Illustration of a Stellar-Mass Black Hole
This is an artist's representation of GRO J1655-40, a binary star system observed in April 2005 by Chandra. This binary consists of a black hole and a normal star shown in blue. Gas is being pulled away from the star and falling onto a red disk spinning around the black hole. Some of this gas spirals in towards the black hole, generating copious amounts of light along the way. This infall of matter is only possible if the gas loses some of its energy either through a wind, shown in blue, or friction in the disk.
(Illustration: NASA/CXC/M.Weiss)

Chandra X-ray Spectrum of GRO J1655-40
This shows an X-ray spectrum obtained by Chandra observations. The dips seen in the spectrum are produced by absorption from a wide variety of atoms in the gas around the black hole, ranging from oxygen to nickel. A detailed study of these absorption features shows that the atoms are highly ionized and are moving away from the black hole in a high-speed wind. The conclusion of this study is that this wind is driven by magnetic fields.
(Credit: NASA/CXC/U.Michigan/J.Miller et al.)

Evidence for Wind in the GRO J1655-40 Spectrum
The X-ray spectra in this figure show evidence for a wind in GRO J1655-40. The dips seen here are produced by absorption from a wide variety of atoms in the gas around the black hole. The blue line shows the Chandra spectrum of J1655 and the yellow line shows a model spectrum. In the model spectrum the absorption dips are plotted at their natural wavelengths, that is their expected location for gas that is not undergoing bulk motion either towards or away from us. Comparing the two spectra shows that the Chandra spectrum is shifted towards shorter wavelengths because of the Doppler effect, giving evidence for a wind blowing towards us.
(Credit: NASA/CXC/U.Michigan/J.Miller et al.)

Illustration of Magnetic Fields in GRO J1655-40
This artist's representation shows how magnetic fields may drive a wind in GRO J1655-40. Rotation in the disk plus magnetic actions in the disk can cause magnetic fields, shown here in this simplified version as black lines, to become coiled up like a snake. This can result in gas being driven upwards and away from the disk by pressure created by the magnetic fields, resulting in the wind observed by Chandra.
(Illustration: NASA/CXC/M.Weiss)

AGN illustration
This is an artist's representation of an active galactic nucleus (AGN) at the center of a galaxy. Gas is pulled towards a supermassive black hole and falls onto a disk, shown in red. Some of this gas spirals inwards, generating massive amounts of radiation before falling onto the black hole. This infall of matter is only possible if the gas loses some of its energy either through a wind, shown in blue, or friction in the disk. The most spectacular AGN behavior is seen in quasars, the brightest objects known in the Universe.
(Illustration: NASA/CXC/M.Weiss)

Comparison of an AGN and a Stellar-Mass Black Hole
These two illustrations compare the basic structure of an active galactic nucleus (AGN) and a stellar-mass black hole in a binary system. The AGN contains a supermassive black hole attracting gas from the central regions of a galaxy, while the stellar-mass black hole, typically with a mass about 5-10 times that of the Sun, is rapidly pulling gas from a normal companion star. Although the stellar-mass black hole is millions of times smaller than the black hole in the AGN, there are many similarities in structure between these two types of object. As shown here, both contain black holes surrounded by a disk of hot gas, and a wind blowing away from the disk. There are also many similarities in observational properties. Stellar-mass black holes can therefore be used as scale-models of AGN, and the mechanism that drives the wind - causing gas in the disk to lose energy and fall onto the black hole - is expected to be the same for both classes.
(Illustration: NASA/CXC/M.Weiss)

A Familiar Disk: Saturn
This illustration shows the rings of Saturn, an example of a disk that is very familiar to us. The material in this disk loses very little energy because of friction. Therefore, compared to a black hole such as GRO J1655-40, the disk is very stable, and is much cooler and fainter.
(Illustration: NASA/CXC/M.Weiss)