From ESA’s HubbleCast. In early 2009, a team of astronauts visited Hubble to repair the wear and tear of twenty years of operating in a hostile environment — and to install two new instruments, the Cosmic Origins Spectrograph, and Wide Field Camera 3 — better known as WFC3.
Hubble has become famous for its striking visible-light pictures of huge clouds of interstellar dust and gas. But sometimes scientists want to know what’s happening behind, or inside, the cloud of dust. Making infrared observations pulls away the veil and reveals the hidden stars.
Until now, infrared imaging was challenging with Hubble. The Near Infrared Camera and Multi-object Spectrometer, or NICMOS, did allow astronomers to study objects in infrared light in ways not possible from the ground, but it forced them to make a difficult choice. Because its images were small — only about 65 000 pixels in total, similar to a mobile phone screen — NICMOS could produce the sharpest images only if it concentrated on a very narrow field of view. Taking in a wider view came at the cost of losing much of the detail.
These improvements mean Hubble is now far better at observing large areas of sky as well as very faint and very distant objects. These are key for the science of cosmology, the study of the origins and development of the Universe.
Because the Universe is expanding, light waves coming from distant objects are stretched as they travel through space, and the waves become longer. The further an object is away, the more its light is stretched on its journey to us, and the redder the light appears. Hence the effect is known as redshift.
For really distant objects, the ultraviolet and visible light is redshifted so much it goes infrared — literally, “below red” — and that is the reason that infrared imaging is so important for spotting these very distant galaxies.
This is the Hubble Ultra Deep Field, a visible light image taken in 2003 and 4 with Hubble’s Advanced Camera for Surveys. The picture is of a little patch of sky almost a hundred times smaller than the area of the full moon. It contains no stars visible with the naked eye — but taking a million second exposure of this little black speck of space reveals these vanishingly faint faraway galaxies.
Studying the same region with WFC3’s infrared photography reveals galaxies more distant still: some of these are so far away that they have been redshifted out of the visible spectrum altogether.
We see galaxies here as they were many billions of years ago. When the light from some of these galaxies started its long journey towards us, our Sun and Earth had not even begun to form.
But what is really exciting cosmologists about WFC3’s infrared imaging of the Hubble Ultra Deep Field is not just what’s in the foreground so to speak, amazing as that is, but the scatter of tiny, faint specks just visible in the background, beyond these already faraway galaxies.
Some of the flecks of light in this fuzzy image are just anomalies within the light detectors, but among them are faint impressions of early galaxies. In this photo we are looking at some of the most remote objects ever seen.
They are so distant, and their light has travelled so far to reach us, that we see these galaxies as they were 13 billion years ago, when the Universe was only about 5% of its current age.
Discovering and studying these galaxies can tell us a lot about the conditions that prevailed in the earliest years of the Universe, and confirm — or perhaps refute — our theories of early galaxy formation.