Image: Carl Knox – OzGrav, ARC Center of Excellence for Gravitational Wave Discovery, Swinburne University of Technology
On a clear night last February, a sophisticated astronomical camera perched on top of a California mountain opened its eyes to the sky after being turned off for several days due to problems. The timing turned out to be impeccable, as the camera, part of the Zwicky Transient Facility (ZTF), immediately spotted a dazzling eruption of light and energy in the distant universe that was unlike anything that had been seen before.
When ZTF astronomers logged into their Slack work the next day, they shared their joy at the brilliant discovery, as well as their bewilderment as to what could have triggered this flash that shone with the light of 1,000 trillion suns.
“My first message on Slack was, ‘Are we starting again with a bang?'” Igor Andreoni, a University of Maryland astronomer who works at ZTF, said in a call with Motherboard that also included his colleague. Michael Coughlin, an astronomer at the University of Minnesota. “Engineers worked tirelessly, including weekends, day and night, to get the camera operational again. And literally the first night it was operational, there was this detection.
Now, a team co-led by Andreoni and Coughlin reports that the mysterious flash was actually a powerful beam of energy – an immensely energetic jet of lightning-fast particles pointed at Earth, powered by a black hole devouring a star at many billions of light-years from our planet. This type of radiant cosmic phenomenon is called a tidal disturbance event (TDE).
The researchers concluded that this unusual explosion, named AT2022cmc, is “the most distant jet TDE discovered to date and the only one for which it has been possible to observe a complex optical light curve which passes from a red component fast to a blue plateau,” according to a study published Wednesday in Nature. An additional study published in natural astronomy at the same time presented a detailed model of the birth of this jet.
The surprise discovery “reaffirms the need to have truly open research on these growing astronomical datasets that we have,” Coughlin said in the call, noting that he and Andreoni were looking for a completely different type of astronomical event. in their ZTF. investigation. “It’s a great example in astronomy of a willingness to think outside the box for exciting things.”
“It’s a source that we didn’t really think about until it was discovered, because it’s so rare,” Andreoni noted. “It’s not quite the first thing you think of – an event that is detected once every 10 years, if that – and has never been discovered before in the optics [wavelengths]. It is unprecedented.
Although black holes are often invisible to light-based astronomy, they can ironically produce some of the brightest light shows in the universe if they feed on frenzy. Stars that wander too close to a black hole can be torn apart by the intense tidal forces in these extreme environments. By consuming its starry meal, a black hole can emit beams of “relativistic” particles, that is to say that they move at a speed close to the speed of light.
Jets that are aimed directly at Earth can be seen for great distances, although none have been as far away as AT2022cmc. Tracking of the event captured by the European Southern Observatory’s Very Large Telescope revealed that this particular jet was born when the universe was just a few billion years old. In addition to breaking the distance record for TDEs, the presence of so much visible light from AT2022cmc opens a new window into the mysterious mechanisms that power these jets.
“It already tells us a story about the environment surrounding this very massive black hole,” Andreoni said. “It also tells us about the time scale of the formation of the jet, relative to the disk of material around the black hole that is building up and continuing to pump energy that we can observe.”
“The other positive effect is that, of course, it is very difficult to estimate how often a [jet] childbirth happens,” Coughlin added. “People had made these estimates based on x-ray detections in the past, but the Zwicky transient facility has been running for about four years now, and we’ve seen one [in optical light]. This actually puts quite strong constraints on how often they can occur.
With these new revelations in hand, astronomers are better equipped to search for more of these mind-boggling events across the universe, which will help unlock their explosive secrets.
“We’re trying to contribute to a cohesive picture of all of these tidal events that we observe, with and without jets,” Andreoni said. “It’s an important question because once you find the connection, you can get a much better idea of what’s really going on when a star is disrupted by a black hole.”
“We just need to observe deeper and deeper,” he concluded. “I think we’ll get much closer to understanding why they’re so rare and the astrophysics of these events.”
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