High-energy neutrinos originate in black-hole powered jets in active galactic nuclei
May 13, 2020
A team of astrophysicists including Yuri Y. Kovalev, affiliated to the MPI für Radioastronomie and Bessel Award of the Alexander von Humboldt foundation, have come close to solving the mystery of where high-energy neutrinos come from in space. The team compared the data on the elusive particles gathered by the Antarctic neutrino observatory IceCube and on long electromagnetic waves measured by radio telescopes. Cosmic neutrinos turned out to be linked to flares at the centers of distant active galaxies, which are believed to host supermassive black holes. As matter falls toward the black hole, some of it is accelerated and ejected into space, giving rise to neutrinos that then coast along through the universe at nearly the speed of light. These results are published in the last issue of The Astrophysical Journal, see the publication here, and a press release from the Moscow Institute of Physics and Technology here.
Jet shapes in active galactic nuclei dissected: changing from parabolic to conical shape and its physical implications
16 April 2020
A team of astronomers led by Yuri Y. Kovalev from Moscow (Lebedev & MIST), also associated to the MPI für Radioastronomie, has presented a work on ten active galactic nuclei in the close universe (redshift smaller than 0.07) displaying a transition from a parabolic to conical shape. They infer that the geometry transition may be a common effect in AGN jets, and observed only when sufficient linear resolution is obtained. This break occurs at distances of hundred thousand to one million gravitational radii from the nucleus. More in detail, this means that the jet shape transition happens when the bulk plasma kinetic energy flux becomes equal to the Poynting energy flux, while the ambient medium pressure is assumed to be governed by Bondi accretion. In general, the break point may not coincide with the Bondi radius. The results are presented in the online version of the journal Monthly Notices of the Royal Astronomical Society, available here.
EHT zoom into 3C 279 reveals inner structure and jet proper motions
Media coverage on 3C 279 Press Release (selection)
Located the site of emission of high-energy gamma rays in the blazar TXS 2013+370
17 February 2020
An international team of astronomers led by the doctoral researcher Efthalia Traianou from the MPI für Radioastronomie has identified the location of the gamma-ray emission in the blazar jet TXS 2013+370. The published results report very-long-interferometry observations of the blazar in the period 2002-13 at four wavelengths up to the challenging 3.5 mm addressed by the Global mm-VLBI Array (GMVA). The images revealed the existence of a spatially bent jet, described by co-existing moving emission features and stationary features. New jet features, lare observed to emerge from the core, accompanied by flaring activity in radio/mm- bands and γ-rays. The work infers that the high energy emission is produced at a distance of the order of about 3 lt-year from the jet apex, suggesting that the seed photon fields for the external Compton mechanism originate either in the dusty torus or in the broad-line region. These results are published in the present issue of the Astronomy & Astrophysics journal, see the original work here.
Effelsberg observes methanol emission in nearby galaxies
17 January 2020
A team of astronomers led by the MPIfR PhD candidate Pedro Kumire has observed 36 GHz emission of methanol (CH3OH) in nearby galaxies using the Effelsbeg 100-m radio telescope. Emission was detected in Maffei 2 (at a distance of 19.6 million lt-yr) and IC 342 (at 11.4 million lt-yr) at 36 GHz (4−1 → 30 E transition), but not at 44 GHz transition. Upper limits were reported for M 82, NGC 4388, NGC 5278, and Arp 220. These results are published in Astronomy and Astrophysics, for more detail, check here.
The neutrino detection in the blazar TXS 0506+056, linked to superluminal expansion and limb brigthening in the sub-parsec scale of the source
2 January 2020
The first letter of the Astronomy & Astrophysical journal in the 2020s, led by Eduardo Ros of the MPIfR, reports on the rapid expansion of the centre of the blazar TXS 0506+056, based on millimetre VLBI observations performe with the VLBA. During the months after the neutrino event associated with this source, the overall flux density was showing a steady increase, happening solely within the core. Notably, the core expands in size with apparent superluminal velocity during these six months so that the brightness temperature drops by a factor of three despite the strong flux density increase. The radio jet of TXS 0506+056 shows strong signs of deceleration and/or a spine-sheath structure in the innermost region. This structure is consistent with theoretical models that attribute the neutrino and gamma-ray production to interactions of electrons and protons in the highly relativistic jet spine with external photons originating from a slower moving jet region. Proton loading due to jet-star interactions in the inner host galaxy is suggested as the possible cause of deceleration. Further details can be found in the original publication here.
The first image of a black hole, scientific highlight of 2019 and even of the 2010s
2 January 2020
The announcement and publication of the first image of a black hole in April 2019, with substantial contribution of the MPIfR and its Radio Astronomy/VLBI department, has been highlighted by different media as one of the major scientific discoveries of the last year and of the 2010s. Here we provide some of the links reporting this fact.