GX 339-4

GX 339-4 is a variable X-ray binary system located in the constellation Ara. It is classified as a black hole candidate due to its X-ray spectral properties and rapid variability, suggesting the presence of a compact object with a mass exceeding the Tolman–Oppenheimer–Volkoff limit for neutron stars.

The system consists of a black hole accreting matter from a companion star, likely a low-mass star. This accretion process forms an accretion disk around the black hole, which heats up to extremely high temperatures and emits copious amounts of X-rays.

GX 339-4 exhibits distinct X-ray spectral states. During its low/hard state, the X-ray spectrum is dominated by a hard power-law component, and radio emission is often observed. As the accretion rate increases, the system transitions to a high/soft state, characterized by a thermal-dominant X-ray spectrum. Outbursts are common in GX 339-4, where the X-ray flux increases dramatically over a short period.

Observations across the electromagnetic spectrum, from radio to X-rays, are used to study the physical processes occurring in the accretion disk and to probe the nature of the black hole. GX 339-4 serves as an important laboratory for understanding black hole accretion and jet formation.