From The Royal Astronomical Society (UK): “Galaxy changes classification as jet changes direction” 

From The Royal Astronomical Society (UK)


Media Contacts
Gurjeet Kahlon
Royal Astronomical Society
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Dr Robert Massey
Royal Astronomical Society
Mob: +44 (0)7802 877699

Makarena Estrella Pacheco
Millennium Institute of Astrophysics (MAS)

Science Contacts
Dr Lorena Hernández-García
Millennium Institute of Astrophysics (MAS) and University of Valparaiso

Dr Francesca Panessa
Institute for Space Astrophysics and Planetology (INAF-IAPS)

Dr Gabriele Bruni
Institute for Space Astrophysics and Planetology (INAF-IAPS)

This artist’s concept shows a “feeding,” or active, supermassive black hole with a jet streaming outward at nearly the speed of light. Not all black holes have jets, but when they do, the jets can be pointed in any direction. If a jet happens to shine at Earth, the object is called a blazar. Credit: NASA/JPL-Caltech.

A team of international astronomers have discovered a galaxy that has changed classification due to unique activity within its core. The galaxy, named PBC J2333.9-2343, was previously classified as a radio galaxy, but the new research has revealed otherwise. The work is published in MNRAS [below].

PBC J2333.9-2343 located 656 844 372 light years away has now been classified as a giant radio galaxy that is 4 million light years across and happens to have a blazar in its core; a blazar is an active galactic nucleus (AGN) with a relativistic jet (a jet travelling close to the speed of light) directed towards an observer. Blazars are very high energy objects and are considered to be one of the most powerful phenomena in the Universe. The research has revealed that in PBC J2333.9-2343, the jet changed its direction drastically by an angle of up to 90 degrees, going from being in the plane of the sky, perpendicular to our line of sight, to pointing directly towards us.

A blazar jet is made of elemental charged particles like electrons or protons that move at velocities close to the speed of light. These move in circles around a strong magnetic field, causing the emission of radiation across the entire electromagnetic spectrum. In PBC J2333.9-2343, the jet is thought to originate from or close to the supermassive black hole in its centre.

With the jet pointing in our direction, the emission is strongly enhanced and can easily exceed that coming from the rest of the galaxy. This in turn drives high-intensity flares stronger than those coming from other radio galaxies, thus changing its categorization.

A coloured image using the z/i/g filters taken from the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) PS1, a system for wide-field astronomical imaging developed and operated by the Institute for Astronomy at the University of Hawaii. The galaxy PBC J2333.9-2343 is located at the centre of the image. The Institute for Astronomy at the University of Hawai’i.

The orientation of the jets to us determines how a galaxy is classified. When two jets point towards the plane of the sky, they are classified as a radio galaxy, but if one of the jets points towards us, then the AGN of the galaxy is known as a blazar. With jets in the plane of the sky and one directed at us, PBC J2333.9-2343 has been reclassified as a radio galaxy with a blazar at its centre.

Changes in the direction of jets have been described in the past, for example with X-shaped radio galaxies. This is the first time that such a phenomenon has been observed where it does not suggest the presence of two different phases of jet activity from its morphology observed at radio frequencies – the direction change appears to have taken place in the same nuclear outburst originating from the AGN.

To find out more about this mysterious galaxy, astronomers had to observe it across a wide range of the electromagnetic spectrum. PBC J2333.9-2343 was observed with radio, optical, infrared, x-ray, ultraviolet and gamma ray telescopes. Data was obtained from the German 100m-Radio Telescope Effelsberg at the MPG Institute for Radio Astronomy, the 1.3m-SMARTS optical telescope, and the Penn State Neil Gehrels Swift Observatory.

The team then compared the properties of PBC J2333.9-2343 with large samples of blazars and non-blazar galaxies provided by the ALeRCE (Automatic Learning for the Rapid Classification of Events) project in Chile with data from the Zwicky Transient Facility (ZTF) and the Asteroid Terrestrial-impact Last Alert System (ATLAS).

