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| This illustration shows a magnetar—a highly magnetic type of neutron star—appearing as a white-blue sphere with powerful magnetic field lines streaming from its poles. |
Researchers using NASA’s Hubble Space Telescope have discovered that a rare and mysterious cosmic object—magnetar SGR 0501+4516—is hurtling across our galaxy, seemingly from an unknown place of origin. This "runaway magnetar" is now the strongest candidate in the Milky Way for a magnetar that wasn’t born in a traditional supernova explosion, as scientists previously believed. The discovery may even help explain the origins of fast radio bursts, one of the universe’s most puzzling phenomena.
“Magnetars are neutron stars — the dead remnants of stars — composed entirely of neutrons. What makes magnetars unique is their extreme magnetic fields,” said Ashley Chrimes, lead author of the study published in the April 15 edition of Astronomy & Astrophysics. Chrimes is a European Space Agency Research Fellow at the European Space Research and Technology Center in the Netherlands.
These celestial objects boast magnetic fields so powerful they defy imagination—about a trillion times stronger than Earth’s. If one flew within half the distance to the Moon, its magnetism would erase every credit card on Earth. At just 600 miles, it could rip atoms apart in the human body.
The magnetar SGR 0501+4516 was first detected in 2008 by NASA’s Swift Observatory, which spotted a burst of intense gamma rays from the galaxy’s outskirts. Only about 30 magnetars are known in the Milky Way, and this one initially appeared to be tied to a nearby supernova remnant called HB9.
But a decade-long study using Hubble and ESA’s Gaia spacecraft challenged that assumption. Using images captured in 2010, 2012, and 2020, researchers tracked the faint infrared glow of SGR 0501+4516. By aligning these images with Gaia’s ultra-precise star map, the team measured the magnetar’s tiny movement across the sky—motion smaller than a single pixel in a Hubble image.
“Being able to robustly perform such measurements really is a testament to the long-term stability of Hubble,” said co-investigator Joe Lyman of the University of Warwick, UK.
By tracing this motion backward in time, researchers found that the magnetar could not have originated from the HB9 remnant—or any other known supernova remnant or massive star cluster. This leaves researchers with two possibilities: either the magnetar is much older than its estimated 20,000 years, or it formed through an entirely different mechanism.
One such alternative is accretion-induced collapse—a process involving a white dwarf in a binary star system that accumulates material from its companion until it collapses into a neutron star. This rare event could explain SGR 0501+4516’s formation and may account for other unusual magnetars scattered across the galaxy.
“Normally, this scenario leads to the ignition of nuclear reactions, and the white dwarf exploding, leaving nothing behind. But under certain conditions, the white dwarf might instead collapse into a neutron star. We think this might be how SGR 0501 was born,” said Andrew Levan of Radboud University and the University of Warwick.
Unlocking the Mystery of Fast Radio Bursts
This finding could also shine a light on the origin of fast radio bursts (FRBs)—brief but ultra-powerful radio signals from deep space. Magnetars born through accretion-induced collapse might explain FRBs observed in ancient stellar environments, where no recent supernovae could have occurred.
“Magnetar birth rates and formation scenarios are among the most pressing questions in high-energy astrophysics,” said Nanda Rea of the Institute of Space Sciences in Barcelona, Spain. “They have implications for some of the universe’s most powerful transient events, such as gamma-ray bursts, super-luminous supernovae, and fast radio bursts.”
The team plans further Hubble observations to trace the origins of other magnetars, offering a deeper look into the formation of these extraordinary cosmic objects.
Operating for more than three decades, the Hubble Space Telescope continues to revolutionize our understanding of the universe. Hubble is a joint project between NASA and ESA, with operations managed by NASA’s Goddard Space Flight Center and the Space Telescope Science Institute in Baltimore.
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