The most accurate observation yet of distant stars that periodically change in brightness may prompt a rethink of the rate at which the universe is expanding — perhaps by settling, or deepening, a long-standing problem in cosmology.
The observation confirms that there is a discrepancy between the two main methods of measuring velocity Universe Expanding, aligning with one and not the other, a new study reports.
Researchers in the Stellar group used data collected by Europe Jaya spacecraft for study Cepheid variable stars, which pulsates regularly, providing a method for accurately measuring cosmic distances. The technique of measuring Cepheid stars is expanding to include other methods, such as those based on Type 1a observations supernovae.
Related: The Hubble Telescope is refining the mystery of the expansion rate of the universe
The light output from supernovae, the giant explosions that occur at the end of the lives of large stars, is so uniform that they are referred to as “standard candles” and make up an important part of what astronomers call the “cosmic distance ladder.” The method of measuring the distance of Cepheid stars adds another “runge” to this metaphorical ladder, and this new research has reinforced that rung.
“We developed a way to search for Cepheids belonging to star clusters of several hundred stars by testing whether stars move together across milky wayStudy co-author Richard Anderson, a physicist at the Federal Polytechnic School of Lausanne (EPFL) in Switzerland, he said in a statement (Opens in a new tab).
“Thanks to this trick, we can take advantage of the best knowledge of Gaia’s parallax measurements while taking advantage of the increase in resolution offered by many stars of the cluster,” Anderson said. “This has allowed us to push the resolution of Gaia’s views to their limits and provides the strongest foundation upon which the distance ladder can rest.”
The cosmic distance scale is also used to measure the expansion rate of the universe, known as the Hubble constant. This new recalibration of the Cepheid “degree” deepens the problem of the expansion rate of the universe, which has come to be known as the “Hubble tension”.
What is the Hubble tension?
In the early 20th century, shock waves became popular in physics and astronomy when Edwin Hubble He revealed evidence that the universe is not static, as was thought at the time, but is, in fact, expanding. So this rate of expansion became known as the Hubble constant.
This concept underwent a major shake-up in the late 1990s, when astronomers discovered through observations of distant supernovae that not only is the universe expanding, but it is also doing so. at an accelerated rate. Since then, measuring the Hubble Constant has become a thorny issue for astronomers and cosmologists, because there are two main ways to determine this value — and they don’t agree.
One method is used galaxiesVelocities as a function of distance yield a Hubble constant value of about 73 ± 1 kilometers per second per megaparsec (km/s/Mpc), with 1 megaparsec representing about 3.26 million light-years. This is known as the “late time” solution, because it comes from measurements of the universe in recent times.
The other way to measure the Hubble constant is to look at the light from an event shortly after the great explosion It’s called the “last scattering,” where electrons combine with protons to form the first atoms. Since free electrons had previously scattered photons (particles of light) too far, preventing them from traveling very far, this event meant that light was suddenly allowed to travel freely through the universe.
This “first light” is now seen as Cosmic microwave background (CMB), and it fills the universe almost uniformly, except for small differences. When astronomers measure these small variations in this fossil radiation, it predicts a modern-day value for the Hubble constant of about 67.5 ± 0.5 km/sec/million blocks.
Oddly enough, the differences between the two estimates of the Hubble constant have only increased as the measurement techniques for both have been refined and become more precise. This difference of 5.6 km/s/megapasc, and the general problems surrounding it, is referred to as the “Hubble tension”. It’s a serious issue for cosmologists, because it suggests something is wrong with our understanding of the basic physical laws that govern the universe.
Related: The universe is expanding very quickly and we may need new physics to explain this
Cepheid variants choose a side
Anderson explained why a difference of a few kilometers/second/Mpc in the Hubble constant is so important, even given the vast scale of the universe. (The width of the visible universe alone is estimated to be about 29,000 MPC.)
“This discrepancy is of great importance,” said Anderson. “Suppose you wanted to build a tunnel by drilling into two opposite sides of a mountain. If you have understood the type of rock correctly and if your calculations are correct, the two holes you are drilling will meet in the centre. But if they do not, then you have made a mistake—either Your calculations are wrong or you are wrong about the type of rock.”
Anderson said this is similar to the Hubble tension and what happens with the Hubble constant.
He added, “The more we are sure of the accuracy of our calculations, the more we conclude that the discrepancy means that our understanding of the universe is wrong, and that the universe is not quite what we thought.”
The improved calibration of the Cepheid Variable Measurement instrument means that this technique finally “takes a side” in the Hubble tension debate, providing agreement with the “late time” solution.
“Our study confirms the rate of expansion of 73 km/s/Mpc, but more importantly, it also provides the most accurate and reliable calibrations of Cepheids as distance measuring instruments to date,” said Anderson. “This means that we have to rethink the fundamental concepts that form the basis of our general understanding of physics.”
The team’s results have other implications, too. For example, the more accurate Cepheid calibration helps better reveal the shape of our galaxy, members of the study team said.
“Because our measurements are so precise, they give us insight into the geometry of the Milky Way,” said study lead author Mauricio Cruz Reyes, Ph.D. student in Anderson’s research group, he said in the same statement. “Extremely accurate calibration (Opens in a new tab) Our development will allow us to better determine the size and shape of the Milky Way as a flat disk galaxy and its distance from other galaxies, for example.”
The new study was published last week in the journal Astronomy and astrophysics (Opens in a new tab).
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