18 black holes captured devouring nearby stars in dramatic tidal disruption events

MIT scientists have discovered a fascinating aspect of our universe. Black holes that shred stars during tidal disruption events are more common than previously thought.

The research team has discovered 18 new tidal disruption events (TDEs), where stars are torn apart by the immense gravitational pull of black holes.

Hunting tidal disruption events (TDEs)

Tidal disruption events occur when a star gets too close to a black hole, resulting in its gravitational disintegration.

As the star is drawn in and torn apart, the black hole releases a massive energy burst across the electromagnetic spectrum.

Traditionally, astronomers have identified TDEs by observing specific bursts in optical and X-ray bands.

However, these methods have only uncovered a handful of such events in the nearby universe, limiting our understanding.

The infrared revelation

The MIT researchers, led by graduate student Megan Masterson, took a novel approach by focusing on the infrared spectrum.

Their findings indicate that infrared emissions can be a reliable indicator of TDEs, especially in ‘dusty’ galaxies.

In these environments, dense galactic debris often obscures optical and X-ray signals, masking the presence of TDEs. Yet, as the dust absorbs energy, it heats up, producing detectable infrared radiation.

Masterson emphasizes the importance of this method, stating, “The majority of these sources don’t show up in optical bands. If you want to understand TDEs as a whole and use them to probe supermassive black hole demographics, you need to look in the infrared band.”

Doubling the known catalog of TDEs

This approach not only doubled the catalog of known TDEs but also unveiled events in varied types of galaxies scattered across the sky.

The team’s research extends beyond just identifying these events. They recently discovered the closest TDE to date, utilizing infrared observations.

This finding has paved a new path for astronomers to search for actively feeding black holes, marking a significant advancement in the field.

For their study, the MIT team, which includes Kishalay De, Christos Panagiotou, Anna-Christina Eilers, Danielle Frostig, and Robert Simcoe, along with assistant professor of physics Erin Kara and collaborators from various institutions, combed through archival data from NEOWISE.

This satellite, part of NASA’s Wide-field Infrared Survey Explorer, scans the sky for infrared transients or brief bursts.

The infrared revelation

The team embarked on their quest by sifting through archived observations from the mission, utilizing an algorithm crafted by co-author Kishalay De.

This specialized algorithm identifies patterns in infrared emissions that hint at transient bursts of radiation, potentially indicating TDEs.

The researchers then meticulously cross-referenced these signals with a comprehensive catalog of nearby galaxies, spanning 200 megaparsecs or 600 million light years.

The key was in discerning the source of each galaxy’s infrared burst. By excluding other possible sources like active galactic nuclei or supernovae, the team honed in on unique infrared patterns indicative of TDEs.

These patterns typically showcase a sharp spike in temperature to about 1,000 kelvins, followed by a gradual decline, a signature of a black hole consuming a star and heating the surrounding dust.

Revealing the hidden wonders of TDEs

This thorough analysis yielded 18 distinct signals of tidal disruption events. Intriguingly, these TDEs were found in a diverse array of galactic systems, dispelling previous notions that they predominantly occur in specific galaxy types.

“If you looked up in the sky and saw a bunch of galaxies, the TDEs would occur representatively in all of them,” explains lead researcher Megan Masterson.

“It’s not that they’re only occurring in one type of galaxy, as people thought based on optical and X-ray searches.”

Edo Berger, a professor of astronomy at Harvard University, who was not involved in the study, commends this advancement, noting, “It is now possible to peer through the dust and complete the census of nearby TDEs.”

“A particularly exciting aspect of this work is the potential of follow-up studies with large infrared surveys, and I’m excited to see what discoveries they will yield,” Berger added.

Resolving long-standing astronomical enigmas

These discoveries address several long-standing enigmas in astrophysics. Previously, TDEs were mostly observed in ‘post-starburst’ galaxies, which are rare and relatively dust-free, making TDEs easier to detect via optical or X-ray emissions.

The MIT team’s approach, focusing on the infrared spectrum, reveals that TDEs are not exclusive to these galaxy types but can occur across a broader range.

Moreover, the study offers an explanation for the “missing energy” problem in TDE research. Theoretical models predict a higher energy output from TDEs than what was observed.

The team’s findings suggest that dust in galaxies may absorb not only visible and X-ray light but also extreme ultraviolet radiation, accounting for this missing energy.

Estimating the frequency of tidal disruption events

These 18 new detections also aid in refining estimates of how frequently TDEs occur. Incorporating these findings, researchers now estimate that a typical galaxy experiences a tidal disruption event once every 50,000 years, aligning closer to theoretical predictions.

“People were coming up with very odd solutions to these puzzles, and now we’ve come to the point where we can resolve all of them,” MIT assistant professor of physics Erin Kara says.

“This gives us confidence that we don’t need all this strange physics to explain what we’re seeing. And we have a better handle on the mechanics behind how a star gets ripped apart and gobbled up by a black hole. We’re understanding these systems better,” Kara concluded.

Beyond the event horizon

In summary, the MIT team’s pioneering research has revolutionized our understanding of tidal disruption events, unveiling the prevalence of star-shredding black holes across various types of galaxies.

By shifting the focus to infrared observations, they have more than doubled the known catalog of TDEs and resolved long-standing puzzles in astrophysics, such as the “missing energy” problem.

This breakthrough paves the way for future explorations and a more comprehensive understanding of the dynamic interactions between stars and supermassive black holes.

Their findings are a testament to the ever-evolving nature of astronomical research and our quest to unravel the mysteries of the universe.

The full study was published in The Astrophysical Journal.

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