Black hole jets in HD
Astronomers have produced the sharpest images ever of twin jets racing outward from the vicinity of a galaxy’s central black hole.
Using the combined power of nine radio telescopes arrayed across the Southern Hemisphere, the images reveal features just 15 light-days across in the heart of the nearby galaxy Centaurus A, 12 million light-years away. At its core, the galaxy contains a black hole as massive as 55 million suns.
The new images home in on a region around the black hole less than 4.2 light-years across — smaller than the distance between the sun and its nearest star, says Roopesh Ojha of NASA’s Goddard Space Flight Center in Greenbelt, Md. Ojha and his colleagues describe their findings in the June Astronomy & Astrophysics.
To obtain the high-resolution radio images, the team combined data from an array of radio telescopes with resolution equivalent to a single superdish about 80 percent of Earth’s diameter.
The images reveal for the first time just how close to a black hole a jet can form, a constraint that must now be incorporated into models of how such jets are generated, Ojha says.
The jets are thought to arise as matter approaches and falls onto the black hole, fueling the beast and radiating energy in the process. But the exact details are unknown, Ojha notes.
The team found that the jets, which near the black hole travel at about one-third the speed of light, are surprisingly narrow near their source. That could be a sign that the gravitational beast pulls in material at a relatively moderate, regular rate.
Another nearby galaxy, M87, has wider jets close to its central black hole, an indication that the hole may swallow its prey in great gulps. M87’s black hole is much heavier, however, “and it might just be a messier eater,” says Ojha.
However, with detailed images of jets from only two nearby black holes, cautions Alan Marscher of Boston University, “I don’t think we need to appeal yet to sloppy versus neat eaters.”