Magnetars

Magnetars

Subject – Science and Tech

Context – Study of distant magnetar reveals facets of the exotic star

Concept –

• A magnetar is a type of neutron star believed to have an extremely powerful magnetic field.
  • Neutron stars are formed when the largest stars in the universe reach the end of their lives. When these stars run out of fuel, their core collapses causing outer layers to come crashing in towards the centre.
• The magnetic-field decay powers the emission of high-energy electromagnetic radiation, particularly X-rays and gamma rays.
• A magnetar is a rare compact type of neutron star teeming with energy and magnetism.
• Magnetars are relatively rare objects, with only about thirty having been spotted within the Milky Way so far.

How magnetars form?

• During the course of their evolution, massive stars – with masses around 10-25 times the mass of the Sun – eventually collapse and shrink to form very compact objects called neutron stars. A subset of these neutron stars are the so-called magnetars which possess intense magnetic fields.
• These are highly dense and have breathtakingly high rotation speeds – they have rotational periods that can be just 0.3 to 12.0 seconds.
• Magnetars have high magnetic fields in the range of 10¹⁵ gauss and they emit energy in the range given by luminosities of 10³⁷– 10⁴⁰ joules per second.
  • Compare this to the luminosity of the sun which is in the order of 10²⁶ joules per second – a factor of at least 10¹¹
• Further, these magnetars emit violent flares.
• Eruptions in magnetars are believed to be due to instabilities in their magnetosphere, or “starquakes” produced in their crust – a rigid, elastic layer about one kilometre thick. This causes waves in the magnetosphere, and interaction between these waves causes dissipation of energy.
• Magnetars are very difficult to observe when they are silent. It is only during a flare that they can be observed, and these flares are so short-lived that it presents a formidable problem.
• They are mostly observed or seen in active transient phases which are very short in duration and are very faint in general for any available instruments or telescopes.
• The active life of a magnetar is short. Their strong magnetic fields decay after about 10,000 years, after which activity and strong X-ray emission cease.

In News –

• An international group of researchers has succeeded in measuring for the first time the characteristics of a flare on a distant magnetar.
• The magnetar they have studied is about 13 million light years away, in the direction of the NGC 253, a prominent galaxy in the Sculptor group of galaxies.
• The flare, which spewed within a few tenths of a second as much energy as the Sun would shed in 100,000 years, was captured accidentally on April 15, 2020, by the Atmosphere-Space Interactions Monitor instrument (ASIM) of the International Space Station.
• The present magnetar is only the second one to be studied which is located outside the galaxy and is also the furthest, at 13 million light years distance.