Universe expands faster than expected

So far the most accurate measurements of the Hubble constant contradict previous values

New readings for the Hubble constant suggest an even faster expansion of the university than previously thought © NASA
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Faster than the theory allows: Our universe expands five to nine percent faster than previously thought. This is indicated by the hitherto most accurate measurement of the Hubble constant, the value that indicates the cosmic expansion rate. The problem with this is that the new values ​​do not match the findings from the cosmic microwave background nor the theories about what drives the expansion of the universe.

Our universe is expanding - this has been the case since the Big Bang. But for a long time it was unclear whether the pace of this expansion remains the same or changes. Only distance measurements of further type 1 supernovae revealed in 1998 that the expansion has been accelerating for six billion years. The engine for this is current theories after the dark energy, a kind of counterforce to gravity.

However, how fast the universe is currently expanding is less clear than you think. Earlier rough measurements and models initially assumed a Hubble constant of 70 to 75 kilometers per second per megaparsec (km / s / Mpc). However, in 2013, ESA's Planck satellite detected a more accurate, but significantly lower, reading of 67.15 km / s / Mpc due to fluctuations in cosmic background radiation.

Cepheids and supernovae as measuring sticks

Now, using the Hubble Space Telescope, astronomers have once again determined the rate of expansion - and come back to different values. They determined the distance and redshifts of 2, 400 changeable stars, so-called Cepheids, in 19 galaxies, as well as of about 3, 000 supernovae of type 1a. Both are regarded as the classical "yardsticks" of the cosmos.

The Hubble constant was measured using Cepheids and supernovae type 1a. © NASA, ESA, A. Feild (STScI), and A. Riess (STScI / JHU)

The surprising result: According to the new measurements, the Hubble constant is 73.2 km / s / Mpc and thus five to nine percent higher than the previous measurements. The universe expands even faster than previously thought. The Hubble observations, however, are considered to be the most accurate determination of this expansion value so far the uncertainty is only 2.4 percent, as the astronomers emphasize. display

Ridiculous deviation

"If you believe in our numbers, and we have made every effort to reduce the uncertainties of measurement more than ever before, then we must come to the conclusion that there is a problem with the previous ones, on measurements of the cosmic Background radiation based assumptions, "says co-author Alex Filippenko of the University of California at Berkeley.

He compares the problem with building a bridge between two shores. The more distant shore stands for the background radiation and the insights derived from it, the nearby shore represents the current Hubble observations. "When you start building on both ends, you expect the bridge to hit the middle if all the plots and measurements were correct, " explains Adam Riess of the Space Telescope Science Institute in Baltimore. "But now the ends do not meet and we have to find out why."

In this nearby spiral galaxy, astronomers observed both Cepheids and a Supernova Type 1a, allowing them to calibrate their measurements. NASA, ESA, and L. Frattare (STScI)

Dark energy, unknown particles or mistakes at Einstein?

But what can cause such a deviation? For this theoretically several causes come into consideration. An explanation would be that the Dark Energy, whose nature is still unexplained, gains power in the course of cosmic history, or has previously unknown properties. It would also be possible, however, that in the early universe a previously unknown type of subatomic particle emerged, which, as a kind of "dark radiation", influenced the behavior of the early cosmos and thus also those measurable today background radiation.

However, it would also be conceivable that Einstein's general theory of relativity and thus the equations describing gravitation is not complete. "Our discrepancies suggest that something is missing in our current physical understanding of the Universe, " says Filippenko.

He and his colleagues are already working to increase the accuracy of the Hubble constant by measuring an even larger number of supernovae. Their goal is an uncertainty factor of only one percent. Astronomers are also hoping for new space telescopes that will launch in the next few years, such as NASA's James Webb telescope, which can look even further into space and thus spy on new cosmic standards. (The Astrophysical Journal, in press; arXiv: 1604.01424)

(University of California Berkeley, Jun 3, 2016 - NPO)