Illustration of gamma ray halo around the Geminga pulsar (right image), a neutron star located 800 light-years away in the constellation Gemini. A pulsar is a rapidly rotating forms of neutron stars, surrounded by clouds of electrons and positrons (cosmic ray particles originating from outside the solar system). A pulsar's strong magnetic field pulls these particles from its surface. Astronomers believed that the Geminga pulsar was a source of high-energy positrons near Earth. These particles were found to be more abundant than previously predicted. To study this, they conducted a study using 10 years of NASA?檚 Fermi telescope data. They were able to detect gamma rays at energies from 8 to 1,000 billion electron volts in the sky around Geminga (left image, centre). When all other sources of gamma rays and diffuse light were removed, they discovered a faint gamma ray halo surrounding Geminga. This gamma ray glow was formed when particles collided with starlight, boosting them to gamma ray energies.