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Delving into the mystery of black hole jets

Relativistic jets spewing out of spinning disks around black holes are possibly the most powerful phenomena in astrophysics. New observations have led to a sea change in our understanding of the processes involved.

Climate Change and Environment

It has long been known that jets can be produced by the massive black holes within active galactic nuclei (AGN). Over the past decade, increasing evidence of jets from nearly all classes of accreting objects has accumulated. Observations of jets from neutron stars, which show strong variability on timescales shorter than the history of astronomy, suggest that the environment of stellar-mass black holes provide less resistance than the environment of AGN. Researchers, working on the EU-funded RELATIVISTIC JETS project investigated a jet emanating from a black hole and a neutron star in close orbit around each other which are luminous in X-rays. While most commonly associated with X-ray emissions, this binary system emits at all observable wavelengths. Observations in the radio, infrared, ultraviolet, X-rays and gamma-rays – part of the electromagnetic spectrum – helped piece together information about particles ejected as a collimated outflow. Going one step further, researchers developed a detailed theoretical model that is able to reproduce the observed spectrum from the binary system Cygnus X-1. Containing a star and a stellar-mass black hole, Cygnus X-1 is tucked within the constellation of Cygnus the swan, inside the Milky Way. Significantly different from other X-ray binaries, the magnetic field within the particle jet was found to be highly ordered. The RELATIVISTIC JETS astronomers turned their telescopes to many different X-ray binaries. Determining whether emissions come from a jet or from some other part of the accretion flow was difficult as any characteristic size scale for the accreting black hole is proportional to its mass. However, they can boast the first direct evidence in optical and infrared wavelengths of a jet shot from a slowly accreting X-ray binary. Research suggest that particle jets shot from black holes produce much of the Universe's budget of high energy gamma rays. Prior failure to realise the importance of emissions at other wavelengths is perhaps the reason why it has taken so long to see jets inflating the interstellar medium from slowly accreting binary systems. Project observations have been made available to the scientific community to elucidate further the physics underlining the formation of black hole jets.

Keywords

Black hole, jets, astrophysics, active galactic nuclei, neutron stars, X-ray binary, gamma rays, Cygnus the swan, Milky Way

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