The cosmic lens to the edge of the universe
Today it is the farthest ‘ telescope ‘ known that nature has made available, but it is not made of glass, mirrors and gears. Its lens is a galaxy far away, at 9.4 billion light years from us, so that its mass has allowed deflecting and amplifying light from another galaxy placed exactly behind it, as required by Einstein’s General Theory of Relativity. To find it was an international team of astronomers led by Arjen van der Wel of the Max Planck Institute for Astronomy and who has participated Andrea Gratian, a researcher at INAF – Observatory Astronomic in Roma.
And to be able to identify this galaxy took two ‘ artificial ‘telescopes and yes, those made of glass, mirrors and a lot of electronic gear, including the most advanced tools for the exploration of the cosmos built to date by man, the telescope binocular LBT (Large Binocular Telescope) in which the INAF is one of the partners, as well as the Hubble Space Telescope.
The discovery of the galaxy – lens was entirely fortuitous. The team was actually looking very massive and evolved objects at long distances in the universe, in the portion of the sky scanned by the Hubble Space Telescope as part of the candles. The candidate objects were then observed with the spectrograph LIGHTS (the instrument Multifunction Large Binocular Telescope Near- infrared Utility with Camera and Integral Field Unit) at the Large Binocular Telescope. It soon became apparent from the data that one of the spectra reproduced the expected characteristics, as it appeared to come from a very young, celestial object and at the same time as far as the other nominated galaxies.
So Van der Wel and his team are back to compare the spectrum with suspicion images produced by the Hubble Space Telescope of the same portion of the sky, finding that the corresponding object was an evolved galaxy which had a ring of blue color, associated to the young galaxies which are in the middle of star formation. A pretty clear indication that exactly behind the galaxy, perfectly aligned along our line of sight, there was another galaxy, whose light was deflected and focused for the phenomenon of gravitational lensing. Combining the available images and subtracting the contribution due to the image bright stars in the galaxy in the foreground, evidence emerged of suspicion, or the so-called ‘ Einstein ring ‘: a circle light, the result of the bending of light from the galaxy remote from the more ‘close‘. The quotes are a must, since the object that has played the role of the natural lens is exceptional distance of 9.4 billion light years, and the effect was produced at a time when the universe was less than a third of its current age. But this discovery is valuable to astronomers also in another respect: the intensity of the gravitational lens is directly related to the mass of the celestial object that acts as a lens. The greater the mass of the galaxy, both the part of ordinary matter that obscures, the more marked is the refraction of light. “This event permits us to predict the mass of the elliptical galaxy by studying its effect of gravitational lensing,” illuminates Andrea Gratian, co-writer of the paper describing the discovery, published today on the website of The Astrophysical Journal Letters. “Therefore we are capable to ‘calibrate’ the supplementary ways and means for the estimation of the masses that are done in an indirect way, that is by comparing the light of distant galaxies with the theoretical predictions which in turn are calibrated to reproduce the physical properties of the galaxies in our cosmic vicinity “. There is an alternative important phase that this finding raises. “Our recent data points to that this type of alignments in the early universe is very rare,” continued Gratian. “The fact that we found this particular configuration in a very small portion of the sky may indicate that cosmic objects that are behind gravitational lenses are far more numerous than expected and it may change the knowledge we have of the early universe. In future investigations, in this field, LBT will continue to play a decisive role. ”