The Hubble Space Telescope has been giving us impressive photos for almost 30 years, authentic works of art that could well be in a museum. One of the best known was taken 27 years ago, on April 1, 1995 and was called “The Pillars of Creation” . This photo was repeated in 2014, taking advantage of the improvements made to the telescope.
Its name has a biblical origin and obviously speaks of the columns of gas and dust that dominate the photograph, referring to the pillars on which all creation would be supported, but they also have a more literal meaning, since these columns, these pillars , they are a place of creation, of birth, they are literally a factory of stars . These light-year-long clouds will eventually succumb to their own gravity and contract to give rise to new stars.
In fact this is already happening. This other photograph, taken by Hubble also in 2014 using only infrared light , shows us the other side of these pillars of gas and dust, which are more transparent to this type of light than the visible light used in the first photograph. Kind of like the fact that your flesh is opaque to visible light but transparent to X-rays from an X-ray. Well, here the number of stars that we are able to observe is multiplied . Regions that were previously hidden behind dust are exposed, revealing a new panorama. We usually think of space and the universe as something immovable, without change, but nothing is further from reality. The pillars of creation are disappearing and it is even believed that they may already have disappeared, although their light has not had time to reach us to show us.
Nearby stars, created in other parts of the Eagle Nebula , of which these structures are a part, or even young stars in the pillars themselves are eroding them. The ultraviolet light emitted by these stars heats and disperses the gas in this region in a process known as photoevaporation , causing the kind of halo seen surrounding the pillars.
But despite everything, this is not a photograph as we usually understand them. The Hubble Telescope is not, after all, a giant digital camera floating in space , it is something more sophisticated. This photograph is the result of combining 32 individual photographs . None of them originally taken in color. Each of the original 32 photographs looks like this.
This in particular is one of the 8 photographs taken from the upper right . All this noise that appears in the photograph is one of the consequences of having the Hubble telescope orbiting outside the protection of the atmosphere . These little white dots that we observe are the marks left by cosmic rays when they collided with the camera’s detector while the picture was being taken, that is, protons, alpha particles and the occasional electron. Of course these particles collide with the detector in a random way so if we take another picture seconds later, the marks will be totally different. Combining both photographs we can obtain a cleaner version, without all these traces. This of course is not the final image, but one of the 16 images that will make up the actual final image.
The definitive and final image shows the combination of the photographs taken at four regions, those corresponding to each corner. For each region, two photographs were also taken using 4 different filters . Each of these filters only lets through light of a specific wavelength, that is, of a specific color. Every element and chemical compound that we observe in space emits light with a very specific profile, typically emitting most of its light at one or two main wavelengths, in what are known as atomic spectra .
The filters used only let through light coming from hydrogen atoms, from sulfur ions that have lost an electron, and from oxygen ions that have lost two electrons. The fourth filter is used to identify starlight. The photographs highlighted above were taken using the oxygen filter. Repeating this same process of taking two photographs, combining them and correcting them, we will obtain the other three photographs corresponding to the oxygen filter. Correcting for warping caused by the telescope’s optics, we would combine all four images to get the full picture, but remember that we’re only looking at light emitted by doubly ionized oxygen atoms here.
Repeating this same process with the hydrogen and sulfur filters, we obtain these three photographs. Comparing the three photographs we can observe certain things. The photograph of the oxygen filter seems the least defined, it seems that in it the gas that occupies the space between columns contributes more than in the other two and without a doubt more than in the photograph of the sulfur filter. This means that this gas will have large amounts of oxygen and hydrogen but no sulfur. On the other hand, in the last photograph, the details within each column appear more defined, so we can deduce that in these regions sulfur will predominate over the other two elements.
As we have said, each of these filters corresponds to a specific wavelength . In increasing order of wavelength, we will have the oxygen, hydrogen and finally sulfur filters. Well, since our brain is not used to dealing with black and white images, converting these images to color will allow us to understand the final image in a more intuitive way . We therefore assign one of the three basic colors, red, green and blue, to each filter, respecting the increasing order of wavelength. With this we will tint the image obtained with the oxygen filter in blue, the one from the hydrogen filter in green and the one from the sulfur filter in red . By combining these three images, we will obtain the final, full-color image . This image was obtained in 1995. Almost twenty years later, in 2014, with a similar process, the improved version was obtained.
