The universe sends out mysterious signals from all directions. We don’t really know what they are or what produces them, but a new analysis of where they come from gives us clues about the sources of the strange emissions we call fast radio bursts (FRBs).
Led by California Institute of Technology astronomer Kritti Sharma, an international team took a census and determined that FRBs are more likely to come from galaxies with relatively young stellar populations. This is somewhat expected. What the researchers didn’t expect was that these galaxies were more likely to be quite large, with a large number of stars – which are actually quite rare.
This suggests that there might be something unusual about how FRBs are generated.
We already have some pretty good ideas about what FRBs are. They are very strong but very short bursts of radio light lasting from fractions of a millisecond to several seconds. They come from all over the sky, their sources being millions or billions of light-years away, often appearing to blink once and never again.
This makes them impossible to predict and difficult to track, but we are getting better at detecting them with wide-view surveillance and also better at locating their host galaxies. The interaction between the object’s magnetic field and gravity can create starquakes that send radio light across the sky.
Clues to the sources of strange emissions
Not all FRBs behave the same, so there may be more than one type of source. Narrowing down where these sources are tells us something about the environmental conditions that are most likely to produce them, which allows us to make inferences about what they are.
Sharma and his colleagues collected observations using a radio interferometer called the Deep Synoptic Array in a new effort to detect FRBs and locate them. They carefully studied the properties of 30 FRB host galaxies and determined that radio bursts typically originate from galaxies with young star populations.
This is not surprising if the FRB progenitors are magnetars. Neutron stars are the collapsed cores of massive stars that have become supernovae through core collapse, and massive stars have shorter lifetimes than small ones. Magnetars are young neutron stars, so we expect to find them in places where most stars are young and short-lived.
Although some FRBs have previously been detected in old star populations and low-mass galaxies, the team’s analysis showed that the most common progenitors are by far high-mass galaxies and young stars.
This suggests that massive and young stellar environments are important for the formation of FRB progenitors; if this were not the case, we would see a wider distribution in all types of galaxies.
Astronomers are constantly discovering more and more signals
It is not known why this happens, but researchers believe that the metallicity of these massive star-forming galaxies may play a role. Massive galaxies typically have a much higher metal content than less massive ones and also tend to produce heavier stars.
But there is one more problem. Core-collapse supernovae occur at a rate similar to the rate of star formation in the Universe. If FRB-producing magnetars form in this way, the FRB distribution should be largely consistent with the collapsing supernova distribution, even for low-mass galaxies – but it is not. This suggests that core-collapse magnetars are not the main progenitors of FRBs.
The team ran simulations and found a solution. FRB-emitting magnetars could form from merging binary stars. This is more likely to happen in environments with more massive stars, such as the galaxies identified by the researchers.
We still do not have a holistic explanation for the origins of FRBs, but the research significantly strengthens the case for magnetars and suggests that there are also special circumstances for the formation of these magnetars.
The FRB study is still in progress, but astronomers are constantly discovering more and more strange signals, he writes ScienceAlert.
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Source: www.descopera.ro
