Cosmos Vastness: Hubble's 'Standard Candle' Unlocks Universe Size, Oct. 5, 1923

A sequence of images displaying the star M31-V1 fluctuating in brightness across a span of weeks. Edwin Hubble made the star’s discovery in 1923.(Image credit: Image: NASA, ESA, Hubble Heritage Project; Acknowledgment: Robert Gendler)QUICK FACTS

Date: Evening of Oct. 5, 1923

Where: Mount Wilson Observatory, located near Pasadena, California

Who: Edwin Hubble

On the evening of Oct. 5 progressing into Oct. 6, 1923, Edwin Hubble identified a novel star — and unveiled the complete magnitude of the cosmos.

Initially, Hubble surmised the entity to be a nova, signifying a type of exploding star, yet closer inspection exposed that the star’s radiation altered in intensity through the night, intensifying, diminishing, and then brightening again in a consistent manner. On one photographic plate, he erased the “N” for nova and substituted it with “VAR!” denoting variable star.

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Designated as M31-V1, the object was recognized as a cepheid variable star, denoting a stellar class with light output that varies with striking regularity. Hubble wasn’t the initial individual to discover these universal “standard candles.” In 1912, Harvard observatory astronomer Henrietta Swan Leavitt documented the brightness and cycle (the manner of brightening and dimming) exhibited by 25 cepheids situated within the Small Magellanic Cloud, a neighboring dwarf galaxy. She concluded that the brighter the cepheid, the slower its flicker.

Nonetheless, Hubble’s findings would prove to be decisive within an ongoing significant discourse. Astronomer Harlow Shapley posited that the Milky Way encompassed the complete universe, while his adversary Heber Curtis had executed a preliminary assessment of the separation distance to adjacent Andromeda, recognized also as Messier 31, intimating our placement inside an “island universe,” abundant in expansive and immensely remote galaxies.

Throughout a dark evening, our neighboring galaxy has always been apparent to the unaided eye, yet across history, stargazers have deliberated whether it constituted a constellation, a nebula, or an independent galaxy.

Hubble’s renowned “VAR!” plate originating from the discovery. The eradicated “N” in the upper right signifies Hubble’s initial assumption of observing a nova, before discerning the star’s brightness variance resembling that of a Cepheid.

Hubble’s finding of the proximate cepheid upheld Curtis’ argument indicating Andromeda as a separate galaxy distinct from our own. Hubble would persist in quantifying M31’s cepheid across numerous nights throughout the year. The star’s oscillating luminous intensity empowered Hubble to assess Andromeda’s vast distance of 900,000 light-years.

Leavitt’s contributions concerning cepheids demonstrated immeasurable worth concerning Hubble’s additional momentous finding: the expansion of the universe. Concurrently with other individuals, such as Georges Lemaître, who had proposed the expanding universe by leveraging Einstein’s theory of general relativity, Hubble substantiated the theory through precise computations.

A visual of Hubble in 1945, spanning more than two decades following his initial observation of the cepheid variable within M31. RELATED STORIES

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He melded Leavitt’s data on cepheid distances alongside information procured from Milton Humason and others that demonstrated galaxies’ “red shift” — a process by which wavelengths associated with radiation stretch, transitioning toward the red end on the spectrum, resulting from the Doppler effect induced by objects receding from our position. More distant objects registered a higher red shift, indicating increased recession velocities compared to closer entities.

Hubble’s determined rate concerning expansion would subsequently be known as the Hubble constant. Subsequent to the discovery of cepheid M31-V1, numerous forms of verification have corroborated the existence of a continuously expanding universe, and with the revelation pertaining to dark energy during the 1990s, our knowledge has advanced, confirming that this expansion accelerates. Contemporary evaluations of the universe’s expansion rate, however, do not consistently align. Resolving the genesis of the disparity might enable the prospect of unveiling novel physics, while also destabilizing currently recognized cosmological paradigms once more.

Tia GhoseSocial Links NavigationManaging Editor

Tia functions in the role of managing editor and previously was a senior writer for Live Science. Her articles have appeared within Scientific American, Wired.com, alongside further venues. Her educational background incorporates a master’s specialization in bioengineering acquired from the University of Washington, a graduate certification focusing on science writing secured through UC Santa Cruz, alongside a bachelor’s qualification within mechanical engineering completed at the University of Texas situated in Austin. Tia contributed as an integral team member at the Milwaukee Journal Sentinel, responsible for publishing the Empty Cradles series centering on preterm births, garnering many accolades, including the Casey Medal for Meritorious Journalism conferred during 2012.

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