Free Astronomy Magazine July-August 2015

COSMOLOGY can achieve: 23 milliarcseconds in the observed band, namely 6 times better than the Hubble Space Tele- scope is capable of in the infrared. In fact, the lensed ring of SDP.81 is so sharp that it is possible to distin- guish ramifications, graininess and other subtle structures never before noticed for such a distant galaxy. These structures, which (although distorted) reflect SDP.81’s internal structures, would nonetheless not have been accessible to ALMA with- out the help of the gravitational lensing effect from the interposed galaxy, a “mere” 3.4 billion light-years away from us, which increased the size and brightness of the remote galaxy. Although a superficial investigation of the images of SDP.81 already allows us to note an uneven distribution of the mass and brightness in- side the galaxy, and hence identify possible regions of intense star for- mation, it is always desira- ble to trace back the original shape of the ga- laxy, in order to determine with certainty the single substructures. The first to do this were two assistant professors at the Univer- sity of Tokyo, Yoichi Ta- mura and Masamune Oguri, who, together with researchers from the Na- tional Astronomical Ob- servatory of Japan (NAOJ), A bove, we can see how the model used on the ring of SDP.81 would have repro- duced the galaxy, using three differ- ent instrumental solutions. It is clearly evident the help provided by the gravitational lensing. Left, a scaled representa- tion of the size of dust and molecu- lar gas clouds identified in SDP.81 (conventio- nally spherical), of “our” Orion Mole- cular Cloud, and of the star-form- ing region NGC 604, belonging to the nearby galaxy M33. [Y. Tamura (The University of Tokyo)/NASA and The Hubble Her- itage Team (AURA/STScI)] The video on the side shows a graphical reconstruction of the formation of the ring of SDP.81. [ALMA (NRAO/ ESO/NAOJ)/Luis Calçada (ESO)] developed what is today the best mathe- matical model of gravitational lensing. Through this model, the astronomers cor- rected the lensing effects and reconstruct- ed the true shape of SDP.81 (or at least of its most active re- gions), showing that this is a monstrous system that is form- ing stars at a rate hun- dreds to thousands of times greater than that of the current Milky Way. The model used by the Japanese researchers has fairly accurately turned the brightest regions of the ring into a series of dust and molecular gas clouds, ranging between 200 and 500 light-years across, distributed in an ellipti-