Star-shattering black holes are everywhere in the sky, if you know how to look for them. That’s the message from a new study published January 29 by scientists at the Massachusetts Institute of Technology. Astrophysical Journal. The study’s authors report the discovery of 18 new tidal disruption events (TDEs), extreme events in which a nearby star is sucked into a black hole and torn apart. During the feast, the black hole emits a massive burst of energy across the electromagnetic spectrum.

Astronomers discovered earlier tidal disruptions by looking for characteristic flares in the optical and X-ray bands. To date, these studies have identified nearly a dozen star-shattering events in the nearby universe. The MIT team’s new TDEs are more than twice as numerous as the known catalog of TDEs in the universe.

Researchers noticed these previously “hidden” events by looking through an unusual range: infrared. In addition to emitting optical and X-ray bursts, TDEs can produce infrared radiation, especially in “dusty” galaxies where the central black hole is covered in galactic debris. Dust in these galaxies typically absorbs and obscures optical and X-ray light, as well as evidence of TDEs in these gaps. The dust also heats up in the process, producing infrared radiation that can be detected. The team found that infrared radiation could therefore serve as a sign of tidal events.

“Most of these sources are not visible in optical ranges,” says lead author Megan Masterson, a graduate student at MIT’s Kavli Institute for Astrophysics and Space Research. “If you want to understand TDEs as a whole and use them to study the demographics of a supermassive black hole, you need to look at the infrared.”

Other MIT authors include Kishalaya De, Christos Panagiotis, Anna-Christina Eilers, Daniel Frostig, and Robert Simko, as well as MIT Associate Professor of Physics Erin Kara and collaborators from many institutions, including the Max Planck Institute for Extraterrestrial Physics in Germany. taking.

temperature increase

The team recently discovered the closest TDE using infrared observations. The discovery opened a new infrared route that astronomers can use to search for actively feeding black holes. This initial discovery led the group to search for more TDE. For their new study, the researchers looked at archival observations made by NEOWISE, an upgraded version of NASA’s Wide Field Infrared Survey Explorer. This satellite telescope was launched in 2009 and, after a brief hiatus, has resumed scanning the entire sky for infrared “transients,” or brief flares.

The team looked at archival observations of the mission using an algorithm developed by co-author Kishalai De. This algorithm highlights patterns in the infrared that are likely signs of a short-duration infrared burst. The team then compared the tagged transients to a catalog of all known nearby galaxies within 200 megaparsecs, or 600 million light-years, away. They found that infrared transmissions could be traced to approximately 1,000 galaxies.

They then zoomed in on each galaxy’s infrared flare signal to determine whether the signal came from a source other than the TDE, such as an active galactic nucleus or a supernova. Ignoring these possibilities, the team then analyzed the remaining signals, looking for infrared patterns characteristic of TDEs; That is, a sharp explosion followed by a gradual collapse reflects the process by which a black hole tears apart a star and suddenly heats the environment. the powder rises to about 1000 kelvin and then cools slowly.

This analysis found 18 “pure” tidal interruption signals. The researchers looked at the galaxies where each TDE was detected and found that they occurred in a range of systems, including dust galaxies in the sky.

“If you look at the sky and see a group of galaxies, TDEs will all occur,” says Masteron. “These do not occur in just one type of galaxy, as people thought based solely on optical and X-ray studies.”

“We can now peer through the dust and complete a count of nearby TDEs,” says Edo Berger, a professor of astronomy at Harvard University who was not involved in the study. “A particularly exciting aspect of this work is the potential for further research with large infrared surveys, and I am excited to see what discoveries these will yield.”

Expanding understanding of tidal disruptions

The team’s findings help answer some important questions in the study of tidal disruption events. For example, before this study, astronomers had mostly seen TDEs in a single type of galaxy; the “post-burst” system, which used to be a star-forming factory but has since settled. Such galaxies are rare, and astronomers have been puzzled as to why TDEs only appear in these rarer systems. These systems are also relatively dust-free, making it easier to detect optical or X-ray emission of TDEs.

Astronomers can now see TDEs in many other galaxies by looking in the infrared. The team’s new results show that black holes can absorb stars in many galaxies, not just in post-collapse systems.

The results also solve the “missing energy” problem. Physicists theoretically predicted that TDEs should emit more energy than is actually observed. But now an MIT team says dust may explain this discrepancy. They found that if a TDE occurs in a dusty galaxy, the dust itself can absorb not only optical and X-ray radiation but also excess ultraviolet radiation in an amount equivalent to the estimated “missing energy.”

The 18 new detections also help astronomers estimate the occurrence rate of TDEs in a given galaxy. Calculating new TDEs from previous detections, they estimate that the galaxy experiences a tidal disruption event every 50,000 years. This speed is close to physicists’ theoretical predictions. With additional infrared observations, the team hopes to determine the speed of TDEs and the properties of the black holes feeding them.

DE with infrared observations. The discovery opened a new infrared route that astronomers can use to search for actively feeding black holes.

This initial discovery led the group to search for more TDE. For their new study, the researchers looked at archival observations made by NEOWISE, an upgraded version of NASA’s Wide Field Infrared Survey Explorer. This satellite telescope was launched in 2009 and, after a brief hiatus, has resumed scanning the entire sky for infrared “transients,” or brief flares.