The discovery of this grand feat may provide more insight into the origin of the relatively abundant positrons observed on Earth.

In 2020, scientists spot it for the first time: a huge bundle of matter and antimatter in space, which appeared to come from a pulsar. However, the entire length of the beam remained shrouded in mystery. Simply because the astronomers were unable to get a complete picture of the beam using the Chandra X-ray observatory.

Follow-up observations

In February and November 2021, the astronomers took another look at the beam. And those follow-up observations allowed them to observe it in its entirety and determine its true magnitude. The bundle appears to have a length of no less than 64 trillion kilometers, it will soon be announced The Astrophysical Journal to read.

Bizarre

A bizarre size. Especially when you consider that the bundle comes from a tiny asterisk. It concerns the pulsar PSR J2030+4415, which is about 1600 light-years away from Earth. A pulsar is a rapidly spinning neutron star with a very powerful magnetic field, which usually – as in the case of PSR J2030+4415 – has a diameter of barely 16 kilometers. “It’s amazing that a pulsar just 16 kilometers wide can create a structure so large that we can observe it from more than 1,000 light-years away,” said researcher Martijn de Vries.

But it’s not just the astonishing size of the bundle that has caught the attention of scientists. The observations may also help explain the mystery of the rather abundant positrons in the Milky Way.

Antiparticles

Positrons are the antiparticles of the fairly well-known electrons. This means that positrons have the same mass as electrons, but have an opposite charge. For example, the electron is a negatively charged particle, while the positron is positively charged. According to physics, every elementary particle has such an antiparticle. But – fortunately, see box – elementary particles are more abundant than antiparticles.

When a particle collides with its antiparticle, they annihilate each other. That means they mutually destroy each other. Fortunately, there is not an antiparticle for every particle, because then there would be nothing. Although we can be glad that there is an imbalance in the universe (more particles than antiparticles), it also raises an interesting and as yet unanswerable question. Because it is assumed that the big bang produced as many antiparticles as particles. And so physicists have been puzzled for years about where all the antimatter has gone.

So the vast majority of the universe consists of ‘ordinary’ matter instead of antimatter. However, this does not alter the fact that researchers do encounter relatively large numbers of positrons (anti-particles of electrons) in detectors on Earth. And that begs the question of where these positrons come from. Perhaps from pulsars like PSR J2030+4415, researchers are now suggesting, based on their observations of the massive beam of matter and antimatter that this pulsar generates. The rapid rotation of the pulsar, combined with its powerful magnetic field, transforms it into a massive particle accelerator that generates electrons and positrons. Normally, these particles have a hard time escaping the powerful magnetic field of a pulsar. But the extremely long matter and antimatter beam now spotted behind PSR J2030+4415 reveals that the particles can sometimes escape a pulsar’s grip. And the researchers also think they know how that happens. They point out that the pulsar is moving through space at a high speed – about 1.5 million kilometers per hour. This creates a shock wave of gas for the pulsar – comparable to a bow wave for a moving boat. About 20 to 30 years ago, however, that shock wave stopped and the pulsar overtook it. This resulted in a collision between the magnetic field of the pulsar and the interstellar magnetic field. “That probably led to a particle leak,” said researcher Roger Romani. “The pulsar’s magnetic field coupled with the interstellar magnetic field and the high-energy electrons and positrons escaped through the gap created by that connection in the pulsar’s magnetic field.” As the particles move along the interstellar magnetic field lines, they glow in X-rays. And so the long beam that Chandra X-ray Observatory has now spotted was created.

The fact that pulsars generate positrons is not new in itself. Previously, researchers have spotted large halos around pulsars, filled with positrons, among other things. Those halos, however, suggested that the positrons had a hard time escaping the pulsar’s grip. PSR J2030+4415 now shows that the particles can still escape into interstellar space and thus eventually reach Earth.