Ultraluminous X-ray source

Great progress has been made by the X-ray observatories XMM-Newton and Chandra, which have a much greater spectral and angular resolution.

The fact that ULXs have Eddington luminosities larger than that of stellar mass objects implies that they are different from normal X-ray binaries.

Beamed emission — If the emission of the sources is strongly beamed, the Eddington argument is circumvented twice: first because the actual luminosity of the source is lower than inferred, and second because the accreted gas may come from a different direction than that in which the photons are emitted.

[2] Intermediate-mass black holes are light enough not to sink to the center of their host galaxies by dynamical friction, but sufficiently massive to be able to emit at ULX luminosities without exceeding the Eddington limit.

Historically, this state was associated with a lower luminosity, though with better observations with satellites such as RXTE, this is not necessarily the case.

The high/soft state is characterized by an absorbed thermal component (blackbody with a disk temperature of (kT ≈ 1.0 keV) and power-law (spectral index ≈ 2.5).

A Chandra image of NGC 4485 and NGC 4490: two potential ULXs
SS 433 - possible ULX ray object
Side-by-side Hubble and Very Large Telescope MUSE images of the environment around NGC 1313 X-1. The MUSE RGB image of the nebula carved by the ULX sitting at its center (indicated by a star) is seen in three narrow filters showing oxygen, sulfur and hydrogen emission [ 6 ] .