With the combined power of Earth-orbiting X-ray telescopes, including NASA’s Swift and ESA’s XMM-Newton, an international team of astronomers has found for the first time a microquasar beyond our Milky Way Galaxy.
In an object like the newly discovered microquasar XMMU J004243.6+412519, a black hole with a mass several times that of the Sun pulls material from its companion star into a rapidly-rotating disk. The disk surrounding the black hole can become so hot it emits X-rays. The disk also propels narrow jets of subatomic particles outward at speeds nearing that of light. The jets generate strong bursts of radio emission.
As the feeding rate of the black hole varies, the levels of X-ray and radio emission change, in an interplay whose details are not yet fully understood.
“This is, we think, the same mechanism at work in quasars at the cores of galaxies, where the black holes are millions of times more massive. However, in the smaller systems, things happen much more rapidly, giving us more data to help understand the physics at work,” said Dr Matthew Middleton of the University of Durham and the Astronomical Institute Anton Pannekoek in Amsterdam, Netherlands, lead author of the study published in Nature.
“Understanding how these things work is important, because we think quasars played a big role in redistributing matter and energy when the Universe was very young,” he said.
The first microquasar was discovered in 1994, and several have subsequently been found, all within our own Milky Way Galaxy.
“Obscuration within our Galaxy makes it difficult to study the disks of these microquasars in the Milky Way, but finding one in a neighboring galaxy means we probably can find many more, thus helping our efforts to better understand their physics,” Dr Middleton said.
Astronomers using ESA’s XMM-Newton detected the microquasar on January 15, 2012. The Swift and Chandra satellites then observed it regularly for more than eight weeks, while the Karl G. Jansky Very Large Array (VLA) and Very Long Baseline Array (VLBA), along with the Arcminute Microkelvin Imager Large Array in the UK, studied the object at radio wavelengths.
The behavior of the object at both X-ray and radio wavelengths closely parallels the behavior of previously-discovered microquasars. In addition, the radio observations indicate that the emission from the object is coming from a small region. Even the supersharp radio vision of the VLBA cannot resolve any detail in the object. The VLA detected variations in radio brightness over the course of minutes, indicating that the emitting region is no larger than the distance between the Sun and Jupiter.
“All these indications show that what we have found is, indeed a microquasar,” Dr Middleton said.
The astronomers estimate that the black hole probably is about ten times more massive than the Sun, and that its companion is a middle-sized, rather than a giant, star.
Bibliographic information: Middleton MJ et al. Bright radio emission from an ultraluminous stellar-mass microquasar in M31. Nature, published online 12 December, 2012; doi: 10.1038/nature11697