Posted: 18 December, 2008
Astronomers have found the most distant occurrence of water yet seen in the Universe in a galaxy more than 11 billion light years from Earth, three billion years more distant than water has ever been detected before.
Astronomers using the 100 metre diameter radio telescope in Effelsberg, Germany, and the National Science Foundation's Very Large Array (VLA) in New Mexico, detected a telltale radio fingerprint of water molecules in the distant galaxy known as MG J0414+0534. This water-logged world hosts a quasar - a supermassive black hole powering bright emission at its core. The water molecules are acting as the radio equivalent of lasers, or masers, to amplify radio waves at a specific frequency.
A radio fingerprint revealed radio emission from water masers in a distant galaxy. The background image is an infrared image from Hubble, and the quasar appears broken up into four components by a foreground galaxy. The inset of galaxy M87 shows how the quasar might be seen from nearby. Image: Milde Science Communication/HST Archive data/CFHT, J.-C. Cuillandre, Coelum.
MG J0414+0534 is seen as it was when the Universe was roughly one-sixth of its current age and the astronomers say their discovery indicates that such giant water masers were more common in the early Universe than they are today.
The astronomers were only able to look closely at the galaxy thanks to the natural effects of gravitational lensing from another galaxy, nearly eight billion light years away, located directly in the line of sight from MG J0414+0534 to Earth. That foreground galaxy's gravity served as a lens to further brighten the distant galaxy and make the emission from the water molecules visible to the radio telescopes. "This cosmic telescope reduced the amount of time needed to detect the water by a factor of about 1,000," says Violette Impellizzeri of the Max-Planck Institute for Radioastronomy (MPIfR) in Bonn, Germany.
The gravitational lens effect produces not one, but four images of MG J0414+0534 as seen from Earth. Using the VLA, the scientists found the specific frequency attributable to the water masers in the two brightest of the four lensed images, while the other two lensed images were too faint for detecting the water signal.
The 100 metre radio telescope in Effelsberg, Germany. Image: MPIfR (Norbert Junkes).
Water masers have also been found in numerous galaxies at closer distances. Typically, they are thought to arise in discs of molecules closely orbiting a supermassive black hole at the galaxy's core. The amplified radio emission is more often observed when the orbiting disc is seen nearly edge-on. However, the astronomers say that MG J0414+0534 is oriented with the disc almost face-on as seen from Earth, which could mean that the water molecules are not in the disc, but in the superfast jets of material being ejected by the gravitational power of the central black hole.
"The water maser we observe is associated with the core of the galaxy, in the region within a few parsecs from the black hole," says Impellizzeri. "The two scenarios we are inspecting are whether it originates from the accretion disc or in the innermost jet region (where the jet impinges on the interstellar medium surrounding the black hole). In both these scenarios we can state that water maser emission comes from, or close to, the core. We cannot exclude water molecules to exist further out, but our data cannot establish that."
The scientists report their results in the 18 December issue of the journal Nature.
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