TESS Detects New Black Hole X-Ray Binary System

NASA’s Transiting Exoplanet Survey Satellite (TESS), a mission primarily designed to identify alien worlds, has serendipitously captured the early stages of an outburst from a black hole X-ray binary system known as AT 2019wey.

The findings, detailed in a research paper submitted on March 25, 2026, and accepted for publication in the Research Notes of the American Astronomical Society (RNAAS), provide the highest time resolution optical rising phase observations of any known black hole X-ray binary (BHXRB).

High-Resolution Optical Observations

Black hole X-ray binaries typically consist of a black hole and a companion star, where the black hole accretes matter from the star, emitting X-rays in the process. Traditionally, these systems are discovered via X-ray surveys that operate with cadences ranging from hours to days.

The TESS data provides a significant shift in how these events are monitored. The satellite sampled images of AT 2019wey at a 30-minute cadence, covering the period from approximately two days prior to the outburst until approximately 25 days after it occurred.

This high-frequency sampling allows researchers to analyze the triggering mechanisms of outbursts, which have historically been elusive due to the lack of early-time optical data.

Technical Analysis of the Outburst

Researchers Alyana Jusino, Kishalay De, and Andrea Antoni applied a piece-wise power law to the rising light curve of the system to determine the exact timing and nature of the event.

The analysis identified an outburst onset time of Modified Julian Date (MJD) 58817.86 ± 0.09, with a power-law rise index of n = 0.74 ± 0.04.

Crucially, this onset time precedes all previous ground-based optical detections. The data suggests that the optical rise began after the initial faint X-ray brightening was detected in MAXI (Monitor of All-sky X-ray Image) data.

Search for Periodic Modulation

As part of the study, the team searched for periodic high-frequency modulation within the system. This process is used to identify specific rhythmic signals that might reveal more about the binary system’s orbital or rotational dynamics.

The researchers reported that they detected no periodic modulation exceeding an amplitude of approximately 0.48 mJy at periods of 1 hour or greater, at a 90% confidence level.

Broader Implications for Time-Domain Astronomy

The serendipitous observation of AT 2019wey highlights the growing importance of large optical time-domain surveys in astrophysics. While TESS is optimized for finding exoplanets by detecting the dip in light as a planet crosses its star, its ability to monitor brightness changes over time makes it a powerful tool for high-energy astrophysical phenomena.

The researchers noted that these optical surveys offer novel avenues for the early detection of BHXRBs and provide critical insights into the mechanisms that trigger their outbursts.

The study was a collaborative effort involving the Department of Astrophysics at the American Museum of Natural History, CUNY City College, the Department of Astronomy and Columbia Astrophysics Laboratory at Columbia University, and the Center for Computational Astrophysics at the Flatiron Institute.