![]() These are supergiant stars with something like 100,000 times the luminosity of our sun. "Prior to Hubble’s 1990 launch," Riess explained, "the expansion rate of the universe was so uncertain astronomers weren’t sure if the universe has been expanding for 10 billion or 20 billion years."įurthermore, there is one star in particular that scientists like to focus on with Hubble to tease out the universe's expansion rate: Cepheids. After some calculations, scientists reason that this kind of information taken from lots (and lots) of stars should help us figure out the Hubble constant. Such brightnesses can tell us how far away those stars are and, because we know the immutable speed of light, for how long that light has been traveling to reach us. That's because it sits above Earth's blurring atmosphere, unlike ground-based observatories hampered by our planet's hazy shield. Hubble is a key device used in resolving Hubble tension because it's able to measure stellar brightnesses with incredible precision. Riess (STScI)) 'I have your back, Hubble,' said the JWST (probably) ![]() The bottom panel is for NGC 4258, a galaxy with a known, geometric distance, with the inset showing the difference in distance moduli between NGC 5584 and NGC 4258 as measured with each telescope. The top panel is for NGC 5584, the Type Ia supernova host, with the inset showing image stamps of the same Cepheid seen by each telescope. The red points are from Webb and the gray points are from Hubble. "Webb measurements provide the strongest evidence yet that systematic errors in Hubble’s Cepheid photometry do not play a significant role in the present Hubble tension," Adam Riess, from the Johns Hopkins University and the Space Telescope Science Institute, said in a statement.Ĭomparison of Cepheid period-luminosity relations used to measure distances. This is a big deal, because Hubble observations are one of the most common features that scientists use to decode the Hubble constant - or more specifically, Hubble observations of Cepheid stars are. ![]() (Back in the 1920s, the American astronomer Edwin Hubble discovered that the universe is expanding.) In a nutshell, it showed that the so-called crisis is probably not due to technical issues with measurements made by its telescope sibling that boasts a very relevant name: the Hubble Space Telescope. Returning to the JWST's results: The spaceborne observatory crossed one more item off that list. As particle physicist David Gross, a former director of the KITP, put it: "We wouldn't call it a tension or a problem but rather a crisis." And ever since, scientists have continued to diligently work out where they might've gone wrong, crossing off possible explanations for Hubble tension on a list you can check out here. In 2019, a number of high-profile physicists even famously gathered at the Kavli Institute for Theoretical Physics in California to officially try and resolve things. In other words, perhaps the models that presently thread our understanding of the universe are missing something? Potentially, this discrepancy either suggests our instruments are not intelligent enough - or maybe we're awfully wrong about that theoretical prediction. ![]() Still others have suggested solutions that fall between the two. But after scanning stars and galaxies across our universe, some experts calculate the constant to be 69.8 km/s/Mpc, while others find it to be as high as 74 km/s/Mpc, depending on the method of measurement. One megaparsec is 1,000,000 parsecs, or about 3,260,000 light-years, for context. Yet, for whatever reason, our theoretical predictions of the constant do not appear to match up with reality.Īccording to most models, the Hubble constant should equal something around 68 kilometers per second per megaparsec (km/s/Mpc). So, what's the problem with calculating the rate?īasically, settling Hubble tension once and for all is dependent on resolving the true value of the Hubble constant, which is a crucial number in calculating the universe's expansion rate.
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