12 Infrared-Lit Black Holes Devouring Stars Emerge Brightly

Supermassive black holes (SMBHs) lie at the heart of nearly all large galaxies, and they can dramatically illuminate their environment when they consume entire stars in events known as tidal disruption events (TDEs). Traditionally, astronomers have detected these occurrences through bursts of visible light or powerful X-rays. However, a team led by researchers from the Massachusetts Institute of Technology (MIT) has discovered 12 such events through infrared light, marking a new method of studying TDEs and showing that they occur more frequently across varied types of galaxies than previously thought.

Infrared light is beneficial to astronomers as it can penetrate cosmic dust clouds that might block visible light and X-rays, obscuring TDEs from view. According to Megan Masterson, the study’s lead author and a graduate student at MIT, most sources don’t show up in optical bands, necessitating the use of infrared bands if one wants to understand TDEs and their role in probing supermassive black hole demographics.

Before this research, most TDEs were detected in post-starburst galaxies, which have recently experienced intense star formation and then quieted down. These starburst episodes often eliminate a galaxy’s dust, leading astronomers to question whether starburst events naturally cause more TDEs or if TDEs in dustier, star-forming galaxies are just more challenging to detect.

The MIT team’s first detection of an infrared TDE occurred in 2023, using archived observations of short light bursts taken by NASA’s NEOWISE mission. The team then used an algorithm to sift through the data, identifying 18 TDE candidates with temporary infrared light surges. This list was narrowed down to 12 following evidence that six of those candidates might be actively feeding on material from a preexisting black hole disk, rather than a single star.

The team’s findings indicate that TDEs occur in different types of galaxies, not just post-starburst galaxies. This helps astronomers understand how often supermassive black holes consume stars in any galaxy, aligning observations more closely with predictions. On average, a galaxy should experience a TDE once roughly every 10,000 years, but known rates from optical and X-ray surveys amount to less than half of that. The new TDE observations suggest that infrared TDEs are about as common as either optical or X-ray TDEs, bringing the total observed rate of TDEs significantly closer to the predicted rate.

In the long term, astronomers hope to use TDEs as tools to measure the fundamental properties of supermassive black holes. Better understanding the full population of TDEs through infrared observations is a crucial step toward that goal.

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