Our targets are black hole systems in our Galaxy, the Milky Way. These black hole systems are called microquasars and the most famous example of this is one called SS433.
At the heart of SS433 is a black hole, probably somewhat more massive than our sun, which is sucking matter from the outer layers of a nearby star. As the matter falls towards the black hole, it flattens into what is known as an accretion disc. From this disc oppositely-directed jets of hydrogen are fired away from the black hole at speeds of a quarter of the speed of light (over 160 million miles an hour!). The directions in which the jets are fired sweep out a cone in space, every 162 days resulting in the corkscrew pattern that can be seen in the above image.
The launch of jets from black holes is a phenomenon exhibited by many objects in space—even in distant quasars whose black holes are as massive as a billion suns. Yet even though these jets are common, the means by which matter and angular momentum are ejected from the vicinity of a black hole is poorly investigated and poorly understood. This is partly because the timescales on which quasar jets vary in response to variations in the fuelling in the innermost nuclei can be hundreds of thousands of years and partly because of the extreme physical conditions from which these phenomena arise which are like nothing on Earth.
Studying SS433 helps enormously: as the jets are launched from its black hole, emission lines from the Balmer hydrogen series are seen, especially the so-called H-alpha line. The motion of the jet plasma that is moving away from us shifts the wavelength of the line and reddens it, and the jet plasma that is moving towards us gives a blue-shifted line. The axis along which the jet plasma is ejected precesses (like the paddle of a kayakist as seen from the kayak) completing one revolution every six months. This causes the redshifting and blueshifting to vary with the same period.
If we can observe SS433 for a sufficiently long time we probe a range of viewing angles into the point at which the jets are launched. At some points of the precession cycle we can see the jet axis in the plane of the sky and the gravity-fed accretion disc of matter encircling the black hole appears edge-on. At other times the disc is tilted towards us and we can see straight into the centre of activity.
It is important to observe—at all these angles—how changes in the rate of fuelling (from its nearby companion star) are manifested as subsequent changes in the jet (for example as further changes in its speed or direction) and other outflows. Due to the small scale of the accretion disc, significant changes occur on timescales of less than a day. The lengthy precession period plus fine-timescale variations mean we need to obtain data every few hours over many months.
By making spectroscopic measurements of the varying emission lines in the nanoquasar SS433, with high spectral resolution over a wide wavelength range, fine-timescale variations in redshifts and blueshifts (variations in jet speed and angle of jet axis), and via a technique called Doppler tomography which tells us about the flow of matter through the accretion disc, with adequate time sampling over a sufficiently long time baseline, will open a whole new window on how jets and outflows are formed and launched near black holes.