Galaxies around the universe are now known to have supermassive black holes at their cores, and these SMBH’s are known for their powerful jets of high energy partcicles streaming away along their north and south poles. Recently, the Chandra X-ray space telescope has been peering through the dense wall of gas and dust which lies between us and our own SMBH, and has finally confirmed that we too have one of these vast jets in our own Milky Way galaxy.High energy jets like the ones discovered by Chandra are considered to be characteristic of all objects posessing strong gravity fields, from black holes of all sizes to young stars whose solar winds are not yet developed enough to disrupt infalling material. As gas and dust fall in towards a black hole, they begin spiralling around, like water down a drain. As they get closer, the resulting disc of material spins faster and faster, until internal friction heats it up to millions of degrees. This heat ionizes the individual atoms, turning the material into a hot plasma of charged particles. The resulting magnetic field scoops some of this material out of the disc and catapults it outwards along the north and south poles of the black hole at speeds measuring in the hundreds of kilometers per second.
This phenomenon has been observed in countless distant galaxies, and is a valuable tool for measuring the age of a galaxy: The stronger and more energetic the jets, the more gas is funneling into the black hole. More gas means a galaxy is still young, as it has not yet had time to convert all that gas into stars. However, astronomers had never been able to confirm that our own galaxy had such a jet coming from its SMBH (known as Sgr-A, because it lies in the constellation of Sagittarius and is a powerful source of radio energy). Any such jet would have to be weak, since Sgr-A is going through a quiet patch; there is very little material near the galactic core for it to consume. But previous attempts to find these jets had failed: They were either inconclusive, or disagreed with other on such basic details as the direction in which the jets are shooting.
Chandra’s observations have changed that, by conclusively demonstrating the presence of one jet (the other is presumably concealed behind a region of gas or dust), which can be seen in the image above as a straight line of gas glowing in X-ray wavelengths (purple). The bulbous shape at the end of the jet comes about because the jet is ploughing into a thin cloud of gas further from the black hole, causing it to begin billowing out into a shock wave. The direction in which it moves confirms previous predictions based on the discoveries of large bubbles above and below the milky way galaxy, which were presumed to have been carved out by the jets in their more powerful earlier years.
“We were very eager to find a jet from Sgr A* because it tells us the direction of the black hole’s spin axis. This gives us important clues about the growth history of the black hole,” said Mark Morris of the University of California at Los Angeles,
Knowing the direction of the jets provides important information about the history of the galaxy. If the Milky Way had interacted with any other galaxies in the past few billion years, we would find that Sgr-A is spinning at a different angle to that of the galaxy as a whole, because it would have eventually merged with the other galaxy’s SMBH. Instead, astronomers have found that the spins of black hole and galaxy are neatly aligned around the same axis, showing that gas and dust have been allowed to fall into the black hole undisturbed for at least the past ten billion years.
The supermassive black hole at the center of the Milky Way is about four million times more massive than our Sun and lies about 26,000 light-years from Earth. The Chandra observations in this study were taken between September 1999 and March 2011, with a total exposure of about 17 days. The results of these observations were published in a paper which will soon be published in The Astrophysical Journal.