Astronomers witness giant galaxy ‘turn on lights’ and awaken from 20-year slumber in real time

A Black Hole Lights Up in Real Time (Image: Canva)

For years, the night sky looked still and silent. Then one day, something blinked—an old galaxy suddenly came alive. This story begins with a spark inside SDSS1335+0728, a quiet galaxy that startled astronomers across the globe. It wasn't just a flash. It was a wake-up call from 300 million light-years away.

A Bright Surprise from the Virgo Constellation

The alert came in December 2019. The Zwicky Transient Facility had spotted an unusual brightening in the Virgo constellation. Its camera captures hundreds of images each night. When it sees something new, it notifies astronomers within seconds.

The light was coming from SDSS1335+0728, a modest spiral galaxy. This galaxy had been quiet for more than two decades. Suddenly, its core lit up with unusual intensity. At the centre lies a black hole, one million times the Sun’s mass. Astronomers believed they were seeing either a star being torn apart or the black hole feeding for the first time.

Four years later, the light still hasn’t faded. This makes it different from regular supernovae or star-eating events. Its brightness continues, yet it is still dimmer than the brilliant quasars. SDSS1335+0728 now floats in a strange place between categories.

ESO astronomer Paula Sánchez Sáez called it an unexpected change. “It looked calm for years,” she said. “Now, the centre is behaving unlike anything we’ve seen before.” Her team launched a worldwide campaign to understand the flare.

Looking Deeper Into the Cosmic Flare

Astronomers usually sort these events into a few groups. Some involve stars falling into black holes. Others mark the start of new activity at a galaxy’s core. Some galaxies shift between bright and dim. But SDSS1335+0728 doesn't quite match any known pattern.

Classifying these flares depends on timing and colour. But more than anything, it depends on the light’s spectrum. The Zwicky Facility already collects millions of images each night. Soon, the Vera Rubin Observatory will gather even more. Computers will help sort them, but rare events still need human eyes.

To learn more, scientists turned to big telescopes. The Very Large Telescope in Chile was among those watching. It detected rising emissions in ultraviolet, optical and infrared light. Then in February 2024, X-rays appeared for the first time.

The galaxy now shows broad light lines near its centre. These lines mean gas is speeding near the black hole. “This behaviour is new to us,” said Sánchez Sáez, who also works with the Millennium Institute of Astrophysics.

Co-author Lorena Hernández García added, “We might be watching a black hole turn active.” If confirmed, this could be the first time such a process is seen live.

What This Means for the Universe

Supermassive black holes usually grew billions of years ago. Most seem quiet now. But SDSS1335+0728 may be one of the few waking up today.

Such awakenings affect more than just light. They shape how stars form and how galaxies change. “These giants usually stay hidden,” said co-author Claudio Ricci. “But now, one has started feeding again.” He added, “Something like this could happen in our own galaxy too.”

Researchers are now gathering more data. They hope to learn whether this event is a slow star death, a new accretion disc, or something new entirely. Each idea could reshape how we understand black holes today.

“This galaxy helps us see how black holes evolve,” said Sánchez Sáez. She added that newer instruments will help answer the many questions still left.

For now, SDSS1335+0728 reminds us that even quiet skies hold secrets. As new telescopes scan the stars, more hidden giants may rise again.