An international team reports decades of monitoring of XID 925, a very faint X‑ray source first seen in 1999 in Chandra's Deep Field South. The source brightened unexpectedly by a factor of 27 between January and March 1999, then rapidly dimmed and continued a long decline to about one‑fortieth of its peak. Researchers propose the star was torn apart by a central supermassive black hole and that a second, companion black hole briefly disturbed the resulting accretion disk, producing the extra X‑ray burst. If confirmed, XID 925 would be the most distant candidate for a TDE shaped by two black holes, shedding light on galactic center dynamics.
Faint X‑Ray 'Scream' From 3 Billion Years Ago May Be a Star Torn Apart by Two Black Holes
Dec 11
Black holes rip matter away from any unlucky stars that come too close. Now, scientists think they've seen two black holes that feasted on the same star in a back-to-back attack. | Credit: ESA/ATG medialab
About three billion years ago, a star may have been caught in a destructive gravitational tug‑of‑war between two supermassive black holes. Today, astronomers detect a faint X‑ray signal that could be the echo of that violent encounter.
An international team reporting decades of observations published a paper accepted in The Innovation in November describing the faintest known variable X‑ray flare and its unusual behavior. The source, designated XID 925, was first detected in 1999 in the Chandra X‑ray Observatory's Deep Field South survey — the deepest and most comprehensive X‑ray map of the sky to date.
Decades of Fading — With a Sudden Flash
Observers tracked XID 925 as it faded from an initial bright spike down to roughly one‑fortieth of that peak over many years. Between January and March 1999, however, the source unexpectedly brightened by a factor of 27, then collapsed back almost as quickly and resumed its long decline.
What Could Cause This?
A sharp rise followed by a long fade is the classic signature of a tidal disruption event (TDE), which occurs when a star passes too close to a supermassive black hole. The black hole's tidal forces shred the star in a process often described as "spaghettification." Debris from the destroyed star settles into a rapidly rotating accretion disk just outside the black hole; friction and gravity heat the gas until it emits X‑rays visible across cosmological distances. As material eventually falls past the event horizon, the disk dims.
A Binary Black Hole Twist
The sudden 1999 flare, the authors argue, is difficult to explain with a single black hole alone. They propose a rarer scenario: a TDE occurring in the presence of two supermassive black holes. In this model a primary, central black hole first tore the star apart and built the accretion disk. A secondary, smaller (but still massive) companion then passed near or through that disk, disturbing it and triggering an extra burst of X‑rays before the emission returned to its long‑term decline.
Analogy used by the researchers: like a car crashing into an already chaotic accident scene, the companion black hole makes the situation messier and briefly releases more energy.
Why It Matters
If confirmed, XID 925 would be the most distant candidate for a tidal disruption event influenced by two supermassive black holes. That would offer a rare window into the dynamics of black holes and stars at the centers of young galaxies and into how binary supermassive systems interact with their surroundings.
The team cautions that the binary‑black‑hole model does not perfectly account for every detail of the observations, but they consider it the most convincing explanation given the data. Continued monitoring and future observations will be needed to test the scenario further.
