From cradle to grave

Astronomers have been using the Chandra X-ray Observatory and radio telescopes to observe two opposing jets of high-energy particles emitted following an outburst, first detected in 1998 by NASA’s Rossi X-ray Timing Explorer, from the double-star system XTE J1550-564. The X-ray jets, which require a continuous source of trillion-volt electrons to remain bright, were observed moving at about half the speed of light. Four years later, they are now more than three light years apart and slowing down. One of the jets has recently been observed to fade. The observations indicate that the eastern jet is moving along a line tilted toward the Earth whereas the western jet is pointed away from the Earth. This alignment explains why the eastern jet appears to have traveled farther from the black hole than the other. However, with this alignment, the eastern jet should be brighter, while the western jet was actually three times brighter. “This poses a puzzle. The simple model for jets doesn’t explain what we are seeing,” said Philip Kaaret of the Harvard-Smithsonian Center for Astrophysics. “Either the black hole may somehow be feeding more energy into the western jet, or that jet has run into a dense cloud.”