A wandering cosmic powerhouse with a magnetic field trillion times stronger than Earth’s is challenging astronomers’ understanding of how the universe’s most extreme objects form. The magnetar, traveling through our galaxy from an unknown birthplace, has stumped scientists with its unusual origin story.
NASA’s Hubble Space Telescope has tracked the mysterious object—designated SGR 0501+4516—over a decade of observations, revealing it likely wasn’t born in the violent supernova explosion that typically creates these ultra-magnetic neutron stars.
“Magnetars are neutron stars — the dead remnants of stars — composed entirely of neutrons. What makes magnetars unique is their extreme magnetic fields,” explains Ashley Chrimes, lead author of the discovery published April 15 in Astronomy & Astrophysics and European Space Agency Research Fellow.
These stellar remnants possess almost comic-book-like powers. If one passed at half the Moon’s distance, it would instantaneously erase every credit card on Earth. At closer range—within about 600 miles—a magnetar would function like a sci-fi death ray, tearing apart the atoms in a human body.
Originally spotted in 2008 when NASA’s Swift Observatory detected intense gamma-ray flashes, the magnetar appeared to be associated with a nearby supernova remnant called HB9. This alignment seemed to confirm the standard theory that magnetars form when massive stars explode.
But Hubble’s exquisite sensitivity, combined with precise star-mapping data from the European Space Agency’s Gaia spacecraft, revealed the magnetar is actually traveling on a trajectory that couldn’t have originated from that supernova remnant—or any other known stellar explosion site.
“All of this movement we measure is smaller than a single pixel of a Hubble image,” said co-investigator Joe Lyman of the University of Warwick. “Being able to robustly perform such measurements really is a testament to the long-term stability of Hubble.”
The discovery suggests alternative formation scenarios for SGR 0501+4516, such as the merger of two lower-mass neutron stars or a process called accretion-induced collapse, where a white dwarf star pulls in too much material from a companion.
“Normally, this scenario leads to the ignition of nuclear reactions, and the white dwarf exploding, leaving nothing behind. But it has been theorized that under certain conditions, the white dwarf can instead collapse into a neutron star. We think this might be how SGR 0501 was born,” explained Andrew Levan of Radboud University and the University of Warwick.
The findings could shed light on one of astronomy’s most recent puzzles: fast radio bursts—powerful flashes of radio waves lasting only milliseconds. Some of these bursts emerge from regions where stars massive enough to create supernovae haven’t existed for billions of years.
“Magnetar birth rates and formation scenarios are among the most pressing questions in high-energy astrophysics, with implications for many of the universe’s most powerful transient events,” said Nanda Rea of the Institute of Space Sciences in Barcelona.
Researchers plan additional Hubble observations to study other magnetars in our galaxy, potentially revealing if SGR 0501+4516 is truly unique or represents an entirely new understanding of how these cosmic extremes come to exist.
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