish the first results only in the fall. By the time of the announcement of the results of Bicep2, the dust card according to the Planck was not ready, but this did not prevent Kovak from saying at a press conference: "For observations, we chose the cleanest section of the sky from all possible." By wondering where to send their telescope in the Antarctic sky, the team relied on all available information - on the data of the already held missions and some theoretical models (and they say , to the picture from the slide of one preliminary presentation of Planck data). And everything indicated that if you choose this small window of the southern sky for observations and monitor the signal at a frequency of 150 gigaigers, then the pollution caused by galactic dust would be the smallest possible. Bicep2 is a hundred times more sensitive tool than Planck, but his field of view is very tiny, which means that the most important thing is to direct it correctly.

Astrophysicists estimated where a needle can be hidden in the haystack, and found it exactly in this place. Confirmation of Planck data seemed to many then, in March 2014, with a pure formality: few doubted that the analysis of the information collected by the cosmic telescope would confirm that the selected Bicep2 window has nowhere to go, and the B-mod signal was manifested throughout the sky.

Confetti turns into dust

The result of BICEP2 (finally published in the referred magazine in mid -June) looked so good that it was difficult to believe in it. And there were enough skeptics: some pointed to parameter R, which significantly surpassed previous grades, others said that the collaboration participants could underestimate the amount of dust in their "cleanest section of the sky". If the press has already announced a new result by the sensation of the century and was not very interested in the further development of history, then more and more curiosity gradually matured in the scientific community. This is probably what spurred by Planck researchers to publish part of the analysis of their data on September 21 - about one and a half months earlier than the schedule. And this publication contained not at all the conclusions that were expected in Bicep2.

The image of the Planck collaboration: averaged dust radiation at 150 GHz: from dark red (the strongest) to dark blue (the weakest). The site observed by Bicep2 is allocated on the right image. It can be seen that there are more promising sections a little south (closer to the center)

Planck is a rude tool, and he did not have enough sensitivity to confirm or refute the presence of a B-mod signal in that place and precisely at that frequency of 150 gigaigers, where they recorded BICEP2. But the space telescope did not look at one small window, but at the entire sky, and not at the same frequency, but at four. On one of them - 353 Gigaigers - dust radiation dominates in the signal, that is, everything that the telescope sees is dust. Astrophysicists divided the sky into small areas (comparable in size to the one that Bicep2 observed) and for each of them they calculated how much the dust is here.

The dependence of the radiation of cosmic dust on the frequency is known, so that, by extrapolating this data, you can make a sufficiently detailed map of dust radiation at that very frequency of Bicep2 150 gigaigers on the scale of the whole sky. Kovak and colleagues suggested that in their small window this noise would be negligible. Planck showed that it will be not just large, but comparable in order with the size of the most discovered bicep2 signal. Kovaka and his colleagues were especially disappointing from the fact that, according to Planck, a much cleaner section of the sky was very close to what they chose a little south. However, there is too much dust there: “We showed that even in those regions of the sky where the dust is very weak, there are no“ clean ”windows,” the authors of the article noted.

In other words, the fact that scientists with Bicep2 considered the print of ancient gravitational waves could be just dust. More precisely, the window in this place turned out to be so dirty that, looking through it, it is easy to confuse the star with a neighboring lantern that has prevailed on the frosty pattern. One of the authors of the article with Planck data, Jonathan from the Institute of Astrophysics ORSE (France) emphasized that “from our work it does not follow that they [bicep2] did not receive any cosmological signal. Various data observation and analysis methods used in Planck and Bicep2 do not allow us to claim which part of the signal they received is the height of dust.”

Dot

Planck preliminary results published at the end of September still retained a small chance that Bicep signals had something other than dust radiation. Both collaborations announced that they were going to compare their data in detail and come to a joint conclusion by the end of the year.

Bicep2 telescope at dusk

“The final results were supposed to be published at the end of December,” says Sergey Popov, “but the Planck team transferred this to a later date, while it comes to February. There will be a large block immediately published-more than 30 articles, so, probably, there is no need to wait for any issues of design and scientific good faith. In early December, there was a conference in Ferrar, where all the results were in Italy, where all the results were in Italia, where all the results In general, they were presented from the graphs that were shown that Planck does not see any appropriate signal of primary gravitational waves.

In a naive view, it seems that an astronomical or astrophysical discovery occurs when scientists saw something in the sky in a telescope-instant and obvious luck. In fact, this is not at all like this: the observation data are collected for years and processed even longer, we look into space at best through the muddy window, and even if it seems to us that this time we managed to wipe it well, the results require a meticulous check. In this sense, in the history of the discovery of Bicep2 there is nothing unique - this is part of a leisurely, gradual scientific search, which so far - has not led to anything.

Thanks to the recent capture of Bozon Higgs, the love between the great science and the mass media flared up with a new, long unprecedented force, and this experience turned out to be equally seductive to Bicep2 scientists, who believed that they managed to make the opening of the 21st century, and for the press, remembering how the hunt for Bozone returned the interest in science of millions of people. This time, love turned out to be barren, cosmic dust prevented the sensation, several reputations were injured, and the allegedly discovered imprint of primitive gravitational waves from the "main scientific discovery of the year" was simply "a study that was most talked about."

Journalists had to break their heads that put in their scientific results of the year, but in science there was no catastrophe: the theory of inflation, as before, remains the most promising model to describe the infancy of the universe, and the method used by Bicep2 will be used to search for B-mods and further: “This is a spent and inexpensive technology, probably in a few years, based on the compiled and compiled. Planck a dust card, some next device will again declare a signal, ”Sergey Popov hopes. And then Andrei Linde will again have a reason to open a bottle of champagne - only this time you will not have to regret it.