Neutron star merger can birth a magnetar, observations suggest

Key facts

• Magnetars—rapidly spinning neutron stars with extreme magnetic fields—can sustain prolonged X-ray emission by converting rotational energy into radiation, unlike black holes or ordinary neutron stars that fade quickly.
• Follow-up observations with the VLT’s FORS2 instrument found no supernova at the merger site, ruling out a collapsing massive star as the source of the X-ray flash and supporting a neutron star merger origin.
• Simulations and observations suggest that neutron star mergers below the Tolman-Oppenheimer-Volkoff limit (~2.6 solar masses) can form magnetars, while heavier mergers typically collapse into black holes.
• Current gravitational wave detectors lack the sensitivity to confirm magnetar formation at a redshift of 0.661, and kilonovae (radioactive glows from neutron-rich merger debris) were too faint to detect at this distance.