Using the observational data, the team concluded that this galaxy has a bright blazar in the centre, with two lobes in the outer areas of the jet. The lobes that are observed are related to the old jets and are no longer being fed by the emission from the nucleus, so these lobes are relics of past radio activity. The AGN no longer drives the lobes as seen in typical radio galaxies.

The team do not yet know what caused the drastic change in direction of the jets. They speculate that it could have been a merging event with another galaxy or any other relatively large object, or a strong burst of activity in the galactic nucleus after a dormant period.

Dr Lorena Hernández-García, lead author of the paper and researcher at the Millenium Institute of Astrophysics, says “We started to study this galaxy as it showed peculiar properties. Our hypothesis was that the relativistic jet of its supermassive black hole had changed its direction, and to confirm that idea we had to carry out a lot of observations.”

She adds, “The fact that we see the nucleus is not feeding the lobes anymore means that they are very old. They are the relics of past activity, whereas the structures located closer to the nucleus represent younger and active jets.”


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The Royal Astronomical Society is a learned society and charity that encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. Its headquarters are in Burlington House, on Piccadilly in London. The society has over 4,000 members (“Fellows”), most of them professional researchers or postgraduate students. Around a quarter of Fellows live outside the UK.

The society holds monthly scientific meetings in London, and the annual National Astronomy Meeting at varying locations in the British Isles. The Royal Astronomical Society publishes the scientific journals MNRAS and Geophysical Journal International, along with the trade magazine Astronomy & Geophysics.

The Royal Astronomical Society maintains an astronomy research library, engages in public outreach and advises the UK government on astronomy education. The society recognizes achievement in Astronomy and Geophysics by issuing annual awards and prizes, with its highest award being the Gold Medal of The Royal Astronomical Society. The Royal Astronomical Society is the UK adhering organization to the International Astronomical Union and a member of the UK Science Council.

The society was founded in 1820 as the Astronomical Society of London to support astronomical research. At that time, most members were ‘gentleman astronomers’ rather than professionals. It became the Royal Astronomical Society in 1831 on receiving a Royal Charter from William IV. A Supplemental Charter in 1915 opened up the fellowship to women.

One of the major activities of the RAS is publishing refereed journals. It publishes two primary research journals, the Monthly Notices of the Royal Astronomical Society [MNRAS] in astronomy and (in association with The German Geophysical Society [Deutsche Geophysikalische Gesellschaft e.V. ](DE)]) the Geophysical Journal International in geophysics. It also publishes the magazine A&G which includes reviews and other articles of wide scientific interest in a ‘glossy’ format. The full list of journals published (both currently and historically) by the RAS, with abbreviations as used for the NASA ADS bibliographic codes is:

Memoirs of the Royal Astronomical Society (MmRAS): 1822–1977[3]
Monthly Notices of the Royal Astronomical Society (MNRAS): Since 1827
Geophysical Supplement to Monthly Notices (MNRAS): 1922–1957
Geophysical Journal (GeoJ): 1958–1988
Geophysical Journal International (GeoJI): Since 1989 (volume numbering continues from GeoJ)
Quarterly Journal of the Royal Astronomical Society (QJRAS): 1960–1996
Astronomy & Geophysics (A&G): Since 1997 (volume numbering continues from QJRAS)

Associated groups

The RAS sponsors topical groups, many of them in interdisciplinary areas where the group is jointly sponsored by another learned society or professional body:

The Astrobiology Society of Britain (UK) (with The NASA Astrobiology Institute)
The Astroparticle Physics Group (with The Institute of Physics – London (UK))
The Astrophysical Chemistry Group (with The Royal Society of Chemistry)
The British Geophysical Association (with The Geological Society of London (UK).
The Magnetosphere Ionosphere and Solar-Terrestrial group (UK)
The UK Planetary Forum
The UK Solar Physics group