An article under review for publication reports a study on the galaxy ESO 253-G003 that classifies it among the ones with an active galactic nucleus that is consuming a star orbiting the central supermassive black hole. A team of researchers led by Anna Payne of the University of Hawaii used observations conducted with various telescopes to study the phenomenon, cataloged as ASASSN-14ko, detecting a series of regular cosmic outbursts that were interpreted as energy emissions linked to the passage of a star too close to the black hole, which destroys a part of it at each orbit.
The history of the observations of the activity in the galaxy ESO 253-G003 began on November 14, 2014, with the detection by the telescopes of the ASAS-SN (All-Sky Automated Survey for Supernovae) network of an outburst that was initially attributed to a supernova. In 2020, examining data collected by the ASAS-SN network regarding active galactic nuclei, Anna Payne found a series of outbursts in the galaxy ESO 253-G003 that followed the first one. The total discovered was 17 outbursts separated by approximately 114 days. Each outburst peaks for about 5 days and then fades away. In the case of the November 7, 2018 outburst, more data were found among the observations conducted with NASA’s TESS space telescope.
Anna Payne and her colleagues tested the periodicity calculated from the data and obtained collaborations to conduct observations with various telescopes including NASA’s Swift Space Telescope and ESA’s XMM-Newton Space Telescope. The first opportunity came on May 17, 2020, when a new outburst was promptly detected. The predictions were confirmed again on September 7 and December 20.
The confirmation of the periodicity of ASASSN-14ko is crucial, the problem of this phenomenon’s cause remains. Data collected from different telescopes at very different frequencies of the electromagnetic spectrum allowed Anna Payne’s team to conduct a very broad analysis. According to them, the most likely explanation for the phenomenon is that the supermassive black hole at the center of the galaxy ESO 253-G003 is slowly destroying a giant star orbiting it. According to this interpretation, the outbursts are so-called tidal disruption events: the orbit of the star is elliptical and, when it passes at the point closest to the black hole, its gravity strips part of the gas that composes it.
The researchers considered alternative hypotheses. The galaxy ESO 253-G003 was also observed within the AMUSING (All-weather MUse Supernova Integral-field of Nearby Galaxies) survey, and in another article under review, a team of researchers including Anna Payne suggests that this galaxy has two supermassive black holes, a consequence of a galaxy merger. The disks of materials around these two black holes could interact, but their orbits are not close enough to account for the frequency of the outbursts.
Another hypothesis is that a star has an inclined orbit that passes through the disk surrounding the central supermassive black hole. However, in this case, the emissions of the outbursts should have asymmetrical shapes because the star would pass through the disk with a different trajectory on the two sides of the disk. Instead, the outbursts show emissions with the same shape.
The periodicity of the outbursts will allow for new observations starting in April 2021. The researchers are also looking for more data on previous outbursts, again among the observations conducted with the TESS space telescope, which is an exoplanet hunter but can also contribute to other types of astronomical research. More information can confirm if ASASSN-14ko is really a tidal disruption event and, in this case, the researchers can try to understand how long it can last before the star is completely destroyed.
