Astronomers found a supermassive black hole in an active galactic nucleus producing rapid and periodic eruptions of X-rays every nine hours. The nucleus contains about 400 000 times the mass of the Sun and is about 250 million light-years from Earth.
According to a study published on September 11, 2019, giant black holes usually flare like a candle but the quick bursts seen in GSN 069 since December 2018 are new. The phenomenon was then called quasi-periodic eruptions.
An X-ray telescope from ESA detected periodic eruptions of X-ray radiation from a massive black hole, and scientists believe that the flares could help explain some enigmatic behaviors of active black holes.
"On December 24, 2018, the source was seen to suddenly increase its brightness by up to a factor of 100, then dimmed back to its normal levels within one hour and lit up again nine hours later." astronomers stated.
Telescopes conducted observations in the following months, confirming that "the distant black hole was still keeping the tempo, emitting nearly periodic bursts of X-rays every nine hours."
Giovanni Miniutti, the lead author of the paper who is from the Spanish Astrobiology Center, explained that the flares "come from material that is being accreted into the black hole and heats up in the process."
He added, "there are various mechanisms in the accretion disk that could give rise to this type of quasi-periodic signal, potentially linked to instabilities in the accretion flow close to the central black hole. Alternatively, the eruptions could be due to the interaction of the disk material with a second body – another black hole or perhaps the remnant of a star previously disrupted by the black hole."
The researchers said that although this phenomenon was never before seen, the flares could be common in the galaxy.
According to them, the phenomenon had not been identified yet before since most black holes are more massive than GSN 069.
"The bigger and more massive the black hole, the slower the fluctuations in brightness it can display, so a typical supermassive black hole would erupt not every nine hours, but every few months or years. This would make detection unlikely as observations rarely span such long periods of time." the researchers explained.
Moreover, the quasi-periodic eruptions could offer a natural framework to identify some complex patterns recorded in a particular fraction of active black holes.
According to Miniutti, if some of the variability corresponds to the increase or decay phases of flares same to that of GSN 069, then the fast variability of the systems could be accounted for.
For now, the astronomers are still organizing the research of the distant galaxy GSN 069.
"GSN 069 is an extremely fascinating source, with the potential to become a reference in the field of black hole accretion," Norbert Schartel, ESA's scientist said.
"Nine-hour X-ray quasi-periodic eruptions from a low-mass black hole galactic nucleus" – G. Miniutti et al. – Nature International Journal of Science – https://doi.org/10.1038/s41586-019-1556-x
In the past two decades, high-amplitude electromagnetic outbursts have been detected from dormant galaxies and often attributed to the tidal disruption of a star by the central black hole1,2. X-ray emission from the Seyfert 2 galaxy GSN 069 (2MASX J01190869-3411305) at a redshift of z = 0.018 was first detected in July 2010 and implies an X-ray brightening by a factor of more than 240 over ROSAT observations performed 16 years earlier3,4. The emission has smoothly decayed over time since 2010, possibly indicating a long-lived tidal disruption event5. The X-ray spectrum is ultra-soft and can be described by accretion disk emission with luminosity proportional to the fourth power of the disk temperature during long-term evolution. Here we report observations of quasi-periodic X-ray eruptions from the nucleus of GSN 069 over the course of 54 days, from December 2018 onwards. During these eruptions, the X-ray count rate increases by up to two orders of magnitude with event duration of just over an hour and a recurrence time of about nine hours. These eruptions are associated with fast spectral transitions between a cold and a warm phase in the accretion flow around a low-mass black hole (of approximately 4 × 105 solar masses) with peak X-ray luminosity of about 5 × 1042 erg per second. The warm phase has kT (where T is the temperature and k is the Boltzmann constant) of about 120 electronvolts, reminiscent of the typical soft-X-ray excess, an almost universal thermal-like feature in the X-ray spectra of luminous active nuclei6,7,8. If the observed properties are not unique to GSN 069, and assuming standard scaling of timescales with black hole mass and accretion properties, typical active galactic nuclei with higher-mass black holes can be expected to exhibit high-amplitude optical to X-ray variability on timescales as short as months or years.
Featured image credit: ESA
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