NASA Commemorates Edwin Hubble’s Groundbreaking Discovery of an Expansive Universe

A century ago, the star was brought to light by Edwin Hubble, an astronomer at the Carnegie Observatories. His groundbreaking discovery expanded our understanding of the vastness of the universe and revealed that the Milky Way is only one among hundreds of billions of galaxies. This moment marked a pivotal change for humankind, allowing us to scientifically explore our existence through the messages conveyed by stars. To commemorate this milestone, Carnegie Science and NASA are hosting a celebration at the 245th meeting of the American Astronomical Society in Washington, D.C.

This unassuming star, referred to simply as V1, unlocked a multitude of mysteries about time and space that continue to challenge astronomers today. Edwin Hubble made his discovery in 1923 using the most powerful telescope of that era, the Carnegie-funded 100-inch Hooker Telescope at Mount Wilson Observatory in California. V1 is a rare type of pulsating star known as a Cepheid variable, which serves as distance markers for far-off astronomical objects. Although there are no measuring tapes in space, Henrietta Swan Leavitt had previously determined that the pulsation period of Cepheid variables correlates directly with their brightness.

For many years, astronomers thought that the edges of the Milky Way simply represented the boundary of the known universe. But Hubble found that V1 was much farther away than anything located within our own galaxy. This discovery led him to the astonishing conclusion that the universe is far more expansive than our Milky Way.

Hubble had long suspected there was a greater universe beyond, but this was definitive proof. Overwhelmed by this revelation, he etched an exclamation mark on the photographic plate of Andromeda to highlight the variable star.

Consequently, the field of cosmology experienced an overnight surge in interest. Hubble’s peer, the esteemed Harvard astronomer Harlow Shapley, was disheartened when he received Hubble’s notification of the finding. “Here is the letter that destroyed my universe,” he expressed to fellow astronomer Cecilia Payne-Gaposchkin, who was present when he read Hubble’s message.

Just three years prior, Shapley had asserted his interpretation of a significantly smaller universe during a debate at the Smithsonian Museum of Natural History. He argued that the Milky Way galaxy, due to its vastness, must encapsulate the entirety of the universe. Shapley believed the oddly blurred “spiral nebulae,” including Andromeda, were merely stars forming at the outskirts of our galaxy and of little importance.

Little did Hubble know that 70 years later, a remarkable telescope named after him would further his legacy from hundreds of miles above the Earth. The “Hubble” telescope became a household name synonymous with incredible astronomical discoveries.

Currently, NASA’s Hubble Space Telescope expands our understanding of the cosmos, observing celestial bodies over ten times farther than Hubble ever could. This remarkable space telescope has unveiled an active universe, filled with energetic stars, colliding galaxies, and runaway black holes, showcasing the dynamic interactions between matter and energy.

Edwin Hubble was the pioneer who took the first significant steps leading to the creation of the Hubble Space Telescope, opening our view to a seemingly endless sea of galaxies. He theorized that despite their numbers, galaxies fell into just a few distinct shapes: spiral, elliptical, and irregular. He believed these shapes could offer insights into galaxy evolution, but the full answer awaited the Hubble Space Telescope’s renowned Hubble Deep Field revelation in 1994.

One of Hubble’s most profound findings was that the farther a galaxy is, the faster it seems to be moving away from Earth. This observation suggested that the universe is expanding, much like a balloon inflating. Hubble established the link between galaxy distance and light redshift, where the light shifted toward the red end of the spectrum as galaxies moved away.

The redshift data were initially gathered by astronomer Vesto Slipher at Lowell Observatory, who observed the “spiral nebulae” a decade before Hubble’s findings. Although Slipher did not recognize them as extragalactic, Hubble made that connection. Slipher interpreted his data as a result of the Doppler effect, noting that all spiral nebulae appeared to be receding from Earth.

Two years before Hubble published his results, Belgian physicist Georges Lemaître analyzed both Hubble’s and Slipher’s observations, concluding that the universe is indeed expanding. This observed relationship between the distances to galaxies and their redshifts is now known as Hubble-Lemaître’s law.

Lemaître further realized that since the universe appeared to be uniformly expanding, one could theoretically reverse the expansion — like rewinding a film — leading to a time when the universe was incredibly tiny, hot, and dense. The term “big bang” didn’t come into common use until 1949.

This discovery was reassuring for Albert Einstein, Hubble’s contemporary, who postulated that the universe could not remain static without collapsing under gravitational forces. The cosmic expansion rate is now referred to as the Hubble Constant.

Ironically, Hubble himself remained skeptical about the runaway universe as an explanation for the redshift data, suspecting some unknown physical phenomenon might create the illusion of galaxies moving apart. He was partially correct, as Einstein’s theory of special relativity explained redshift as an effect of time dilation related to expanding space. Galaxies don’t accelerate away; it’s space expanding between them.

After years of precise measurements, the Hubble telescope quantified the expansion rate, suggesting the universe’s age is approximately 13.8 billion years. This involved establishing what astronomers term the “cosmic distance ladder,” providing a means to measure far-off galaxies. These galaxies are akin to V1, Cepheid variable stars that the Hubble telescope can detect much farther from Earth than Hubble’s original star discovery.

Astrophysics experienced another upheaval in 1998 when Hubble and other observatories indicated that the universe is expanding at an accelerating pace due to an unknown force dubbed “dark energy.” Einstein had initially pondered a repulsive force in space, referring to it as the cosmological constant.

Even more perplexing, the current rate of expansion seems inconsistent with predictions from modern cosmological models, leaving theorists puzzled. Today, astronomers grapple with the notion that whatever is causing the acceleration may change over time. NASA’s forthcoming Roman Space Telescope, designed for extensive cosmic surveys, is expected to shed new light on the characteristics of dark matter and dark energy. Roman may also measure the Hubble constant using lensed supernovae.

This remarkable century-long journey, exploring the depths of the unknown, commenced with Hubble capturing an image of a faint light, the Andromeda galaxy, at Mount Wilson Observatory, high above Los Angeles.

In summary, Edwin Hubble transformed our understanding of the universe, replacing an outdated view with one that portrays humanity as a mere speck in the vast cosmos.