Subscribe to Astronomy Now
Astronomy Now Home
Home Magazine Resources Store

On Sale Now!

The October 2014 issue of Astronomy Now is on sale! Order direct from our store (free 1st class post & to UK addresses). Astronomy Now is the only astronomy magazine specially designed to be read on tablets and phones. Download the app from Google Play Store or the Apple App Store.

Top Stories

Earthshine used to test life detection method
...By imagining the Earth as an exoplanet, scientists observing our planet's reflected light on the Moon with ESO's Very Large Telescope have demonstrated a way to detect life on other worlds...

Solid buckyballs discovered in space
...Astronomers using NASA’s Spitzer Space Telescope have detected a particular type of molecule, given the nickname “buckyball”, in a solid form for the first time...

Steamy water-world gets the Hubble treatment
...Hubble Space Telescope observations of a 7 Earth-mass planet find an unusual water-rich world swathed in a thick, steamy atmosphere...

Mysterious magnetar harbours hidden magnetic field
Posted: 22 August 2013

Scientists using ESA’s XMM-Newton space telescope have discovered that a curious dead star has been hiding one of the strongest magnetic fields in the Universe all along, despite earlier suggestions of an unusually low magnetic field.

Artist impression of a magnetar with a ‘magnetic loop'. This is the interpretation of data collected by ESA’s XMM-Newton space telescope of the magnetar known as SGR 0418, which boasts one of the strongest magnetic fields in the Universe. Credit: ESA/ATG Medialab
The object, known as SGR 0418+5729 (or SGR 0418 for short), is a magnetar, a particular kind of neutron star.

A neutron star is the dead core of a once massive star that collapsed in on itself after burning up all its fuel and exploding in a dramatic supernova event. They are extraordinarily dense objects, packing more than the mass of our Sun into a sphere only some 20 km across – about the size of a city.

A small proportion of neutron stars form and live briefly as magnetars, named for their extremely intense magnetic fields, billions to trillions of times greater than those generated in hospital MRI machines, for example. These fields cause magnetars to erupt sporadically with bursts of high-energy radiation.

SGR 0418 lies in our galaxy, about 6500 light years from Earth. It was first detected in June 2009 by space telescopes including NASA’s Fermi and Roscosmos’ Koronas-Photon when it suddenly lit up in X-rays and soft gamma rays. It has been studied subsequently by a fleet of observatories, including ESA’s XMM-Newton.

“Until very recently, all indications were that this magnetar had one of the weakest surface magnetic fields known; at 6 x 1012 Gauss, it was roughly a 100 times lower than for typical magnetars,” said Andrea Tiengo of the Istituto Universitario di Studi Superiori, Pavia, Italy, and lead author of the paper published in Nature.

“Understanding these results was a challenge. However, we suspected that SGR 0418 was in fact hiding a much stronger magnetic field, out of reach of our usual analytical techniques.”

Magnetars spin more slowly than neutron stars, but still complete a rotation within a few seconds. The normal way of determining the magnetic field of a magnetar is to measure the rate at which the spin is declining. Three years of observations of SGR 0418 had led astronomers to infer a weak magnetic field.

The new technique developed by Dr Tiengo and his collaborators involves searching for variations in the X-ray spectrum of the magnetar over extremely short time intervals as it rotates. This method allows astronomers to analyse the magnetic field in much more detail and has revealed SGR 0418 as a true magnetic monster.

“To explain our observations, this magnetar must have a super-strong, twisted magnetic field reaching 1015 Gauss across small regions on the surface, spanning only a few hundred metres across,” said Dr Tiengo.

“On average, the field can appear fairly weak, as earlier results have suggested. But we are now able to probe sub-structure on the surface and see that the field is very strong locally.”

A simple analogy can be made with localised magnetic fields anchored in sunspots on the Sun, where a change in configuration can suddenly lead to their collapse and the production of a flare or, in the case of SGR 0418, a burst of X-rays.

“The spectral data provided by XMM-Newton, combined with a new way of analysing the data, allowed us to finally make the first detailed measurements of the magnetic field of a magnetar, confirming it as one of the largest values ever measured in the Universe,” adds Norbert Schartel, ESA’s XMM-Newton Project Scientist.

“We now have a new tool to probe the magnetic fields of other magnetars, which will help constrain models of these exotic objects.”

The Planets
From tiny Mercury to distant Neptune and Pluto, The Planets profiles each of the Solar System's members in depth, featuring the latest imagery from space missions. The tallest mountains, the deepest canyons, the strongest winds, raging atmospheric storms, terrain studded with craters and vast worlds of ice are just some of the sights you'll see on this 100-page tour of the planets.

Hubble Reborn
Hubble Reborn takes the reader on a journey through the Universe with spectacular full-colour pictures of galaxies, nebulae, planets and stars as seen through Hubble's eyes, along the way telling the dramatic story of the space telescope, including interviews with key scientists and astronauts.

3D Universe
Witness the most awesome sights of the Universe as they were meant to be seen in this 100-page extravaganza of planets, galaxies and star-scapes, all in 3D!


© 2014 Pole Star Publications Ltd.