Deep Field

A not-so-empty space.

The Hubble Space Telescope is undoubtedly one of the most successful scientific experiments, with multiple discoveries that have solved great unknowns about the universe; one of these were his deep-field images.

In addition to providing probably the most spectacular images of space, the Hubble Space Telescope has helped in several experiments that have answered key questions, such as the age of the universe (13.8 billion years), or the discovery of exo-planets, or planets orbiting distant stars (Such as the planet Fomalhaut b, at 25 light years from Earth). But one of Hubble’s greatest contributions is to capture images of the early universe, but more important is to show that the universe has many more galaxies than initially estimated.


How empty is the void in space?

Hubble’s deep-field imagery was an experiment that Astronomer Bob Williams proposed in 1995; but this proposal was still at a very complicated time for the Hubble telescope, which had a very bad start due to a fault in its main mirror, this problem was fortunately repaired in an incredible mission carried out by the crew of the Endeavor space shuttle in December 1993.

mage of the M100 galaxy before and after the Hubble repair

Image of the M100 galaxy before and after the Hubble repair (

After this complicated start, the Hubble telescope was finally in operation and with all its capacity occupied, making multiple and varied observations. And when Williams proposed to focus the telescope for ten consecutive days at a specific point in the space where there was clearly no objects but only the vacuum of space to be observed, this was a controversial idea; considering the limited time allowed to make observations in this telescope and the possibility that the light of the objects in this observation were too weak for the telescope to detect.

But Williams was determined, and had an advantage, by being the director of the Space Telescope Science Institute, he had control over the Hubble’s 10% usage time. He took this risk, contradicting the advice of several colleague astronomers and commented that “if this is so bad, I will resign; I will fall on my own sword”. So, in December 1995, Hubble stared at an empty area in the Ursa Major constellation for more than 100 hours, in a this 10-day period.


Deep field images

The Hubble Space Telescope made 342 separate takes of this region in this span of 100 hours in a region of space near the Big Dipper, this point was chosen since it allowed to maintain a line of sight at this point all the time, while the telescope orbited the earth; During this period Hubble made 150 orbits around Earth. The images of these observations, once they were processed, revealed much more than expected.

These images were taken in an area of 2.6 arc minutes per side; this is similar to taking one of 24 million parts in which the whole sky would be divided; being this area a sphere shape; sphere that’s divided into 360 degrees of arc; and a minute of arc is a sixtieth of an arc degree. As comparison, on average it is considered that the Moon occupies a space of 30 minutes of arc in the night sky.


And well, what is relevant to this event?

After processing the data generated by Hubble, the results of this experiment showed that what until then was considered as “empty space” in the sky turned out to be full of galaxies, many more than could have been considered; some of them being the most distant, and therefore oldest, ever recorded (approximately thirteen billion years, only 800-thousand years after the “big bang”).

Most distant galaxy

Most distant galaxy (

The most surprising was the recorded quantity, the image composed of these observations (and shown in this article), contains approximately 3,000 galaxies. To verify if this result was the same in all points in space, this experiment was repeated in a similar location in space, but this time in the Southern Hemisphere, and the results were similar, showing again that an area supposedly empty in the sky, It was also full of galaxies. These shots allowed estimating the total number of galaxies in the observable universe, yielding an estimated two hundred-billion galaxies.

This type of experiment has been repeated with different instruments in space, as well as on land, and considering the light emitted at different frequencies, mainly in the infrared and ultraviolet. With these new shots, a study conducted in 2016 showed that this total estimate of galaxies was wrong by a factor of 10, and the new number of galaxies is estimated at two-billion, each galaxy with an average of one hundred-thousand millions of stars

Given these enormous quantities, we can consider that there are more stars in the universe, estimated at 10 sextillions (or a 1 followed by 22 zeros), that grains of sand on all the beaches of the earth, estimated number of 4 sextillions (or a 4 followed by 21 zeros).


Ghosts of past stars.

Universe development

Universe development (

See images of objects at these distances, it is like traveling in time, since these images show the light of galaxies at different but very great distances, light that has traveled the same number of years to be received by these telescopes both on land and in the space, this means, that most of the stars that generated this light have ceased to exist a long time ago, considering that a typical star like our sun lives approximately 10-billion years. Therefore, these deep-field images are composed of light from stars and galaxies that no longer exist, leaving us only the remnant of light that until now has had the time to reach us. These shots are the most real and most dramatic images of the past.

Regards Alex – ScienceKindle


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