Edwin Powell Hubble's Work and Legacy

In honor and memory of Edwin Powell Hubble, the space telescope launched in 1990 is named after him.

When we look at the sky on a moonless night and in an unlit place, we mostly see stars. The stars are distributed across the entire sky, but are more concentrated along a band that the ancient Greeks called the "Galaxy" and the Romans "The Milky Way". Both terms mean the same: a milky streak, as if milk had been spilled from heaven.

With the development of telescopes it was possible to observe in detail other celestial objects, such as nebulae. Nebulae are extensive clouds of gas and dust. For a long time, some of these nebulae intrigued astronomers. They were more diffuse and appeared to have a spiral structure, also grouping stars together. To these “fuzzy nebulae” Edwin Hubble has devoted most of his professional life.

The importance of Edwin Hubble's contributions to XNUMXth century science is reflected in the most productive space telescope to date that bears his name.

Hubble was born in 1889 in Missouri, United States of America. He graduated in Astronomy and Mathematics at the University of Chicago, although his father did not appreciate the idea of ​​his son dedicating himself to the study of the stars. When he received a scholarship to study at Oxford, UK, and shortly before his father died, Edwin promised him that he would graduate in law.

Returning to the United States, he practiced law for only one year. He was a Physics and Mathematics teacher at a secondary school, where he also excelled as a basketball teacher. He ended up returning to Astronomy and the University of Chicago to do his doctorate.

 

Andromeda Galaxy

spiral nebulae

In 1917, while writing his thesis, Edwin Hubble received an invitation to join the team at Mount Wilson Observatory in California. This observatory had opened a new telescope, at the time the largest in the world. It was a reflecting telescope with a mirror 2,5 meters in diameter, an excellent instrument for photographing in detail the diffuse objects in the sky. Precisely, Hubble's thesis was about photographic investigations of diffuse nebulae.

However, at that time the United States entered World War I and Hubble was mobilized to France. Fortunately, he was never on the battlefield and returned alive to the United States in 1919.

The case of Edwin Hubble makes us think of the millions of men who died in the trenches and who could have contributed to Humanity's knowledge and progress, as Hubble would.

Finally, part of the Mount Wilson Observatory team, Hubble began by continuing his doctoral work, studying the “diffuse spiral nebulae”.

At one point he discovered what at first glance appeared to be a new star in what was then called the Andromeda Nebula. It turned out to be after all a star of variable brightness, and of a certain type, what astronomers call Cepheids (the first of these stars was discovered in the constellation Cepheus).

An astronomer, also American, Henrietta Leavitt, had discovered in 1912 a close relationship between the average brightness of Cepheid stars and the period of variation of this brightness. This relationship made it possible to use these stars to determine distances in the Universe.

Having discovered a Cepheid in the Andromeda Nebula, Hubble used the method proposed by Leavitt to know the distance to the nebula. He calculated the value of nearly one million light years (the known value today is over two million light years).

Hubble's colleague, Harlow Shapley, had used the same method as Henrietta Leavitt, but with another type of variable stars, to determine the size of the galaxy, that is, to know how far the stars we see in the sky are distributed in space. . He found that these extended up to 300 000 light years (the size of the Milky Way accepted today is 100 000 light years).

Clearly, the Andromeda Nebula was outside the cluster of stars we see in the sky. Edwin Hubble continued his work by studying other "spiral nebulae" and subsequently found that they were also found far beyond the distance determined by Shapley.

 

New York Times News, 1926

Discovery of the Cosmos

These data obtained by Edwin Hubble were released in 1925, at a time when the astronomical community was already divided over the nature of these spiral nebulae.

Ironically, Harlow Shapley believed that "spiral nebulae" were part of the galaxy, that is, like many of his colleagues, he believed that the galaxy was the entire universe and that these nebulae were relatively small and situated within the galaxy's boundaries.

In this matter, Shapley had been confronted in 1920 by another American astronomer, Heber Curtis. Curtis represented another view in the astronomical community, which held that these fuzzy objects were large, distant stellar clusters, other island universes like the galaxy.

It was Hubble who had the credit of solving this problem, showing that Curtis's view was correct. Newspapers published the news of the discovery of “another universe beyond ours”, using the term “universe” for what we now call “galaxy”.

With this discovery, Hubble exploded our notion of Space and revealed the Cosmos to Humanity, showing that our galaxy, where the Solar System is located, is one of hundreds (today we know they are billions) of other island universes .

Edwin Hubble, with access to an excellent telescope, was able to photograph these galaxies in detail, which he continued to call “extragalactic nebulae”, meaning nebulae that are outside (our) galaxy. He studied their shapes and proposed a classification.

Although Hubble's classification was interpreted by some as a possible evolution between types of galaxies, he stressed that it was just a morphological classification. Astronomers still use it today, referring to galaxies with the same terms put forward by Hubble: elliptical, lenticular, spiral, barred and irregular spiral.

 

the flight from galaxies

Another astronomer named Vesto Slipher at the Lowell Observatory had wondered whether the “spiral nebulae” were standing still or moving. Analyzing the light coming from these, he verified that they rotate on themselves, and also that they all move away from us.

Hubble continued this work. First he associated the speeds determined by Slipher with the distances he himself was gathering for these objects. With the help of a colleague, Milton Humason, he pieced together speeds and distances for yet other "extragalactic nebulae."

It came to a curious relationship: the further away they are from us, the faster they are moving away. The only way to interpret this relationship is that space is expanding, in such a way that each of the “island universes” within it moves away from all the others.

This revelation was published in 1929, at a time when Albert Einstein was already famous for his Theory of General Relativity. In fact, the expansion of the Universe was already in their equations published in 1915. At that time, however, even before the “other universes” discovered by Hubble were known, the scientific community believed that the Universe was static.

Einstein had then inserted a constant into his equations so that his solution would be a static universe. After Hubble's revelation, Einstein claimed that this constant had been the biggest mistake of his life.

 

A homonymous telescope and a new revolution

In honor and memory of Edwin Powell Hubble, the space telescope launched in 1990 is named after him. For nearly 30 years in space, the Hubble telescope is still used to produce science. Interestingly, it was used in the late 1990s to continue Hubble's work.

An international team used a type of stellar explosion (a certain type of supernova) similar to Hubble's use of the Cepheid stars. He did so, however, to determine even greater distances, and to know the speed of even more distant galaxies.

In addition to confirming once again the expansion of the Universe, they found that the more distant galaxies not only are moving away faster, they are doing so at an accelerated pace. This seems to indicate that the expansion will be irreversible.

Even more extraordinary, it points to the existence of a force that counteracts gravity and drives this expansion. Scientists call it “dark energy”.

Much like Edwin Hubble revealed the Cosmos, the Hubble Space Telescope helped reveal that three-quarters of that Cosmos are made of something – this dark energy – whose nature is still totally unknown to us.

 

"Stars that shine in time” is a rubric with which the Institute of Astrophysics and Space Sciences associates itself with the celebration of the 100 years of the International Astronomical Union (IAU), recalling important figures in the history of astronomy over the past 100 years.

 

Author Sérgio Pereira is a Science Communicator at the Institute of Astrophysics and Space Sciences, where he plans and produces content, events and projects with the aim of involving society in science and technology linked to Space and the Universe.
He holds a master's degree in Science Communication with a specialization in magazine journalism and initial training in Communication Design. He worked for several years developing web solutions for digital communication agencies.

© 2020 – Science in the Regional Press / Ciência Viva

 




 

 

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