It’s hard to believe, but in 1917 Albert Einstein postulated in his relativistic cosmological model – the first of its kind – that the cosmos must be evenly populated by large galaxies like the Milky Way and is ultimately consistent with the theory of the universe -islands In the early 1920s, philosopher Immanuel Kant was still debating whether nebulae like Andromeda were part of our galaxy or not.
The solution to the question began on the night of October 5th to 6th, 1923 by the astronomer Edwin HubbleEdwin Hubble, who, as Futura explained in the previous article below, carried out Andromeda observations that night with the most powerful telescope of that time. at Mount Wilson Observatory in California.
Hubble photographed three suspected novae in one of Andromeda’s spiral arms and wrote the letter “N” for novanova next to each of the three suspected candidates on photographic plates made with a 45-minute exposure time.
A nova? No, a Cepheid variable star
But by analyzing other images, Edwin Hubble quickly realized that one of the stars was not a nova, but a variable star, as its luminosity changed much faster than a classic nova. Hubble took out his marker, crossed out the “N” next to the new Cepheid variable, and wrote “VAR” for variable, followed by an exclamation point (see image below).
Hubble eventually named it V1 and plotted its light curve, finding a period of 31.4 days, indicating that the object was a Cepheid variable. He can then use the relationship between the absolute luminosity of a Cepheid at maximum brightness and its period to derive the distance from Andromeda, knowing the apparent, lower luminosity of V1.
Given the accuracy of the measurements at the time, the star was found to be 1 million light-years from Earth, more than three times the diameter of the Milky Way as calculated by Shapley. Andromeda’s apparent size also shows that it is an object at least as large as our galaxy.
Shapley was one of those who did not believe in Kant’s ideas, but when confronted with the letter Hubble had sent him explaining the details of his discovery with V1, he accepted the evidence and, according to legend, said to one Colleagues: “This is the letter that destroyed my world.”
Hubble will continue to revolutionize our vision of the universe, providing evidence of the expansion of the observable cosmos in 1929, again thanks to the Cepheids. In reality, Georges Lemaître is the one who really understands what Hubble discovered and who can even be said to have foreseen it… but that’s another story…
V1, the variable star that changed the universe
Article by Jean-Baptiste Feldmann, published on May 30, 2011
The Hubble Space Telescope tracked brightness fluctuations of a famous Cepheid, providing a new view of the universe in 1923.
It’s a nice nod that astronomers from the Space Telescope Science Institute have just made to the history of cosmology. They decided to use the Hubble Space Telescope to photograph the fluctuations of a particular variable star, a Cepheid called V1, located in the large Andromeda galaxy M 31.
Until 1920, many astronomers, as well as famous cosmologists such as Harlow Shapley, believed that spiral nebulae, the most famous example of which is M 31, were part of the Milky Way, our galaxy. At that time, a young astronomer named Edwin Powell Hubble had just arrived at the Wilson Observatory after a remarkable work on nebulae. Hubble had the 2.5-meter-diameter Hooker Telescope, then the most powerful in the world, and began studying the luminosity of a Cepheid in the Andromeda Galaxy, a variable star that has since been named Hubble Variable Number 1 has accepted (V1).
A decisive measure
We have known since 1912 and the work of Henrietta LeavittHenrietta Leavitt that there is a mathematical connection that links the luminosity of the Cepheids to their pulsation period. By measuring the period of V1, the Cepheid of the Andromeda Galaxy, Edwin Hubble was able to determine the intrinsic brightness of this star and compare it with its apparent brightness to infer its distance and therefore that of M 31. Suddenly, the Andromeda Galaxy Andromeda itself was discovered ejected from our Milky Way (the distance from M 31 is currently estimated to be just over 2 million light-years) and the boundaries that had previously been set for the universe were spectacularly shifted. Edwin Hubble continued to study Cepheids in many galaxies to measure their distance and then their speed, and in 1929 discovered the expansion of the universe.
As a tribute to the work of Edwin Hubble, scientists gave the space telescope its name. On April 24, 1990, the space shuttle Discovery launched with the famous telescope on board and images of V1 taken by the American astronomer in 1923. These images flew again in 2009 aboard the space shuttle Atlantis during STS-125, the space telescope’s fifth and final servicing mission. This telescope was used to photograph changes in the brightness of the star V1 over several weeks last winter.