Astronomers Process Hubble’s Deepest Image to get Even More Data, and Show that Some Galaxies are Twice as big as Previously Believed

It allowed us to spot auroras on Saturn and planets orbiting distant suns. It permitted astronomers to see galaxies in the early stages of formation, and look back to some of the earliest periods in the Universe. It also measured the distances to Cepheid variable stars more accurately than ever before, which helped astrophysicists constrain how fast the Universe is expanding (the Hubble Constant).

It did all of this and more, which is why no space telescope is as recognized and revered as the Hubble Space Telescope. And while it’s mission is currently scheduled to end in 2021, Hubble is still breaking new ground. Thanks to the efforts of a research team from the Instituto de Astrofísica de Canarias (IAC), Hubble recently obtained the deepest images of the Universe ever taken from space.

The study that describes the research team’s work, titled “The missing light of the Hubble Ultra Deep Field“, recently appeared in the journal Astronomy and Astrophysics. For the sake of their study, the team used original Hubble images from the Hubble Ultra-Deep Field (HUDF) – the deepest view of the Universe ever taken, which was the result of hundreds of images being taken from over 230 hours worth of observations.

The images were acquired with Hubble’s Wide Field Camera 3 (WFC3), which had been installed on Hubble in May of 2009. These images were then combined to reveal some of the earliest galaxies in the Universe. However, the method of combining images is not ideal when it comes to the detection of faint extended objects.

These include the arms of spiral galaxies and the disk of lenticular galaxies, where the concentrations of stars and gas is less dense than in the center. By improving the process of image combining, the research team was able to recover a large quantity of light from the HUDF, specifically in the outer zones of the largest galaxies. As Alejandro S. Borlaff, the lead researcher on the team, explained in a recent IAC press release:

“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.”

Processing these images to find the “missing light” was a major challenge for the researchers, since it required that the WFC3’s camera and telescope be tested and calibrated. But since they are both currently on board Hubble and in orbit, it was impossible to do this on the ground.

To overcome this, the team launched the ABYSS HUDF Project, which was dedicated to the optimization of infrared and WFC3 data acquired by Hubble to preserve the properties of the low surface brightness regions. This consisted of analyzing several thousand images of different regions on the sky to improve the calibration of the orbiting telescope.

The process worked, leading to new mosaics that successfully recovered the low surface brightness structure removed on the previous HUDF images. This in turn revealed that the largest galaxies imaged in the HUDF were almost twice as large as previously measured.

As Borloff explained, this latest view of the Universe “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”.

This new picture of the earliest period in the Universe could have significant implications for cosmology. Knowing that early galaxies were larger and more massive than previously thought is likely to revise some of our timelines, indicating that galaxy formation either began sooner or was more rapid than we thought.

And it demonstrates that after 30 years of service, Hubble is still capable of providing groundbreaking discoveries!

Further Reading: IAC, Astronomy and Astrophysics