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‘Awakening’ of a black hole witnessed for the first time 

In late 2019, the previously unremarkable galaxy SDSS1335+0728 unexpectedly brightened, prompting astronomers to investigate the cause using data from various observatories, including the European Southern Observatory’s Very Large Telescope (ESO’s VLT). 

The study, recently published in the journal Astronomy & Astrophysics, suggests an unprecedented event: the sudden awakening of the massive black hole at the galaxy’s core.

Dramatic changes in a distant galaxy 

“Imagine you’ve been observing a distant galaxy for years, and it always seemed calm and inactive,” said Paula Sánchez Sáez, an astronomer at ESO.

“Suddenly, its core starts showing dramatic changes in brightness, unlike any typical events we’ve seen before.” 

While phenomena like supernova explosions or tidal disruption events can cause galaxies to suddenly light up, these typically last only a short period. 

However, SDSS1335+0728 has continued to grow brighter over four years. The galaxy, located 300 million light-years away in the constellation Virgo, displayed unusual brightness variations.

Unprecedented behavior 

To understand these changes, the team used archival data and new observations from several facilities, including the VLT’s X-shooter instrument. 

By comparing data from before and after December 2019, they found that SDSS1335+0728 now emits much more light at ultraviolet, optical, and infrared wavelengths. 

Additionally, the galaxy began emitting X-rays in February 2024. “This behavior is unprecedented,” Sánchez Sáez said.

Activation of a massive black hole

“The most tangible option to explain this phenomenon is that we are seeing how the [core] of the galaxy is beginning to show activity,” noted study co-author Lorena Hernández García, an astronomer at the Valparaiso University

If this is true, it would be the first time the activation of a massive black hole has been observed in real time.

Massive black holes, with masses over one hundred thousand times that of our Sun, exist at the centers of most galaxies. “These giant monsters usually are sleeping and not directly visible,” said co-author Claudio Ricci, an astronomer at the Diego Portales University

“In the case of SDSS1335+0728, we were able to observe the awakening of the massive black hole, which suddenly started to feast on gas available in its surroundings, becoming very bright.”

Witnessing the black hole’s awakening

This process had never been observed before. While previous studies have reported inactive galaxies becoming active after several years, this is the first time the actual awakening process has been witnessed. 

“This is something that could happen also to our own Sgr A*, the massive black hole located at the center of our galaxy,” although the likelihood is uncertain, Ricci said.

Studying a brightening galaxy

Follow-up observations are needed to rule out alternative explanations, such as a slow tidal disruption event or a new phenomenon. 

If it is a tidal disruption event, it would be the longest and faintest one ever observed. Regardless of the cause, this event provides valuable insights into how black holes grow and evolve. 

“We expect that instruments like [MUSE on the VLT or those on the upcoming Extremely Large Telescope (ELT)] will be key in understanding why the galaxy is brightening,” Sánchez Sáez concluded.

Awakening of black holes

The awakening of a black hole refers to the process when a dormant or inactive black hole becomes active again. 

This can occur when the black hole begins to accrete material from its surroundings, such as gas, dust, or even a star that ventures too close. 

As the black hole pulls in this material, the intense gravitational forces cause the matter to heat up and emit radiation, often in the form of X-rays. This radiation can be detected by astronomers, signaling that the black hole has “awakened.”

Active galactic nuclei

In the case of supermassive black holes located at the centers of galaxies, their reawakening can lead to the formation of active galactic nuclei (AGN). 

These AGN can emit vast amounts of energy, sometimes outshining the entire galaxy in which they reside. 

Particle jets

The process of awakening can also produce powerful jets of particles that shoot out from the black hole’s poles at nearly the speed of light.

These jets influence the surrounding interstellar medium and potentially trigger star formation in nearby regions.

Mysterious objects 

The awakening of a black hole is a dynamic event that provides valuable insights into the behavior of these mysterious objects and their impact on their cosmic environment.


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