Tracking a black hole eruption.

On Oct. 29, astronomers around the world were alerted that a massive, compact body 40,000 light-years from Earth was once again shooting off fireworks. Within 2 days, scientists had trained an array of radio telescopes on the object, a suspected black hole partnered by an ordinary star.

For 2 weeks, the telescopes tracked the evolution of two oppositely directed jets of radio-emitting gas spewed by the black hole system, known as GRS 1915+105. Each jet races at 90 percent of the speed of light. Because one of the jets points toward Earth, it appears to move twice as fast as this cosmic speed limit.

Astronomers had previously observed superluminal motion of material expelled by GRS 1915+105, notably during a giant outburst 3 years ago (SN: 9/3/94, p. 150). The network of telescopes employed during the most recent event, however, tracked the activity closer to the black hole than ever before--within about 400 light-years, says Thomas W.B. Muxlow of the University of Manchester in England. He and his colleagues announced their findings this week.

Known as MERLIN (multi-element radio-linked interferometer network), the telescope array consists of six detectors spread across England, working in concert to create radio images sharper than the Hubble Space Telescope can generate in visible light. Other arrays, even larger than MERLIN, can home in on smaller objects but can't detect such faint emissions, Muxlow notes.

GRS 1915+105 is called a microquasar because its stream of X rays and blasts of radio-emitting gas resemble a scaled-down version of the action of quasars in faraway galaxies. By monitoring this nearby source, "we can apply [what we learn] to much more distant objects in the universe," says Muxlow.