Key Takeaways:

  • Black holes fire jets of stellar debris years after destroying a star, not just shortly after as previously thought.
  • This delayed ejection is a complete surprise to astronomers, forcing them to rethink how black holes devour stars.
  • The current understanding of how black holes form swirling disks of stellar material after a meal might be incorrect.
  • Scientists are unsure why this delayed ejection happens, ruling out explanations like a second event or the jet initially pointing away from Earth.
  • Astronomers need to refocus their observations to study black holes beyond the initial tidal disruption event.

A study has discovered that black holes can expel star remnants years after they have destroyed them, and no one knows why.

For a very long time, astronomers have been aware that, after destroying an unfortunate star, black holes can release a shining burst of energy known as a tidal disruption event (TDE). Nonetheless, it was anticipated that these jets would be visible within a few months of the initial TDE.

The new study, which has not yet been peer-reviewed, found that 10 out of 24 black holes observed started spewing matter between two to six years after the TDE.

According to Yvette Cendes, a lead author on the research from the Harvard and Smithsonian Center for Astrophysics, the finding, which has baffled astronomers, might indicate that we have misunderstood what happens when black holes devour a star. She made this statement in a thread on X, formerly Twitter.

“The real short answer to what’s causing this is ‘we don’t really know, but no one was predicting it,'” she stated.

No one saw this coming because no one was looking

We hadn’t witnessed this before for a good reason—no one had anticipated it happening. A TDE happens when a star gets too close to a supermassive black hole. The star is destroyed in a matter of hours.

Astronomers generally believe that at this point, roughly half of the star’s material will begin to swirl around the black hole, forming the “accretion disk.” The idea is that the remaining half of the matter will then be released in a single, energy-filled jet that can be observed from Earth.

The light burst is predicted by astronomers to occur a few weeks or months after the TDE. They shift their telescopes to another location if nothing is detected during that period. “Radio telescope time is precious! And why look YEARS after the explosive event for something you didn’t see right after said explosive event?” Cendes stated on X.

But this view started to change in 2022, when Cendes and her co-workers spotted a black hole that woke up again two years after swallowing a star.

The collaborators have been tracking 24 black holes with their instruments for years since that time. More than half of them awoke years after the initial star-swallowing incident, according to their findings.

Six years later, one black hole appeared to go back in time.

“If you know anything about physics, you know this time scale doesn’t make sense!” Cendes stated in a Reddit post. Cendes observed the black holes peaking, fading, and then reactivating in two more cases. “That’s completely new and unexpected,” Cendes told Live Science. “People were thinking that you’d have one outflow, and then it’s kind of done,” she explained.

Everything we know about accretion disks may be wrong

According to Cendes, the results may force us to reconsider how black holes eat stars. As of right now, we are aware of what is not occurring.

Cendes has ruled out that this could be due to a second TDE, or that the jet started straight after the TDE, but was directed away from Earth at first. She’s also ruled out some of the more fanciful explanations, such as the jet being delayed because the black hole was messing with time in the area.

But what that really leaves us with is a mystery. “Our best guess is ‘everything we assumed about accretion disc formation in TDEs is wrong”” Cendres stated on X. “What if the optical flash is NOT a disc forming, but streams of material interacting, and the disc doesn’t form until YEARS later? We don’t know the full details but def possible,” she said.

The recent discoveries imply that astronomers will need to reconsider how stars and black holes interact. “I’ve had great fun getting looks of incomprehension from theorists over recent months, believe you me!” Cendes stated on X.

The results were posted on the pre-print server arXiv.

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