INTEGRAL helps to get to the bottom of a spitting black hole
V404 Cyg (GS 2023+338) is a black hole X-ray binary, in which a black
hole is feeding on a nearby star (see also INTEGRAL POMs
July 2015,
November 2015,
July 2016,
October 2016,
April 2017).
The gas pulled off
the companion star forms a disk of material that spirals in towards the
black hole under gravity. This inflow of gas also powers the ejection of
material and energy in the form of fast-moving, collimated jets.
Radio data from the Very Long Baseline Array together with high-energy
data from INTEGRAL and other facilities have helped shed light on the
behaviour of the jets, and how it is affected by the motion of gas in
the innermost regions of the disk, very close to the black hole.
While jets are usually thought to shoot straight out from the poles of
black holes, in a direction perpendicular to the accretion disk, these
jets were seen to move away in different directions at different times.
And they were changing direction very quickly — on timescales of less
than a couple of hours!
What’s different in V404 Cyg is that it is thought that the disk of
material and the black hole are misaligned. The spinning black hole
pulls spacetime around with it, in a phenomenon known as 'frame
dragging'. This causes the inner part of the disk to precess, making it
wobble around like a spinning top. Since the black hole was feeding very
quickly, the disk became puffed up. It is likely that this allowed it
to redirect the jets as it changed orientation, causing them to move
outwards in different directions. Similar dynamics should be expected in
any rapidly-feeding black hole whose spin is misaligned with the
inflowing gas. This would both affect the observational characteristics
of the jets, and distribute their energy more uniformly over the
surrounding environment.
Movies captions: Left panel:
Movie made from high-resolution radio images taken on 22nd
June 2015 with the National Science Foundation's Very Long Baseline
Array. It shows clouds of plasma in the precessing jets moving away from
the black hole in different directions. The scale of the images is
approximately the size of our Solar System, and time is shown by the
clock. Credits: ICRAR and the University of Alberta
Right panel:
An animation of the precessing jets and accretion flow in
V404 Cygni narrated by Associate Professor (and Nature article first
author) James Miller-Jones of Curtin University and ICRAR. Zooming in
from the high-speed plasma clouds observed with our radio telescope, we
see the binary system itself. Mass from the star spirals in towards the
black hole via an accretion disk, whose inner regions are puffed up by
intense radiation. The spinning black hole pulls spacetime (the green
gridlines) around with it, causing the inner disk to precess like a
spinning top, redirecting the jets as it does so. Credit: ICRAR