Infrared search finds large cluster of star-destructing black holes

Virtually anything in space could be a potential meal for a supermassive black hole, and that includes entire stars. Even stars larger than our Sun can fall victim to the black hole's intense gravity and be pulled into its expanding mouth. It's a terrifying phenomenon, but how often does it actually happen?

Tidal disturbance events (TDEs) — when a black hole's tidal forces overwhelm a star's gravity and tear it apart — are Believed to happen Once every 10,000 to 100,000 years in any given galaxy. TDEs can be detected by the massive amounts of energy they release. While its observations are still very rare, an international team of researchers has now discovered 18 of them that had not been discovered in previous searches. Why?

Many TDEs can be found in dusty galaxies. Dust blocks many wavelengths of radiation, from light rays to X-rays, but long infrared wavelengths are less susceptible to scattering and absorption. When the team examined the galaxies in infrared, they found 18 TDEs that had previously eluded astronomers.

Hidden in plain sight

To date, most tidal disturbance events have been detected in the optical and X-ray range. Searches for TDEs that emitted optical (meaning visible light) and X-ray emissions led to an increase in TDE discoveries in the 2000s. These methods can still detect some TDEs, but not all. The problem is that both types of radiation have short wavelengths that can be easily scattered and absorbed by dust, obscuring objects and phenomena within any dust-rich galaxies.

The supermassive black hole at the heart of the galaxy is what causes TDEs. The dust and gas in the black hole's accretion disk does not aid detection.

Most of the TDEs discovered by the research team had not been previously discovered in the optical range by Sage or newyz Infrared observatory mission. When they looked for these events in data from NASA's WISE (Wide-field Infrared Survey Explorer) and NEOWISE missions, along with data from other missions like SRG's eROSITA All-Sky Survey, the optical and X-ray bands didn't turn up much. It was only when the researchers looked at the mid-infrared WISE/NEOWISE data that they discovered hidden TDEs.

In a different light

Tidal disturbance events that can only be observed in the infrared have huge implications for the actual TDE counts found there, which have been difficult to estimate based on those detected only in the optical and X-ray bands. It also solves the mystery of why there are no TDEs in star-forming galaxies, which tend to be dust-rich.

The 18 newly discovered events include what is now the closest known TDE to Earth. It resides in a particularly dusty star-forming galaxy, which would have made it impossible to see without infrared observations.

Star formation has had an impact on where astronomers look for TDEs. Until now, galaxies that were no longer forming stars were considered ideal places to look for TDEs because they were low in dust. Since stars are born in massive clouds of dust and gas, it appeared as if there were no TDEs in star-forming galaxies when they were observed at shorter wavelengths. This explains why TDEs most likely occur in galaxies where star formation has stopped or almost stopped.

Dust might get in the way most of the time, but it has one feature that has helped researchers find some previously unknown TDEs. An enormous amount of heat is produced when stars are chopped up by supermassive black holes. Dust echoes They occur when dust particles are heated and emit radiation, generally infrared. These dust echoes can also help detect hidden TDEs.

The infrared detection of many TDEs will also likely answer the “missing energy” question. TDEs are theoretically expected to produce more energy than we observed, so where did the rest of that energy go? The researchers who discovered the new TDEs suggest that the impression of energy loss came from our inability to observe radiation blocked by dust and gas – there was no energy lost; He just went undetected.

It turns out that TDEs may not be as rare as we thought. They may also become less elusive before long. Astronomers will have a clearer idea of ​​the inhabitants after future surveys, such as the Legacy Survey of Space and Time (LSST) at Vera Rubin Observatory, look for them with infrared vision. Surveys this powerful may be able to find hundreds, even thousands, of TDEs each year.

“This work represents the cleanest sample of [infrared]-TDEs selected so far,” said the research team at A Stady Recently published in the Astrophysical Journal. “As such, it provides new insights into the population structure of TDEs in the local universe and allows us to explore the properties of a class of TDEs that were previously overlooked.”

The Astrophysical Journal, 2024. DOI: 10.3847/1538-4357/ad18bb