Emission from the centre of a galaxy has a serpentine shape
An international group of scientists led by members of the National Instituto of Astrophysics (Osservatorio Astronomico di Torino (INAF-OATo) has discovered a peculiar spiral-shaped blazar jet with many twists. The results of these observations are published today in Nature magazine.
A blazar is an astronomical object within an elliptical galaxy occupied by a central supermassive black hole that emits jets of radiation and particles with high energy. When these are directed towards the Earth, astronomers can detect them. They are among the most energetic phenomena in the universe.
In the second half of last year, the blazar CTA 102, which is 7,600 million light years from Earth, brightened considerably, drawing the attention of all the astronomers who specialise in this kind of object. The peak emission was detected on December 28th when it was 3,500 times greater than the brightness minima observed in previous years. This event was so exceptional that for a few days, this object was the brightest blazar ever observed.
To follow this event, the researchers of the Astrophysical Observatory of Turin (OATo) coordinated an intense multifrequency observational campaign in the framework of of the international collaboration Whole Earth Blazar Telescope (WEBT). More than 40 telescopes in the Northern Hemisphere took thousands of observations in the visible, radio and near infrared ranges, which enabled the production of detailed light curves. Among the telescopes used in the collaboration were the Carlos Sánchez Telescope and the IAC-80 and STELLA telescopes, all of them at the Teide Observatory (Izaña, Tenerife).
"This large quantity of data has enabled us to verify the hypothesis that the variability of this object is due to changes in the relativistic Doppler factor" explains José Antonio Acosta Pulido, a researcher at the IAC/ULL and one of the authors of the article, which is published today in Nature.
The researchers' interpretation is that the jet is "serpentine and inhomogeneous" because it emits radiation over a range of frequencies and from different zones, which change their orientation due to the instabilities in the jet, or to orbital motions.
Acosta says, "The incredible rise in luminosity was due to the increased alignment of the emitting zone of the jet with our line of sight to the object." Thanks to these observations, the model used in this research is supported both theoretically and observationally.
"Three-dimensional numerical simulations, taking into account the magnetohydrodynamic properties and the relativistic velocities, predict the appearance and the propagation of instabilities in the jet, which then distort it," explains Acosta. "In addition, the images obtained by radio-interferometry show on scales of one parsec (some three light years) that the jet appears to be helical, and contains many vórtices. The picture that emerges is one of a twisting jet whose emission is amplified at different wavelengths at different times, by the lighthouse effect." The orientation in December 2016 was especially favourable for the extraordinary amplification observed.
More information: C. M. Raiteri et al, Blazar spectral variability as explained by a twisted inhomogeneous jet, Nature (2017). DOI: 10.1038/nature24623
Journal information: Nature
Provided by Instituto de Astrofísica de Canarias (IAC)