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The universe is developing faster and faster. This accelerated expansion has been measured in different ways, but there is one major problem. Depending on whether you are looking at the very distant universe or not, you get two different numbers for the rate of expansion of the universe.
This crisis in cosmology has worried astrophysicists for several years now. A new study measured the rate of expansion of the universe with a different method and found that the gap in the number is definitely there.
In an article accepted in The Astrophysical Journal, the team described how they measured the infrared properties of 63 elliptical galaxies 330 million light-years (100 million parsecs) from Earth. Astronomers have used the Surface Luminosity Fluctuation (SBF) technique, which works for elliptical galaxies because they are old and have a consistent population of old stars.
The researchers measured the Hubble constant – also known as H0 (H-nothing or H-zero) – find a value of about 73 kilometers per second per megaparsec. This means that if two galaxies are 1 million parsecs apart, they appear to be moving away from each other at a speed of 73 kilometers (45 miles) per second,
This is consistent with other methods that have looked at the rate of expansion in the local universe, but it is greater than what has been measured in the very old universe. Observation of the cosmic background of put H microwaves0 at about 68 kilometers (42 miles) per second per megaparsec.
“To measure the distances of galaxies up to 100 megaparsecs is a fantastic method,” said co-author Professor Chung-Pei Ma, University of California, Berkeley, in a statement. “This is the first paper that brings together a large homogeneous set of data, on 63 galaxies, with the aim of studying H-nothing using the SBF method.”
The fact that several independent methods all find different values is really a challenge. There may be something we haven’t factored into our theories – or maybe the measurement uncertainty is too optimistic.
“The jury’s out,” Prof Ma said. “I think it’s really in the error bars. But assuming everyone’s error bars aren’t underestimated, the tension becomes uncomfortable. “
Whatever the cause, this tension is here to stay. Cosmology is at an important crossroads. Humanity’s understanding of the universe is both the best it has ever been and yet limited. We hope that new observatories, on the ground and in space, will provide new ways of looking at the universe and help solve this mystery.
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