Why is it in the News?

India’s first multi-wavelength space-based observatory, AstroSat, has detected intense sub-second X-ray bursts emanating from a neutron star with an ultrahigh magnetic field, known as a magnetar.

What is X-ray Bursts?

• X-ray bursts manifest in low-mass X-ray binary systems featuring a neutron star and a low-mass main sequence star orbiting each other.
• The occurrence of these bursts is intricately linked to the gravitational dynamics of the neutron star and its companion.
• In this system, the proximity and intense gravitational forces of the neutron star cause the companion star to exceed its Roche-lobe, leading to the formation of an accretion disk around the neutron star.
• This disk becomes a repository for hydrogen drawn from the overflowing companion star.
• As hydrogen accumulates on the neutron star's surface, the extreme temperatures and pressures prevailing there catalyze its transformation into helium.
• This ongoing process results in the formation of a thin surface layer of helium.
• When this helium layer reaches a critical mass, a sudden explosive ignition occurs, elevating the entire neutron star's surface temperature to several tens of millions of degrees and releasing a burst of X-rays.
• Following the outburst, the binary system returns temporarily to a quiescent state, allowing the neutron star to reaccumulate the helium surface layer gradually.
• This cyclic process leads to the recurrence of X-ray bursts, typically unfolding at regular intervals separated by several hours or days.

About Indias’ AstroSat:

• AstroSat stands as India’s first dedicated multi-wavelength space observatory, pioneering a mission focused on the simultaneous study of celestial sources across X-ray, optical, and UV spectral bands.
• Launched with a lift-off mass of 1515 kg, AstroSat took flight aboard the Indian launch vehicle PSLV from the Satish Dhawan Space Centre in Sriharikota on September 28, 2015.
• It entered a 650 km orbit, inclined at an angle of 6 degrees to the equator.
• The Mission Operations Complex (MOX) at ISRO Telemetry, Tracking and Command Network (ISTRAC) in Bengaluru oversees the satellite throughout its mission life.
• With a minimum useful life of around 5 years, AstroSat is dedicated to achieving the following scientific objectives:
  • Understanding high-energy processes in binary star systems housing neutron stars and black holes.
  • Estimating magnetic fields associated with neutron stars.
  • Investigating star birth regions and high-energy processes in star systems beyond our galaxy.
  • Detecting new, briefly bright X-ray sources in the celestial sphere.
  • Conducting a limited deep-field survey of the Universe in the Ultraviolet region.