Astronomers have recorded the third giant flare in the galaxy IC 3599

For the first time, astronomers have been able to track in real time the development of the third giant X-ray flare of the active core of the galaxy IC 3599. Previous similar events occurred in 1990 and 2010, but they were discovered and analyzed in detail after the brightness decrease. This was reported in the magazine on July 21. Phys.org .

We are not talking about the explosion of the black hole itself, but about a sharp increase in the radiation of matter that moves around it and falls inside from the accretion disk. IC 3599 refers to active galactic nuclei with a changing spectral appearance: as the brightness increases, radiation lines appear or intensify in the object's spectrum, which are almost invisible in a calm state.

After the outbreaks of 1990 and 2010, scientists began to regularly observe the object using the Neil Gehrels Swift Space Observatory. The monthly monitoring has been ongoing since 2013. On October 31, 2025, the telescope recorded that the X-ray brightness of IC 3599 was more than 50 times higher than the usual low level. The total amplitude of the event subsequently exceeded 100 times.

The spectrum of the flash turned out to be extremely mild: the Swift equipment practically did not register photons with energies above 2.5 keV. This means that the bulk of the energy came from relatively low-energy X-rays. At the peak of brightness, the radiation intensity corresponded to accretion near the Eddington limit, at which the radiation pressure begins to counteract the further fall of matter into the black hole. Its mass is estimated at about 2 million times the mass of the Sun.

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During the 120,000-second XMM-Newton observation, scientists detected pronounced fluctuations in X-ray brightness. The strongest signal corresponded to a period of about 7.4 hours. At the same time, the observation covered only four estimated cycles, so it is premature to talk about detecting a stable periodicity.

During the observations, the brightness could change twice in 3.6 hours. At the beginning of the XMM-Newton session, the radiation flux increased by about 2.5 times in just 1.75 hours. The authors compared this pattern with quasi-periodic oscillations, which are rarely found in active galactic nuclei, but emphasized that the result needs to be verified with longer observations.

Optical telescopes have registered a sharp increase in a large number of emission lines, including lines of highly ionized iron. Some of them were absent or were significantly weaker in a calm state. This indicates that the flare illuminated and ionized the gas at a considerable distance from the central region of the galaxy.

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The researchers named the instability of the accretion disk caused by radiation pressure as the most likely cause of the recurring events. According to this model, matter gradually accumulates in the inner region of the disk, after which instability provokes a sharp influx of gas to the black hole and a powerful flare. The area is then emptied, cooled, and begins to fill up again.

The intervals between the three known outbreaks differed, so the authors consider unlikely models that require a strictly regular repetition of the event. In particular, this weakens the theory of a compact object that moves in a constant orbit and periodically perturbs the disk. In this case, scenarios of repeated partial destruction of the star or the existence of a system of two black holes are not definitively excluded.

The magazine Phys.org On July 15, he announced the confirmation of the age of the Universe by the stars of the Milky Way. According to the study, the age of the oldest star is approximately 13.73 billion years old.