Twenty years on, and the Hubble Space Telescope is still pushing the boundaries of astronomy. Ever since its faulty primary mirror was corrected, it has produced some of the most beautiful and iconic images in astronomy. And even though there are telescopes on the ground with better light-gathering power and resolution than Hubble, Hubble can do one thing which the others can’t, and that is stare at a piece of sky for hundreds of hours.
In 1995, it was pointed in the direction of the constellation of Ursa Major and stared at a patch of sky the size of a tennis ball one hundred metres away for ten days. The image is famous and is called the Hubble Deep Field (HDF). It images the dimmest and therefore most distant galaxies. Due to the time taken by light to travel across space, the further away we look the younger the galaxies appear to be and so we are able to investigate galaxy formation in the very early universe.
2004 saw the release of the Hubble Ultra Deep Field (HUDF), created by looking in the constellation Fornax (the furnace) for a stretch of eleven days which looked even further back in time than the HDF – to a time between 400 and 800 million year after the Big Bang.
On the 25th September 2012, NASA revealed the Hubble eXtreme Deep Field (XDF). This zoomed in on the HUDF. It took 23 days of exposure and looks back 13.2 billion years, just 0.5 billion years after the universe began. The field shows young galaxies growing, sometimes through violent collisions with each other. It is hoped this will help astronomers find a theory of galaxy formation.
However, we haven’t reached the magnification limit. The light from youngest galaxies yet to be observed is off the visible spectrum (Hubble’s vision) in the Infra-red due to the expansion of the universe stretching the light. NASA’s Infra-red James Webb Space Telescope will look even further into the XDF and see the time when the first stars and galaxies were beginning to form.