by It’s a cosmic jungle for stars that pass too close to black holes. A team from the Massachusetts Institute of Technology has discovered 18 new examples of black holes ripping apart stars and feasting on their remnants.
This result more than doubles the number of stellar Terrible Tidal Disruption Events (TDEs) seen in the local universe. The results could help astronomers better estimate the number of TDEs occurring across the universe, bringing the rate closer to theoretical predictions.
TDEs occur when a star passes too close to a black hole, and the gravitational influence of the latter object generates tidal forces in the star so great that the stellar body is stretched vertically and squeezed horizontally, a process known as “spaghetization.”
The material from the star forms a flattened disk around the black hole, some of it accreting to the black hole’s core, while other stellar material is sent to the poles by powerful magnetic fields and blasted out as light-speed jets.
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Previously, astronomers had believed that black holes rip apart and eat stars by exploding highly energetic jets in galaxies that have recently undergone periods of intense star birth known as “starbursts”.
However, this research suggests that TDEs can occur across a wider range of galaxies and may help explain the actual physics seen around such events.
“People were coming up with very strange solutions to these puzzles, and now we’ve come to the point where we can solve them all,” said Erin Kara, a team member and assistant professor of physics at MIT , in a statement.
How the Tidal Break Event began
The MIT team began searching for more black holes that have consumed a star after finding the closest TDE to Earth ever seen. It was seen in the form of a flare from the galaxy NGC 7392, located about 137 million light years from Earth.
This opened up a whole new way of seeing actively feeding black holes, they said. It uses infrared light and an algorithm that looks for patterns in infrared data that indicate brief or “transient” bursts of radiation. The technique that was completed was based on historical data collected by NASA’s Wide Field Infrared Survey Explorer (NEOWISE). Since its launch in 2009, NEOWISE has been searching the sky above Earth for brief bursts of infrared light.
The team then cross-referenced the transients they found with a catalog of galaxies within 600 million light-years from Earth, revealing that the infrared bursts could be traced back to about 1,000 galaxies.
As they zoomed in on these galaxies, the researchers tried to determine whether the signals they had detected came from TDEs or whether they could have been triggered by other violent events, such as the supernova explosion of a dying massive star. It would also be possible for them to come from supermassive black holes in the hearts of galaxies feeding on dust and falling gas.
Ultimately, 18 legitimate TDE signals were found that were the result of the gravitational influence of black holes generating the tidal forces of stars that eventually led to mass extinctions.
Surprisingly, the team found that TDEs appear to occur across a range of galaxies across the entire sky, including ones filled with thick dust clouds.
“If you looked up in the sky and saw many galaxies, the TDEs would occur representatively in all of them,” said lead research author and MIT Kavli Institute for Astrophysics and Space Research graduate student Megan Masterson.
Hidden cosmic crimes
In the grand scheme of things, this research helps solve some big questions about tidal interference.
Previously, astronomers had observed these star-shredding events mainly occurring in post-stellar galaxies with recently closed stellar factories.
Such galaxies are relatively rare, and scientists were puzzled as to why the TDEs seemed to be limited to them. This research alleviates that confusion by finding gory TDEs in a range of galaxy types.
The reason TDEs seem to have been absent from other galaxies is that, although post-stellar galaxies are devoid of thick gas and dust because they have consumed the materials while creating a wealth of new stars, the material is still abundant. by other galaxies. Gas and dust can absorb or block optical and X-ray light, but infrared slips through the material more easily.
Thus, X-ray and optical emissions were fine for detecting TDEs in dust-depleted galaxies, but infrared observations were critical for finding star-striped black holes in dusty galaxies.
“It’s not that they’re only happening in one type of galaxy, as people thought based on optical and X-ray searches alone,” Masterson said. “If you want to fully understand TDEs and use them to investigate the demographics of supermassive black holes, you need to look in the infrared band.”
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The findings from the MIT researchers may also explain why TDEs do not appear to absorb as much energy as predicted by theory, with the team suggesting that the energy deficit is a result of dust absorption of optical emissions and X-ray, as well as. extreme ultraviolet radiation from TDEs.
Adding the 18 new TDEs they discovered to previously observed events of this type, the MIT team estimates that galaxies experience TDEs about once every 50,000 years, which is in line with previous theoretical predictions.
“This gives us confidence that we don’t need all this alien physics to explain what we’re seeing,” Kara said. “And we have a better handle on the mechanics behind how a star is ripped apart and overtaken by a black hole. We’re understanding these systems better.”
The team’s research was published on Monday (January 29) in the Astrophysical Journal.
