Scientists detect energetic explosion from magnetic neutron star

Magnetars are among the most extreme objects in the universe — a class of compact stellar remnants called neutron stars, which have immensely strong magnetic fields. Every now and then they produce huge bursts of gamma rays, in the strongest release of non-destructive energy known in the cosmos.

Scientists have now detected the most distant known example of one of these flares, called a giant flare, from a magnetar in a galaxy known as Messier 82, or M82.

This wave of gamma rays — the most energetic form of light — released in just a tenth of a second the amount of energy that our sun emits over a period of approximately 10,000 years, scientists said.

Only two confirmed giant explosions were observed in our galaxy, the Milky Way, in 2004 and 1998, and only one had been identified in another galaxy, in 1979, in the Large Magellanic Cloud, neighboring the Milky Way, according to the researchers.

“Giant explosions are very rare events,” said astrophysicist Sandro Mereghetti, from Italy’s National Institute of Astrophysics (INAF), in Milan, lead author of the research published this Wednesday in the journal Nature.

“The Milky Way contains about 30 magnetars, possibly many more, that have not been seen emitting giant flares.”

M82 — nicknamed the “cigar galaxy” because, when viewed head-on, it has an elongated, cigar-like shape — is 12 million light-years from Earth, in the constellation Ursa Major. A light year is the distance that light travels in one year (9.5 trillion km). The giant explosion of the Large Magellanic Cloud’s magnetar was about 160,000 light-years from Earth.

The giant M82 explosion was the most distant known, but not the most energetic. The 2004 one had an energy equivalent to about 1 million years of solar production.

Although there are more energetic cosmic events, such as supernova explosions at the end of a large star’s life and gamma-ray bursts caused by the merger of two neutron stars, these events involve destruction, unlike giant explosions.

Magnetars also emit occasional bursts of gamma rays and X-rays at lower energy levels than giant explosions.

Neutron stars are born in the explosion and collapse of stars, with 8 to 25 times the mass of the Sun, at the end of their life cycle. They compress one or two times the mass of the sun into a sphere the size of a city.

“They are the most compact and dense astrophysical objects. They are as dense as atomic nuclei,” said INAF astrophysicist and study co-author Michela Rigoselli about neutron stars.

The main feature that differentiates magnetars from other neutron stars is a magnetic field 1,000 to 10,000 times stronger than the normal magnetism of a neutron star and a trillion times greater than the sun.

“We can say that magnetars are neutron stars powered by their own magnetic energy. This does not happen in ordinary neutron stars,” he said.

“A giant explosion originates from a reconfiguration and reconnection of the magnetar’s magnetic field,” Rigoselli added.