Schematic diagram of the use of Cepheid variables to measure the Hubble constant, which describes the expansion rate of the universe. (NASA, ESA, A. Feild [STScI), and A. Riess [STScI/JHU])
[The Epoch Times, March 31, 2024](Compiled and reported by Epoch Times reporter Linda) Astronomers combined data from the Hubble Space Telescope and the Webb Space Telescope (JWST) to conduct a study of the cosmic Hubble Constant. The results of the new measurement confirmed the accuracy of the previously measured Hubble constant value, further confirming the differences between the measurement results of different methods. This highlights that existing theories of the universe may be in desperate need of a breakthrough.
The new study was published on February 6 inAstrophysical Journal Letters“(The Astrophysical Journal Letters). The Hubble constant is a measure of how fast the universe is expanding, and the long-standing difference between values obtained through different observation methods is called “Hubble tension.”
basic concept
There was a time when scientists believed the universe was static, but that changed with the advent of Einstein’s theory of general relativity. Alexander Friedmann published a set of equations in 1922 suggesting that the universe might actually be expanding, and Georges Lemaitre later independently derived it and came to the same conclusion. Edwin Hubble confirmed this expansion with observational data in 1929. Previously, Einstein had been trying to modify general relativity by adding a cosmological constant in order to derive a static universe from his theory. It is said that after the emergence of Hubble’s new theory, Einstein said that his attempt to introduce a cosmological constant and maintain a static universe was the biggest mistake of his life.
The Hubble constant is used to measure the expansion rate of the universe. Its unit is the number of kilometers of expansion per million parsecs per second (km/s·Mpc. Megaparsec is a unit for measuring length in the universe. One parsec is about is 3.26 light years). In other words, every megaparsec area of the universe expands by a certain number of kilometers in one second. To look at it another way, if we have a relatively stationary object located one million parsecs away, its distance from us will increase by a few kilometers with every passing second.
different measurement methods
So how many kilometers exactly is it? This is where the problem lies. Scientists basically use three methods to measure the Hubble constant: observing nearby objects to see how fast they are moving, gravitational waves from collisions of black holes or neutron stars, and measuring tiny deviations in the Big Bang’s afterglow, the so-called “afterglow.” Also called the Cosmic Microwave Background (CMB). However, different methods yield different values. For example, the value obtained by tracking and observing distant supernovae is 73km/s·Mpc, while the value obtained by measuring the CMB using the Planck satellite is 67km/s·Mpc.
Just last year, researchers made the third independent measurement of the expansion of the universe by tracking supernovae seen using gravitational lensing, in which the distortion of space-time caused by massive objects acts as a lens, magnifying objects in the background. The best fitting results of these models are all slightly lower than the Hubble constant value obtained from the CMB, and the difference is within the statistical error range. This is a new method with considerable uncertainties, but does provide an independent method of obtaining the Hubble constant.
Ars Science editor John Timmer writes: “We measured it using information from the cosmic microwave background and got a value. Measured using the apparent distance of objects in the universe today It gives values that differ by about 10%. As far as is known, there are no problems with both measurements, but there is no way to unify. One hypothesis is that the early universe briefly experienced some kind of repulsive gravity (similar to the dark energy concept) “recoil” and then mysteriously disappear. But this remains a guess, although physicists may be excited about it. “
Using Cepheids
Now, the latest measurements build on last year’s data from the Webb telescope, confirming that Hubble’s early measurements of the expansion rate were accurate, at least for modest cosmic scales. But it could still contain errors that could add to deeper observations of the universe, particularly brightness measurements of more distant stars.
Therefore, the new research team conducted additional observations of Cepheid variable stars, a total of 1,000 stars in five host galaxies as far away as 130 million light-years away, and correlated them with Hubble data. Webb is able to see through the interstellar dust that blurs and overlaps Hubble’s images of these stars, so astronomers can use Webb to more easily distinguish individual stars.
The results further confirmed the accuracy of Hubble’s data. “We have gone across the entire range of Hubble observations and confirmed that the measurement error comes from Hubble tension,” said co-author and team leader Adam Riess, a physicist at Johns Hopkins University. Combining it with Hubble provides the best of both worlds. We found that Hubble measurements remain reliable as we climb farther along the cosmic distance ladder. Once the measurement errors are eliminated, what remains is this: We may have misunderstood the reality of the universe. , which is exciting.”
It seems that the existing theory of the universe needs to be re-examined urgently, and perhaps the next theoretical breakthrough is not far away from us. ◇#
Editor in charge: Sun Yun
