How far can the universe expand?
Cosmic expansion : The universe is on an unexpectedly rapid growth path
Bigger, faster, further: the universe is growing faster than expected. This is confirmed by new studies with the “Hubble” space telescope. The rate of expansion of the cosmos is currently around ten percent above the value actually expected by astrophysicists.
Cosmic yeast dough
Researchers led by US Nobel Prize winner Adam Riess from Johns Hopkins University and the Space Telescope Science Institute in Baltimore present their studies in the journal "The Astrophysical Journal". The study supports earlier findings that the rate of expansion of space deviates from the predictions.
Since the Big Bang 13.8 billion years ago, the universe has been expanding like a yeast dough with raisins: The distance between all the raisins in the dough increases, and the faster the further the raisins are from each other. It is the same with the galaxies in space - the greater their distance, the faster they move away from each other. The measure for cosmic expansion is the Hubble constant. Their expected value is 67 kilometers per second per megaparsec. A megaparsec is an astronomical unit of length and corresponds to around 3.3 million light years - a light year in turn is the distance that light travels in one year: almost ten trillion kilometers.
The further, the faster
This means that a galaxy at a distance of 3.3 million light years should move away from us at 67 kilometers per second, one at 33 million light years away at 670 kilometers per second, and so on. This value is based on extremely precise observations of the very young universe with the “Planck” satellite of the European space agency Esa, which examined the echo of the Big Bang and thus looked back in time. Measurements in our cosmic environment show, however, that the Hubble constant is now 74 kilometers per second per megaparsec.
For years researchers have been trying to find out whether this deviation is due to random fluctuations or possibly due to previously undiscovered physical factors. Riess and his team have now calibrated cosmic milestones more precisely, which astronomers often use to measure distances. These are variable stars of the Cepheid type, the brightness of which fluctuates regularly. The length of the fluctuation depends on the absolute brightness of the stars. If you know the rhythm of a Cepheid, you can calculate its absolute brightness from it. The measured brightness then shows how far away the star is.
With a little help from the Cepheids
With the “Hubble” space telescope, the researchers analyzed dozens of the Cepheids in the Large Magellanic Cloud, a satellite galaxy of our Milky Way, which are often helpful in answering astronomical questions. Thanks to independent distance measurements, the relationship between the absolute brightness of the Cepheids and their rhythm could be determined much more precisely. This reduces the probability of a random deviation between the measured and the expected Hubble constant from one in 3000 to one in 100,000. The deviation has thus reached a point that can no longer be described as a coincidence, emphasized Riess in a communication from his university .
"These are not just two experiments that do not match," explains the Nobel Prize winner. Rather, it is a fundamental difference. “One is a measurement of how fast the universe as we see it is expanding today. The other is a prediction, based on measurements and the physics of the early universe, of how fast it should expand. If these values do not match, there is very likely something missing in our cosmological model that connects the two epochs. "
Causes in the dark
When searching for the cause of the more accelerated expansion of the universe, the researchers are literally still groping in the dark: a possible role could be played by the mysterious dark energy, which today makes up almost 70 percent of the universe's content and whose nature is still completely unknown. It is probably driving the universe apart ever faster and could possibly also explain the even faster expansion. Another possibility would be that the equally mysterious dark matter, which is more than five times more abundant in the universe than the matter we are familiar with, interacts more strongly with radiation and ordinary matter than assumed. (Till Mundzeck, dpa)
Editor's note: An error had crept into the caption of this article. There was something about a neighboring galaxy in our universe, which of course meant a neighboring galaxy of our own galaxy, also known by the German translation of the name of a well-known chocolate bar. We corrected the mistake.
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