AT 2021lwx

AT 2021lwx (also known as ZTF20abrbeie or "Scary Barbie" ) is the most energetic non-quasar optical transient astronomical event ever observed, with a peak luminosity of 7 × 1045 erg per second (erg s−1) and a total radiated energy between 9.7 × 1052 erg to 1.5 × 1053 erg over three years. Despite being lauded as the largest explosion ever, GRB 221009A was both more energetic and brighter. It was first identified in imagery obtained on 13 April 2021 by the Zwicky Transient Facility (ZTF) astronomical survey and is believed to be due to the accretion of matter into a super massive black hole (SMBH) heavier than one hundred million solar masses. It has a redshift of z = 0.9945, which would place it at a distance of about eight billion light-years from earth, and is located in the constellation Vulpecula. No host galaxy has been detected.

Forced photometry of earlier ZTF imagery showed AT 2021lwx had already begun brightening by 16 June 2020, as ZTF20abrbeie. It was also detected independently in data from the Asteroid Terrestrial-impact Last Alert System (ATLAS) as ATLAS20bkdj, and the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) as PS22iin. At the Neil Gehrels Swift Observatory, X-ray observations were made with the X-ray Telescope and ultraviolet, with the Ultraviolet-Optical Telescope (UVOT).

Subrayan et al. originally interpreted it to be a tidal disruption event between an SMBH (~108 ) and a massive star (~14 ). Wiseman et al. disfavor this interpretation, and instead believe the most likely scenario is "the sudden accretion of a large amount of gas, potentially a giant molecular cloud" (~1,000 ), onto an SMBH (>108 ).

The inferred mass of the SMBH, based on the light to mass ratio, is about 1 hundred million - 1 billion solar masses, given the observed brightness. However, the theoretical limit for an accreting super massive black hole is 1 hundred million solar masses. Given the best understood model of accreting SMBH's, this even may be the most massive SMBH to possibly accrete matter.