Understanding the origin, acceleration and propagation of high-energy cosmic rays has been a century-old mystery in astrophysics. Recently, joint observations from China’s Einstein Probe (EP) satellite and the Large High Altitude Air Shower Observatory (LHAASO) showed an extraordinarily long X-ray tail near a pulsar about 4,600 light-years (27 quadrillion miles) from Earth—one that had never before been seen in full. The tail extends about 42 light-years (250 trillion miles) and stretches in the same direction as ultrahigh-energy gamma-ray emission detected by LHAASO, with the two showing a close spatial match.
