Study: The conflicting values ​​of the Hubble constant are not due to a measurement error

Astronomers have made new measurements of the planet Hubble is fixedIt is a measure of how quickly the universe is expanding, by combining data from the Hubble Space Telescope and the James Webb Space Telescope. Their results confirmed the accuracy of previous Hubble measurements of the value of the constant, according to their results Recent paper It was published in The Astrophysical Journal Letters, with the consequence of a long-standing discrepancy in values ​​obtained by various observational methods known as the “Hubble tensor”.

There was a time when scientists thought the universe was static, but that changed with Albert Einstein's general theory of relativity. Alexander Friedmann published a set of equations showing that the universe might indeed be expanding in 1922, and Georges Lemaitre later made an independent derivation to reach the same conclusion. Edwin Hubble confirmed this expansion with observational data in 1929. Before that, Einstein had been trying to modify general relativity by adding a cosmological constant in order to obtain a fixed universe from his theory; After the discovery of Hubble, Legend saysHe referred to this effort as his biggest blunder.

As mentioned earlier, the Hubble constant is a measure of the expansion of the universe expressed in units of kilometers per second per megaparsec. Therefore, every second, every million parsec of the universe expands by a certain number of kilometers. Another way to think about this is in terms of a relatively stationary object a million parsecs away: every second, it becomes a number of kilometers farther away.

How many kilometers? That's the problem here. There are three ways scientists use to measure the Hubble Constant: looking at nearby objects to see how fast they are moving, gravitational waves produced by colliding black holes or neutron stars, and measuring tiny aberrations in the afterglow of the Big Bang known as the cosmic microwave background (CMB). However, different approaches have found different values. For example, tracking distant supernovae produced a value of 73 kilometers per second Mpc, while CMB radiation measurements using the Planck satellite produced a value of 67 kilometers per second Mpc.

Just last year, researchers made a third independent measurement of the expansion of the universe by tracking the behavior of a gravitationally lensed supernova, where distortion in spacetime caused by a massive object acts as a lens to magnify a background object. The best fits between these models ended up just below the CMB-derived Hubble constant, with the difference within statistical error. Values ​​closer to those derived from other supernova measurements were a significantly better fit to the data. This method is new, with a large amount of uncertainty, but it provided an independent means of arriving at the Hubble constant.

“We measured it using information in the cosmic microwave background and got a single value,” wrote Ars Science editor John Timmer. “We measured it using the apparent distance of objects in the present universe and got a value that differed by about 10 percent. As far as anyone can tell, there is nothing wrong with either measurement, and there is no clear way to measure it.” Get them to agree.” One hypothesis is that the early universe briefly experienced a kind of “kick” of repulsive gravity (akin to the idea of ​​dark energy) that then mysteriously stopped and disappeared. But it remains a speculative, if interesting, idea for physicists.

This last measurement depends on Confirmed last year 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 scale. But there is still the possibility of as-yet-undetected errors that could further look deeper (and thus back in time) into the universe, especially for measurements of the brightness of distant stars.

So a new team made additional observations of Cepheid variable stars — a total of 1,000 stars in five host galaxies up to 130 million light-years away — and linked them to the Hubble data. The Webb telescope is able to see beyond the interstellar dust that has made Hubble's images of those stars more blurry and overlapping, so astronomers can easily distinguish between individual stars.

The results also confirmed the accuracy of Hubble's data. “We have now covered the full scope of what Hubble observed, and we can rule out measurement error as a cause of Hubble jitter with very high confidence.” said co-author and team leader Adam Rees, 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. With measurement errors eliminated, 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 digital IDs).