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Astronomers are witnessing a sight never before seen in the universe: the awakening of a supermassive black hole at the center of a distant galaxy.
In late 2019, a team of astronomers noticed an otherwise unremarkable galaxy called SDSS1335+0728, 300 million light-years away in the constellation Virgo. A sudden increase in the galaxy’s brightness was automatically detected by the telescope of the Zwicky Transient Facility at Palomar Observatory in California.
With an extremely wide-field view, the camera scans the entire northern sky every two days, capturing data about celestial objects such as near-Earth asteroids and distant, bright supernovae.
An interdisciplinary team of astronomers and engineers followed up Zwicky’s observation using information from space- and ground-based telescopes to see how the galaxy’s brightness changed over time.
To their surprise, researchers realized that they had witnessed a unique moment when a cosmic monster woke up. The study findings have been accepted for publication in the journal Astronomy and Astrophysics.
“Imagine that you have been observing a distant galaxy for years and it always seems calm and motionless,” lead study author Paula Sánchez Sáez, an astronomer at the European Southern Observatory in Germany, said in a statement. “Suddenly (the nucleus) begins to show dramatic changes in brightness, unlike the typical events we’ve seen before.”
The team classified the galaxy as having an active galactic core or a bright, compact region supported by a supermassive black hole.
A number of celestial scenarios can cause a galaxy to suddenly brighten, such as supernova explosions or stars coming too close to black holes and breaking apart during an event called tidal disruption events.
But such events last only dozens or hundreds of days, and SDSS1335+0728’s brightness continues to increase more than four years after researchers first observed its brightness increasing, like the flicking of a cosmic light switch.
And the brightness variations in the galaxy are unlike anything astronomers have seen before; This only serves to surprise them even more.
An unprecedented cosmic event
To find answers, the team consulted archival data from NASA’s Wide Field Infrared Survey Explorer and Galaxy Evolution Rover, the Two Micron All-Sky Survey, the Sloan Digital Sky Survey, and other observatories.
The researchers compared the data with follow-up observations taken by the European Southern Observatory’s Very Large Telescope (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 provide a broad portrait of the galaxy before and after the December 2019 observation, revealing that the galaxy began emitting much more ultraviolet, visible and infrared light in recent years, and began emitting X-rays starting in February. behavior, Sánchez Sáez said.
Given that the galaxy is 300 million light-years away, the events astronomers see occurred in the past; but the light from these events is now reaching Earth after traveling through space for millions of years. A light year is the distance light travels in one year; that is, 5.88 trillion miles (9.46 trillion kilometers).
“The most concrete option to explain this phenomenon is that we see how the (core) of the galaxy begins to show activity (…)” said astronomer Lorena Hernández García from the Millennium Institute for Astrophysics and the University of California. Valparaíso, both in Chile, said in a statement. “If so, this is the first time we’ve seen the activation of a massive black hole in real time.”
sleeping sky giants
Supermassive black holes are classified as having a mass greater than 100,000 times the mass of our sun. They can be found at the centers of most galaxies, including the Milky Way.
“These giant beasts are usually sleeping and cannot be seen directly,” study co-author Claudio Ricci, an associate professor at Diego Portales University in Chile, said in a statement. “In the case of SDSS1335+0728, we were able to observe the awakening of the massive black hole, which suddenly began to feed on the surrounding gas and became very bright.”
Previous research has pointed to inactive galaxies becoming active after a few years, often triggered by black hole activity, but the process of a black hole waking up has not been directly observed until now, Hernández García said.
Ricci said the same scenario could apply to Sagittarius A*, the supermassive black hole at the center of the Milky Way, but astronomers aren’t sure how likely that is.
Astronomers cannot rule out that their observations could be an unusually slow tidal disruption event or an unknown new celestial event.
“Whatever the nature of the variations, (this galaxy) provides valuable information about how black holes grow and evolve,” Sánchez Sáez said. “We expect instruments like (MUSE at the VLT or those at the upcoming Extremely Large Telescope) to be key to understanding (why the galaxy shines).”
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