Making Hubble’s Deepest Images Even Deeper

The new version of Hubble’s deep image. In dark grey you can see the new light that has been found around the galaxies in this field. That light corresponds to the brightness of more than one hundred billion suns. Image Credit: NASA/ESA/STScI/A. S. Borlaff et al.

January 26, 2019 – A group of researchers from the Instituto de Astrofísica de Canarias (IAC), led by Alejandro S. Borlaff, has used original images from the Hubble Space Telescope to produce the deepest image of the Universe from space. The group improved the process for combining several images and was able to recover a large quantity of light from the outer zones of the largest galaxies in the Hubble Ultra-Deep Field (HUDF).

The HUDF is the result of combining hundreds of images taken with Hubble’s Wide Field Camera 3 (WFC3) during more than 230 hours of observation. In 2012, those observations yielded the deepest image of the Universe taken up to that point. But the method of combining the individual images wasn’t ideally suited for detecting faint extended objects.

Recovering light, emitted by stars in the outer zones, was equivalent to recovering the light from a complete galaxy “smeared out” over the whole field, and for some galaxies this missing light shows they have diameters almost twice as large as previously measured.

“What we have done is to go back to the archive of the original images, directly as observed by the HST, and improve the process of combination, aiming at the best image quality not only for the more distant smaller galaxies, but also for the extended regions of the largest galaxies,” said Borlaff.

The WFC3, designed and built by Ball Aerospace in Boulder, Colorado, was installed by astronauts in May 2009. Hubble had already been in space for 19 years, and a major challenge of the instrument was that it couldn’t be tested and calibrated with the telescope before it was installed in space. To overcome this issue, several thousand images of different regions on the sky were analyzed by researchers, with the aim of improving the calibration of the telescope on orbit.

The image of the universe which is now the deepest “has been possible thanks to a striking improvement in the techniques of image processing which has been achieved in recent years — a field in which the group working in the IAC is at the forefront,” said Borlaff.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C.