Mysterious Source of Fast Radio Bursts – “We Could Not Believe It”

The Fast Radio Bursts (FRBs) are millisecond-long bursts of radiation recorded on radio waves. They are extraordinarily highly effective — for instance, throughout one of many brightest flashes lasting 5 milliseconds, as a lot power is radiated as our Sun generates in a month. The scale of the phenomenon is troublesome to think about.

The first radio bursts have been “discovered” barely 15 years in the past. Until April 2020, all of the FRBs noticed by astronomers got here from cosmological distances of lots of of tens of millions of sunshine years. It was solely two years in the past that additionally they managed to trace flashes originating in our Galaxy. It is vital to notice that because of the gear and related sensitivity restrict, researchers are solely in a position to observe essentially the most luminous objects within the Universe, essentially the most highly effective bursts.

“FRBs are currently one of the hottest topics in contemporary astrophysics. Discovered accidentally in 2007 during a review of archival data, and currently under intensive observation, they are still a great mystery,” explains Dr. Marcin Gawronski from the Institute of Astronomy on the Faculty of Physics, Astronomy and Informatics Nicolaus Copernicus University (Torun, Poland). “The results gathered so far make it possible to divide the FRB phenomena into different classes, but we still have not found out whether they are emanations of one or many separate physical processes.”

Cosmic catch

Researchers usually are not 100 % positive what causes the bursts. Astrophysicists have varied hypotheses that would clarify their formation, together with the existence of extraterrestrial civilizations. However, thus far magnetars have been thought-about to be the supply of FRBs.

Source of mysterious radio alerts: an artist’s impression of a magnetar in a cluster of historic stars (in crimson) near the spiral galaxy Messier 81 (M81). Credit: Daniëlle Futselaar, artsource.nl

“Magnetars are neutron stars with extremely strong magnetic fields, they are formed after supernova explosions,” says Dr. Gawronski. “So far, scientists have agreed that they are responsible for the FRBs. Why? Because in order to produce an FRB, it is necessary to have a huge amount of energy, which can be quickly released and used in various processes. The only sources of this type known to us are either the magnetic fields of a cluster of neutron stars — these magnetars — or the gravitational energy of black holes.”

Although astronomers agree that quick radio flashes are the results of violent processes occurring within the rapid neighborhood of extremely magnetized neutron stars, it’s nonetheless unclear why most of them seem as single alerts, whereas different sources might be noticed on radio waves repeatedly. In some instances, the bursts are moreover characterised by periodic exercise, i.e., they happen at common time intervals. This, nevertheless, solely helps in planning observations.

There are additionally fairly a couple of difficulties that astronomers must cope with in FRB observations. “Studying FRB activity is very difficult because flashes are random phenomena. It seems a bit like fishing — we cast a fishing rod and wait. So, we set up radio telescopes and we have to wait patiently,” says Dr. Gawronski. “Another problem is that radio telescopes “see” fairly a big subject of the sky, e.g., ours in Piwnice covers an space half the dimensions of the Moon’s disk within the radio band, which we normally use for FRB observations. There are many objects over such a big space, so it’s troublesome to pinpoint one specific flash. Another concern is the large quantity of information that we accumulate throughout such observations — we will report as much as four gigabits of information per second, so we’d like very giant storage capacities. So, we’ve to course of, analyze and delete this knowledge on an ongoing foundation to make room for the subsequent.”

Dr. Marcin Gawronski from the Institute of Astronomy on the Faculty of Physics, Astronomy and Informatics Nicolaus Copernicus University (Torun, Poland). Credit: Andrzej Romanski/NCU, Torun, Poland

As you may see, there are numerous puzzles and difficulties linked with quick radio bursts Astrophysicists are engaged on fashions to elucidate this phenomenon, however the latest discovery, by which Dr. Marcin Gawroñski additionally participated, brings one more thriller to be solved.

Cosmic inquisition

Last yr a global group of astronomers, together with Dr. Gawronski, pointed radio telescopes in the direction of the galaxy M81.

“It is a big and near us galaxy, much like the Milky Way — it is located about 12 million light-years away from us, in summer when the weather is good you can see it with a regular set of binoculars, and e.g., with the Hubble telescope you can observe single stars in it,” explains Dr. Gawronski. “Canadians from the CHIME project told us that there was a source of fast radio bursts in the vicinity of this galaxy, and what’s more, some of its properties indicated that this object was related to the M81. We thought it would be a great opportunity to try to find out what specifically generated the FRBs.”

