Why in the News?

NASA’s Imaging X-ray Polarization Explorer (IXPE) has, for the first time, probed the internal structure of a white dwarf binary system by studying X ray polarisation. Observations of EX Hydrae revealed unexpected details about gas flows, magnetic accretion, and reflected X ray emission.

Significance of IXPE observations

• Enabled estimation of the height of hot accretion columns.
• Detected X rays reflected off the white dwarf surface, a first for such systems.
• Provided direct evidence to test theories of accretion physics, magnetic fields, and extreme states of matter.

White Dwarf System

A white dwarf system usually consists of a white dwarf and a companion star bound in a binary system. Matter from the companion is pulled towards the white dwarf due to its strong gravity.

How it forms

• A Sun like star exhausts nuclear fuel and sheds outer layers as a planetary nebula.
• The leftover dense core becomes a white dwarf.
• In binary systems, gas from the companion star accretes onto the white dwarf.
• EX Hydrae belongs to a class called intermediate polars, where a moderate magnetic field partially disrupts the accretion disc and channels gas along magnetic field lines.

Key characteristics

• Extreme density: Mass comparable to the Sun, radius similar to Earth.
• Degenerate matter: Supported by electron degeneracy pressure based on the Pauli Exclusion Principle, not fusion.
• High energy emissions: Infalling gas heats to tens of millions of degrees, producing X rays.
• Magnetic accretion: Gas flows in columns rising thousands of kilometres above the surface.
• Chandrasekhar limit: Maximum stable mass about 1.4 times the Sun.

Prelims Pointers

• IXPE studies X ray polarisation, not imaging alone.
• EX Hydrae is an intermediate polar type white dwarf system.
• Accretion driven X ray emission occurs due to magnetic channeling.
• White dwarfs are supported by electron degeneracy pressure.

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