NASA/ESA/CSA/STScI/A. Lease (JHU)
astronomers are hubble constantIt combines data from the Hubble Space Telescope and the James Webb Space Telescope to measure how fast the universe is expanding. Their results confirmed the accuracy of Hubble’s initial measurements of the constant’s value. recent papers This represents a longstanding discrepancy in the values obtained by different observation methods, known as the “Hubble tension,” and was published in The Astrophysical Journal Letters.
There was a time when scientists believed the universe was stationary, but Albert Einstein’s theory of general relativity changed the situation. Alexander Friedman published a set of equations in his 1922 year showing that the universe may actually be expanding, and Georges Lemaître later made independent derivations to reach a similar conclusion. Edwin Hubble confirmed this expansion in his observational data in 1929. Prior to this, Einstein had attempted to modify general relativity by adding a cosmological constant to obtain a static universe from his theory. After discovering Hubble, That’s what the legend sayshe called the effort his greatest failure.
As previously reported, the Hubble constant is a measure of the expansion of the universe expressed in kilometers per second/megaparsec. Therefore, every second, each megaparsec of the universe expands by a certain number of kilometers. Another way to think about this is in terms of a relatively stationary object 1 megaparsec away. In other words, it moves several kilometers away every second.
How many kilometers? That’s the question. There are basically three methods that scientists use to measure the Hubble constant. One method is to observe nearby objects and determine their speed, gravitational waves produced by colliding black holes and neutron stars, and small deviations in the Big Bang’s afterglow. Cosmic microwave background radiation (CMB). However, different methods yield different values. For example, tracking a distant supernova gave a value of 73 km/s Mpc, while measurements of his CMB using the Planck satellite gave a value of 67 km/s Mpc.
Just last year, researchers made a third independent measurement of the expansion of the universe by tracking the behavior of gravitational lensing supernovae. In supernovae, the distortions in space and time caused by massive objects act as lenses that magnify objects in the background. The best fits of these models all resulted in slightly lower values of the Hubble constant derived from the CMB, and the differences were within statistical error. Values close to those obtained from measurements of other supernovae were a fairly poor fit to the data. Although this method is new and has significant uncertainties, it provided an independent means of obtaining the Hubble constant.
![Comparison of Hubble and Webb views of Cepheid variables.](https://cdn.arstechnica.net/wp-content/uploads/2024/03/hubble2-640x358.jpg)
NASA/ESA/CSA/STScI/A. Lease (JHU)
“We measured it using information from the cosmic microwave background radiation and came up with one value,” writes ArsScience editor John Timmer. “And when we measured it using the apparent distances to objects in the universe today, we got values that were about 10 percent different. As far as anyone can tell, there’s nothing wrong with either measurement. There’s also no obvious way to check that.” Get them to agree. ” One hypothesis is that the early universe briefly experienced some kind of “kick” from repelling gravity (similar to the concept of dark energy), then mysteriously powered down and disappeared. is. But it remains a speculative, though potentially exciting, idea for physicists.
This latest measurement result is based on Last year’s confirmation Based on Webb’s data, Hubble’s measurements of the expansion rate were accurate, at least for the first few rungs of the cosmic distance ladder. But especially when measuring the brightness of more distant stars, there was still the potential for undetected errors to increase the deeper we looked into the universe (that is, further back in time).
So the new team observed a total of 1,000 additional Cepheid variable stars in five host galaxies 130 million light-years away and correlated them with Hubble data. The Webb telescope can now see beyond the interstellar dust that makes Hubble’s own images of stars blurry and overlapping, allowing astronomers to more easily distinguish individual stars.
The results further confirmed the accuracy of the Hubble data. “We now have the entire range observed by Hubble and can rule out measurement errors as the cause of the Hubble tension with very high confidence.” Co-author and team leader Adam Rees said:, a physicist at Johns Hopkins University. “Combining Webb and Hubble gives us the best of both worlds. We find that Hubble’s measurements remain reliable as we climb further along the cosmic distance ladder. Measurement errors are negated. So what remains is the real and exciting possibility that we have misunderstood the universe.”
The Astrophysical Journal Letters, 2024. DOI: 10.3847/2041-8213/ad1ddd (About DOI).