The observations were made by researchers working primarily in the PRECISE consortium.

“This is a team of researchers whose main objective is to locate FRB sources, estimate the distances to them, and study the properties of the environment in which FRBs are placed. In this way, we can try to say something about the evolution of the sources of fast bursts and the very processes in which FRB objects are generated,” says Dr. Gawronski. “In a sense, we act in parallel to EVN (European Very Long Baseline Interferometry Network), as we try to gather European radio telescopes outside the time allocated for standard observations within this consortium, to which, of course, the NCU Institute of Astronomy belongs together with the RT4 radio telescope.”

Dr. Marcin Gawronski from the Institute of Astronomy at the Faculty of Physics, Astronomy and Informatics Nicolaus Copernicus University (Torun, Poland). “In these observations, we used the largest European radio telescopes: a 100-meter dish in Effelsberg, Germany, and a 60-meter dish on Sardinia and RT4 in Piwnice,” says Dr. Gawronski. Credit: Andrzej Romanski/NCU, Torun, Poland

The researchers are very lucky. The first time they pointed their radio telescopes at the vicinity of the M81 galaxy, they found a series of four bursts. It wasn’t long before they caught two more. However, the new findings came as a surprise to the researchers.

“When we saw the first results, we could not believe it, and at first, we even thought that we had made a calculation error. It turned out that we had not. It was like in the Monty Python’s sketch ‘Nobody expects the Spanish Inquisition.’ Because none of us expected such a thing,” says Dr. Gawronski.

A young one among the old?

Firstly, the burst came from a globular cluster. So, the first disappointment came at the beginning — a cluster of this type consists of a huge number of densely packed stars, so it was impossible to pinpoint the specific object that was the source of the FRB, even with the help of the Hubble orbiting telescope. More interestingly, globular clusters are composed of very old stars, formed up to 10 billion years ago — they are the oldest star systems in the galaxies. It is therefore futile to look for “young” magnetars there.

“Many questions came to our minds: where did the magnetar come from there? We assumed that it must have been the source of the bursts. In fact, the magnetar could not have been there. And if it was, it could not have been formed in a classical way, i.e., following an explosion of a massive star,” explains Dr. Gawronski. “Such massive stars live for a very short time and within an estimated time of several tens of millions of years after their formation they end their lives in a very impressive phenomenon, called a supernova explosion. It is known that stars do not form in globular clusters for a long time, so no new magnetars can form there during a supernova phenomenon.”

If we reject the chance that there are star wars going down fairly close to us, by which planets are destroyed — and such a speculation is probably not straight out of science fiction movies, since many scientists consider that FRBs could also be technosignatures — then there are a number of different hypotheses.

“Theoretically, a brand new magnetar might have been born from an previous star, or extra exactly from the explosion of a white dwarf. Such a phenomenon can occur in a binary system, where a white dwarf slowly “eats” its companion and at some point, it exceeds the mass for which its stable structure can exist. Then this unstable dwarf explodes in a thermonuclear explosion, during which a neutron star may also be formed, such as a magnetar,” explains Dr. Gawronski. “However, it is not such a simple explanation: if there was a supernova explosion in a globular cluster (but of a different type than the death of massive stars), it must have happened not so long ago on a cosmic scale. According to current theories, magnetars are active for only a few million years after birth. The effects or remnants of such an explosion should be noticeable to us, but so far nothing has been observed.”

The other possible explanation is the merger of two compact, old stars — white dwarfs and/or neutron stars — and the formation of a young object in the so-called kilonova phenomenon. However, the chance of such an event occurring in our “local” Universe is rather slim.

The astronomers’ discovery is as interesting as it is mysterious. For now, one thing is certain — the bursts are the result of some as yet unrecognized phenomenon. The work of astrophysicists may contribute to its description and investigation. The results have been published in the prestigious journal Nature. The article “A repeating fast radio burst source in a globular cluster,” co-authored by Dr. Marcin Gawroñski, concerning the astronomers’ latest discovery is topic no. 1 in the latest issue of the journal.

What were the FRB observations like?

