A. Supernovae explosions

B. Red giant stars

C. White dwarf mergers

D. Pulsar collisions

Details About Magnetars are believed to be formed from the remnants of:

A star with a mass 10–25 times that of the Sun collapsed to create them. A tablespoon of the material inside a magnetar would have a mass of more than 100 million tons due to the magnetar’s internal density.