From Ethan Siegel: “Meet The Largest X-Ray Jet In The Universe”

From Ethan Siegel
July 1, 2019

Discovered by NASA’s Chandra X-ray observatory, it’s powered by a supermassive black hole.

2019 marks 20 years of NASA’s Chandra, humanity’s most powerful X-ray observatory.

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Artist illustration of the Chandra X-ray Observatory. Chandra is the most sensitive X-ray telescope ever built, and its mission was extended through at least 2024 as the flagship X-ray observatory in the NASA arsenal. (NASA/CXC/NGST TEAM)

It’s viewed everything from pulsars to colliding gas to galaxy clusters and supermassive black holes.

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A map of the 7 million second exposure of the Chandra Deep Field-South. This region shows hundreds of supermassive black holes, each one in a galaxy far beyond our own. The GOODS-South field, a Hubble project, was chosen to be centered on this original image. Its view of supermassive black holes is only one incredible application of the NASA’s Chandra X-ray observatory. (NASA/CXC/B. LUO ET AL., 2017, APJS, 228, 2)

In 2015, it set its sights on a galaxy some 485 million light-years away: the radio-loud behemoth known as Pictor A.

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The jet of the active galaxy Pictor A, with X-rays in blue and radio lobes in pink. When galaxies merge together, they’re expected to activate similarly to how this one has. (X-RAY: NASA/CXC/UNIV OF HERTFORDSHIRE/M.HARDCASTLE ET AL., RADIO: CSIRO/ATNF/ATCA)

When Chandra took a look at it with its X-ray eyes, it saw something unprecendented and spectacular: a jet 300,000 light-years long.

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The X-ray (B&W) and radio (red contours) emissions from the galaxy Pictor A. The greyscale image shows all the X-rays emitted with 500 to 5000 eV of energy, more than enough to ionize any atoms or molecules it encounters. The red contours are radio data shown superimposed atop the X-ray data. (M.J. HARDCASTLE ET AL. (2015), FROM ARXIV.ORG/ABS/1510.08392)

Like all known active galaxies, Pictor A is powered by a supermassive black hole many millions to billions of times our Sun’s mass.

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The galaxy Centaurus A is the closest example of an active galaxy to Earth, with its high-energy jets caused by electromagnetic acceleration around the central black hole. The extent of its jets are far smaller than the jets that Chandra has observed around Pictor A. (NASA/CXC/CFA/R.KRAFT ET AL.)

Black holes can accelerate and eject infalling matter, leading to intense emissions.

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A black hole more than six billion times the mass of the Sun powers the X-ray jet at the center of M87, which is many thousands of light-years in extent. If this image looks familiar, it might be: M87 is the first galaxy to have its event horizon imaged directly, owing to the incredible collaborative work of scientists working on the Event Horizon Telescope. (NASA/HUBBLE/WIKISKY)

The light released spans the spectrum from high-energy X-rays to low-energy radio waves.

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Appearing on a scale far greater than the scale of the galaxy itself, the jet emitted from Pictor A can be seen in the data at various points, thanks to the interactions between these high-energy emissions and the gas in the surrounding environment of the galaxy itself. The ‘hot spot’ at the end of the jet can be seen at the far right of the upper view of this image. (M.J. HARDCASTLE ET AL. (2015), FROM ARXIV.ORG/ABS/1510.08392)

The radio lobes of gas provide a medium for high-energy X-rays to interact with.

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While distant host galaxies for quasars and active galactic nuclei can often be imaged in visible/infrared light, the jets themselves and the surrounding emission is best viewed in both the X-ray and the radio, as illustrated here for the galaxy Hercules A. The gaseous outflows are highlighted in the radio, and if X-ray emissions follow the same path into the gas, they can be responsible for creating hot spots owing to the acceleration of electrons. (NASA, ESA, S. BAUM AND C. O’DEA (RIT), R. PERLEY AND W. COTTON (NRAO/AUI/NSF), AND THE HUBBLE HERITAGE TEAM (STSCI/AURA))

When these interactions cause electrons to exceed the speed of sound in the gaseous medium, it creates intense shock waves.

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An annotated version of the X-ray/radio composite image of Pictor A, showing the counterjet, the Hot Spot, and many other fascinating features. (X-RAY: NASA/CXC/UNIV OF HERTFORDSHIRE/M.HARDCASTLE ET AL., RADIO: CSIRO/ATNF/ATCA)

The “hot spot” illustrated on the above NASA image is the definitive evidence of the jet-like nature of these X-rays and accelerated electrons.

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Artist’s impression of an active galactic nucleus. The supermassive black hole at the center of the accretion disk sends a narrow high-energy jet of matter into space, perpendicular to the disc. A blazar about 4 billion light years away is the origin of many of the highest-energy cosmic rays and neutrinos, but even the full suite of active galaxies cannot compete with Pictor A in terms of raw size of the X-ray jet. (DESY, SCIENCE COMMUNICATION LAB)

Alternative explanations involving boosted CMB photons have been ruled out.

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The most distant X-ray jet in the Universe, from quasar GB 1428, located 12.4 billion light years from Earth. This jet comes from electrons heating CMB photons, but that mechanism is ruled out for Pictor A. (X-RAY: NASA/CXC/NRC/C.CHEUNG ET AL; OPTICAL: NASA/STSCI; RADIO: NSF/NRAO/VLA)

Pictor A possesses the largest X-ray jet in the known Universe.

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Despite many years of observations, we still don’t know whether the galaxy Pictor A, shown as viewed in optical light (main) and ultraviolet light (inset), is a spiral, elliptical, or irregular galaxy. Superior observations of the galaxy itself have yet to be acquired. (DIGITIZED SKY SURVEY 2 (MAIN); NASA/GALEX (INSET))

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“Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan