It was time for some black hole research! In recent months, astrophysicists have announced the discovery of the most powerful gamma-ray burst ever recorded (due to the formation of a black hole), a monster black hole in our cosmic backyard, the frame-dragging effects of a binary black hole, and the remnant of the 2017 Kilonova event (spoiler alert: it was a black hole). And with the help of citizen scientists, a team of astronomers recently discovered a single black hole in a galaxy about a billion light-years away that is firing a relativistic jet into another galaxy.
The research was conducted by a team led by Ananda Hota, a researcher at the UM-DAE Center of Excellence in Basic Sciences. He was joined by researchers from the Indian Institute of Astrophysics, Sorbonne University Laboratory for the Study of Radiation and Matter in Astrophysics and Atmospheres (LERMA), Arecibo Observatory, Amity Institute of Applied Sciences, Thapar Institute of Engineering and Technology. and [email protected] Citizen Science Collaboration. The paper describing their findings was published on October 12 in Monthly Notices of the Royal Astronomical Society Letters.
Galaxies are usually divided into three main categories based on size, shape and composition. First, there are ellipticals, which represent about one-third of all galaxies in the Universe ranging from nearly circular to very elongated. Then there are spiral galaxies, which are distinguished by their distinct spiral arms and appear as flat disks with large yellowish bulges in their centers. Finally, there are irregular galaxies, which are neither elliptical nor spiral and were more common in the early Universe (before they evolved into the other two classes).
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When it comes to elliptical galaxies, astronomers have noticed that the formation of new stars is very rare and appears to have largely stopped billions of years ago. Although the reason for this remains a mystery, modern research suggests that the presence of supermassive black holes (SMBHs) may be responsible. These “monster black holes” cause the centers of massive galaxies to become Active Galactic Nuclei (AGN) – aka. Quasar – where the core is more energetic than all the stars in the disk combined.
In many cases, AGNs also have massive jets ejected from their poles that accelerate gas and dust to relativistic velocities (close to the speed of light). The ejection of this matter towards other galaxies is thought to deplete the elliptical galaxies of the cool gas and dust that would otherwise be fuel for star formation. Another mystery facing astronomers is how these AGN-driven jets bind to the gas of the merging galaxies, causing positive feedback. This temporarily leads to enhanced star formation, followed by negative feedback and a decrease in star formation.
To address this latest mystery, Dr. Hota and colleagues observed the SMBH at the center of RAD12, an elliptical galaxy located about 1 billion light-years from Earth. This unique nature of this galaxy first became apparent in 2013 based on optical data from the Sloan Digitized Sky Survey (SDSS) and radio data from the Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) survey by Very Large Array (VLA). But when Dr Hota and his team observed it again using the Giant Meter Wave Radio Telescope (GMRT) in India, they noticed that RAD12 appeared to eject matter from only one pole.
These observations were confirmed using archival radio and optical data from the MeerKAT array in Australia and the Canada-France-Hawaii telescope (respectively). Unlike other jets that eject matter in pairs and opposite directions, RAD12 appeared to eject matter only toward its neighboring galaxy, RAD12-B. Their observations also revealed a jet of young plasma that is conical in shape at the stem and shoots out in a mushroom shape at the tip (shown above). The yellow features represent the galaxies – the largest is RAD12 (left) and RAD12-B (right) – and the plasma jet is shown in red.
The entire structure spans 440 thousand light-years and is much larger than the host galaxy itself. This is the first time a jet has been observed colliding with a large galaxy like RAD12-B. As Dr Hota said in a recent Royal Astronomical Society (RAS) news release:
“We are excited to have identified a rare system that helps us understand the radio spectrum feedback of supermassive black holes in the star formation of galaxies during mergers. Observations with GMRT and data from several other telescopes, such as the MeerKAT radio telescope, strongly suggest that the radio star in RAD12 is colliding with its companion galaxy. An equally important aspect of this research is the demonstration of public participation in making discoveries through it [email protected] Citizen Science Research Collaboration”.
Thanks to the observations of Dr Hota and his team, astronomers are now one step closer to understanding the impact such interactions have on elliptical galaxies. Their findings could lead to a new understanding of how star formation is interrupted in elliptical galaxies, solving a long-standing mystery about galactic evolution. It is also a testament to the kind of research that is possible today through collaboration between citizen scientists and astronomers.
Further reading: RA
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