Using NASA’s Chandra X-ray Observatory, Astronomers have imaged a beam of matter and antimatter extending from a relatively tiny pulsar. This beam could help explain the surprisingly large number of positrons in the Milky Way with its tremendous scale.
The beam was originally discovered in 2020. At that time, astronomers were unaware of its full length as it was beyond the edge of the Chandra detector.
Scientists made follow-up observations using Chandra in February and November 2021. The observations revealed that the filament is about three times as long as originally seen. It spans about half the diameter of the Full Moon on the sky, making it the longest one from a pulsar as seen from Earth.
This beam came from a pulsar called PSR J2030+4415 (J2030 for short). Located about 1,600 light-years from Earth, J2030 is a dense, city-sized object formed from a massive star’s collapse and currently spins about three times per second.
Martijn de Vries of Stanford University in Palo Alto, California, who led the study, said, “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. With the same relative size, if the filament stretched from New York to Los Angeles, the pulsar would be about 100 times smaller than the tiniest object visible to the naked eye.”
A close-up view in the right panel shows the X-rays created by particles flying around the pulsar itself. When the pulsar moves through space, some particles escape and create the long filament. In both panels, optical light data from the Gemini telescope on Mauna Kea in Hawaii have been used and appear red, brown, and black. The full length of the filament is shown in a separate image.
Universe has more matter than antimatter. What are the possible sources of this antimatter? This new study of J2030 suggests that pulsars could be one answer.
The combination of fast rotation and high magnetic fields of pulsars — leads to particle acceleration and high-energy radiation that creates electron and positron pairs.
The winds generated by pulsars contain particles confined with their powerful magnetic fields as the pulsar travels through the space, the wind trails behind it. A bow shock of gas moves along in front of the pulsar.
However, about 20 to 30 years ago, the bow shock’s motion appears to have stalled, and the pulsar caught up to it, resulting in an interaction with the interstellar magnetic field running in almost a straight line from left to right. This might have caused a particle leak.
Co-author Roger Romani, also of Stanford, said, “The pulsar wind’s magnetic field linked up with the interstellar magnetic field, and the high-energy electrons and positrons squirted out through a nozzle formed by connection.”
Previously, astronomers have observed large halos around nearby pulsars in gamma-ray light. This suggests that the energetic positrons generally have difficulty leaking out into the Galaxy. This undercut the possibility that pulsars explain the positron excess that scientists distinguish. However, pulsar filaments that have recently been discovered, like J2030, show that particles actually can escape into interstellar space and eventually could reach Earth.
- Martijn de Vries, Roger W. Romani. The Long Filament of PSR J2030+4415. DOI: 10.48550/arXiv.2202.03506