How Edwin Hubble unlocked the universe: This Week in Astronomy with Dave Eicher

 



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A single Cepheid variable star within the Andromeda Galaxy (M31) proved to be the important thing that helped Edwin Hubble unlock the true scale of our universe.

The Andromeda Galaxy is the closest giant galaxy to us — however it was solely 100 years in the past that Hubble proved it to be a galaxy separate from the Milky Way. Credit score: Massimo Di Fusco

On Oct. 4, 1923, Edwin Hubble took a photographic plate of the Andromeda Nebula (because it was recognized then) utilizing the 100-inch Hooker telescope at Mount Wilson. The following evening, he took one other plate and located {that a} star that appeared to belong to the nebula had modified in brightness. At first, he thought this was a nova, a kind of stellar explosion. However finally, he realized it was a selected sort of variable star — and this meant he may precisely measure the gap to this star.

From finding out these variable stars — referred to as Cepheids — in our personal galaxy, astronomers already knew that the time period over which they diversified was associated to their intrinsic luminosity. Henrietta Leavitt, an astronomer at Harvard Faculty Observatory, had labored out in 1912 that the longer Cepheids take to pulsate, the brighter (and presumably bigger) they’re.

So by understanding the star’s true brightness and evaluating it to how faint it appeared, Hubble may calculate how far-off the star was. His reply: 1 million light-years. This was an astonishing consequence, one which settled an ongoing debate about whether or not such “spiral nebulae” had been a part of the Milky Way Galaxy or objects at a lot larger distances.

At present, we all know the Andromeda Galaxy (M31) is about 2.5 million light-years away, not 1 million light-years. However the implications of Hubble’s measurement stands. What he discovered modified our conception of the universe endlessly and confirmed that Andromeda and its nebulous brethren had been actually whole galaxies separate from the Milky Way — island universes of their very own.

For extra on this well-known Cepheid, named M31-V1, take a look at Rod Pommier’s story in our August 2022 challenge, through which he described his hunt to picture the star.

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