Swift J1727.8−1613

Swift J1727.8-1613 (also known as J1727) is a ultraluminous low-mass x-ray binary 8,800 light years away with an orbital period of about 7.6 hours.^[1][2] The compact object in the system is a stellar-mass black hole with a mass of at least 3.12±0.10 M_☉︎, in orbit with an early K-type companion star.^[1][3] The black hole's relativistic jet is the most resolved continuous X-ray binary jet, and one of the most physically extended X-ray binary jets yet discovered.^[1][4] The system was first detected in August 2023.^[1][3]

System properties

Light curves for Swift J1727.8−1613 in four photometric bands, showing several flares. Adapted from Vincentelli et al. (2025)^[5]

The system reached a peak optical magnitude of approximately 12.7, making it an interest of research into black hole x-ray binaries. In x-ray wavelengths, J1727 transitions between soft and hard x-ray states.^[3] In the soft state, the X-ray emission has a spectrum suggesting a geometrically thin, optically thick accretion disk. The accretion disk is believed to extend down to the innermost stable circular orbit of the black hole.^[6][2]

Relativistic jets

In August 2023, a bright outburst from the binary system was detected that would last for another 10 months.^[3] This observation was suggestive of a jet oriented in the north-south direction in the hard x-ray state.^[2] The jet is believed to extend for 95-160 astronomical units.^[1]