Magnetar (IMAGE) University of Copenhagen - Niels Bohr Institute Caption Magnetars are some of the most extreme objects we know in the universe. They are extremely compact objects with masses like the Sun, but with radii of only 10-20 km. At the same time, magnetars are extremely powerful magnetic fields -- the strongest magnetic fields we know in the universe. Credit NASA Usage Restrictions Credit: NASA License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.