* Astronomy

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RE: V404 Cygni

Blobrana · L

Distance to black hole no longer a secret

An international team of astronomers has accurately measured the distance from Earth to a black hole for the first time. Without needing to rely on mathematical models the astronomers came up with a distance of 7800 light years, much closer than had been assumed until now. The researchers achieved this breakthrough by measuring the radio emissions from the black hole and its associated dying star. Due to the much lower error margin (<6%), astronomers can now gain a better picture of how black holes evolve, for example. Moreover, an exact distance is important for measurements of the black hole´s spin.
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V404 Cygni.kmz
Google Sky file (1kb, kmz)

Position(2000): RA 20 24 03.78, Dec +33 52 03.2

Blobrana · L

Title: Zooming in on a sleeping giant: milliarcsecond HSA imaging of the black hole binary V404 Cyg in quiescence
Authors: J.C.A. Miller-Jones (1), E. Gallo (2), M.P. Rupen (1), A.J. Mioduszewski (1), W. Brisken (1), R.P. Fender (3,4), P.G. Jonker (5,6,7), T.J. Maccarone (3) ((1) NRAO, (2) UCSB, (3) U. Southampton, (4) U. Amsterdam, (5) SRON, (6) U. Utrecht, (7) CfA)

Observations of the black hole X-ray binary V404 Cyg with the very long baseline interferometer HSA (the High Sensitivity Array) have detected the source at a frequency of 8.4 GHz, providing a source position accurate to 0.3 mas relative to the calibrator source. The observations put an upper limit of 1.3 mas on the source size (5.2 AU at 4 kpc) and a lower limit of 7 x 10^6 K on its brightness temperature during the normal quiescent state, implying that the radio emission must be non-thermal, most probably synchrotron radiation, possibly from a jet. The radio lightcurves show a short flare, with a rise time of about 30 min, confirming that the source remains active in the quiescent state.

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