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Ultra Deep Field The launch of the James Webb Space Telescope offers unprec- edented new opportunities for astronomers. It's also a timely op- portunity to reflect on what pre- vious generations of telescopes have shown us. Astronomers rarely use their tel- escopes to simply take pictures. The pictures in astrophysics are usually generated by a process of scientific inference and imag- ination, sometimes visualised in artist's impressions of what the data suggests. In an inspired idea, astrono- mers decided to point Hubble at a blank patch of sky for several days to discover what extremely distant objects might be seen at the edge of the observable uni- verse. The Hubble Ultra Deep Field con- tains nearly 10,000 objects, al- most all of which are very distant galaxies. The light from some of these galaxies has been travel- ling for over 13 billion years, since the universe was only about half a billion years old. Some of these objects are among the oldest and most distant known. Here we're seeing light from ancient stars whose local contemporaries have long since been extinguished. The oldest galaxies formed dur- ing the epoch of reionisation, when the tenuous gas in the uni- verse first became bathed in star- light which was capable of sepa- rating electrons from hydrogen. This was the last major change in properties of the universe as a whole. The fact that light carries so much information, allowing us to piece together the history of the uni- verse, is remarkable. The launch of the James Webb Space Tele- scope will give us some vastly im- proved infrared images, and will inevitably raise new questions to challenge future generations of scientists. 14 maltatoday | SUNDAY • 2 JANUARY 2022 EYEWITNESS HUBBLE ULTRA DEEP FIELD