Multiple Views of Galactic Chaos

Centurus A is an active galaxy 11 million light years away in the constellation Centaurus. It's a complex knot of hot and cold gases and dust, tracing out a collision from time long gone past. By looking at it in multiple wavelengths, astronomers can get a better understanding of its structure.

This top image is layers of X-ray data: the lowest-energy are red, intermediate energy are green, and the highest energy are blue. It blends an equivalent of nine and a half days of solid observing between 1999 and 2012.


A hundred million years ago, a small galaxy collided with Centaurus A, creating a mess of turbulence and turmoil that is ongoing. Jets of cold gas and dust fire out at an angle, high-energy particle jets marking the supermassive active black hole at the center of the mess. The massive, 25,000 light-year diameter arcs of gas are heated to millions of degrees, part of a ring produced by an explosion ten million years ago. The theory goes that an eruption in the galactic nucleus produced galaxy-wide shockwaves, producing an expanding ring moving at millions of miles per hour and sparking a dramatic increase in star formation.

This next image is a composite blending wavelengths captured from different parts of the spectrum by a trio of telescopes. Radio wave are in red and green, optical wavelengths are in yellow, and X-ray data is in blue.

Along the bottom are the wavelengths broken out into their individual contributions: a single haze of blue X-ray data from Chandra X-Ray Observatory matching the same shape as the top X-ray image, but without the graduations of colour for each major energy level. In the optical image captured by the Deep Sky Survey, the chaos is an almost uniform sphere of glowing gold, with a single central ring of structural detail but no evidence of jets. The jets of colder gas and dust dominate the radio continuum image from National Radio Astronomy Observatory, prominent sweeps from a single point-source. Finally, the same observatory filtered to just 21-centimeter wavelengths traces out the same ring as the optical image, but in less detail. Each telescope sees something different in the chaos, and the full picture is only seen by layering all the images together.


Astronomer William Keel, who previously dug up 1970s astronaut toys for us, has contributed one of his optical images of the same region. This is a mosaic image of the top jet, with an H-alpha filter. H-alpha is a specific dark-red visible-light (656.28 nm) spectral line produced by an electron in the hydrogen atom falling from the third to second lowest energy state. An H-alpha filter is designed to only transmit a narrow bandwidth of light around the H-alpha spectral line. While H-alpha filters are useful for cutting out light pollution, here it also enhances the contrast of gas filaments as most of their total optical light is within the narrow bandwidth, while most of a star's light is not.


In Keel's image, the colours match brightness: blue are the darkest stars, up through white to the brightest stars. The radio source is ionizing the cold gas, tracing out the jet in a streamer of hot gas.

The final composite is a blend of submillimeter data in orange (a blend of the green and orange radio sources in the previous image), X-rays in blue, and visible light in white. The X-ray jet extends 13,000 light years from the black hole, travelling at half the speed of light.


Top image credit:X-ray: NASA/CXC/U.Birmingham/M.Burke et al. Middle-top image credit:X-ray (NASA/CXC/M. Karovska et al.); Radio 21-cm image (NRAO/VLA/J.Van Gorkom/Schminovich et al.), Radio continuum image (NRAO/VLA/J. Condon et al.); Optical (Digitized Sky Survey U.K. Schmidt Image/STScI). Middle-bottom image credit:X-ray: NASA/CXC/CfA/R.Kraft et al.; Submillimeter: MPIfR/ESO/APEX/A.Weiss et al.; Optical: ESO/WFI. Bottom image credit: William Keel/ESO/MPI


For more X-ray Chandra goodness, here's a very strange supernova, and a supernova in a binary system.

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