Composition of Gas Around Active Black Hole (MIRI Spectra)

Stephan’s Quintet is a visual grouping of five galaxies located in the constellation Pegasus. Together, they are also known as the Hickson Compact Group 92 (HCG 92). Although called a “quintet,” only four of the galaxies are truly close together and caught up in a cosmic dance. The fifth and leftmost galaxy, called NGC 7320, is well in the foreground compared with the other four.

Tight groups like this may have been more common in the early universe when their superheated, infalling material may have fueled very energetic black holes called quasars. Even today, the topmost galaxy in the group – NGC 7319 – harbours an active galactic nucleus, a supermassive black hole 24 million times the mass of the Sun. It is actively pulling in material and puts out light energy equivalent to 40 billion Suns.

Scientists using the NASA/ESA/CSA James Webb Space Telescope studied the active galactic nucleus in great detail with the Medium-Resolution Spectrometer (MRS) that is part of the Mid-Infrared Instrument (MIRI). The spectrometer features integral field units (IFUs) – a combination of a camera and spectrograph. These IFUs provided the Webb team with a “data cube,” or collection of images of the galactic core’s spectral features.

Using IFUs, scientists can measure spatial structures, determine the velocity of those structures, and get a full range of spectral data. Much like medical magnetic resonance imaging (MRI), the IFUs allow scientists to “slice and dice” the information into many images for detailed study.

MIRI’s MRS pierced through the shroud of dust near the active galactic nucleus to measure the bright emission from nearby hot gas that is being ionised by powerful winds and radiation from the black hole. The instrument saw the gas near the supermassive black hole at a level of detail never seen before, and it was able to determine its composition.

When a supermassive black hole feeds, some of the infalling material becomes very hot and is pushed away from the black hole in the form of winds and jets. MIRI probed many different regions, including the black hole’s outflowing wind – indicated by the smaller circle – and the area immediately around the black hole itself – indicated by the larger circle. It showed that the black hole is enshrouded in silicate dust similar to beach sand, but with much smaller grains.  

The top spectrum, from the black hole’s outflow, shows a region filled with hot, ionised gases, including iron, argon, neon, sulphur and oxygen as denoted by the peaks at given wavelengths. The presence of multiple emission lines from the same element with different degrees of ionisation is valuable for understanding the properties and origins of the outflow.

The bottom spectrum reveals that the supermassive black hole has a reservoir of colder, denser gas with large quantities of molecular hydrogen and silicate dust that absorb the light from the central regions of the galaxy.

MIRI was contributed by ESA and NASA, with the instrument designed and built by a consortium of nationally funded European Institutes (The MIRI European Consortium) in partnership with JPL and the University of Arizona.

For a full array of Webb’s first images and spectra, including downloadable files, please visit: https://esawebb.org/initiatives/webbs-first-images/

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