At the heart of every large galaxy lurks a supermassive black hole. Sometimes a star wanders too close, and the black hole tears it apart like a child pulling apart a lump of clay. This releases a tremendous amount of light, and astronomers see a brilliant flare. But in some galaxies, the black hole is wrapped in a dense cloud of dust that acts like a curtain: it hides the flare from our telescopes.
The scientists used data from the WISE space telescope, which scanned the sky in infrared for ten years. They looked for galaxies where the dust's color suddenly changed, a sign that the dust had been heated by a flare. That's how they found two galaxies where stars appear to have been torn apart. One flare was visible in ordinary light as well, but the other was only seen in infrared because dust completely hid it. It's like a firecracker going off behind a thick curtain: we don't see the explosion itself, but we see the curtain glow as it heats up.
This discovery shows that infrared telescopes can spot such hidden flares. Now the scientists want to check all the galaxies in the WISE catalog to find out how often stars are destroyed in the dusty centers of galaxies. That will help us understand how black holes grow and how galaxies evolve.
The flare in J2150−1132 was so hidden by dust that it was completely invisible in the optical, even though it brightened by two magnitudes in the infrared. It is like a powerful explosion happening behind a thick curtain: we only see the curtain heating up, not the explosion itself.
The micro-TDE scenario, where a star is torn apart by a small black hole hiding in the accretion disk of a giant black hole, echoes science fiction ideas about secondary black holes populating the vicinity of supermassive objects, such as in Terry Goodkind's novel 'Pillars of Creation' or in some episodes of 'Star Trek' where characters encounter unexpected sources of gravity in dense stellar clusters.