The name Hubble is closely associated with space. Most people probably associate it with the first telescope put into orbit, which bears his name. This spacecraft was named because of one of the most important discoveries ever made in astronomy. Its author – Edwin Hubble – discovered that the universe is expanding.
This fact has been one of the foundations of our understanding of space and the processes taking place in it for nearly a hundred years.
At what rate is the universe expanding?
Now three physicists from the University of Michigan in the US: Nhat Minh Nguyen, Dragan Hutterer and Yue Win have proposed a change in the current model created by Hubble, which could help solve one of the most vexing problems in science.
It has to do with the expansion of the universe, or more precisely, the rate at which it is expanding. We don’t really know what causes the constant expansion of space. We assume it’s something we call dark energy. As if that wasn’t enough, we’re also unable to pinpoint the exact rate at which this occurs. It is referred to as H0, or the Hubble constant. What keeps astronomers up at night is that different ways of measuring it give different results.
We write a lot about space on the Spider’s Web:
When measuring the expansion of the universe, we focus on examining its remnants, that is, the remnants of light in the cosmic microwave background radiation or sound waves Frozen right on time.
Another way is to measure the distance to objects with known internal brightness, i.e. type Ia supernovae or variable stars whose light changes regularly due to pulsations. Their pulsations cause periodic changes in the star’s size, surface temperature, and the type of spectral light it emits.
The first way to measure the expansion rate of the universe suggests an expansion rate of about 67 kilometers per second per million parsecs. The second is about 73 kilometers per second per megaparsec. The discrepancy between these two values is known as the Hubble tension. This is a difference of only 7 kilometers per second, which is negligible on the scale of objects discussed. However, this difference is too large and too persistent across different studies to be ignored.
The main justification for building the Hubble Space Telescope was to solve this very problem. Hubble has better resolution for visible wavelength observations than any ground-based telescope because it is located above Earth’s atmosphere. As a result, we can determine the varying brightnesses of stars in galaxies more than 100 million light-years away, and measure the time interval over which their brightness changes.
To get past the light-blocking dust, observations must be made in the near-infrared range, a part of the electromagnetic spectrum for which Hubble is not particularly well suited. This means that there is always some uncertainty in the data obtained from this telescope.
What does the Webb Space Telescope tell us?
But now we have a second telescope in space, the new James Webb Space Telescope (JWST). It is capable of performing infrared observations, and any data it collects is not subject to the same restrictions as its predecessor.
Scientists pointed for the first time to a galaxy at a known distance to calibrate the telescope for the brightness of Cepheid variables. They then proceeded to observe Cepheids in other galaxies. In total, the James Webb Space Telescope has observed 320 Cepheid planets. It turns out that the Hubble data were consistent with Webb’s observations. This means that we still cannot rule out H0 calculations based on the Hubble data. The universe’s aforementioned expansion rate of 73 kilometers per second per million parsecs has remained constant so far, and human error – at least in this case – cannot explain the Hubble jitter.
We still do not know the reason for this tension
One prime candidate is dark energy — a mysterious, unknown but seemingly fundamental force that seems to push the universe inward, like filling a balloon with air.
The three scientists from Michigan decided to look at one of the cosmological models called ΛCDM (Lambda-CDM). It may contain an explanation for Hubble tension. If we observe the pace of expansion and understand the forces behind it, we can trace this process from its beginning. That is, from the Big Bang to the moment when galaxies form and eventually come together in clusters spanning unimaginable distances, creating the largest known structures in the entire universe.
The researchers used a combination of measurements including so-called ripples in the network of galaxies in space, gravitational lensing, and microwave background data to reach the statistically convincing conclusion that galaxy clusters are expanding more slowly than predicted by the ΛCDM cosmology model.
how He said One of the three scholars, Minh Nguyen:
The difference in growth rates that we are likely to detect becomes more pronounced the closer we get to the present moment in our simulations. So either we are missing systematic errors in each of the computational methods used, or we are missing something new and unknown in the Standard Model.
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