Scientists use a cosmic distance ladder to measure the rate of expansion of the universe. The path, symbolically shown here, is a series of stars and other objects in galaxies that have known distances. By combining these distance measurements with the speeds at which objects move away from us, scientists can calculate this expansion rate.
Credit: NASA / JPL-Caltech
This year marks the 90th anniversary of an overwhelming discovery: the universe is expanding.
The discovery was spearheaded by Edwin Hubble for whom the orbiting Hubble Space Telescope was named. As an astronomer at the Mount Wilson Observatory in Los Angeles, Hubble had access to today's most modern equipment, especially the 1
Since 1919, Hubble had discovered new galaxies from the observatory, according to the Carnegie Institution for Science. In 1923, he developed a method for measuring the distance between a distant galaxy and the Milky Way, which involved calculating the star's actual brightness in another galaxy and then comparing that value with how bright they appeared from Earth. [11 Fascinating Facts About Our Milky Way Galaxy]
This work led to another revelation. According to the Carnegie Institution, Hubble also knew the work of a former astronomer, Vesto Melvin Slipher, who had figured out he could measure how quickly a galaxy moved toward or away from the winter road looking for changes in the wavelengths of light coming from the galaxy. Measurement is called the Doppler shift, and the principle is the same as the tone change, which seems to happen as an ambulance siren approach, blares by and recedes, except with light instead of sound. In the case of light, wavelengths emitted by an object moving toward a stationary observer occur more frequently and thus more bluishly. Wavelengths released by a backward object seem less frequent and thus rescued.
Armed with information on the distance to other galaxies and their Doppler shifts, Hubble and his colleagues released a paper in 1929 that would change astronomy. The paper "A distance to radial velocity ratio of extra-galactic nebulae" showed that the galaxies visible from the Milky Way all seemed to be faster away. (On January 17, 1929, the paper was "disseminated" to the National Academy of Sciences.)
What Hubble and his co-authors had observed was the very expansion of the universe itself. To apply a famous analogy, the galaxies are like raisins in the bread dough of the universe. As the dough rises, all the raisins move further apart, but they are still stuck in the same dough. The discovery made it possible to calculate the age of the universe: about 13.7 billion years old.
90 years after the Hubble team reported its findings, researchers are still trying to understand how this expansion works. Last year, astronomers reported that the telescope named after Hubble used the expansion faster than expected – 73 kilometers per hour. Second per second Megaparsec, to be precise. A megaparsec is 3.3 million light-years, so this measurement means that every 3.3 million light-years from Earth, a galaxy looks to fall to 73 kilometers per second faster.
A few months later, the same researchers found more distant stretches of the universe seem to grow less rapidly, at 67 kilometers per square meter. second per second megaparsek. The inconsistencies suggest that something – perhaps dark energy or dark matter – affects the expansion of the universe in ways that are not yet understood.
Originally published on Live Science.