MIT astronomers have made an exciting discovery, detecting a new tidal disruption event (TDE) in infrared light. TDEs occur when a passing star is ripped apart by a supermassive black hole at the center of a galaxy, resulting in a sudden burst of radiation. While TDEs have been observed in distant galaxies before, this is one of the first times scientists have directly identified a TDE in the infrared band. The outburst, named WTP14adbjsh, was found in a galaxy called NGC 7392, which is the closest TDE ever observed at a distance of 137 million light-years from Earth. The scientists suspect that traditional X-ray and optical surveys may have missed the nearby TDE due to dust obscuring the radiation and emitting heat in the form of infrared energy. The team’s findings suggest that there could be a large population of previously hidden TDEs in star-forming galaxies that conventional methods have missed, and searching in the infrared band could reveal many more of these events. The study’s results were published in Astrophysical Journal Letters, with a team of authors from MIT, Caltech, and the National Science Foundation’s National Optical-Infrared Astronomy Research Laboratory.
A flash of possibility
The discovery of the new tidal disruption event (TDE) in a nearby galaxy was not the primary focus of Panagiotou and his colleagues’ research. They were searching for general transient sources in archival data taken by NASA’s NEOWISE mission at infrared wavelengths, using a search tool developed by De.
They came across a bright flash that appeared in the sky towards the end of 2014, and traced it to a galaxy 42 megarparsecs away from Earth. To determine the cause of the flash, the team considered various astrophysical processes that could have produced a similar event, such as supernovae.
However, they were able to eliminate all possibilities except for a TDE, based on the brightness and timing of the flash. The scientists were able to observe the temporal evolution of the TDE, which followed the expected pattern for such an event.
The team believes that conventional surveys may have missed TDEs in star-forming galaxies because of the dust produced by these galaxies, which can obscure the X-ray and UV light emitted by these events. They suggest that searching for TDEs in the infrared band may reveal more hidden events in active, star-forming galaxies, providing a more complete picture of black holes and their host galaxies.
Red or green
After discovering the TDE, the team decided to investigate the galaxy where it occurred. They gathered data from various telescopes, including ground- and space-based instruments, to estimate the mass of the galaxy’s supermassive black hole. Their analysis revealed that the black hole was approximately 30 million times more massive than the sun, which is significantly larger than the black hole at the center of our own galaxy.
Additionally, the team discovered that the galaxy is actively producing new stars, classifying it as a star-forming “blue” galaxy. Interestingly, most TDEs detected to date have been traced to “green” galaxies, which lie between blue and red galaxies in terms of star formation. This finding had previously puzzled scientists, as blue galaxies were expected to exhibit more TDEs due to their higher number of stars.
However, the team also found that star-forming galaxies produce a lot of dust, which can obscure X-ray and UV radiation from TDEs. This could explain why TDEs have been difficult to detect in star-forming galaxies using conventional optical methods. The team’s observations provide a new perspective on the relationship between TDEs and galaxy type, suggesting that dust may play a significant role in detecting these rare events.
Suvi Gezari, who is an associate astronomer and chair of the Science Staff at the Space Telescope Science Institute in Maryland and was not part of the research team, highlights the significance of the study’s findings. She explains that the failure of optical and X-ray surveys to detect this bright TDE close to us is revealing, as it shows that these surveys only offer a limited view of the complete TDE population. Gezari further notes that using infrared surveys to capture the dust echo of TDEs that are obscured can help uncover a population of TDEs in dusty, star-forming galaxies that have previously gone unnoticed.