This is just the second known example of a rapid radio eruption, or rapid radio burst (FRB), permanently very active. Discovered in 2019 by China’s FAST spherical radio telescope, the world’s largest radio telescope with a single antenna, FRB 190520 raises a number of questions today, asked by astronomers who discovered and studied it in a paper published on Wednesday, June 8, 2022 in the review Nature. Why does the frequent and continuous eruption of radio waves emit when more than 95% of the hundreds of FRBs known to date do not recur? And what is the reason for this difference?
In fact, since the very first detection of FRBs in 2007, the list of questions about these very intense and very short radio wave emissions seems to be growing. With a key question in suspense: what do they correspond to? In fact, if we attribute cosmic explosions to them, we still know nothing about their nature and their origin. However, astronomers agree on one point: FRBs come from galaxies far, far away.
There is also no doubt that an FRB is marked by an extreme phenomenon. It can emit in a few milliseconds what is equivalent to the energy that the Sun emits in 80 years! Two hypothetical sources have now been put forward to explain these eruptions: disasters, such as collisions between very dense and very massive objects (the fusion between two black holes, two neutron stars or a black hole and a neutron star) or objects having periodic radio emission, such as very massive neutron stars with strong magnetic fields.
Upon closer examination using the National Science Foundation’s Karl G. Jansky Very Large Array (VLA) and direct observations with the Subaru Optical Telescope in Hawaii, the researchers were able to determine that FRB 190520 was an object on the edge of a dwarf galaxy located nearly 3 billion light-years from Earth. VLA observations also revealed that this object consistently emitted weaker radio waves between eruptions. For decades, astronomers believed that there were two types of observable radio sources in the universe: increasing supermassive black holes and activity due to star formation. Today we say that “it is no longer possible to be so categorical”relates to Science and the Future Casey Law, astrophysicist at Caltech and co-author of the article. “There is a ‘newcomer to the city’, and we should take that into account when studying the populations of radio sources in the universe.”
A twin of 121102 FRB
The astrophysicist admits to having been “extremely surprised” to note that this new FRB was a perfect “twin” of an earlier discovery, FRB 121102, identified in 2014, but recorded as early as 2012. “So our subject confirmed that this very first example was not a stroke of luck”, says Casey Law. In fact, some believed that FRB 121102, a recurring but non-periodic source of rapid outbreaks (with more than 200 incidents recorded between late 2012 and late 2017), was linked to a radio source by chance that originated from an unrelated object in the same galaxy.
In order, an optical, infrared and radio wave image of FRB 190520. Credits: Caltech / Subaru / MOIRCS / VLA
However, the discovery of FRB 121102 had made great progress as it was possible to obtain the first information on the environment and the distance to a FRB. Yet his combination of repeated outbursts and sustained radio broadcasts between outbursts had made him a copy apart. “Now it’s a question of explaining why FRBs and renewable radio sources sometimes end up together. Is this common when FRBs are young? Or maybe the object producing the eruptions is a massive black hole that consumes a nearby star in ruins? Theorists now have many more details to work with, narrowing the possibilities for explanation. “ asks Casey Law.
Astronomers have speculated that FRB 190520 could be a “newborn”, still surrounded by dense material thrown out of the supernova explosion that left the neutron star. When this material eventually disappears, the scattering of signals from the explosion also decreases. According to this scenario, repeated outbreaks could therefore be characteristic of young FRBs and decrease with age. “The FRB area is changing very fast at the moment and new discoveries are being made every month. However, there are still big questions and this object gives us some challenging clues to these questions.”said Sarah Burke-Spolaor, of WVU.