Massive Galactic Arc Found in Early Universe

A recent study conducted using the Hubble Space Telescope has revealed a huge arc of light behind a very distant galaxy cluster. The last-named is acting as a gravitational lens, amplifying the light from another galaxy behind it, but astronomers say that the object should not event exist.

The main problem is that the massive cluster is located some 10 billion light-years away, and appears to us as it looked when the Universe was less than a quarter of its current age. If that is the case, then the light arc behind it belongs to a structure even more distant.

But this discovery contradicts established models that correlate the evolution of the Universe to that of galaxies. The golden rule has always been that cluster sizes always decrease the further back you look in time. However, this appears not to be the case with the new discovery.

The galaxy whose light is distorted and amplified by the massive galaxy cluster in front of it should not exist at all. If it is located behind the cluster, then it's definitely older than the latter, meaning that it appeared closer to the time of the Big Bang.

The problem with that is that current cosmological models do not allow too much time for galaxies to accumulate the type of mass this one appears to display. The large cluster was found using the Spitzer Space Telescope, while the light arc was identified by the Hubble Space Telescope.

“When I first saw it, I kept staring at it, thinking it would go away. According to a statistical analysis, arcs should be extremely rare at that distance,” explains University of Florida in Gainesville (UFG) expert and study team leader, Anthony Gonzalez.

“At that early epoch, the expectation is that there are not enough galaxies behind the cluster bright enough to be seen, even if they were 'lensed,' or distorted by the cluster,” adds the expert, whose team also includes researchers from the NASA Jet Propulsion Laboratory (JPL), in Pasadena, California.

“The other problem is that galaxy clusters become less massive the further back in time you go. So it's more difficult to find a cluster with enough mass to be a good lens for gravitationally bending the light from a distant galaxy,” he goes on to say.

The cluster providing the lensing effect is called IDCS J1426.5+3508. The thousands of galaxies it contains give it a mass of nearly 500 trillion Sun, astronomers calculate. It is between 5 to 10 times larger than any other cluster found at a similar distance.

Experts say that the chance of them finding such a massive galaxy cluster in the narrow portion of sky they surveyed was less than 1 percent. This means either that they were very lucky, or that such objects are more common than models predict.

Details of the investigation were published in a series of three papers, which appear in the June 26 issue of the esteemed Astrophysical Journal. The papers will also be published in an upcoming print issue of the journal.