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Post Info TOPIC: Messier 87


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RE: Messier 87
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Galactic particle accelerator located
An unprecedented measuring campaign has succeeded in precisely defining the place of origin of high-energy gamma radiation in the galaxy Messier 87. This radiation can only be produced by accelerating elementary particles to very high energies in enormous cosmic objects. Now the underlying extreme physical processes and inherent implications can be investigated in more detail.
Our neighbouring galaxy Messier 87 (M87) accelerates elementary particles to extremely high energies - millions of times higher than anything possible with the particle accelerator LHC (Large Hadron Collider) at CERN. These particles contribute to the cosmic radiation that can be measured on earth. For the first time, physicists can now locate exactly where the acceleration of the particles takes place, i.e. right next to the black hole in the centre of the galaxy.

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An international team of scientists that includes two Washington University researchers have discovered very high energy gamma rays coming from an area close to a supermassive black hole.
The discovery took place in a galaxy, M87, which is about 50 million light years from earth. At its center is a black hole more than six billion times larger than the sun.

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M87
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Title: The Black Hole Mass, Stellar M/L, and Dark Halo in M87
Authors: Karl Gebhardt, Jens Thomas
(Version v2)

We model the dynamical structure of M87 (NGC4486) using high spatial resolution long-slit observations of stellar light in the central regions, two-dimensional stellar light kinematics out to half of the effective radius, and globular cluster velocities out to 8 effective radii. We simultaneously fit for four parameters, black hole mass, dark halo core radius, dark halo circular velocity, and stellar mass-to-light ratio. We find a black hole mass of 6.4(0.5)x10^9 Msun(the uncertainty is 68% confidence marginalised over the other parameters). The stellar M/L_V=6.30.8. The best-fitted dark halo core radius is 142 kpc, assuming a cored logarithmic potential. The best-fitted dark halo circular velocity is 71515 km/s. Our black hole mass is over a factor of 2 larger than previous stellar dynamical measures, and our derived stellar M/L ratio is 2 times lower than previous dynamical measures. When we do not include a dark halo, we measure a black hole mass and stellar M/L ratio that is consistent with previous measures, implying that the major difference is in the model assumptions. The stellar M/L ratio from our models is very similar to that derived from stellar population models of M87. The reason for the difference in the black hole mass is because we allow the M/L ratio to change with radius. The dark halo is degenerate with the stellar M/L ratio, which is subsequently degenerate with the black hole mass. We argue that dynamical models of galaxies that do not include the contribution from a dark halo may produce a biased result for the black hole mass. This bias is especially large for a galaxy with a shallow light profile such as M87, and may not be as severe in galaxies with steeper light profiles unless they have a large stellar population change with radius.

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RE: Messier 87
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The most massive black hole yet weighed lurks at the heart of the relatively nearby giant galaxy M87.
The supermassive black hole is two to three times heftier than previously thought, a new model showed, weighing in at a whopping 6.4 billion times the mass of the sun. The new measure suggests that other black holes in nearby large galaxies could also be much heftier than current measurements suggest, and it could help astronomers solve a longstanding puzzle about galaxy development.

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A halo of stars surrounding a galaxy in the relatively nearby Virgo cluster is missing, possibly torn away by a neighbouring galaxy or snuffed out by the collapse of the cluster itself.
The victim is the giant elliptical galaxy Messier 87, which lives about 50 million light-years away in the center of the Virgo, the closest galaxy cluster to Earth.


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Giant Galaxy Messier 87 finally sized up
Using ESO's Very Large Telescope, astronomers have succeeded in measuring the size of giant galaxy Messier 87 and were surprised to find that its outer parts have been stripped away by still unknown effects. The galaxy also appears to be on a collision course with another giant galaxy in this very dynamic cluster.
The new observations reveal that Messier 87's halo of stars has been cut short, with a diameter of about a million light-years, significantly smaller than expected, despite being about three times the extent of the halo surrounding our Milky Way. Beyond this zone only few intergalactic stars are seen.

"This is an unexpected result. Numerical models predict that the halo around Messier 87 should be several times larger than our observations have revealed. Clearly, something must have cut the halo off early on" - co-author Ortwin Gerhard.

The team used FLAMES, the super-efficient spectrograph at ESO's Very Large Telescope at the Paranal Observatory in Chile, to make ultra-precise measurements of a host of planetary nebulae in the outskirts of Messier 87 and in the intergalactic space within the Virgo Cluster of galaxies, to which Messier 87 belongs. FLAMES can simultaneously take spectra many sources, spread over an area of the sky about the size of the Moon.

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HST-1
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Title: Variability Timescales in the M87 Jet: Signatures of E-Squared Losses, Discovery of a Quasi-period in HST-1, and the Site of TeV Flaring
Authors: D. E. Harris (SAO), C. C. Cheung (GSFC), Lukasz Stawarz (KIP/Stanford), J. A. Biretta (STScI), E. S. Perlman (FIT)

We investigate the variability timescales in the jet of M87 with two goals. The first is to use the rise times and decay times in the radio, ultraviolet and X-ray lightcurves of HST-1 to constrain the source size and the energy loss mechanisms affecting the relativistic electron distributions. HST-1 is the first jet knot clearly resolved from the nuclear emission by Chandra and is the site of the huge flare of 2005. We find clear evidence for a frequency-dependent decrease in the synchrotron flux being consistent with E-squared energy losses. Assuming that this behavior is predominantly caused by synchrotron cooling, we estimate a value of 0.6 mG for the average magnetic field strength of the HST-1 emission region, a value consistent with previous estimates of the equipartition field. In the process of analysing the first derivative of the X-ray light curve of HST-1, we discovered a quasi-periodic oscillation which was most obvious in 2003 and 2004 prior to the major flare in 2005. The four cycles observed have a period of order 6 months. The second goal is to search for evidence of differences between the X-ray variability timescales of HST-1 and the unresolved nuclear region (diameter <0.6"). These features, separated by more than 60 pc, are the two chief contenders for the origin of the TeV variable emissions observed by HESS in 2005 and by MAGIC and VERITAS in 2008. The X-ray variability of the nucleus appears to be at least twice as rapid as that of the HST-1 knot. However, the shortest nuclear variability timescale we can measure from the Chandra data (<= 20 days) is still significantly longer than the shortest TeV variability of M87 reported by the HESS and MAGIC telescopes (1-2 days).

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Title: Hubble Space Telescope observations of an extraordinary flare in the M87 jet
Authors: Juan P. Madrid (McMaster U. Canada)

HST-1, a knot along the M87 jet located 0.85 arcsec from the nucleus of the galaxy has experienced dramatic and unexpected flaring activity since early 2000. We present analysis of Hubble Space Telescope Near-Ultraviolet (NUV) imaging of the M87 jet from 1999 May to 2006 December that reveals that the NUV intensity of HST-1 has increased 90 times over its quiescent level and outshines the core of the galaxy. The NUV light curve that we derive is synchronous with the light curves derived in other wavebands. The correlation of X-ray and NUV light curves during the HST-1 flare confirms the synchrotron origin of the X-ray emission in the M87 jet. The outburst observed in HST-1 is at odds with the common definition of AGN variability usually linked to blazars and originating in close proximity of the central black hole. In fact, the M87 jet is not aligned with our line of sight and HST-1 is located at one million Schwarzchild radii from the super-massive black hole in the core of the galaxy.

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RE: Messier 87
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