Understanding neutron-star evolution from magnetar flares

Image: A rupture in the crust of a highly magnetized neutron star, shown here in an artist's rendering, can trigger high-energy eruptions. Fermi observations of these blasts include information on how the star's surface twists and vibrates, providing new insights into what lies beneath. Credits: NASA's Goddard Space Flight Center/S. Wiessinger

Some of the most intriguing neutron stars are the magnetars: highly magnetised objects whose surface fields are inferred to be in excess of 10¹⁴ G in some cases, and whose interior fields may reach 10¹⁶ G.

In contrast with many older, more predictable neutron stars, magnetars are volatile, alternating between quiescent states and highly energetic bursts and flares. Their most spectacular events are the giant flares, releasing over ~ 10⁴⁵ erg of energy in a very brief flash and decaying X-ray tail.

The giant flares of magnetars are believed to be powered by colossal magnetic energy reservoirs.

In a recent paper (Lander 2016) the author sketches an evolutionary picture in which the process of giant flare energy release, from a twisted corona, begins with internal field evolution.

Given the ages of magnetars and the energy of their flares, he suggests that their evolution is driven by a novel evolutionary mechanism: magnetic flux transport/decay due to persistent plastic flow in the crust, which would invalidate the common assumption that the crustal lattice is static and evolves only under Hall drift and Ohmic decay.

He estimates the field strength required to induce plastic flow as a function of crustal depth, and the viscosity of the plastic phase. Field evolution in the superconducting core may also play a role in magnetar field evolution, depending on the star's spindown history and how rotational vortices and magnetic fluxtubes interact.

The author suggests that plastic flow will dominate NS crustal field evolution for B > 10¹⁵ G, compete with Hall drift in the outer crust for B ~ 10¹⁴ G, and probably be irrelevant for B < 10¹³ G. This suggests that it plays a key role for young magnetars, in particular.

Lander 2016 (preprint) - Understanding neutron-star evolution from magnetar flares - (arXiv)

Comments

A Sapphire Super-Earth

Twenty-one light years away, in the constellation Cassiopeia, a planet by the name of HD219134 b orbits its star with a year that is just three days long. With a mass almost five times that of Earth, it is what is known as a super-Earth. Unlike our planet, however, these super-Earths were formed at high temperatures close to their host star and contain high quantities of calcium, aluminum and their oxides – including sapphire and ruby. HD219134 b is one of three candidates likely to belong to a new, exotic class of exoplanets. These objects are completely different from the majority of Earth-like planets. They have 10 to 20 percent lower densities than Earth. Researchers looked at different scenarios to explain the observed densities. For example, a thick atmosphere could lead to a lower overall density. But two of the exoplanets studied, 55 Cancri e and WASP-47 e, orbit their star so closely that their surface temperature is almost 3,000 degrees and they would have lost this ...

Hubble Spots Expanding Light Echo around Supernova

Light Echo around SN 2014J in M82 . Credits NASA , ESA , and Y. Yang (Texas A&M University and Weizmann Institute of Science, Israel). Acknowledgment: M. Mountain (AURA) and The Hubble Heritage Team ( STScI /AURA) Light from a supernova explosion in the nearby starburst galaxy M82 is reverberating off a huge dust cloud in interstellar space. The supernova, called SN 2014J, occurred at the upper right of M82, and is marked by an “X.” The supernova was discovered on Jan. 21, 2014. The inset images at top reveal an expanding shell of light from the stellar explosion sweeping through interstellar space, called a “light echo.” The images were taken 10 months to nearly two years after the violent event (Nov. 6, 2014 to Oct. 12, 2016). The light is bouncing off a giant dust cloud that extends 300 to 1,600 light-years from the supernova and is being reflected toward Earth. SN 2014J is classified as a Type Ia supernova and is the closest such blast in at least four ...

Forest of Molecular Signals in Star Forming Galaxy

Spiral Galaxy NGC 253. Credit: ESO Astronomers found a rich molecular reservoir in the heart of an active star-forming galaxy with the Atacama Large Millimeter/submillimeter Array (ALMA). Among eight clouds identified at the center of the galaxy NGC 253, one exhibits very complex chemical composition, while in the other clouds many signals are missing. This chemical richness and diversity shed light on the nature of the baby boom galaxy. Ryo Ando, a graduate student of the University of Tokyo, and his colleagues observed the galaxy NGC 253 and for the first time, they resolved the locations of star formation in this galaxy down to the scale of a molecular cloud, which is a star formation site with a size of about 30 light-years. As a result, they identified eight massive, dusty clouds aligned along the center of the galaxy. “With its unprecedented resolution and sensitivity, ALMA showed us the detailed structure of the clouds,” said Ando, the lead author of the research paper...

SpaceTime

Search This Blog