Mysterious magnetar has unknown origins

Magnetars are ultra-dense remnants of massive stars, known for possessing the strongest magnetic fields in the universe – trillions of times more powerful than Earth’s magnetic field. A magnetar named SGR 0501+4516 is challenging what scientists thought they knew about how these bizarre stars come into being.

In a new study, researchers from Radboud University and the University of Warwick used the Hubble Space Telescope to track the magnetar SGR 0501+4516 as it moves across our galaxy. The findings suggest that this object might not have been formed in a traditional supernova, as previously believed.

Instead, the mysterious magnetar could have originated from a much rarer and less understood process – one that may even hold answers to the mystery of fast radio bursts.

What makes magnetars so unique?

“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.

If a magnetar came within half the distance to the Moon, its magnetism could erase every credit card on Earth. A human within 600 miles would be physically torn apart by the force.

The magnetar in question, SGR 0501+4516, was first spotted in 2008 by NASA’s Swift Observatory, which detected its brief and intense gamma-ray flashes. At the time, scientists assumed it had formed in a supernova explosion.

After all, it was located near the remnants of a supernova known as HB9. But new data from Hubble and the European Space Agency’s Gaia spacecraft is telling a different story.

Magnetar with mysterious origins

With data collected in 2010, 2012, and 2020, the researchers used Hubble’s steady view and infrared imaging to measure the magnetar’s movement over time.

The experts compared its position to a precise stellar map provided by Gaia, which allowed them to trace the magnetar’s slow drift across the sky.

“All of this movement we measure is smaller than a single pixel of a Hubble image,” said co-investigator Joe Lyman. “Being able to robustly perform such measurements really is a testament to the long-term stability of Hubble.”

The results were surprising. The direction and speed of SGR 0501+4516’s journey showed that it likely didn’t originate from the nearby supernova remnant. When scientists traced its path back thousands of years, they found no sign of any known supernova remnants or star clusters that could explain the birth.

Explaining the magnetar’s origins

If it wasn’t born from a supernova, what could explain the magnetar’s existence? The researchers suggest it may have formed in a different way entirely – either from the collision of two smaller neutron stars or through something called accretion-induced collapse.

“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,” noted study co-author Andrew Levan.

This theory involves a white dwarf in a binary system pulling in too much gas from its companion. If it gets heavy enough, it can collapse under its own weight – not explode – and possibly become a magnetar.

Clues to fast radio bursts

This discovery might also help explain one of the biggest puzzles in astrophysics: fast radio bursts (FRBs). These are brief but powerful bursts of radio waves that have been detected across the universe.

SGR 0501+4516 is now the top candidate in our galaxy for a magnetar that may have formed through an accretion-induced collapse or merger — both of which are scenarios that could generate FRBs. That’s especially significant for bursts that appear in old star populations where no new massive stars (and thus no new supernovae) are expected.

“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, such as gamma-ray bursts, super-luminous supernovae, and fast radio bursts,” said study co-author Nanda Rea.

More to discover across our galaxy

The research team plans to continue using Hubble to study other magnetars across the Milky Way. With new findings, researchers gain more knowledge about the mysterious origins of magnetars like SGR 0501+4516.

Each new observation could bring us closer to understanding how these powerful magnetic stars are born – and what role they might play in some of the universe’s strangest phenomena.

The research is published in the journal Astronomy & Astrophysics.

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