Ministerio de Ciencia, Innovación y Universidades Gobierno de Canarias Universidad de La Laguna CSIC Centro de Excelencia Severo Ochoa

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· More scientific highlights from this year.

Black holes' magnetism is surprisingly weak

Author/s: Y. Dallilar, S. S. Eikenberry, A. Garner, R. D. Stelter, A. Gottlieb, P. Gandhi, P. Casella, V. S. Dhillon, T. R. Marsh, S. P. Littlefair, L. Hardy, R. Fender, K. Mooley, D. J. Walton, F. Fuerst, M. Bachetti, A. J. Castro-Tirado, M. Charcos, M. L. Edwards, N. M. Lasso-Cabrera, A. Marin-Franch, S. N. Raines, K. Ackley, J. G. Bennett, A. J. Cenarro, B. Chinn, H. V. Donoso, R. Frommeyer, K. Hanna, M. D. Herlevich, J. Julian, P. Miller, S. Mullin, C. H. Murphey, C. Packham, F. Varosi, C. Vega, C. Warner, A. N. Ramaprakash, M. Burse, S. Punnadi, P. Chordia, A. Gerarts, H. de Paz Martín, M. Martín Calero, R. Scarpa, S. Fernandez Acosta, W. M. Hernández Sánchez, B. Siegel, F. Francisco Pérez, H. D. Viera Martín, J. A. Rodríguez Losada, A. Nuñez, A. Tejero, C. E. Martín González, C. Cabrera Rodríguez, J. Molgó, J. Esteban Rodriguez, J. I. Fernández Cáceres, L. A. Rodríguez García, M. Huertas Lopez, R. Dominguez, T. Gaggstatter, A. Cabrera Lavers, S. Geier, P. Pessev, A. Sarajedini

Reference: 2017 Science 358 1299 | Link

Multiwavelength (radio, near-infrared, optical, and X-ray) light curves of V404 Cygni during our observations on BJD 57198 during the 2015 outburst. The IR/optical light curves show slow modulations punctuated by fast red flares. Note that the two optical/IR "bumps" at ~54 minutes and ~63 minutes correlate with bright X-ray flares, while the optical/IR bump at ~58 minutes has much smaller (if any) X- ray activity, indicating that simple models invoking X-ray reprocessing are unlikely.
Multiwavelength (radio, near-infrared, optical, and X-ray) light curves of V404 Cygni during our observations on BJD 57198 during the 2015 outburst. The IR/optical light curves show slow modulations punctuated by fast red flares. Note that the two optical/IR "bumps" at ~54 minutes and ~63 minutes correlate with bright X-ray flares, while the optical/IR bump at ~58 minutes has much smaller (if any) X- ray activity, indicating that simple models invoking X-ray reprocessing are unlikely.

Black holes are famous for their supposed strength. They are normally imagined to be able to tear apart entire stars and devour them. To launch streams of matter into space at almost the speed of light. But reality turns out to be a bit different. It was now discovered that their magnetic fields are weaker than it was thought up to now. The black hole called "V404 Cygni" is about 8000 light-years from earth. The magnetic energy in its surroundings was now determined to be about 400 times lower than previously estimated. This is a step towards the understanding of black holes' magnetism, and also the behaviour of matter in the most extreme conditions, which for example might help with the development of nuclear fusion reactors. The result will also help with solving the mystery of why at the same time at which they swallow everything else, black holes are launching a jet of particles at nearly the speed of light. The surprisingly low measurements rule out theoretical models which involved strong magnetic fields accelerating and directing the jet flows. The authors derived the results from multiwavelength data obtained in 2015 during a rare outburst of the black hole V404 Cygni. The data set included those taken with the near-infrared camera CIRCE at the Gran Telescopio Canarias in fast photometry mode with 0.1 s time-resolution in Ks filter. Such small black holes, like the one in this study, show sudden outbursts which are short-lived. The 2015 event of V404 Cygni only lasted a few weeks, while its previous outburst had been in 1989.

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