There is a lot of antimatter in the Universe. Scientists keep detecting more and more antimatter in the form of positrons, even though ordinary matter is more plentiful. Standard models predict more positrons reaching Earth. Where do they come from?
A new study strengthens the idea that pulsars are a source.
The antimatter is equivalent to electrons. They are the same mass, but they are positively charged. They are produced by decay in some naturally occurring radioactive isotopes and also by a process called pair production. There are more positrons reaching Earth than there should be.
The results of previous experiments that found the same thing were confirmed by the Alpha Magnetic Spectrometer (AMS-02), which detected more positrons than expected. It has been difficult to establish that pulsars are a source of positrons.
Researchers imaged a pulsar called PSR J2030+4415. The beam of matter and antimatter that is 40 trillion miles long is captured by the Chandra X-ray Observatory. The excess of positrons could be accounted for by a pulsatile beam.
“It’s amazing that a pulsar that’s only 10 miles across can create a structure so big that we can see it from thousands of light-years away.”
Martijn de Vries, lead author, Stanford University.
The study was published in The Astrophysical Journal Letters.
A pulsar is a rapidly spinning star. They are very dense as collapsed stars. They are about the size of a large city, but can emit jets on an epic scale.
It's amazing that a pulsar that's only 10 miles across can create a structure so big that we can see it from thousands of light-years away.
The authors think that structures like this one could be a significant source of positrons. There is a combination of rapid rotation and powerful magnetic fields. These forces cause high-energy radiation and accelerate particles. Einstein explains how this works. The process of converting mass into energy is reversed in his equation.
The stellar wind of the pulsar has a powerful magnetic field that keeps it confined. There is something happening with PSR J2030+4415.
It is travelling through space at a rate of 1.6 million km/h. A bow shock is in front of the pulsar. The bow shock stopped and the wind caught up to it. There was an interaction between the pulsar and the magnetic field.
The co-author said that it was likely that a particle leak occurred.
New magnetic field lines were found after the particles escaped. They slowed and moved along the magnetic field lines at a third of the speed of light. Chandra believes that they emitted x-rays that were long.
Positrons weren't leaking into the galaxy when researchers observed them before. They were in a kind of halo around the pulsar. Shortly after the core-collapse supernova created the pulsar, the halo of the wind nebula appeared. The halo's edge is the bow shock, and the positrons were confined to it.
The idea that pulsars are a source of antimatter was not supported by those observations. There is a long filament coming from PSR J2030+4415 and it shows that there are positrons that can reach Earth. The excess of positrons detected by the AMS-02 instrument is explained by this.
The researchers say that J2030 has more to teach us about the structure of pulsars and antimatter positrons. The root of positron escape is the subject of particular interest. The authors point out that J2030 has some special features that are similar to other known pulsars.
The authors write that it is one-sided, initially narrow, and has an approximate linear expansion.
The authors referred to a previous study to understand what this means. The same way J2030 does, that study paid particular attention to the bowshocks created by pulsars moving through the ISM.
The bow-shock nebula with extended tail was created by the interaction of a fast- moving pulsar wind with the ISM. The ISM ram pressure confines the pulsar wind, which produces two shocks, a forward shock in the ISM and a reverse/termination shock.
This is important to the positrons.
The authors of the newer study say that the one-sidedness may be connected with the small spin-velocity angle. The long x-ray filaments seen in the Chandra images are caused by the reconnection of the ISM field lines.
Scientists have been wondering about the source of positrons for decades. Some of the mystery around antimatter can be traced back to this research. It outlines a potential source. Some studies say that pulsars can be the source.
The source of antimatter detected here at Earth is too far away to come from nearby pulsars. The flow is too diffuse to be detected.
The dark matter is another candidate source. Dark matter particles could cause Positrons. There is no way to observe that and it is largely theoretical.
That brings us back to the stars.
The last word on the subject of antimatter reaching Earth isn't the study showing that pulsars can be the source of antimatter. Astronomers don't know a lot about pulsars, bow shocks, and ISM magnetic field lines. The authors of the new paper say that a more detailed study could strengthen the idea that the source of antimatter is in the form of a pulsar.
Scientists need more detailed data to understand if pulsars are a significant source of positrons. J2030 changes rapidly, and that is part of the problem in understanding it.
The authors say they are beginning to understand when the x-ray filaments flare bright. They can organize extensive x-ray campaigns if they can predict the flaring in advance. When combined with other data, the x-ray results will be a powerful tool for probing the conditions needed for efficient reconnection.
They conclude that all of that work may have important implications for the propagation of pulsar cosmic ray positrons through the nearby ISM to Earth detectors.
Antimatter is not dangerous because it sounds like science fiction weaponry. It has been around for as long as the Universe has existed.
Scientists are drawn to excess positrons because of a mystery source.
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