Astronomers stunned as sleeping Black Hole roars back to life after 20 years
The advancement in technology every day is giving ways to observe the universe and witness cosmic events that happen over days, weeks, or even years, events that were previously considered too rare or distant to catch in action.
One such surprise came up during late 2019, when a quiet galaxy, SDSS1335+0728, suddenly lit up in the Virgo constellation, located about 300 million light-years from Earth. What followed has kept astronomers captivated for over four years, and the show isn't over yet.
What is happening in the cosmos?
In December 2019, astronomers spotted that the quiet core of SDSS1335+0728, a spiral galaxy in the Virgo constellation, suddenly brightened by several orders of magnitude. Located about 300 million light-years away, this galaxy had shown no signs of activity for over two decades. Now, its center home to a supermassive black hole roughly a million times the mass of the Sun was blazing to life.
Astronomers immediately suspected either a tidal disruption event, where a star gets torn apart by a black hole's gravity, or the first signs of an active galactic nucleus (AGN) waking up.
But what made this case unusual was the duration. More than four years later, the flare hasn't faded, far exceeding the timescale of typical star-eating episodes or supernovae.
'This behavior is unprecedented,' said Paula Sánchez Sáez, lead author of the study published in Astronomy & Astrophysics and an astronomer at the European Southern Observatory (ESO) in Germany.
Instruments including ESO's X-shooter spectrograph detected a consistent rise in ultraviolet, optical, and infrared light—and in February 2024, X-ray emissions began for the first time.
The spectrum now reveals broad emission lines, meaning gas moving near light-speed close to the black hole.
'Suddenly, its core starts showing dramatic changes in brightness, unlike any typical event we've seen before,' Sánchez Sáez added. Co-author Lorena Hernández García of the Millennium Institute of Astrophysics (MAS) in Chile noted, 'If so, this would be the first time that we see the activation of a massive black hole in real time.'
There is a new nuclear activity in space
That makes SDSS1335+0728 a cosmic rarity. It doesn't shine as brightly as classic quasars, but its persistence rules out most common flare types. It sits in a gray area, possibly marking a new category of nuclear activity.
'This could also happen to our own Sgr A*, the massive black hole at the center of our galaxy,' said Claudio Ricci of Diego Portales University in Chile. 'But it's unclear how likely that is.'
Researchers are now trying to determine whether this is a very slow tidal disruption, the birth of a new accretion disk, or something never seen before. Each scenario could reshape models of how supermassive black holes evolve today.
'We expect that instruments such as MUSE on the VLT and those on the upcoming Extremely Large Telescope will be key to understanding why the galaxy is brightening,' said Sánchez Sáez.
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