An unexpected new measure of the universe suggests that we need to upgrade our physics


For the first time, astronomers used supermassive black holes shortly after the Big Bang to measure the rate of expansion of the Universe. Now we have a greater mystery in our hands than the answer that this effort provided.

It turns out that the universe is growing faster than expected. This could mean that the dark energy believed to direct the acceleration of this expansion, also sometimes interpreted as the cosmological constant described by Albert Einstein, is not so cosmologically constant after all.

Instead, it could be strengthening.

The rate of expansion of the Universe is called the Hubble Constant, and has been incredibly difficult to define. Each test seems to arrive at a different result; Recently, data from the Planck satellite, which measured the cosmic microwave background, put it at 67.4 kilometers per second per megaparsec, with less than 1% uncertainty.

Other methods typically involve the use of standard candles, objects with known luminosity, such as Cepheid variable stars or Type Ia supernovae, whose distance can be calculated on the basis of their absolute magnitude.

Last year a Hubble Constant Cepheid Variable Star calculation returned a result of 73.5 kilometers (45.6 miles) per second per megaparsec. So you can see why astronomers continue to nudge this strange cosmic bear.

But a few years ago, astronomers realized that the distance from another object could be accurately calculated as well. Enter quasars along with their black holes.

Quasars are among the brightest objects in the Universe. Each is a galaxy that orbits a supermassive black hole that actively feeds on material. Its light and radio emissions are caused by material around the black hole, called an accretion disk, which emits intense light and heat by friction, while it runs like water circling a drain.

They also emit X-rays and ultraviolet light; and, as discovered by astronomers Guido Risaliti of the Università di Firenze in Italy and Elisabeta Lusso of the University of Durham, UK, the proportion of these two wavelengths produced by a quasar varies depending on the ultraviolet luminosity.

Since this luminosity is known, calculated from this relation, the quasar can be used like any other standard candle.

And that means we can measure farther back in the history of the Universe.

"Using quasars as standard candles has great potential, since we can observe them at much greater distances from ourselves than Type Ia supernovae, and use them to investigate earlier times in the history of the cosmos," said Lusso.

The researchers collected UV data of 1,598 quasars from just 1.1 billion to 2.3 billion years after the Big Bang, and used their distances to calculate the rate of expansion of the early universe.

They also compared their results to the results of the Type Ia supernova, which cover the most recent 9 billion years, and found similar results where they overlapped. But at the beginning of the Universe, where only quasars provide measurements, there was a discrepancy between what they observed and what was predicted on the basis of the standard cosmological model.

"We observed quasars back only a billion years after the Big Bang, and we found that the rate of expansion of the Universe to the present day was faster than we expected," said Risaliti.

"This may mean that dark energy is getting stronger as the cosmos ages."

We do not really know what dark energy is – we can not see or detect it. It is just the name we give to the unknown repulsive force that seems to be accelerating the expansion of the Universe over time.

(Based on this rate of expansion, astrophysicists have calculated that dark energy makes up about 70% of the Universe – so a more accurate rate of expansion will also give us a more accurate calculation of dark energy volume.)

If the density of dark energy is increasing over time, scientists think this would mean that it is not Einstein's cosmological constant, after all. But that would explain the odd numbers – and maybe even the discrepancy between the previous results of the Hubble Constant.

For now, there is much more work to be done to test this result and see if it stands firm.

"This model is quite interesting because it can solve two puzzles at once, but the jury has definitely not come out yet and we will have to look at many models in greater detail before we can solve this cosmic puzzle," said Risaliti.

"Some scientists have suggested that new physics may be needed to explain this discrepancy, including the possibility that dark energy is growing in strength. Our new findings agree with this suggestion."

The team's research was published in the journal Astronomy of Natureand can be read in full in the arXiv of the preprint feature.


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