Astronomers have detected faint radio signals from a neutron star that was thought to be completely silent for decades. Known as 1E 1207.4-5209, the object belongs to a rare class of neutron stars called central compact objects (CCOs). These remnants sit at the centers of supernova debris but, unlike most neutron stars, they have never shown the radio pulses astronomers typically expect to find.
Using South Africa’s MeerKAT radio telescope, a team led by Zhang Lei from the National Astronomical Observatories of the Chinese Academy of Sciences finally picked up a signal from one of these elusive objects. The results, published in Nature Astronomyon June 25, show that at least one supposedly silent CCO has been quietly emitting radio waves all along, or has only recently started doing so.
A Faint Signal Hidden In Plain Sight
When a massive star explodes as a supernova, its core can collapse into a neutron star. Most newborn neutron stars spin rapidly and generate powerful magnetic fields that produce narrow beams of radio waves. As those beams sweep across Earth, they create the regular flashes that give pulsarstheir name.
Central compact objects have always stood apart. About a dozen are known, but none had produced detectable radio signals despite years of observations. One idea was that their magnetic fields were simply too weak to generate radio beams. The new observations tell a different story. MeerKAT detected radio pulses from 1E 1207.4-5209 every 424 milliseconds, exactly matching the object’s known spin period. As reported in Nature Astronomy, the signal is incredibly faint, which helps explain why it escaped detection for so long.
The neutron star is located around 10,000 light-years from Earth in the Milky Way, at the center of a supernova remnant left behind by an explosion that occurred more than 4,100 years ago.
A Spin Glitch May Hold The Answer
AstronomerLi Diof Tsinghua University gave the neutron star its nickname, the “Blue Eye Pulsar.” The name comes from the way bright X-ray images combine with the newly detected radio emission, giving the object the appearance of a glowing blue eye.
The neutron star already had an unusual history. In 2015, X-ray observations revealed that it had experienced a spin glitch, a brief increase in its rotation rate. These events are thought to happen when material inside the dense neutron star shifts unexpectedly.
The research team believes that this glitch may have strengthened the object’s magnetic field, changed its orientation, or both. If that happened, it could have switched on the radio emission, or simply made an already weak signal visible to today’s instruments.
The authors also point out that if the neutron star gradually returns to its earlier rotation rate, the radio signal could fade again. Continued observations should reveal whether that happens.
A New Clue to Missing Pulsars
The finding has implications well beyond a single neutron star. The study suggests there could be many more pulsars in theMilky Waythat have gone unnoticed because their radio signals are too weak to detect. It also raises the possibility that some pulsars currently classified as old may actually be much younger objects producing unusually faint radio emission.
The same idea could help explain why some supernova remnants appear to be missing a pulsar altogether. The researchers point to Supernova 1987A in the Large Magellanic Cloud, where indirect evidence strongly suggests that a neutron star exists, even though no radio pulsations have been detected.
The study also shows that at least one central compact object once considered radio silent is capable of producing detectable radio waves. For astronomers searching for hidden neutron stars, that small signal could carry much bigger implications.
