Magnétar
A magnetar is a very rare type of neutron star characterized by an extraordinarily intense magnetic field, about 1,000 times stronger than that of an ordinary pulsar and a million billion times stronger than Earth’s magnetic field. These objects, among the most extreme in the universe, regularly release immense bursts of X-rays and gamma rays without warning.
An Extraordinary Neutron Star
Like all pulsars, magnetars are born from the gravitational collapse of a massive star during a supernova explosion. But when the star’s core collapses, certain specific configurations allow the progenitor’s magnetic field tobe amplified to unprecedented intensities. The result is a neutron star about ten kilometers in diameter with a magnetic field of theon the order of 10 to the 14th to 10 to the 15th power gauss.
Bursts of radiation
Magnetars are distinguished by their ability to produce soft gamma-ray bursts (SGRs) and anomalous X-ray pulsars (AXPs). When their crust rearranges under the influence of the extreme magnetic field—a phenomenon called starquake— they release, in a few fractions of a second, more energy than the Sun will emit over tens of thousands of years. These events can be detected throughout the galaxy.
A Short and Intense Life
Magnetars are ephemeral objects on an astronomical scale: their intense magnetic field dissipates in just a few tens of thousands of years. After this active phase, they become ordinary neutron stars. About 30 magnetars are currently known in the Milky Way, but their shortactivity suggests that a large population of extinct magnetars exists but cannot be detected.
Importance in Astronomy
Magnetars are unique laboratories for studying physics under extreme conditions that are inaccessible on Earth. Their magnetic fields distort matter and light in unusual ways, puttingtest theories of quantum electrodynamics. Some magnetars are also suspected ofbe the source of the mysterious fast radio bursts (FRBs), extragalactic radio signals lasting a few milliseconds that are still poorly understood.
Concrete example: SGR 1806-20
In December 2004, the magnetar SGR 1806-20, located about 50,000 light-years away, produced one of the most energetic events ever detected. In a fraction of a second, it released more energy than the Sun produces in 100,000 years. The burst even partially ionized Earth’s upper atmosphere despite the distance.
Did you know?
A magnetar’s magnetic field would be lethal to a human being even at a distance of 1,000 kilometers— it would destroy biological molecules by distorting chemical bonds. Even atoms would be warped into elongated cigar shapes.
Frequently Asked Questions
What is the difference between a magnetar and a pulsar?
Both are neutron stars, but a magnetar has a magnetic field that is 100 to 1,000 times stronger. This difference radically changes their behavior: ordinary pulsars emit radiation regularly due to their rotation, while magnetars are powered by the dissipation of their extreme magnetic field.
How many magnetars exist in the galaxy?
About 30 have been confirmed, but their magnetar phase lasts only a few tens of thousands of years. The total population of former magnetars that are now extinct could number in the tens of millions in the Milky Way.
Could a magnetar pose a threat to Earth?
A massive outburst from a nearby magnetar—less than 10 light-years away— could damage the ozone layer and affect the biosphere. Fortunately, no known magnetar is close enough to pose such a threat.