Neutron star field decay could impact what we know

February 26, 2007 By Miranda Marquit, PhysOrg.com, Phys.org feature

Neutron star field decay could impact what we know
The trend of neutron star temperature (in kilo-electron volts) versus magnetic field strength for different strongly-magnetized neutron stars. The research group interprets the general increase of temperature with field strength as strong evidence that a star´s temperature is controlled by heat from the magnetic field after a certain age. The solid line shows a prediction assuming that cooling by surface emission is balanced by heating from the magnetic field. The position of the line implies an average decay time of about one million years. The diamonds and stars represent magnetars. Red symbols indicate stars younger than about 104 years which have not yet had time to cool down onto the solid line. Vertical lines represent uncertainty ranges, vertical arrows denote upper limits, and horizontal arrows denote upper limits on the field. Credit: Bennett Link
“[W]hat we have found could have profound impacts on what we know about how neutron stars evolve, how old they are and even what they are made of,” Bennett Link tells PhysOrg.com.

Until now, explains Link, a professor of physics at Montana State University in Bozeman, all evidence indicated that neutron star magnetic fields last essentially forever, except in very strongly-magnetized stars -- magnetars -- which have magnetic fields in excess of 1014 G. Link and his colleagues, José Pons, Juan Miralles and Ulrich Geppert from the Department of Applied Physics at the University of Alacant in Alacant, Spain present the findings from their study of about 30 neutron stars in a Letter published in Physical Review Letters. Their observations, and the conclusions drawn from them can be found in “Evidence for Heating of Neutron Stars by Magnetic-Field Decay.”

The major finding from the team’s work is that stars with fields in excess of about 1012 G show evidence for decay of their magnetic fields. Previously, such stars were assumed to have constant magnetic fields like stars with weaker fields. “Our work fills the gap between the lower-field stars and the magnetars,” Link says. As the energy of the field dissipates into space, the cooling of these more strongly magnetized stars is delayed.

A neutron star is a super-dense stellar remnant created from a supernova explosion. More mass than is contained in the Sun is packed into an object 20 km across. One reason these objects are so interesting is because they contain matter denser than anything we can study on Earth. “You can only study the properties of dense matter to a certain point in the laboratory,” Link explains. “But if you could figure out what’s going on in a neutron star, then you could learn more about how some of the more exotic particles that you get in particle accelerator experiments, like pions, hyperons and quarks, interact.”

“One way to approach this problem is to look at how neutron stars lose their residual heat as they age. What we have found could have profound impacts on our understanding of how neutron stars cool, how old they are and even what they are made of,” Link says.

It appears that only about five percent of neutron stars, the most strongly magnetized, undergo significant field decay; this may be why previous studies, which considered the entire neutron star population, missed the effect. Link expects that expanding the study to more stars will support the work presented by him and his colleagues in Spain. However, he points out, “expanding the sample will have to await the next generation of x-ray observatories.”

And the implications of field decay? Link points out that since most neutron star ages are estimated assuming that a star’s magnetic field is constant, field decay would change estimates of neutron star ages. “If field decay takes place over about a million years, as our analysis indicates, then what we thought was a 10 million year old star may only be 2 million years old. If we’re getting the ages wrong for some stars, our whole picture of neutron star evolution should be reconsidered.”

Age determinations are not the only thing that could change in the face of magnetic field decay. “These large field neutron stars are different from other neutron stars,” Link says. “It could be that magnetic fields in ordinary, lower-field, neutron stars decay little or not at all, due to the way the field was established at the stars’ births. More research is needed to consider the possibilities.”

“We’ve opened a new can of worms,” Link continues. “There’s a lot more to be understood about how neutron star thermal and magnetic evolution proceeds. I hope we’ve opened up new lines of discussion and new areas of research that will eventually further our understanding of neutron star cooling and composition.”

You can learn more about Bennett Link’s work by visiting www.physics.montana.edu/people … ?id_PersonDetails=15 .

Copyright 2007 PhysOrg.com.
All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com.

Explore further: Astronomers observe evolution of a black hole as it wolfs down stellar material

Related Stories

The 'stuff' of the universe keeps changing

February 1, 2019

The composition of the universe—the elements that are the building blocks for every bit of matter—is ever-changing and ever-evolving, thanks to the lives and deaths of stars.

Computer simulation sheds new light on colliding stars

January 8, 2019

Unprecedented detail of the aftermath of a collision between two neutron stars depicted in a 3-D computer model created by a University of Alberta astrophysicist provides a better understanding of how some of the universe's ...

Recommended for you

Trembling aspen leaves could save future Mars rovers

March 18, 2019

Researchers at the University of Warwick have been inspired by the unique movement of trembling aspen leaves, to devise an energy harvesting mechanism that could power weather sensors in hostile environments and could even ...

Quantum sensing method measures minuscule magnetic fields

March 15, 2019

A new way of measuring atomic-scale magnetic fields with great precision, not only up and down but sideways as well, has been developed by researchers at MIT. The new tool could be useful in applications as diverse as mapping ...

Researchers report new light-activated micro pump

March 11, 2019

Even the smallest mechanical pumps have limitations, from the complex microfabrication techniques required to make them to the fact that there are limits on how small they can be. Researchers have announced a potential solution—a ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.