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We can add another way to measure the expansion of the universe in the controversy that could be the most exciting story of cosmology today.
The universe is expanding. Measurements of the most distant detectable electromagnetic radiation predict a value of expansion rate, but measurements taken from closer objects reveal different values. If the values are really incompatible, this could be a sign that the great theory currently used to describe the evolution of the universe is broken. Nowadays, a team of scientists is excited by a new method they have developed, which relies less on human assumptions about how the universe works.
"Our method is insensitive to the choice of the cosmological model," said Gizmodo Inh Jee, the first author of the study at the Max Planck Institute of Astrophysics. "That's what we really want to focus on."
Edwin Hubble convinced astronomers in the 1920s that distant objects were moving away from us, but the rate at which they were moving away, called Hubble's constant, has been the subject of debate since that time. New telescopes have led to new observations, and today, Planck satellite calculations have determined that Hubble's constant is 67.4 kilometers per hour per megaparsec. which means that for 3.26 million light-years away (called megaparsec), objects appear. distance from each other by 67.4 km / hour. But observations based on a large number of properties of nearer light sources have revealed other values for the rate of expansion, always larger.
Physicists are now wondering whether these values are really larger and, if so, whether they are due to the way they calculate distances to these objects or whether it is really a sign of undiscovered physics. A recent and excellent article by Quanta Magazine summarizes the story and its drama.
The problem lies mainly in the difficulty of measuring the distance to objects. Scientists usually rely on objects of known brightness, called standard candles, which are brighter, and closer, and fainter, farther away. These objects include some supernovae and stars that twinkle at a rate depending on their brightness. Scientists can also use so-called standard rules, objects whose size is known and whose distance can be calculated according to their size or size in the sky.
One of the Hubble Constant measurement teams, called H0LiCOW (used this method), used one of these methods to determine the distances and has now improved it so that it's better. it's less based on human assumptions, Jee explained. This method calculates the radius of a remote object (called the gravitational lens) and uses it as a rule. this rule can then help provide an accurate absolute distance to standard candlestick supernovae, according to the document published in Science.
When you look at a massive object like a galaxy, you will see around it multiple images of the light objects behind it, because its enormous gravity distorts the light as a goal (hence its name "gravitational lens"). Sometimes background objects appear even in a ring. If a background object flickers, each of its images may flash at different times, depending on the distance traveled by the curved light. Scientists can also measure the speed of stars in orbit in these distant galaxies, revealing the gravitational potential and mass of the galaxy. Combining this information allows them to calculate the distance and size of the lens galaxy.
The researchers can then use the lens galaxy as a standard rule and calibrator to calculate the absolute distance to some supernovae (those traditionally used to determine the Hubble constant). This allows them to calculate the constant in a way that relies less on human assumptions such as the amount of dark matter and dark energy existing in the universe.
With their new method, the researchers calculated a value for the expansion of the universe based on only two objects. They have reached a very high 82.4 kilometers per hour per megaparsec, but with statistical error bars so big that it is not really worth taking them into account at the moment. After all, this study is just a pilot project.
Adam Reiss, Johns Hopkins University astronomer and leader of Hubble's constant measurement team called SH0ES, told Gizmodo in an email that the result was inconclusive, but that it was nice to see people looking for alternative methods, so accessories for that.
And removing the dependence on the assumptions is "important in trying to determine the source of the discrepancies between different techniques," wrote Tamara Davis, Australian astrophysicist at the University of Queensland, in a commentary accompanying Science.
There are many different methods in the work to determine the Hubble constant, whether using candles and standard rules or even using colliding neutron stars (although one must actually detect more than one). 39 neutron stars collide for this method to work).
The H0LiCOW team plans will soon reduce their experimental error and use their method to determine distances from the stars by measuring more lenses and the movement of stars inside the lenses, said Jee to Gizmodo. .
Hubble's ongoing discussion will continue to be important to physicists, as it represents a place where our most successful theory of the universe collapses – a place for new ideas and new experiences for physicists. reveal the actual functioning of the cosmos.
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