In the study of cosmology, a cosmological conundrum known as the Hubble constant sheds light on the rate of the Universe's expansion. However, there is still tension surrounding it.
The Universe's Expansion
According to Science Alert, the reality of the Universe's expansion has been familiar to humanity since the 1920s. It was back in 1908 when Henrietta Leavitt, a US astronomer, discovered a method of gauging the brightness of the Cepheid variable. The brightness measured did not refer to how bright it looked from Earth's viewpoint. Rather, it focused on the star's actual brightness.
During their usual cycle, these Cepheids become brighter and dimmer. Leavitt was able to showcase how this intrinsic brightness was associated with how long this cycle took place.
Now, Leavitt's Law enables scientists to make use of Cepheids as standard candles, which are objects with known intrinsic brightness. Because of this, their distance can also be measured.
In a phenomenon known as the inverse-square law for light, such light proportionately fades according to distance. With this, if one can know the brightness of a light and how bright it must be, one can decipher the distance of a light pole.
Back in 1929, Edwin Hubble, another astronomer from the US, was able to spot several Cepheid stars from other galaxies and gauge their distance. Based on such a distance as well as other measurements, Hubble was able to determine the Universe's expansion.
Space.com reports that by looking into the cosmic expansion's present rate, also called the Hubble constant, scientists may gauge the Universe's age and fate.
While there were two main strategies used by scientists to measure the Hubble constant, these were found to be inconsistent, as they produced two different value results. Such inconsistency suggests that the standard model could contain errors.
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Hubble Constant Re-examined
Now, two studies have focused on using novel techniques to re-examine this Hubble constant. These papers were published in the Astrophysical Journal and Science journal respectively.
The work is grounded in the Supernova Refsdal. Back in 2014, the recent research team found several shots of the said supernova. This marked the first time a gravitationally lensed supernova was observed. Rather than spotting a single supernova, the researchers reportedly found five.
The supernova's light burst in different directions. However, it moved through space that was warped by the strong gravitational fields of huge galaxy clusters. This then bent some of the paths of the light for it to come to Earth in several routes. Science Alert reports that each supernova's appearance enabled them to observe a different path in the Universe.
The lensed image reveals the same supernova that exploded at a certain point. However, each image moved along a unique path. This allowed a unique and different measurement of the Universe's growth.
Through the studies, the authors find that such measurements are closer to the cosmic microwave background measurement than the supernova and Cepheid measurements. However, considering where it is located, the authors infer that it could be closer to the supernova and Cepheid measurements.
Such findings may not settle the Hubble constant debate, but they may still offer clues on how such a constant can be viewed.
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