The black hole lies in SDSS1335+0728, an otherwise unremarkable galaxy in Virgo. After decades of inactivity, it began flaring in optical wavelengths in 2019. This transformation led scientists to identify its central region as an active galactic nucleus, now dubbed 'Ansky.' The initial optical brightening sparked a wave of follow-up investigations, but early X-ray searches, including from NASA's Swift and eROSITA, found no emissions.
This changed in February 2024 when astronomers led by Lorena Hernandez-Garcia at Valparaiso University detected repeating X-ray flares from Ansky. These quasi-periodic eruptions (QPEs), which have only been identified a handful of times since their first discovery in 2019, are still not fully understood. Ansky's case is unique, marking the first time QPEs have been linked to a newly awakened black hole.
"This rare event provides an opportunity for astronomers to observe a black hole's behaviour in real time, using X-ray space telescopes XMM-Newton and NASA's NICER, Chandra and Swift. This phenomenon is known as a quasiperiodic eruption, or QPE. QPEs are short-lived flaring events. And this is the first time we have observed such an event in a black hole that seems to be waking up," explains Lorena.
ESA's XMM-Newton proved particularly critical, offering the sensitivity needed to capture the faint X-ray glow between the violent bursts. This capability enabled researchers to calculate the energy Ansky unleashes during each flare.
Current theories suggest QPEs may result from smaller objects, like stars or compact remnants, disturbing the matter swirling in an accretion disc around a black hole. Yet in Ansky's case, there's no evidence of a recent stellar disruption. Researchers suspect the flares might instead originate from energetic shocks caused by a smaller object repeatedly plunging through a gas-rich disc formed from surrounding galactic material.
"The bursts of X-rays from Ansky are ten times longer and ten times more luminous than what we see from a typical QPE," says Joheen Chakraborty, a PhD student at MIT. "Each of these eruptions is releasing a hundred times more energy than we have seen elsewhere. Ansky's eruptions also show the longest cadence ever observed, of about 4.5 days. This pushes our models to their limits and challenges our existing ideas about how these X-ray flashes are being generated."
By observing Ansky's eruptions as they unfold, astronomers hope to refine theories about black hole activity and the mechanisms behind QPEs. The insights may also offer complementary data to future gravitational wave detections.
"For QPEs, we're still at the point where we have more models than data, and we need more observations to understand what's happening," says ESA Research Fellow and X-ray astronomer, Erwan Quintin.
"We thought that QPEs were the result of small celestial objects being captured by much larger ones and spiralling down towards them. Ansky's eruptions seem to be telling us a different story. These repetitive bursts are also likely associated with gravitational waves that ESA's future mission LISA might be able to catch."
"It's crucial to have these X-ray observations that will complement the gravitational wave data and help us solve the puzzling behaviour of massive black holes."
Research Report:Discovery of extreme Quasi-Periodic Eruptions in a newly accreting massive black hole
Related Links
XMM-Newton at ESA
Understanding Time and Space
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