Researchers use the EVN infrastructure, primarily the huge disk capacities that were dedicated to the PRECISE consortium.

“We check which radio telescopes are available at a given time and apply for time — we organize this ad hoc, about 3-4 weeks in advance,” says Dr. Marcin Gawronski. “We have to connect at least five radio telescopes together, creating a network. In these observations we used the largest European radio telescopes: a 100-meter dish in Effelsberg, Germany, and a 60-meter dish on Sardinia. They are large and therefore have a significant collecting area, so we analyzed the data gathered by them first.”

After completing further series of observations, researchers must then study the recorded signal for the presence of FRBs as soon as possible, and inform the EVN stations that selected data can be deleted as irrelevant.

Recently, the system for observation, data collection and analysis has been improved. Firstly, the English e-MERLIN radio telescope network has granted up to 400 hours of availability of its instruments to the PRECISE. Secondly, and no less importantly, thanks to investments in equipment from the University Centre of Excellence “Astrophysics and Astrochemistry,” the researchers in Piwnice have the possibility to process and study the recorded signal autonomously through their radio telescope.

“You can say that I am giving some servers a hard time, as they are working practically non-stop, processing huge amounts of data,” says Dr. Gawronski. “Apart from the PRECISE project, there is also our internal research team monitoring the known sources of FRB. We conduct observations by means of three radio telescopes: our RT-4 from Piwnice near Torun, the Dutch Westerbork and the Swedish Onsala. Thanks to these additional observations, we study the activity of the known FRB sources at frequencies above 1.4 GHz. The addition of a local computing node should greatly expand the capabilities of our research team.”

References:

“A repeating fast radio burst source in a globular cluster” by F. Kirsten, B. Marcote, K. Nimmo, J. W. T. Hessels, M. Bhardwaj, S. P. Tendulkar, A. Keimpema, J. Yang, M. P. Snelders, P. Scholz, A. B. Pearlman, C. J. Law, W. M. Peters, M. Giroletti, Z. Paragi, C. Bassa, D. M. Hewitt, U. Bach, V. Bezrukovs, M. Burgay, S. T. Buttaccio, J. E. Conway, A. Corongiu, R. Feiler, O. Forssén, M. P. Gawronski, R. Karuppusamy, M. A. Kharinov, M. Lindqvist, G. Maccaferri, A. Melnikov, O. S. Ould-Boukattine, A. Possenti, G. Surcis, N. Wang, J. Yuan, K. Aggarwal, R. Anna-Thomas, G. C. Bower, R. Blaauw, S. Burke-Spolaor, T. Cassanelli, T. E. Clarke, E. Fonseca, B. M. Gaensler, A. Gopinath, V. M. Kaspi, N. Kassim, T. J. W. Lazio, C. Leung, D. Z. Li, H. H. Lin, K. W. Masui, R. Mckinven, D. Michilli, A. G. Mikhailov, C. Ng, A. Orbidans, U. L. Pen, E. Petroff, M. Rahman, S. M. Ransom, K. Shin, K. M. Smith, I. H. Stairs and W. Vlemmings, 23 February 2022, Nature.
DOI: 10.1038/s41586-021-04354-w

“Burst timescales and luminosities as links between young pulsars and fast radio bursts” by K. Nimmo, J. W. T. Hessels, F. Kirsten, A. Keimpema, J. M. Cordes, M. P. Snelders, D. M. Hewitt, R. Karuppusamy, A. M. Archibald, V. Bezrukovs, M. Bhardwaj, R. Blaauw, S. T. Buttaccio, T. Cassanelli, J. E. Conway, A. Corongiu, R. Feiler, E. Fonseca, O. Forssén, M. Gawronski, M. Giroletti, M. A. Kharinov, C. Leung, M. Lindqvist, G. Maccaferri, B. Marcote, K. W. Masui, R. Mckinven, A. Melnikov, D. Michilli, A. G. Mikhailov, C. Ng, A. Orbidans, O. S. Ould-Boukattine, Z. Paragi, A. B. Pearlman, E. Petroff, M. Rahman, P. Scholz, K. Shin, K. M. Smith, I. H. Stairs, G. Surcis, S. P. Tendulkar, W. Vlemmings, N. Wang, J. Yang and J. P. Yuan, 23 February 2022, Nature Astronomy.
DOI: 10.1038/s41550-021-01569-9