Science

Hundreds of rapid radio bursts detected in deep space

Because they are unpredictable and only last a few milliseconds, rapid radio bursts (or FRBs for fast radio burst) are particularly difficult to observe and study. The physical process at the origin of these bursts is still unknown to this day. Nevertheless, thanks to the CHIME telescope, located at the Federal Radio Astrophysical Observatory in Canada, scientists will no doubt be able to better understand this phenomenon. And for good reason: the machine detected 535 new FRBs between 2018 and 2019.

The discovery of rapid radio bursts is relatively recent: the first burst was only detected in 2007, in the Small Magellanic Cloud. Other FRBs have since been detected – notably thanks to the radio telescope of the Arecibo observatory, now dismantled following its collapse – and recent work suggests that these phenomena could have their origin in magnetars.

The CHIME telescope (Canadian Hydrogen Intensity Mapping Experiment) was designed to map the density of hydrogen in the Universe, in order to study its expansion. The instrument has a large instantaneous field of view and covers a wide range of frequencies (from 400 to 800 MHz), which also makes it an excellent detector of rapid radio bursts: more than 500 signals have been detected in this way. during its first year of operation.

Nearly 800 FRB every day in the sky

CHIME consists of four antennas, four cylindrical reflectors of around one hundred meters (similar to half-pipes used in snowboarding). Most radio astronomical observations are made by rotating a large dish towards various parts of the sky; to detect an FRB, it means looking in the right place at the right time. CHIME, on the contrary, remains pointed at a single area of ​​deep space: it captures all of the incoming signals using a correlator, generating nearly 7 terabits of data per second. ” Digital signal processing is what allows CHIME to reconstruct and “look” in thousands of directions simultaneously. Says Kiyoshi Masui, assistant professor of physics at MIT.

The 535 new signals detected by CHIME considerably extend the list of known FRBs (around 140 since 2007). ” With all of these sources, we can really start to get a sense of what FRBs look like as a whole, what astrophysics might be behind these events, and how they can be used to study the world. universe in the future “Says Kaitlyn Shin, member of CHIME, a graduate student in the physics department at MIT.

By analyzing these new signals, the scientists also noticed that they were clearly divided into two distinct classes: the repeated FRBs, and the occasional FRBs. In particular, they identified 61 repeated bursts, emitted by 18 sources. In addition, these repetitive signals are distinguished from others by their duration and radio frequencies: they last slightly longer and emit more focused frequencies than point FRBs. Therefore, specialists believe that these two types of rapid bursts could come from separate mechanisms and sources.

But whatever their type, they are evenly distributed in the sky, which suggests that the phenomenon is ultimately very common. The CHIME collaboration even determined that these events were happening at a rate of about 800 per day across the sky. While FRBs are difficult to observe, they are therefore far from rare.

A record of the structure of the universe

Not only does the FRB catalog compiled by the researchers now contain many more items, but it also includes more information on the locations and properties of each of these rapid bursts. Scientists now hope to determine which natural phenomena emit these signals; the fact that the bursts are bright enough to be detected by CHIME suggests that they are from extremely energetic sources.

The most likely hypothesis is that of magnetars – neutron stars with extremely strong magnetic fields, emitting electromagnetic waves of very high energy. ” They are the only thing that we know of that could possibly produce such energetic flashes in such a short time. ”Said Kiyoshi Masui. The study of repeated FRBs will undoubtedly allow them to elucidate this mystery: when a burst is repeated, it is indeed easier to go back to its point of origin.

These bursts could also make it possible to map the distribution of gas in the universe: when these radio waves pass through space, they are indeed likely to encounter gas or plasma, which results in distortions, changes in their properties and / or their trajectory. By examining an FRB, it is thus possible to estimate the distance traveled by these radio waves and the amount of gas they have crossed on their way. In other words, an FRB constitutes ” a record of the structure of the universe it has passed through from the source to us », Summarizes Masui.

Therefore, by discovering enough rapid radio bursts, it may be possible to map the large-scale structure of the universe. For Masui, the FRBs thus constitute “the ultimate tool for studying the universe”.

Sources: MIT and Nature

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