From CfA: “Magnetic Fields in Powerful Radio Jets”

Smithsonian Astrophysical Observatory
Smithsonian Astrophysical Observatory

December 25, 2015
No Writer Credit

X-ray jets from the galaxy Pictoris A. The greyscale image was taken by the Chandra X-ray Observatory and reveals the detailed X-ray structure of the jets, which extend over nearly one million light-years. The red contours show the radio emission. Astronomers analyzing these and other data have concluded that the X-ray emission is produced by rapidly moving charged particles in magnetic fields. NASA/Chandra, Hardcastle et al.

Super-massive black holes at the centers of galaxies can spawn tremendous bipolar jets when matter in the vicinity forms a hot, accreting disk around the black hole. The rapidly moving charged particles in the jets radiate when they are deflected by magnetic fields; these jets were discovered at radio wavelengths several decades ago. In the most dramatic cases, the energetic particles move at speeds close to the speed of light and extend over hundreds of thousands of light-years, well beyond the visible boundaries of the galaxy. The physical processes that drive these jets and cause them to radiate are among the most important outstanding problems of modern astrophysics.

One of the most significant and unexpected discoveries of the Chandra X-ray Observatory was that bright X-rays are also emitted by these jets.

NASA Chandra Telescope
NASA Chandra

The X-rays are also produced by the acceleration of charged particles, at least according to some models, but there are other possible mechanisms as well. Fast-moving particles can scatter background light, boosting it into the X-ray band. Alternatively, shocks can generate X-ray emission (or at least a significant portion of it), either as the jets interact with stellar winds and interstellar medium or, within the jet, as a consequence of jet variability, instability, turbulence, or other phenomena.

Original NASA description: The Hubble Space Telescope imaged this view in February 1995. The arcing, graceful structure is actually a bow shock about half a light-year across, created from the wind from the star L.L. Orionis colliding with the Orion Nebula flow.
Date February 1995
Source NASA

NASA Hubble Telescope

CfA astronomer Aneta Siemiginowska and her colleagues have studied the bright radio jet galaxy Pictoris A, located almost five hundred million light-years away, using very deep Chandra measurements – the observations used an accumulated total of over four days of time, spread over a fourteen year period. These data enabled the first detailed analysis of the spectral character of the emission all along the jets. The emission turns out to be remarkably uniform everywhere, something that is extremely unlikely if scattering were responsible, but which is a natural consequence of the magnetic field process. The scientists therefore reject the scattering model in favor of the latter. However, the jets do have within them many small clumps, internal structures, and lobes. Shocks and/or scattering are possible explanations for the emission in some of these structures. Although these new results represent some dramatic improvements in our understanding of Pic A, high-resolution radio measurements of a large sample of similar jets are now needed to refine and extend the models. Large-scale X-ray jets, for example, have been also detected in very distant quasars. The results from Pic A, together with future Chandra observations, will help astronomers determine the extent to which these distant jets also rely on the same processes, or if they invoke other ones.


“Deep Chandra Observations of Pictor A,” M.J. Hardcastle, E. Lenc, M. Birkinshaw, J.H. Croston, J.L. Goodger, H.L. Marshall, E.S. Perlman, A. Siemiginowska, Ł. Stawarz, and D.M. Worrall, MNRAS 2015 (in press).

See the full article here .

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About CfA

The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy. The long relationship between the two organizations, which began when the SAO moved its headquarters to Cambridge in 1955, was formalized by the establishment of a joint center in 1973. The CfA’s history of accomplishments in astronomy and astrophysics is reflected in a wide range of awards and prizes received by individual CfA scientists.

Today, some 300 Smithsonian and Harvard scientists cooperate in broad programs of astrophysical research supported by Federal appropriations and University funds as well as contracts and grants from government agencies. These scientific investigations, touching on almost all major topics in astronomy, are organized into the following divisions, scientific departments and service groups.