Researchers have made progress in understanding the timing of jets and outflows from black holes that devour stars, addressing a long-standing question in astrophysics about when these cosmic phenomena occur.
Black holes are known to be inefficient consumers of stellar material. When a star ventures too close to a black hole, the gravitational forces stretch it in a process called spaghettification. According to scientists, only about half of the disrupted star actually gets consumed by the black hole, while the remaining material is ejected back into space through powerful jets and outflows that can affect the evolution of entire galaxies.
For years, the timing of these ejections had puzzled researchers, with observations showing the jets could occur anywhere from one to several years after the initial stellar disruption. Using radio telescopes to examine 20 instances of stars being torn apart by supermassive black holes, a team including researchers from Curtin University and the Institute for Advanced Study identified a pattern.
The study, published in Nature Astronomy, found that jets are released during two specific phases of a black hole’s feeding cycle. The first occurs when material is being consumed at extremely high rates. The second phase takes place hundreds to thousands of days after the star is destroyed, when the feeding rate drops to approximately 2 percent of the maximum rate at which a black hole can consume material. Notably, this same threshold had already been observed to trigger jets from stellar-mass black holes, which are significantly smaller objects.
The discovery suggests that black holes of different sizes follow similar patterns in their behavior, potentially enabling scientists to predict when jets will be released with greater precision and optimize the use of limited telescope observation time.
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