Theories, discussions and proof: 100 years since the discovery of other galaxies
Until a hundred years ago, in literature, both professional and popular, the universe was described more simply and modestly than today.
Although there were some doubts, e.g. Immanuel Kant believed that apart from ours, there are also long galaxies. The prevailing opinion was that the galaxy in which we are is the only one and that it fills everything that exists, the entire existing expanse and that the universe is the same as the galaxy.
Some faint objects were seen in the distance, but they belonged, it was thought, also to our galaxy. Because of their nebulous appearance, these objects were called nebulae, and one of the most famous, which can be seen with the naked eye, was the Andromeda Nebula.
However, at the beginning of the last century, the debate about the nature of these nebulae began to flare up.
- Some once again advocated the idea that nebulae are cosmic islands made of stars and that they are located outside the Milky Way.
- Others insisted on the common opinion that the nature of those islands is different and that they are nebulae within the Milky Way.
Ah, those were the times!
In order to solve the dilemma in 1920, a discussion was organized between the then most prominent astronomers who knew the deep sky, namely Harlow Shapely (1885-1972) Herbert Curtis, (Heber Doust Curtis, 1872-1942) each with their own idea about the contents of the cosmos and each with their own evidence.
At that time Shapley was the greatest expert on the Milky Way, so a man of undisguised authority, etc. It was he who estimated the diameter of the galaxy at about 100,000 light years, which was significantly more than earlier estimates, and therefore, he believed that everything visible even with the most powerful telescopes must simply be inside the galaxy.
Herbert Curtis again believed that there are other galaxies beyond the Milky Way. He based his opinion on several facts:
- Spiral nebulae (as they were then called) actually have the characteristics of galaxies.
- The new stars in the spiral nebulae were much fainter than the new stars in the Milky Way (and therefore were far outside the Milky Way).
- Spiral nebulae were scattered all over the sky, which was inconsistent with the idea that they were part of our galaxy, etc.
And, of course, after the discussion, everyone still held up their own opinion.
And then, four years after that debate, on November 23, 1924, an article appeared on page six of the New York Times with the results of Edwin Hubble’s measurements of distant stars.
“Picture yourself during the early 1920’s inside the dome of the [Mount Wilson Observatory]. … [Milton] Humason is showing [Harlow] Shapley stars he had found in the Andromeda Nebula that appeared and disappeared on photographs of that object. The famous astronomer very patiently explains that these objects could not be stars because the Nebula was a nearby gaseous cloud within our own Milky Way system. Shapley takes his handkerchief from his pocket and wipes the identifying marks off the back of the photographic plate.
Of course, Hubble came along in 1924 and showed that it was just these Cepheid variable stars in the Andromeda Nebula which proved it was a separate galaxy system.”
— Halton Christian Arp, In Quasars, Redshifts and Controversies (1998).
It turns out that distant spiral nebulae, or at least some of them, are actually full of stars and are far, far farther than the diameter of our galaxy, so that these spiral nebulae are actually other galaxies.
Thus, Herbert Curtis won this controversy.
When Shapley received a letter from Hubble with data on the distances of distant stars, he said to his colleague, “Here is the letter that destroyed my universe.”
