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After 30 years of observations, the results obtained by the Hubble Space Telescope form a scientific and cultural legacy of the most fabulous in the history of humanity.
Image display
Who has not been fascinated by the wonderful images of the universe taken by the Hubble Space Telescope? Professional astronomers, amateurs and laymen in the field, we have all been moved by the memorable Pillars of Creation or by many other memorable images. Far beyond being 'beautiful images', these snapshots - crossing borders and all kinds of cultural or linguistic barriers - have spurred everyone's curiosity to know more about the cosmos and have hinted at the fantastic achievements of contemporary astronomy.
Now, on the occasion of the 30th anniversary of its launch , Hubble dazzles us again with a series of new images that reveal more wonders of the cosmos, such as the very detailed view of the Rubin galaxy that heads this article. Also known as UGC 2885, this galaxy is 232 million light years distant, in the Perseus constellation, it is 2.5 diameter larger than the Milky Way galaxy and contains 10 times as many stars. The name of the galaxy pays tribute to the great astronomer Vera Rubin who, in the 1980s, measured the rotation speeds of stars in this galaxy, deducing, from them, the existence of dark matter.
The pandemic has forced to postpone a series of face-to-face events that had to be held now around the world commemorating this 30th anniversary, but the NASA website dedicated to Hubble has a whole display of images and information about the telescope. It is to be hoped that in the fall most of the scheduled events will take place and that these events will be used to reveal new images.
Exciting story
It is time to remember the great Hubble adventure. Since it was launched aboard the space shuttle Discovery on April 24, 1990, Hubble has traveled more than 6 billion kilometers in its orbit around Earth and has given us very exciting stories, such as its repair in orbit. Indeed, after the first test observations, when astronomers realized that the images were not as sharp as could be expected, NASA tracked the problem down to finding a flaw in the shape of the mirror. The problem had to be repaired by astronauts who installed an optical corrector (those famous 'Hubble glasses') in a risky mission in 1993.
But Hubble's history dates back much earlier, to ideas developed by visionary Lyman Spitzer around 1946 (although there were other earlier ideas about space telescopes, these were much less elaborate). Spitzer was an astronomer specializing in the study of the interstellar medium, in whose excellent book Physical processes in the interstellar medium many of us acquired our first knowledge of interstellar matter. Although primarily theoretical, this great astronomer would greatly enjoy Hubble's achievements until his death in 1997 but, unfortunately, he did not see the launch of another great space telescope that was launched in 2003 bearing his name: the Spitzer Infrared Telescope.
Scientific treasure
Observations made by Hubble have covered objects from the solar system to very distant galaxies, leaving an absolutely outstanding legacy to astronomy. Among its results we must highlight the images known as the Deep Field and the Ultra Deep Field. Combining snapshots of the same region of the sky obtained over more than fifteen years, the most sensitive images in the history of optical astronomy have been obtained, small regions of the sky that contain up to 200,000 galaxies of different types and at very different distances . Some of the galaxies detected, the most distant, formed only 500 million years after the Big Bang and the comparison between galaxies at different distances (and, therefore, of different ages) allows us to study the evolution of galaxies throughout the cosmic time.
Objects of the solar system, star formation regions (such as the famous Pillars of Creation already mentioned), evolved stars, etc. In all fields of astronomy, Hubble has obtained, and continues to obtain, outstanding results.
Between July 16 and 22, 1994, the world stared in ecstasy, largely through Hubble, at the impressive collision of Comet Shoemaker-Levy 9 with Jupiter's atmosphere. The comet, as it approached the gas giant, had broken into numerous fragments and Hubble retransmitted the fall of each of these fragments onto the planet in stunning detail.
The space telescope delighted us with some of the most detailed observations of protoplanetary gas and dust disks (so-called proplyds) around young stars in the Orion clouds. Later it was found that this type of dusty disks is very common in the initial phases of stars, since they constitute the places where planetary systems form.
Galaxies and dark energy
Hubble has found evidence of the presence of supermassive black holes in numerous galaxies of all kinds, both large and small, and has been able to estimate their masses. An interesting result is that the masses of these holes are in relation to those of the galaxies that host them.
The high sensitivity and high resolution of the telescope have also allowed us to observe details in the Einstein rings that are created when light from a distant galaxy passes in the vicinity of another one closer to Earth. This is the phenomenon known as gravitational lens caused by the distortion of space-time created by the effects of General Relativity. Through these observations it has been possible to measure the mass of galaxy clusters and study the distribution within them of dark matter.
By observing Cepheid stars in remote galaxies, Hubble refined the value of the age of the universe (estimated today at 13.8 billion years). On the other hand, by observing very distant supernovae (both from Hubble and from Earth), proof was found in 1998 that the universe is expanding rapidly. This acceleration in expansion is explained today by the presence of a "dark energy" that must constitute 73% of the total composition of the universe . These results were awarded the 2011 Nobel Prize in Physics.
So far the telescope has made more than a million individual observations that occupy about 75 terabytes of data, and continues to send about 17 gigabytes of data daily. Despite its age, Hubble continues to receive numerous requests for observation time. Astronomers from around the world request its use to carry out a thousand projects per year, which is a factor 6 more than the telescope can carry out. It is estimated that some 15,000 scientific articles have already been published with the results of their observations.
Relay in space
Hubble's days are numbered: NASA's current commitment is to keep it in orbit until 2021 and, in any case, due to technical problems, it is not expected that it could continue observing beyond the year 2025.
The Hubble relay will be carried out by the James Webb Space Telescope, which began to be developed in 1997 to be launched around the year 2007. Despite the long delays suffered, the construction of this telescope is already completed and its launch is scheduled for year 2021 . It is an instrument designed to work especially in the infrared. Its mirror is 6.5 meters in diameter and its mass exceeds six tons. It will be located much farther than Hubble: 1.5 million kilometers from Earth, that is, about five times farther than the Moon. This telescope is the result of collaboration between the North American (NASA), European (ESA), Canadian (CSA) and French (CNES) space agencies.
Due to the Covid-19 pandemic, the technical ground tests of the James Webb, which had continued until very recent days, had to be stopped on March 20, but the scheduled launch date continues to be in March 2021.
Rafael Bachiller is director of the National Astronomical Observatory (National Geographic Institute) and academic of the Royal Academy of Doctors of Spain.
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