Astronomy: Cosmic triangles and black-hole masses
Nature 515, 7528 (2014). doi:10.1038/515498a
Authors: Martin Elvis
A geometric measurement of the distance to a nearby galaxy implies a larger mass for its central black hole than previously calculated, and a consequent increase for most other masses of such black holes. See Letter p.528
A dust-parallax distance of 19 megaparsecs to the supermassive black hole in NGC 4151
Nature 515, 7528 (2014). doi:10.1038/nature13914
Authors: Sebastian F. Hönig, Darach Watson, Makoto Kishimoto & Jens Hjorth
The active galaxy NGC 4151 has a crucial role as one of only two active galactic nuclei for which black hole mass measurements based on emission line reverberation mapping can be calibrated against other dynamical techniques. Unfortunately, effective calibration requires accurate knowledge of the distance to NGC 4151, which is not at present available. Recently reported distances range from 4 to 29 megaparsecs. Strong peculiar motions make a redshift-based distance very uncertain, and the geometry of the galaxy and its nucleus prohibit accurate measurements using other techniques. Here we report a dust-parallax distance to NGC 4151 of megaparsecs. The measurement is based on an adaptation of a geometric method that uses the emission line regions of active galaxies. Because these regions are too small to be imaged with present technology, we use instead the ratio of the physical and angular sizes of the more extended hot-dust emission as determined from time delays and infrared interferometry. This distance leads to an approximately 1.4-fold increase in the dynamical black hole mass, implying a corresponding correction to emission line reverberation masses of black holes if they are calibrated against the two objects with additional dynamical masses.
Astronomy: Merged stars dodge black hole
Nature 515, 7527 (2014). doi:10.1038/515315c
A mysterious cloud-like object that survived a close encounter with a black hole might be a merged pair of stars.Andrea Ghez of the University of California in Los Angeles and her team used the Keck telescopes on Mauna Kea in Hawaii to observe the
The power of relativistic jets is larger than the luminosity of their accretion disks
Nature 515, 7527 (2014). doi:10.1038/nature13856
Authors: G. Ghisellini, F. Tavecchio, L. Maraschi, A. Celotti & T. Sbarrato
Theoretical models for the production of relativistic jets from active galactic nuclei predict that jet power arises from the spin and mass of the central supermassive black hole, as well as from the magnetic field near the event horizon. The physical mechanism underlying the contribution from the magnetic field is the torque exerted on the rotating black hole by the field amplified by the accreting material. If the squared magnetic field is proportional to the accretion rate, then there will be a correlation between jet power and accretion luminosity. There is evidence for such a correlation, but inadequate knowledge of the accretion luminosity of the limited and inhomogeneous samples used prevented a firm conclusion. Here we report an analysis of archival observations of a sample of blazars (quasars whose jets point towards Earth) that overcomes previous limitations. We find a clear correlation between jet power, as measured through the γ-ray luminosity, and accretion luminosity, as measured by the broad emission lines, with the jet power dominating the disk luminosity, in agreement with numerical simulations. This implies that the magnetic field threading the black hole horizon reaches the maximum value sustainable by the accreting matter.
Philae’s 64 hours of comet science yield rich data
Nature 515, 7527 (2014). http://www.nature.com/doifinder/10.1038/515319a
Author: Elizabeth Gibney
Comet lander is now hibernating, but has already altered our understanding of these objects.