Over 10 days in December 1995, the Hubble Space Telescope took 342 images of the same tiny patch of sky in the constellation Ursa Major. The resulting data set, the Hubble Deep Field, revolutionized the study of the early universe by revealing the profusion of galaxies in that faint and distant era when the first galaxies were forming.
Now, the MUSE instrument on ESO’s Very Large Telescope has given astronomers the best ever three-dimensional view of the deep Universe. After staring at the Hubble Deep Field South region for only 27 hours, the new observations reveal the distances, motions and other properties of far more galaxies than ever before in this tiny piece of the sky. They also go beyond Hubble and reveal previously invisible objects.
By taking very long exposure pictures of regions of the sky, astronomers have created many deep fields that have revealed much about the early Universe.
MUSE is two things: a camera that images celestial light-emitting objects, and a spectrograph that measures the wavelength of that light. Using the instrument, astronomers at ESO don’t just receive an image full of pixels. They also receive information about the intensity of the pixel’s component colors—information that lets them learn about a galaxy’s distance from Earth, its elemental composition, and even its rotation. And thanks to adaptive optics that improve resolution, MUSE can see not just bright nearby galaxies, but very faint ones as well.
“After just a few hours of observations at the telescope, we had a quick look at the data and found many galaxies — it was very encouraging,” Roland Bacon, principal investigator of the MUSE instrument, said in the same statement.
“And when we got back to Europe we started exploring the data in more detail. It was like fishing in deep water and each new catch generated a lot of excitement and discussion of the species we were finding.”
Each tiny region of the MUSE view of HDF-S reveals a spectrum of the intensity of light’s different components of colors (about 90,000 spectra overall). This allows researchers to estimate the compositions and internal motions of far-off galaxies. The image also picked up 20 faint objects in a patch of sky that had not been spotted by previous Hubble images.
“The greatest excitement came when we found very distant galaxies that were not even visible in the deepest Hubble image. After so many years of hard work on the instrument, it was a powerful experience for me to see our dreams becoming reality,” Bacon said.
The image allowed the research team to measure the distances to 189 galaxies, which is more than 10 times the number of measurements that previously existed for this region of the sky.
“Now that we have demonstrated MUSE’s unique capabilities for exploring the deep Universe, we are going to look at other deep fields, such as the Hubble Ultra Deep field. We will be able to study thousands of galaxies and to discover new extremely faint and distant galaxies. These small infant galaxies, seen as they were more than 10 billion years in the past, gradually grew up to become galaxies like the Milky Way that we see today,” concludes Roland Bacon.