Fast radio bursts reveal hidden matter around galaxies

We don’t know their origin yet, but they might prove useful. In a study published in the journal natural astronomyResearchers were able to calculate Dimensions halos diffuse who surround galaxies between a quick radio burst and getting in the way. First discovered in 2007, fast radio bursts, often abbreviated FRB Fast radio bursts are very fast signals, from a duration on average of a few milliseconds that take place in the radio wave range. Very energetic, in those few thousandths of a second they release just as manyenergy than the sun in a day! First attributed to instrumental biases or extraterrestrial civilizations, they could come from many energetic astronomical objects: supernovaof pulsarof black holesand even magnetars !

The halos surrounding galaxies are difficult to study

What is certain is that we get them from everywhere, and in large quantities, up to 10,000 a day! Some also have periodicity or repeat themselves indefinitely, such as FRB 20190520B, a rapid eruption that repeats itself over and over again without researchers being able to define a cycle! But when we didn’t understand them perfectly, we used them to explore others Stars very famous ? It is the idea of ​​the researchers from the California Institute of Technologywho decided to examine the haloes of gas diffuse surrounding the galaxies.

In fact, these consist of much more than just theirs matter seen from ours telescopes. Beyond the stellar halo lies the galactic corona: made up of hot gas that fuels star formation while collecting debris left behind by violent stellar explosions. supernovae. but Cloud Matter is difficult to observe due to its low density of less than one particle per cubic centimeter. “These gas reservoirs are huge. If theEye If humans could see the spherical halo surrounding the nearby Andromeda galaxy, the halo would appear a thousand times larger than that moon », explains Liam Connor, first author of the study and postdoctoral researcher in astronomy at Caltech. But what surrounds this immense halo is not: still beyond the galactic crown is a halo of black matter. It is present in all galaxies, surrounding them well beyond their visible envelope and contributing most of their mass.

Fast radio bursts, “spikes” of matter between our telescopes and their source

Today, researchers propose an innovative solution for studying galactic halos: observing the propagation of fast radio bursts and deducing the gaseous mass they passed through. In fact, the latter correspond to pulses emitted in a range of frequencies, and can therefore be split into several single-frequency signals. On their way to us they meet electrons that accompany the surrounding material, especially that of galactic halos. However, each time an electron strikes, these signals are slowed down: in general, the longer the wavelength (ie, the lower the frequency), the greater the deceleration. Measurements of dispersion consist in studying the elongation of a signal by measuring the accumulated delay and deducing from this the amount of electrons, and therefore matter, that it has encountered. “We used fast radio bursts to shine a light through the halos of nearby galaxies Milky Way and measure their hidden matter”explains Liam Connor.

To test their method, the researchers used a sample of 474 fast radio bursts recorded by the Canadian Earth Mapping Experiment.hydrogen (BELLS), a radio telescope is located in British Columbia. Then they compared the dispersion measurements for each outburst and combined that data with the presence or absence of galaxies in their path. And they concluded that the overlapping galaxy outbursts were actually much slower than the others. “Our study shows that FRBs can act as skewers of all matter between our radio telescopes and the source of the radio waves”, enthuses Liam Connor. They also calculated the mass encountered by these fast radio bursts, which matched the galactic halo encountered, and measured an amount of matter twice the theoretical amount! “That’s just the beginning”says Vikram Ravi, co-author of the study and professor of astronomy at Caltech. “As we discover more FRBs, our techniques can be applied to study individual halos of different sizes and environments, and the unsolved problem of matter distribution in theuniverse. »

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