It’s a cosmic jungle for stars who dare to get too close to black holes. A team from the Massachusetts Institute of Technology has found 18 new examples of black holes tearing stars apart and feasting on their remains.
This result more than doubles the number of catastrophic, star-shattering Tidal Disruption Events (TDEs) seen in the local universe. The findings could help astronomers better estimate the number of TDEs occurring in the universe, bringing the rate closer to theoretical predictions.
TDEs occur when a star comes too close to a black hole, and the gravitational impact of the second object produces such large tidal forces on the star that the stellar body is stretched vertically while being crushed horizontally; This process is called “spaghettification”.
Material from the star forms a flattened disk around the black hole, and some of it collects in the heart of the black hole, while other star material is directed towards the poles by strong magnetic fields and ejected in jets at near-light speed.
Relating to: Black hole rips apart star in a cosmic feeding frenzy that has astronomers excited
Previously, astronomers believed that black holes rip apart and destroy stars as they blast high-energy jets in galaxies that have recently undergone intense periods of star birth called “starbursts.”
But this research implies that TDEs may occur in a wider range of galaxies and could help explain the extreme physics seen around such events.
“People were coming up with very exotic solutions to these puzzles, and now we’ve gotten to the point where we can solve them all,” team member Erin Kara, an assistant professor of physics at MIT, said in a statement. she said.
How did the hunt for the Tidal Disruption Event begin?
After discovering the closest TDE ever seen to Earth, the MIT team began searching for more star-eating black holes. It was seen as a flare from the galaxy NGC 7392, located approximately 137 million light-years from Earth.
They said this opens up a completely new way of detecting actively feeding black holes. It involves the use of infrared light and an algorithm that looks for patterns in the infrared data that indicate short or “transient” bursts of radiation. The completed technique 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 skies on Earth for short bursts of infrared light.
The team then cross-referenced the transients they found with a catalog of galaxies 600 million light-years from Earth and found that the infrared bursts could be traced to nearly 1,000 galaxies.
Zooming in on these galaxies, the researchers sought to discover whether the signals they detected came from TDEs or could be triggered by other violent events, such as a supernova explosion of a dying massive star. It could also be possible that they come from supermassive black holes at the hearts of galaxies, as they feed on falling dust and gas.
This ultimately led to the discovery of 18 legitimate TDE signals, which were the result of the gravitational impact of black holes producing tidal forces in stars, eventually leading to some bloody stellar deaths.
Surprisingly, the team found that TDEs occur in a number of galaxies across the sky, including those filled with thick dust clouds.
“If you look at the sky and see a group of galaxies, TDEs will occur representatively in all of them,” said Megan Masterson, lead author of the study and a graduate student at MIT’s Kavli Institute for Astrophysics and Space Research.
Concealing cosmic crimes
In the grand scheme of things, this research helps resolve some important questions about tidal disruption events.
Previously, astronomers had seen these stellar disintegration events occur in post-starburst galaxies with recently shut down star factories.
Such galaxies are quite rare, and scientists were confused as to why TDEs seemed limited to them. This research alleviates this confusion by finding bloody TDEs in various types of galaxies.
The reason why TDEs are apparently absent from other galaxies is that post-starburst galaxies lack thick gas and dust as they consume material while creating a wealth of new stars, while other galaxies still have abundant material. Gas and dust are adept at absorbing or blocking optical and X-ray light, but infrared passes through matter more easily.
Therefore, X-ray and optical emissions were sufficient to detect TDEs in dust-depleted galaxies, but infrared observations were key to finding star-shattering black holes in dusty galaxies.
“These don’t occur in just one type of galaxy, as people thought based solely on optical and X-ray studies,” Masterson added. “If you want to understand TDEs as a whole and use them to study supermassive black hole demographics, you need to look at the infrared band.”
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The findings from MIT researchers may also explain why TDEs do not emit as much energy as predicted in theory; The team proposes that the energy gap is a result of dust absorption as well as optical and X-ray emissions. Excessive ultraviolet radiation from TDEs.
By adding the 18 new TDEs they discovered to previously observed events of this nature, the MIT team estimates that galaxies experience a TDE roughly every 50,000 years; This is consistent with previous theoretical predictions.
“This gives us confidence that we don’t need all this exotic physics to explain what we’re seeing,” Kara said. “And we’re better understanding the mechanism behind how a star gets torn apart and swallowed by a black hole. We’re better understanding these systems.”
The team’s research was published Monday, January 29, in the Astrophysical Journal.