Unexpected periodic flare-ups can shed light on the accumulation of black holes

The ESA X-ray space telescope, XMM-Newton, has detected unpublished periodic X-rays from a distant galaxy, which could help explain some enigmatic behaviors of active black holes.

XMM-Newton, the most powerful X-ray observatory, has discovered mysterious lightning bolts from the active black hole at the heart of the GSN 069 galaxy, about 250 million light-years away. On December 24, 2018, it was found that the source suddenly increased its brightness by a factor of 100, then returned to its normal level in one hour and returned to light nine hours later.

"It was completely unexpected," says Giovanni Miniutti, of the Centro de Astrobiología de Madrid, Spain, lead author of a new article published in the journal Nature aujourd & # 39; hui.

"Giant black holes flicker regularly like a candle, but the quick and repeated changes seen in GSN 069 from December are something completely new."

Other observations, made with the help of XMM-Newton and NASA's Chandra X-ray observatory over the next few months, confirmed that the distant black hole still maintained the tempo, emitting nearly periodic X-ray bursts every nine hours. Researchers call this new phenomenon "quasi-periodic eruptions" or QPE.

"The X-ray emission comes from a material that accumulates in the black hole and that heats up during the process," Giovanni explains.

"There are different mechanisms in the accretion disk that could give rise to this type of quasi-periodic signal, potentially related to instabilities in the accretion flux near the central black hole.

"Alternatively, the eruptions could be due to the interaction of the disc material with a second body – another black hole or perhaps the remainder of a star previously disturbed by the black hole."

Although never observed before, Giovanni and his colleagues think that periodic eruptions like these could actually be quite common in the universe.

It is possible that the phenomenon was not identified before because most of the black holes in the heart of distant galaxies, from a mass of several million to billions of times the mass of our Sun, are much larger than that of GSN 069, which is only 400,000 times more massive than our sun.

The larger and larger the black hole, the more brightness fluctuations that it can display are slow. Thus, a typical supermassive black hole will occur not every nine hours, but every few months or years. This would make detection unlikely, as observations rarely cover such long periods.

And there's more. Quasi-periodic eruptions such as those found in GSN 069 could provide a natural framework for interpreting some surprising patterns observed in a significant fraction of active black holes, whose luminosity seems to vary too rapidly to be easily explained by current theoretical models .

"We know of many massive black holes whose luminosity increases or decreases considerably in a matter of days or months, while we expect them to vary much more slowly," says Giovanni.

"But if part of this variability corresponds to the rise or fall of eruptions similar to those found in GSN 069, the rapid variability of these systems, which currently seems impossible, could naturally be taken into account. and other studies will indicate whether this analogy really holds. "

The quasi-periodic eruptions observed in the GSN 069 could also explain another intriguing property observed in the X-ray emission of almost all supermassive shiny and ascending black holes: the so-called "soft excess".

It consists of an improved emission at low X-ray energies, and there is still no consensus on its cause, according to a prominent theory invoking an electron cloud heated near the disk of 39; accretion.

As for similar black holes, GSN 069 exhibits such an excess of mild X-rays during explosions, but not between eruptions.

"We may be witnessing the formation of the soft real-time excess, which could illuminate its physical origin," said co-author Richard Saxton of the XMM operating team -Newton of the ESA astronomy center in Spain.

"The way the electron cloud is created is not clear at the moment, but we are trying to identify the mechanism by studying GSN 069 X-ray spectrum changes during eruptions. "

The team is already attempting to determine the properties that define GSN 069 at the time the periodic eruptions were first detected to look for more cases to study.

"One of our immediate objectives is to look for quasi-periodic x-ray eruptions in other galaxies, to better understand the physical origin of this new phenomenon," adds the co-author. Margherita Giustini from the Centro de Astrobiología de Madrid.

"GSN 069 is an extremely fascinating source, which could become a benchmark in the field of black hole accretion," said Norbert Schartel, scientist of ESA's XMM-Newton project.

The discovery would not have been possible without the capabilities of XMM-Newton.

"These bursts occur in the low-energy part of the X-ray band, where XMM-Newton is unbeatable.We will definitely have to use the observatory again if we want to find more events of this type at the same time. Future, "Norbert concludes. .

"Nine-hour quasi-periodic x-ray eruptions from a galactic low-mass black hole nucleus", by G. Miniutti et al., Are published in Nature.