![]() This illustration shows the three steps astronomers used to measure the universe's expansion rate to an unprecedented accuracy, reducing the total uncertainty to 2.3 percent. These data were cross-correlated with even farther milepost measurements of exploding stars, supernovas, to build a cosmic “distance ladder.” The measurement of the Hubble constant improved from 10 percent uncertainty at the start of the 2000s to less than 2 percent by 2019. Another team of astronomers continues to streamline and strengthen this by calibrating more Cepheids ever more distant than the local universe. Once the star’s true brightness is known, astronomers can calculate a precise distance to it.īy the late 1990s, the refined value of the Hubble constant was reduced to an error of only about 10 percent. The period of this oscillation is directly linked to the Cepheid’s intrinsic brightness. These stars go through rhythmic pulsations where they slightly rise and fall in brightness. They made observations of a class of star called Cepheid Variables. This allowed astronomers to begin refining distance measurements that are needed to calculate a more precise value for the Hubble constant. In 1994, astronomers began refining the Hubble constant by making precise distance measurements out to the Virgo cluster of galaxies, located 56 million light-years away. These data refined estimates for the expansion rate of the universe. The galaxy M100, located 56 million light-years away, is shown here. Early Hubble observations looked for cosmic milepost markers, the Cepheid variable stars, in ever-farther galaxies. The younger value presented a huge problem it would mean the universe was younger than the oldest known stars. This meant that the universe could be as young as 9.7 billion years or as old as 19.5 billion years. When the Hubble Space Telescope was launched, the uncertainly over the universe’s expansion rate was off by a factor of two. A precise value for the Hubble constant is a critical anchor point for calibrating other fundamental cosmological parameters for the universe. However, the age estimate is only as reliable as the accuracy of the distance measurements. Astronomers later realized that redshift was a consequence of the expansion of space itself, as predicted in Einstein's theory of special relativity. Hubble, therefore, concluded that the redshift phenomenon was an unknown property of space and not a measurement of true space velocity. However, Edwin Hubble's estimates of the expansion implied that the universe was younger than the age of the Earth and the Sun. Hubble noted that light from faraway galaxies appeared to be stretched to longer wavelengths, or reddened, a phenomenon called redshift.īy precisely determining the expansion rate, called the Hubble constant, the cosmic clock can be rewound and the age of the universe calculated. ![]() ![]() This means that the universe is expanding uniformly in all directions. Using the largest telescope of the time, he discovered that the more distant a galaxy is from us, the faster it appears to be receding into space. In 1929, Edwin Hubble provided the first observational evidence for the universe having a finite age. Now, with a lot of perseverance and precise observations, they are approaching one percent accuracy. At first, astronomers were delighted to narrow the expansion estimate to 10 percent accuracy. This value is needed to calculate the age of the universe, estimate its evolution over billions of years, and understand the forces driving it. Four Successful Women Behind the Hubble Space Telescope's Achievementsīefore the Hubble telescope was launched, there was a huge uncertainty over the expansion rate of the universe.Characterizing Planets Around Other Stars.Measuring the Universe's Expansion Rate.
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