Magnetar

In News

• An international group of researchers has succeeded in measuring for the first time the characteristics of a flare on a distant magnetar. 

About

• 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 spewed within a few tenths of a second as much energy as the Sun would shed in 100,000 years.
• It was captured by the Atmosphere-Space Interactions Monitor instrument (ASIM) of the International Space Station. 

Image Courtesy: TH

Magnetar

• About: 
  • A magnetar is a rare compact type of neutron star teeming with energy and magnetism. 
  • They are relatively rare objects, with only about thirty having been spotted within the Milky Way so far. 
• Study: 
  • 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 but is the first study to characterise such a flare from such a distant magnetar.
• 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. 
• High luminosity:
  • 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 lower. Further, these magnetars emit violent flares.
• Energy dissipation:
  • 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. 
• Cosmic lighthouses:
  • A few magnetars are also pulsars, those celestial lighthouses that sweep the sky with powerful radio beams (and, rarely, beams of visible light too, such as in the case of the Crab Nebula). Recently, detecting a magnetar that is also a pulsar enabled astronomers to establish an accurate distance to a magnetar for the first time.

Significance

• The observations revealed multiple pulses, with a frst pulse appearing only for about tens of microseconds, much faster than other extreme astrophysical transients
• Studying these flares will not only help us understand the physics of magnetars, it will also help in understanding fast radio bursts, which are among the most enigmatic phenomena in astronomy.

Conclusion

• Magnetars are neutron stars with the strongest-known magnetic fields.
• They have up to a thousand times the intensity of typical neutron stars and up to 10 trillion times the strength of a refrigerator magnet.

Source: TH