* Astronomy

In our violent, discordant, and effervescent universe, reality always seems to be stranger than fiction. Case in point: there is a galaxy 54 million light-years away that is shooting out a 5,000-light-year-long, narrow beam of radiation and plasma that is as opulent as a Star Wars light sabre and as destructive as the film's Death Star. This extragalactic jet is being fuelled and ejected from the vicinity of a monster black hole that is 3 billion times the mass of our Sun. The disk around a rapidly spinning black hole has magnetic field lines that entrap ionised gas falling toward the black hole. These particles, along with radiation, flow rapidly away from the black hole along the magnetic field lines. The rotational energy of the spinning accretion disk adds momentum to the outflowing jet.
NASA's Hubble Space Telescope has been used to keep an eye on these million-degree fireworks for more than a decade. Hubble has caught the jet flickering. In particular, a glowing knot in the outflowing stream has gotten as bright as the galaxy's star-crowded nucleus, only to dim and then brighten again. Astronomers don't know why the black-hole torch is fluctuating, but it may be similar to the physics that causes flares to explode on the Sun. Plasma trapped in the Sun's magnetic field gets pinched and heated as the lines collapse and put the squeeze on it. Or, more simply, the jet may be ploughing into an unseen clump of interstellar matter -- at more than half the speed of light!

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M87, the central galaxy of the Virgo cluster in a distance of only 50 million light years, was observed by Yuri Kovalev from the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn and his colleagues with the VLBA (Very Long Baseline Array) at 2 cm wavelength. The resulting image provides details down to a resolution of one milli-arcsecond, corresponding to a linear resolution of only three light months. The new image of the inner radio jet of M87 shows a highly collimated jet which appears limb-brightened, and also a faint counter-jet. It is unprecedented in its combination of sensitivity and spatial resolution.


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The Inner Jet of the Radio Galaxy M87 located in the Virgo cluster. The angular resolution of this false-color radio image observed by the VLBA at 2 cm wavelength is approximately one milli-arcsecond, fifty times better than that of the Hubble Space Telescope at optical wavelengths. The image shows a limb brightened jet and a faint counter-jet. The central gap is consistent with the presence of a fast inner jet which is beamed away from the observer surrounded by a slower moving outer plasma seen by the VLBA.
Image: Y.Y. Kovalev, MPIfR Bonn

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Title: Filaments, Bubbles, and Weak Shocks in the Gaseous Atmosphere of M87
Authors: W. Forman, E.Churazov, C. Jones, M. Markevitch, P. Nulsen, A. Vikhlinin, M. Begelman, H. Bohringer, J. Eilek, S. Heinz, R. Kraft, F. Owen, M. Pahre
(version, v2)

We present the first results from a 500 ksec Chandra ACIS-I observation of M87. At soft energies (0.5-1.0 keV), we detect filamentary structures associated with the eastern and southwestern X-ray and radio arms. Many filaments are spatially resolved with widths of ~300 pc. This filamentary structure is particularly striking in the eastern arm where we suggest the filaments are outer edges of a series of plasma-filled, buoyant bubbles whose ages differ by ~6 x 10^6 years. These X-ray structures may be influenced by magnetic filamentation. At hard energies (3.5-7.5 keV), we detect a nearly circular ring of outer radius 2.8' (13 kpc) which provides an unambiguous signature of a weak shock, driven by an outburst from the SMBH. The density rise in the shock is ~1.3 (Mach number, M~1.2). The observed spectral hardening in the ring corresponds to a temperature rise T_shock / T_0 ~ 1.2, or M~1.2, in agreement with the Mach number derived independently from the gas density. Thus, for the first time, we detect gas temperature and density jumps associated with a classical shock in the atmosphere around a supermassive black hole. We also detect two additional surface brightness edges and pressure enhancements at radii of ~0.6' and ~1'. The ~0.6' feature may be over-pressurised thermal gas surrounding the relativistic plasma in the radio cocoon, the ''piston'', produced by the current episode of AGN activity. The over-pressurised gas is surrounded by a cool gas shell. The ~1' feature may be an additional weak shock from a secondary outburst. In an earlier episode, the ''piston'' was responsible for driving the 2.8' shock.

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Title: The gaseous atmosphere of M87 seen with XMM-Newton
Authors: A. Simionescu, H. Böhringer, M. Brüggen, A. Finoguenov

M87 is a key object whose study can reveal the complex phenomena in cooling cores. We use a deep XMM-Newton observation of M87 to produce detailed temperature, pressure and entropy maps in order to analyse the physical processes of cooling cores and of their heating mechanisms. We employed both broad-band fitting and full spectroscopical one-temperature model analysis to derive temperature and surface brightness maps, from which the pseudo-deprojected entropy and pressure were calculated. We discuss possible physical interpretations of small deviations from radial and elliptical symmetry in these maps. The most prominent features observed are the E and SW X-ray arms that coincide with powerful radio lobes, a weak shock at a radius of 3', an overall ellipticity in the pressure map and a NW/SE asymmetry in the entropy map which we associate with the motion of the galaxy towards the NW. For the first time we find evidence that cold, metal-rich gas is being transported out of the centre, possibly through bubble-induced mixing. Several edges in the abundance map indicate an oscillation of the galaxy along the NW/SE direction. Furthermore, the radio lobes appear to rise along the short axis of the elliptical pressure distribution, following the steepest potential gradient, and seem to contain a nonthermal pressure component.

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