ESA’s XMM-Newton discovers strange X-ray emissions

ESA’s XMM-Newton space telescope has made a discovery that is revolutionizing our understanding of supermassive black holes. An international research team, led by the Massachusetts Institute of Technology (MIT) and with the participation of scientists from the National Institute for Astrophysics (INAF), has detected quasi-periodic oscillations in the X-ray signals coming from the “corona” of particles surrounding a hole supermassive black located at the heart of a nearby galaxy.

These oscillations, presented at the 245th meeting of the American Astronomical Society and in an upcoming paper on Naturerepresent a completely unexpected phenomenon. Current theories of black hole accretion fail to fully explain these rapid variations in X-ray signals.

XMM-Newton observations revealed that the celestial object in question, the supermassive black hole 1ES 1927+654 exhibits anomalous behavior. After an eruption that temporarily destroyed the X-ray corona, Quasi-periodic oscillations, i.e. regular variations in X-ray intensity, have been observed.

Black holes are celestial objects with a gravitational force that traps anything that approaches beyond a certain point, called the event horizon. During the final fall into the black hole, matter forms an accretion disk that heats up, emitting mostly ultraviolet (UV) light. This UV light interacts with a cloud of electrically charged gas (plasma) around the black hole, called the corona. These interactions transform UV light into X-rays, observable by XMM-Newton.

XMM-Newton has been observing the supermassive black hole 1ES 1927+654 since 2011. Initially, X-ray emissions were normal. But in 2018, something changed. The black hole underwent an eruption that apparently destroyed the surrounding X-ray corona. Gradually, corona returned, and by the beginning of 2021 everything seemed to be back to normal.

However, in July 2022, XMM-Newton observed that the X-ray emission varied by about 10% on time scales between 400 and 1000 seconds. These quasi-periodic oscillations (QPOs) are difficult to detect in supermassive black holes.

The oscillations could indicate the presence of a massive object, such as a star, within the accretion disk, orbiting the black hole before being swallowed up. Calculations suggest that this object could be a white dwarf, a dense stellar remnant, traveling at incredible speeds.

Theoretical predictions indicated that the object was expected to pass the event horizon in January 2024with the consequent disappearance of the oscillations. However, in March 2024, XMM-Newton continued to detect oscillations, with the object traveling at half the speed of light.

This unexpected discovery led researchers to consider other possibilities. There may be a mechanism other than gravitational waves at playor the initial hypothesis may need to be modified. One possibility is that the white dwarf is slowly being “devoured” by the black hole rather than being swallowed whole.

In 2030, ESA will launch LISA, a space observatory dedicated to detecting gravitational waves right in the frequency range emitted by 1ES 1927+654. If the researchers’ predictions are correct, LISA could provide us with valuable information about what happens near this supermassive black hole.

Image Credits: NASA/Sonoma State University, Aurore Simonnet