Sometimes astronomers may feel caught in a cosmic ''fun house'' where trick lenses make them see what doesn't exist. That's what happened with the ''brightest object ever seen'' whose ''discovery'' was announced four years ago.
Astronomers fell for a mirage.
Gone are romantic speculations of a galaxy giving birth to its first stars or of two galaxies in collision. Instead, there's another example of how the powerful gravity of a massive object bends light to form distorted images of other objects that lie behind it.
It's the gravitational lensing that Einstein foresaw in his theory of general relativity. In this case, it made a galaxy that shines mainly by infrared (heat) radiation appear brighter than 300 trillion suns.
It has taken several years of telescopic sleuthing to convince astronomers that they are dealing with Einstein and not a new cosmic wonder. Now an electronic mail note from Britain's Royal Astronomical Society reports that the evidence is ''overwhelming'' that the Einstein effect fooled initial investigators.
Astronomers at Oxford University and the European Southern Observatory have produced what seems to be the clinching evidence. Details of their work are published in the current issue of the society's Monthly Notices.
This still is an important discovery for astronomers. Gravitational lensing is rapidly becoming an important tool in their investigations as well as being an intriguing effect to study in its own right. It is making visible many objects too faint to see otherwise.
For example, one-third of the energetic, compact objects called quasars may be so faint that astronomers only detect them because gravitational lensing magnifies their images. It's as though a cosmic joker were both teasing and helping earthbound observers by placing imperfect lenses randomly over the sky.
The effect works as follows: A concentrated mass - whether a planet, star, or entire galaxy - distorts space in its vicinity. Light, radio waves, or infrared waves traveling through that distorted space bend in a way similar to the bending of light by a glass lens. In this way, a massive galaxy can produce images of objects that lie more or less behind it as seen from Earth.
If the object is directly behind the lensing galaxy, its image is a ring - a so-called Einstein ring. When objects are off to one side, the lensing galaxy can produce multiple images or images distorted into arcs. That's what happened with an infrared galaxy known as FSC 10214+4724. In 1991, an international team involving four British and two American universities reported that the galaxy appeared to lie some 16 billion light-years away in the constellation Ursa Major (the Big Bear). It also seemed to shine with a luminosity 30,000 times brighter than that of our own galaxy, with 99 percent of its radiation in infrared wavelengths. Follow-up telescopic observations showed what appeared to be an arc of material connecting with another galaxy, raising suspicion of a massive collision.
Skeptics suspected the gravitational trickster was at work, however. Evidence of such deception has accumulated as more telescopic studies have been made. Now Stephen Serjeant, Mark Lacy, Steve Rawlings, and Lindsay King at Oxford University, and Dave Clements of the European Southern Observatory have shown that one galaxy is well in front of the infrared wonder.
It magnifies the infrared galaxy's image tenfold. Without that imaging, this latter galaxy ''would appear no more luminous than other infrared galaxies nearer to us,'' according to Stephen Serjeant.
Astronomers no longer need to speculate about massive star formation or cataclysmic collision to explain the galaxy's output. But they have yet another incentive to learn to make the most of the opportunities that gravitational lensing provides.