Research Highlights

Here we show recent research results from the Radio Astronomy/Very-Long-Baseline Interferometry department.

European Commission facilitates use of European telescopes more

The monster awakes: galaxy flares after years of silence

28 October 2020

The narrow-line Seyfert 1 galaxy Markarian 335 hosted a very bright X-ray active nucleus which faded since 2007.  Observations from the Swift observatory led by S. Komossa at the MPI für Radioastronomie show a sequence of bright and rapid flare events in the X-ray band, after a long "quiet" time.  The new activity in the source can be explained by a decrease of the amount of matter between the active nucleus and us, which partially covered the bright emission.  The curtain is lifted, and it shows, the "monster" seems to be awake, but was always there.  This work is published in the present issue of Astronomy & Astrophysics, see here.

After the footprints of stellar formation: isotope dating of the clouds to the Galactic Centre

23 October 2020

The present issue of the Astronomy & Astrophysical journal reports about spectral-line observations towards the Galactic centre clouds, in a project led by the PhD researcher Pedro Humire.  This study shows a drop in the production of massive stars at the Galactic centre, based on measurements of the carbon and sulphur abundances in the interstellar medium.  For that different isotopes int he CS molecule were studied (combinations of atomic weight values of 12 and 13 for carbon, and of 32, 33, and 34 for sulphur).  Isotopic ratios can be computed for the different species, and the study shows that the decreasing trend in the 32S/34S ends at about 425 light-years from the centre of our galaxy.  More details can be checked at the original publication, here.

The connection between gamma rays and radio emission in radio galaxies

23 September 2020

A work presented by R. Angioni from the MPI für Radioastronomie gives new clues on the connection between the low-energy (radio) and the high-energy (gamma) emission in radio galaxies.  This is part of a larger work which is presented in a series of publications; the present report focus on prominent radio galaxies in the Southern hemisphere which were not detected by the Fermi/LAT telescope, and gives details on the jet kinematics for several objects.  In general, the study shows that high-energy emission from radio galaxies is related to parsec-scale radio emission from the inner jet, but is not driven by relativistic Doppler boosting effects, in contrast to the situation in blazars.  The results are presented in the last issue of Astronomy & Astrophysics, for more information see here

Turbulent evolution of the M 87* black hole image from 2009 to 2017 more

The Wobbling Shadow of the M87* Black Hole

This animation presents about three years in the life of M87*, as predicted by numerical simulations. It shows the expected appearance and dynamics of the supermassive black hole as observed by the EHT. You can see turbulent gas heated to billions of degrees swirling around the event horizon, before finally plunging into the black hole. A sharp bright ring surrounding the black hole shadow is an effect of extremely strong lensing near the so-called photon shell

The blurred portion of the animation corresponds to the effective resolution of the EHT. The dashed black ring measures 42 microarcseconds in diameter. The clock hand indicates the position of the bright side of the fitted crescent. We expect that the bright side should be most of the time located in the bottom of the image, where the velocity of the rotating gas is pointed in the observer’s direction. However, because of the turbulence, the fitted position angle varies quite a bit - the crescent wobbles. By studying the time-variability of the M87* image with the EHT, we can learn about the physics of matter in an extreme environment very near the event horizon, and understand the relations between the black hole and the accretion flow surrounding it. 

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Looking sharper, blobs become filaments: RadioAstron Observations of 0836+710

Zoom into the blazar 0836+710.  RadioAstron observations show the plasma blobs becoming filaments.

September 4, 2020

A new study published in the present issue of Astronomy & Astrophysics shows the striking improvement in resolution provided by the space-VLBI mission RadioAstron.  The work is based in a study made in the framework of the PhD thesis of Laura Vega-García, performed at the MPI für Radioastronomie.  The RadioAstron images reveal a wealth of structural detail in the jet of S5 0836+710 on angular scales ranging from 0.02 mas to 200 mas. Brightness temperatures in excess of 1013 K are measured in the jet, requiring Doppler factors of ≥100 for reconciling them with the inverse Compton limit.  Furthermore, several oscillatory patterns are identified in the ridge line of the jet and can be explained in terms of the Kelvin–Helmholtz (KH) instability.  For more information, check here

Binary super massive black hole and jet activity in the quasar OJ 287

27 July 2020

A team of  astronomers led by S. Komossa from the MPI für Radioastronomie has observed a very bright X-ray–UV–optical outburst of OJ 287 in 2020 April–June, the second brightest since late 2015. The outburst is predominantly powered by jet emission.  The study reports evidence for reprocessing around the iron region in the source core, consistent with an absorption line.  If confirmed, it implies matter in outflow at a tenth of speed light.  The monitored source brigthness shows multiple episodes of flaring or dipping with a total amplitude of variability of one order of magnitude over the last four years prior to the 2020 outburst.  This outburst is consistent with an after-flare predicted by a binary black hole model, where the disc impact of the secondary black hole triggers time-delayed accretion and jet activity of the primary black hole.  This work is presented in the latest issue of the British journal Monthly Notices of the Royal Astronomical Society, see the publication here

Andrea Niehaus, director of the Dt. Museum Bonn, received on June 24th, 2020 the picture of the black hole in M 87 from the chairman of the Event Horizon Telescope Collaboration, J. Anton Zensus, director at the MPI für Radioastronomie.

Picture: © Deutsches Museum Bonn, Eric Lichtenscheidt more

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.

First Event Horizon Telescope Images of a Black-Hole Powered Jet more

EHT zoom into 3C 279 reveals inner structure and jet proper motions

Media coverage on 3C 279 Press Release (selection)

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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

A wobbling jet with a two-year period

12 February 2020

The quasar PG 1553+113 is the first one showing an approximately two-year quasi-periodic pattern in its γ-ray light curve, which is also revealed at optical frequencies.  A study by an international team of radio astronomers led by the MPIfR scientist Rocco Lico has analysed very-long-baseline interferometry observations of the source with a two-month cadence at three bands.  The study shows  a core-dominated source with a limb-brightened jet structure whose position angle varies in time in the range of 40° to 60°.  The core region polarisation percentage varies in the range  of a few percent, and the polarisation angle varies from being roughly parallel to roughly transverse to the jet axis.  Although the jet wobbling motion indicates that geometrical effects can produce an enhanced emission through  Doppler boosting modulation, additional mechanisms are required in order to account for the quasi-periodic variability patterns observed in γ-rays.  Further details of this work are presented in the original publication at Astronomy & Astrophysics, see 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.

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