A team of international astronomers has discovered a galaxy that has changed classification due to unique activity within its nucleus. The galaxy, named PBC J2333.9-2343, was previously classified as a radio galaxy, but new research has revealed otherwise. The work is published in Monthly Notices of the Royal Astronomical Society. 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 has a blazar at its core; a blazar is an active galactic nucleus (AGN) with a relativistic jet (a jet traveling close to the speed of light) directed toward an observer. Blazars are very high energy objects and are considered one of the most powerful phenomena in the Universe. Research has revealed that at PBC J2333.9-2343, the jet drastically changed its direction by up to 90 degrees, from being in the plane of the sky, perpendicular to our line of sight, to pointing directly at us.
A jet blazar is made of charged elementary particles such as electrons or protons that move at speeds 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. At PBC J2333.9-2343, the jet is believed to originate near the supermassive black hole at its center.
Con el chorro apuntando en nuestra dirección, la emisión se ve fuertemente potenciada y puede superar fácilmente a la procedente del resto de la galaxia. Esto, a su vez, genera destellos de alta intensidad más fuertes que los que provienen de otras radiogalaxias, cambiando así su categorización.
La orientación de los chorros hacia nosotros determina cómo se clasifica una galaxia. Cuando dos chorros apuntan hacia el plano del cielo, se clasifican como una radiogalaxia, pero si uno de los chorros apunta hacia nosotros, entonces el AGN de la galaxia se conoce como blazar. Con chorros en el plano del cielo y uno dirigido hacia nosotros, PBC J2333.9-2343 ha sido reclasificada como una radiogalaxia con un blazar en su centro.
En el pasado se han descrito cambios en la dirección de los chorros, por ejemplo, con radiogalaxias en forma de X. Esta es la primera vez que se observa un fenómeno de este tipo que no sugiere la presencia de dos fases diferentes de actividad de chorro a partir de su morfología observada en frecuencias de radio: el cambio de dirección parece haber tenido lugar en el mismo estallido nuclear que se originó en el AGN.
Para saber más sobre esta misteriosa galaxia, los astrónomos tuvieron que observarla en una amplia gama del espectro electromagnético. PBC J2333.9-2343 se observó con telescopios de radio, ópticos, infrarrojos, de rayos X, ultravioleta y de rayos gamma. Los datos se obtuvieron del radiotelescopio alemán Effelsberg de 100 m en el Instituto Max Planck de Radioastronomía, el telescopio óptico SMARTS de 1,3 m de la Universidad de Yale y el Observatorio Neil Gehrels Swift de Penn State.
A jet blazar is made of charged elementary particles such as electrons or protons that move at speeds 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. At PBC J2333.9-2343, the jet is believed to originate near the supermassive black hole at its center.
The team then compared the properties of PBC J2333.9-2343 with large samples of blazar and non-blazar galaxies provided by the ALeRCE (Machine Learning for Rapid Event Classification) 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 center, 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 powered by emission from the nucleus, so these lobes are relics of past radioactivity. The AGN no longer drives the lobes as seen in typical radio galaxies. The team does not yet know what caused the drastic change in the direction of the jets. They speculate that it could have been a merger event with another galaxy or some other relatively large object, or a strong burst of activity in the galactic core after a period of inactivity.
Dr. Lorena Hernández-García, lead author of the paper and a researcher at the Millennium Institute of Astrophysics, says: “We started to study this galaxy because it displayed peculiar properties. Our hypothesis was that the relativistic jet from its supermassive black hole had changed direction. , and to confirm that idea we had to carry out many observations.