White dwarf system
Kartavya Desk Staff
Source: TOI
Subject: Science and Technology
Context: NASA’s Imaging X-ray Polarization Explorer (IXPE) has, for the first time, probed the internal structure of a white dwarf system, revealing unexpected details about gas flows and X-ray behaviour in the binary system EX Hydrae.
About White dwarf system:
What it is?
• A white dwarf system typically consists of a white dwarf—the dense, Earth-sized remnant of a Sun-like star—often paired with a companion star in a binary arrangement.
Discovered / studied by:
• White dwarfs as a class were identified in the early 20th century through stellar spectroscopy.
• The current breakthrough comes from NASA’s IXPE mission, which studied EX Hydrae, about 200 light-years away in the constellation Hydra, by analysing X-ray polarisation, not just brightness.
How it forms?
• A star like the Sun exhausts its nuclear fuel, sheds its outer layers as a planetary nebula, and leaves behind a hot, compact core—the white dwarf.
• In a binary system, the white dwarf’s gravity pulls gas from its companion star.
• In systems like EX Hydrae, known as intermediate polars, the white dwarf’s moderate magnetic field partially disrupts the accretion disc and channels gas along magnetic field lines onto its surface.
Key characteristics:
• Extreme density: Mass comparable to the Sun, size similar to Earth.
• Degenerate matter: Supported by electron degeneracy pressure (Pauli Exclusion Principle), not nuclear fusion.
• High-energy emissions: Infalling matter heats to tens of millions of degrees, emitting X-rays.
• Magnetic influence: In intermediate polars, gas forms columns rising thousands of kilometres above the surface.
• Chandrasekhar limit: Maximum mass ~1.4 times the Sun, beyond which collapse or explosion occurs.
Significance:
• IXPE’s polarisation data allowed scientists to estimate the height of hot gas columns and detect X-rays reflecting off the white dwarf’s surface—details previously inaccessible.
• Enables direct testing of theories about accretion, magnetism, and extreme matter.