Sunday, November 23, 1924 was not just another day in the history of humanity. Exactly 100 years ago, the renowned media The New York Times published a historical article on page 6 of his newspaper: “Spiral nebulae discovered to be star systems: Dr. Hubbell confirms they are ‘island universes’ similar to our own”, reflected the journalistic note.
The article, then, explained the astronomical revelations reached by Dr. Edwin Powell Hubble – who must have seen with surprise the spelling mistake in his name – those who claimed to have discovered two spiral nebulaeobjects formed from gas and stars, which were previously believed to live within the boundaries of our Milky Way. However, these objects were outside of it, which led to a historic discovery: the American astronomer had given with two new galaxies, outside the limits known until then.
Edwin Hubble’s historic discovery
One hundred years ago, the astronomer gave substance – for the first time – to the galaxies that would later be named Andromeda and Messier 33. The discovery was the kickoff of a new field to be explored by astronomy: these galaxies were the closest to the Milky Way, but they were only two among the several billion that exist and were estimated today.
Hubble’s revelation happened in a special context: four years before the announcement, an event called “the great debate”. It was carried out by American scientists Harlow Shapley and Heber Curtis.
Shapley had recently shown that Milky Way It was greater than what had been measured until then. In this way, the astronomer maintained that it could house spiral nebulae inside. On the other side, Curtis defended the existence of galaxies beyond our own.
Despite having lost the argument years later – following the discovery that occurred a century ago – Shapley provided a key method for measure distances across the Milky Way which would occupy a central role in Hubble’s research.
After this, she would be the young American Henrietta Swan Leavitt who delved into Shapley’s methodology. Hired to analyze images from telescopic observations at the Harvard College Observatory, the astronomer studied photographic plates of telescopic analyzes of another galaxy called the Small Magellanic Cloud, made by other researchers at the observatory.
Their search was aimed at finding stars whose brightness changed over time. From among more than a thousand variable (changing) stars, He identified 25 that belonged to a type known as Cepheids, a result he published in 1912.
Thanks to this, Leavitt arrived at a decisive concept: Cepheids that pulsed more slowly were intrinsically brighter (more luminous) than those that pulsed more quickly. This was called the period-luminosity relationship. This relationship and the arrival of another study – stellar parallax – is what later allowed calculate the distance between celestial bodies.
In this scenario, Hubble worked with a telescope – the Hooker – which contained a mirror 100 inches (2.5 meters) in diameter to collect light: it was the largest telescope of the time. Large telescopes are not only more sensitive, but they also create sharper images, a determining factor for the astronomer to make the discovery.
When Hubble compared his photographic plates taken with Hooker with those taken on previous nights by other astronomers, he was excited to see that a bright star seemed to change brightness over time, as would be expected for a Cepheid. Based on Leavitt’s calculations, the American astronomer realized that the distance he had measured for the celestial body It exceeded the size that Shapley had determined for the Milky Way, which would account for the existence of other nearby galaxies.
The expansion of the universe
But Hubble’s revelation did not stop there. The use of telescopes also It allowed us to measure the speed at which a galaxy is approaching or moving away from Earth. To do this, astronomers measure the spectrum of a galaxy.
In detail, this concept refers to the different wavelengths of light that comes from each of these places in the universe. They also calculate the so-called Doppler effect and apply it to that spectrum.
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Saying Doppler effect It occurs in both light and sound waves. It, for example, is responsible for the tone of a siren increasing when an emergency vehicle approaches and decreasing when it passes by us.
When a galaxy moves away from Earth, the characteristics of the spectrum known as absorption lines have longer wavelengths what if they weren’t moving. This is due to the Doppler effect, and we say that these galaxies have “redshifted”.
In 1904, the American astronomer Vesto Slipher used the Doppler technique with a 24-inch telescope at the Lowell Observatory in Flagstaff (Arizona). and discovered that all nebulae – including Andromeda -, were redshiftedthat is, they were moving away from the Earth at speeds of up to a thousand kilometers per second.
Hubble then built on Slipher’s measurements with his distance estimates for each galaxy and discovered a relationship: The farther a galaxy is from us, the faster it moves away from us. This phenomenon can be explained thanks to the theory of Big Bang, which details the expansion of the universe from a common origin.
Both discoveries were announced a century ago. Today, Hubble occupies a privileged place in the history of science and, specifically, astronomy. So much so that the Aeronautics and Space Administration – NASA for its acronym in English – named one of the most powerful scientific instruments ever created in honor of the astronomer: the Hubble space telescope.
The Hubble telescope is one of the most important instruments in modern astronomy. In detail, it is a reflecting telescope orbiting the Earth at approximately 593 kilometers altitude.
It was launched on April 24, 1990 and its design and operation are the result of a collaboration between the NASA and the European Space Agency (ESA). This tool allowed us to obtain high-resolution images of the universe – including different astronomical objects, from galaxies to exoplanets – which revolutionized the current understanding of the universe.
Source: Ambito
