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Astronomers are witnessing a never-before-seen spectacle in the cosmos: the awakening of a supermassive black hole at the center of a distant galaxy.
End of 2019 a team of astronomers have noted an otherwise unremarkable galaxy called SDSS1335+0728, located 300 million light-years away in the constellation Virgo. A sudden spike in the galaxy’s brightness was automatically detected by the Zwicky Transient Facility telescope at the Palomar Observatory in California.
With its extremely wide field of view, the camera scans the entire northern sky every two days, capturing data on celestial objects such as near-Earth asteroids, as well as distant, bright supernovae.
An interdisciplinary team of astronomers and engineers followed up on Zwicky’s observation by using information from space-based and ground-based telescopes to see how the galaxy’s brightness changed over time.
To their surprise, the researchers realized they were witnessing a unique moment when a cosmic monster awakened. Their research results have been accepted for publication in the journal Astronomy & Astrophysics.
“Imagine if you had been observing a distant galaxy for years, and it always seemed calm and inactive,” lead study author Paula Sánchez Sáez, an astronomer at the European Southern Observatory in Germany, said in a statement. “Suddenly, its (core) begins to show dramatic changes in brightness, unlike any typical event we’ve seen before.”
The team classified the galaxy as an active galactic core, or a bright, compact region powered by a supermassive black hole.
A number of celestial scenarios can cause a galaxy to suddenly brighten, such as supernova explosions or when stars get too close to black holes and are torn apart during a phenomenon called tidal disruption events.
But such events last only tens or hundreds of days — and SDSS1335+0728 continues to grow in brightness, more than four years after researchers first observed it increasing in brightness, like flipping a cosmic light switch.
And the brightness variations in the Milky Way look nothing like anything astronomers have seen before, which only further confused them.
To find answers, the team consulted archival data from NASA’s Wide-field Infrared Survey Explorer and Galaxy Evolution Explorer, the Two Micron All Sky Survey, the Sloan Digital Sky Survey and other observatories.
The researchers compared the data with follow-up observations from the European Southern Observatory’s Very Large Telescope, or VLT, in Chile, the Southern Astrophysical Research Telescope in Chile, the WM Keck Observatory in Hawaii, and NASA’s space-based Neil Gehrels Swift and Chandra. X-ray observatories.
Together, the datasets provided a broad portrait of the galaxy both before and after the December 2019 observation, showing that the galaxy has shifted in recent years, emitting much more ultraviolet, visible and infrared light, and also emitting X-rays starting in February – which is unprecedented. behavior, Sánchez Sáez said.
Given that the galaxy is 300 million light-years away, the events astronomers see occurred in the past – but light from these events is only now reaching Earth after traveling through space for millions of years. One light year is the distance light travels in one year, 5.88 trillion miles (9.46 trillion kilometers).
“The most tangible option to explain this phenomenon is to see how the (core) of the Milky Way (…) begins to show activity,” says co-author Lorena Hernández García, an astronomer at the Millennium Institute of Astrophysics and the University of Valparaíso, both in Chile, in a statement. “If so, this would be the first time we have seen the activation of a massive black hole in real time.”
Supermassive black holes are classified as having masses more than 100,000 times that of our Sun. They are found at the center of most galaxies, including the Milky Way.
“These giant monsters are usually asleep and not immediately visible,” said co-author Claudio Ricci, an associate professor at Diego Portales University in Chile, in a statement. “In the case of SDSS1335+0728, we were able to observe the awakening of the massive black hole, which suddenly started feeding on gas available in its environment and became very bright.”
Previous research has pointed to inactive galaxies that appeared to become active after a few years, which is usually caused by black hole activity, but the process of a black hole’s awakening has never been directly observed until now, Hernández García said.
The same scenario could happen with Sagittarius A*, the supermassive black hole at the center of the Milky Way, but astronomers aren’t sure how likely it is to happen, Ricci said.
Astronomers cannot rule out that their observation could be an unusually slow tidal disruption, or an unknown new celestial phenomenon.
“Regardless of the nature of the variations, this galaxy provides valuable information about how black holes grow and evolve,” says Sánchez Sáez. “We expect instruments like (MUSE on the VLT or those on the upcoming Extremely Large Telescope) will be critical to understanding (why the galaxy is brightening).”