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| In honor of Edwin Hubble's discovery of the Cepheid variable star V1 in the Andromeda galaxy 100 years ago, astronomers partnered with the American Association of Variable Star Observers (AAVSO) to track its light curve over six months. This data allowed the Hubble Space Telescope to observe the star at its brightest and dimmest, confirming that Andromeda lies far outside the Milky Way and marking a pivotal step in our understanding of the expanding universe. |
For humanity, the Sun is the most important star in the universe. But far beyond it, tucked within the Andromeda galaxy, lies the second-most crucial star in human history. Known as V1, this faint, flickering star is located 2.2 million light-years away and is only 1/100,000th as bright as the faintest star visible to the naked eye. Despite its inconspicuous nature, V1 holds a profound significance in our understanding of the cosmos.
A century ago, Edwin Hubble’s discovery of V1, an unassuming Cepheid variable star, changed the course of astronomy. This star, along with Hubble’s groundbreaking work, revealed that the Milky Way is just one of countless galaxies, opening humanity's eyes to the vastness of the universe. Carnegie Science and NASA are marking this monumental achievement at the 245th meeting of the American Astronomical Society in Washington, D.C., in honor of the 100th anniversary of Hubble’s discovery.
In 1923, using the Carnegie-funded 100-inch Hooker Telescope at Mount Wilson Observatory, Hubble identified V1 as a Cepheid variable, a rare pulsating star that astronomers use as cosmic mile markers. This discovery was pivotal because it showed that Cepheid variables' pulsation periods are linked to their luminosity, a relationship first uncovered by Henrietta Swan Leavitt. By measuring the brightness of such stars, astronomers could calculate their distances, revealing the vastness of space.
Before Hubble’s work, many astronomers, including Harlow Shapley, believed the Milky Way was the entire universe. Shapley had argued that "spiral nebulae," like Andromeda, were part of our galaxy, but Hubble’s observations shattered that belief. He realized that the Andromeda galaxy, containing V1, was far beyond the Milky Way, suggesting that the universe was far larger than anyone had imagined. Hubble’s astonishment was evident when he scribbled an exclamation mark on a photographic plate of Andromeda after making the discovery.
The discovery ignited a revolution in cosmology, with scientists now grasping that the universe was not only expansive but composed of countless galaxies. In an emotional response, Shapley lamented, "Here is the letter that destroyed my universe," to fellow astronomer Cecilia Payne-Gaposchkin.
As a result, Hubble’s discovery opened the door to a broader understanding of cosmic evolution. His contributions, along with those of his contemporaries, laid the groundwork for the development of modern cosmology. Though Hubble himself could not fully embrace the concept of an expanding universe, his observations, coupled with Vesto Slipher's redshift data, set the stage for the development of Hubble's law, which shows that galaxies farther away from Earth are receding at faster speeds. This realization led to the formulation of the idea that the universe is expanding, akin to a balloon inflating.
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| The image titled "Cepheid Variable Star V1 in M31 HST WFC3/UVIS" shows the star's changing brightness over time, with four boxes each displaying the star's varying light intensity on different dates: Dec. 17, 2020, Dec. 21, 2010, Dec. 30, 2019, and Jan. 26, 2011, demonstrating the rhythmic fluctuation of its brightness. |
In the years that followed, scientists such as Georges Lemaître and Albert Einstein contributed to the understanding that the universe began from an incredibly dense, hot state—a theory later coined the "Big Bang." Hubble’s work, though initially seen through the lens of galaxy shapes and distance measurements, was critical in determining the age of the universe, pegged at 13.8 billion years thanks to the precision of the Hubble Space Telescope.
Hubble’s legacy was further cemented with the launch of the Hubble Space Telescope in 1990. This modern marvel of science continues to push the boundaries of our knowledge, unveiling breathtaking images and discoveries, from active stars to colliding galaxies. In 1998, the Hubble Space Telescope made an even more astonishing discovery: the universe's expansion is accelerating, a phenomenon attributed to the mysterious "dark energy." The observation that the rate of expansion of the universe is not constant but is increasing over time adds yet another layer of complexity to our understanding of the cosmos.
As the Hubble Space Telescope continues its mission, it is paving the way for future exploration, with the upcoming Roman Space Telescope expected to further our understanding of dark matter and dark energy. Together, these instruments will deepen our knowledge of the forces shaping the universe, answering questions that continue to perplex astronomers.
From a modest star in the Andromeda galaxy to groundbreaking discoveries that redefined our place in the universe, Edwin Hubble’s contributions have had an indelible impact on science. His discovery not only reshaped the field of astronomy but also shifted humanity’s perception of itself in the vast expanse of the cosmos. The Hubble Space Telescope’s ongoing work is a fitting tribute to his legacy, continuing to unlock the mysteries of the universe that Hubble first began to explore a century ago.
As we look back on the past 100 years, it is clear that Edwin Hubble’s vision has not only expanded our knowledge but has changed how we see the universe, making us aware of our small but significant place in it.
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