An Unexpected New Measurement of The Expanding Universe Suggests We Need to Update Our Physics

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For the first time ever, astronomers successfully studied supermassive black holes from just after the Big Bang, to measure the expansion rate of the Universe. The answer this effort provided has now opened a bigger mystery for us. It was found that the Universe is growing faster than expected. 

This could imply that the ‘Dark Energy’ sometimes interpreted as Albert Einstein’s cosmological constant, and previously considered as the cause driving the acceleration of this expansion, is not so cosmologically constant after all. In its place, it seems to be growing stronger.

The rate of expansion of our Universe is called the Hubble Constant, and it’s been extremely complicated to calculate. 

Every test and attempt ended with a different result but recent incoming data from the Planck satellite that measured the cosmic microwave background set the rate of universe’s expansion at 67.4 kilometers i.e. 41.9 miles per second per megaparsec, with less than 1 percent uncertainty.

Other approaches typically involve the usage of ‘standard candles’ i.e. objects with known luminosity like ‘Cepheid variable stars’ or ‘Type Ia supernovae’, from which distance can be deliberated based on their absolute magnitude. 

Last year, calculation of the Hubble Constant using such a cepheid variable star gave a final result of 73.5 kilometers (45.6 miles) per second per megaparsec. 

But a few years ago, astronomers realized that just like the distance from, the distance to another object could also be calculated accurately. This approach led to quasars and their black holes.

Quasars are among the brightest entities in the Universe. Each Quasar is a galaxy that orbits around a supermassive black hole actively feeding on the surrounding material. 

The light and radio emissions of the quasar, called an accretion disc, are caused by all the material around the black hole, that emits intense light and heat from friction as it churns like water spinning down a drain. 

They also emit X-ray and ultraviolet light. Astronomers Guido Risaliti of Università di Firenze, Italy, and Elisabeta Lusso of Durham University, UK, discovered that the ratio of these two wavelengths produced by a quasar varies as per the ultraviolet luminosity. 

Once this luminosity is identified, by calculation from that ratio, the quasar can be treated just like any other standard candle. And that means that we can venture farther back into the Universe’s history. 

Lusso said, “Using quasars as standard candles has great potential, since we can observe them out to much greater distances from us than Type Ia supernovae, and so use them to probe much earlier epochs in the history of the cosmos.” 

The researchers’ accumulated UV data on 1,598 quasars from just 1.1 billion-2.3 billion years post the Big Bang and utilized their distances to compute the expansion rate of the early Universe. 

They correspondingly cross-checked their results against the Type Ia supernova results that belong to the more recent 9 billion years and found similar results when they overlapped. 

But, in the early Universe timeframe, where only quasars could provide measurements, there seemed a discrepancy between their observation, and what the predictions based on the standard cosmological model. 

The team’s research was recently published in the journal Nature Astronomy.
Risaliti noted, “We observed quasars back to just a billion years after the Big Bang and found that the Universe’s expansion rate up to the present day was faster than we expected. This could mean dark energy is getting stronger as the cosmos grows older. We don’t really know what dark energy is – we can’t see it or detect it. It’s just the name we give to the unknown repulsive force that seems to be accelerating the Universe’s expansion over time.

Astrophysicists have figured that dark energy constitutes about 70 percent of the Universe based on this expansion rate, so a more exact expansion rate will lead to a more accurate calculation of dark energy volume. 

If the density of dark energy is found to increase over time, these scientists think it would prove that it’s not Einstein’s cosmological constant after all. 

But it would explain the strange figures and maybe even justify the discrepancy between all the previous Hubble Constant results. For the moment, there’s a lot more work to be done to further test and verify these result.

Risaliti concluded that, “This model is quite interesting because it might solve two puzzles at once, but the jury is definitely not out yet and we’ll have to look at many more models in great detail before we can solve this cosmic conundrum. Some scientists suggested that new physics might be needed to explain this discrepancy, including the possibility that dark energy is growing in strength. Our new results agree with this suggestion.