First ‘wind nebula’ spotted around rare magnetar

Astronomers have identified a vast cloud of high-energy particles known as a “wind nebula” around an unusual ultra-magnetic neutron star, or magnetar, according to a new report in The Astrophysical Journal.

The first discovery of such a phenomenon provides a unique window into the characteristics, habitat and emission history of magnetars, which are the most powerful magnets in the universe, the study team said.

A neutron star is the squashed core of an enormous star that ran out of fuel, collapsed under its own weight and exploded as a supernova. Each one squeezes the equivalent mass of half a million Earths into a ball just 12 miles across, or approximately the length of Manhattan Island. Neutron stars are most frequently discovered as pulsars, which generate radio waves, light, X-rays and gamma rays at numerous locations in their encompassing magnetic fields. When a pulsar rotates these regions toward Earth, astronomers identify pulses of emission.

A surprising high-energy find

The typical pulsar has a magnetic field that could be 100 billion to 10 trillion times more powerful than Earth’s. Magnetar fields are even stronger, and researchers don’t know how they are created. Of the approximately 2,600 known neutron stars, only 29 are magnetars.

A nebula envelopes the newly discovered magnetar, dubbed Swift J1834.9-0846-J1834.9. NASA astronomers said the object is connected with the W41 supernova remnant, situated approximately 13,000 light-years away, toward the middle part of our galaxy.

“For me, the most interesting question is, why is this the only magnetar with a nebula? Once we know the answer, we might be able to understand what makes a magnetar and what makes an ordinary pulsar,” co-author Chryssa Kouveliotou, a physics professor at George Washington University, said in a news release.

The most well-known wind nebula, powered by way of a pulsar under a thousand years old, lies in the middle of the Crab Nebula supernova remnant from the constellation Taurus. Young pulsars spin rapidly, often dozens of times a second. The pulsar’s quick rotation and powerful magnetic field collaborate to speed up electrons and other particles to extreme energies. This produces an outflow astronomers call a pulsar wind that can serve as the origin of particles comprising in a wind nebula.

“Making a wind nebula requires large particle fluxes, as well as some way to bottle up the outflow so it doesn’t just stream into space,” said co-author Alice Harding, an astrophysicist at NASA’s Goddard Space Flight Center. “We think the expanding shell of the supernova remnant serves as the bottle, confining the outflow for a few thousand years. When the shell has expanded enough, it becomes too weak to hold back the particles, which then leak out and the nebula fades away.”

When the magnetic field in a magnetar abruptly reconfigures to a lower-energy condition, energy is quickly released in the form of X-rays and gamma rays. Hence, magnetars produce brief gales of accelerated particles, unlike pulsars that typically release a steady wind.

“The nebula around J1834.9 stores the magnetar’s energetic outflows over its whole active history, starting many thousands of years ago,” said team member Jonathan Granot, an associate professor of natural sciences at the Open University in Israel. “It represents a unique opportunity to study the magnetar’s historical activity, opening a whole new playground for theorists like me.”

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Image credit: NASA Goddard

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