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Modern technology used to further refine how rapidly the universe expands



  Cherenkov Telescope

The team analysis paves the way for better measurements in the future using telescopes from the Cherenkov array. Credit: Daniel Lopez / IAC

The Clemson team collaborates to quantify one of the most basic laws of the cosmos.

Featuring state-of-the-art technology and techniques, a team of astrophysicists at Clemson University has added a new approach to quantify one of the most fundamental laws of the universe.

In a document published on Friday, November 8, 201

9, in the Astrophysical Journal scientists from Clemson Marco Agello, Abhishek Desai, Lea Marcotouli and Dieter Hartman collaborated with six other scientists around the world to create a new measurement of the Hubble constant, the unit of measure used to describe the rate of expansion of the universe.

"Cosmology is about understanding the evolution of our universe – how it evolves in the past, what it does now, and what happens in the future," said Aelo, an associate professor in the Department of Physics and Astronomy at the College of Science. "Our knowledge is based on a number of parameters – including the Hubble Constant – that we strive to measure as accurately as possible. In this document, our team analyzes data from both orbital and terrestrial telescopes to come up with one of the latest measurements, but how quickly the universe expands. "

The concept of an expanding universe was developed by the Americans astronomer Edwin Hubble (1889-1953), who is the eponymous names of the Hubble Space Telescope . In the early 20s and Hubble became one of the first astronomers to conclude that the universe was made up of multiple galaxies. His subsequent research led to his most famous discovery: that galaxies are moving away from each other at a speed proportional to their distance.

  Marco Aelo, Lea Marcotuli, Abhishek Desai and Dieter Hartman

Left, Marco Aelo of Clemson, Lea Marcotulli, Abhishek Desai and Dieter Hartmann co-authored a book in The Astrophysical Journal.
Credit: College of Science

Hubble initially estimated an expansion rate of 500 kilometers per second per megaparsec, with a megaparsec equivalent to about 3.26 million light-years. Hubble concluded that a galaxy two megaparsecs away from our galaxy is twice as fast as a galaxy in just one megaparsecon. This estimate became known as the Hubble Constant, which proved for the first time that the universe was expanding. Astronomers have recalibrated it – with mixed results – ever since.

Using jumping technology, astronomers came up with measurements that were significantly different from Hubble's original calculations – slowing the speed of expansion to between 50 and 100 kilometers per second per megaparsec second. And over the past decade, sophisticated instruments such as Planck's satellite have increased the accuracy of Hubble's original measurements in a relatively dramatic way.

“Cosmology is about understanding the evolution of our universe – how it has evolved in the past, what it does now and what will happen in the future. "- Marco Aelo

In an article entitled" A New Measurement of Hubble's Permanent and Material Content in the Universe Using Extragalactic Light-Gamma Background Damping, "a collaboration team compared the latest gamma-ray damping data from the Fermi Gamma-Ray Space Telescope and the Imaging Atmospheric Cherenkov to create their estimates from extragalactic models of background light. This new strategy resulted in the measurement of approximately 67.5 kilometers per second per megaparsec.

Gamma rays are the most energetic form of light. Extragalactic Background Light (EBL) is a cosmic mist composed of all the ultraviolet, visible and infrared light emitted by stars or dust in their vicinity. When gamma rays and EBL interact, they leave a noticeable imprint – a gradual loss of flux – that scientists have been able to analyze in formulating their hypothesis.

  Alberto Dominguez

Lead author Alberto Dominguez of the University of Madrid at Complutens is a former doctoral researcher in the Marco Aelo group in Clemson. Dominguez is shown here at the Roque de los Muchachos Observatory in La Palma, Spain. Credit: Alberto Dominguez

"The astronomical community invests a great deal of money and resources in performing precise cosmology with all different parameters, including Hubble's persistence," says Dieter Hartman, professor of physics and astronomy. "Our understanding of these fundamental constants has defined the universe as we know it now. As our understanding of the laws becomes more precise, our definition of the universe also becomes more precise, leading to new insights and discoveries.

A common analogy to the expansion of the universe is a bubble filled with spots, with each spot representing a galaxy. When the bubble explodes, the spots spread farther and farther away.

"Some theorize that the bubble will expand to a certain point and then collapse again," says Desai, a graduate fellow in the Department of Physics and Astronomy. "But the most common belief is that the universe will continue to expand as long as everything is so far apart, there will be no more observable light. At that point, the universe will suffer a cold death. But this is nothing to worry about. If that happens, it will be trillions of years. "

But if the analogy of a balloon is accurate, what exactly is it that blows a balloon?

" Matter – the stars, the planets, even us – is only a small part of the entire makeup of the universe, "Aelo explained. "Most of the universe is made up of dark energy and dark matter. And we believe that dark energy is a "bubble burst." Dark energy pushes things away. The gravity that draws objects to one another is a stronger force locally, which is why some galaxies continue to collide. But at cosmic distances, dark energy is the dominant power. "

Other contributing contributors include lead author Alberto Dominguez of the University of Madrid of Complutense; Radek Wojtak of the University of Copenhagen; Justin Fink of the Naval Research Laboratory in Washington, D.C .; Kari Helgason of the University of Iceland; Francisco Prada of the Instituto de Astrofisica de Andalucia; and Waidehi Palia, a former doctoral student at the Ajello group in Clemson, who is now at the Deutsches Elektronen-Synchrotron in Zeuthen, Germany.

"It is remarkable that we use gamma rays to study cosmology. Our technique allows us to use an independent strategy – a new methodology independent of existing ones – to measure key properties of the universe, "said Dominguez, who is also a former doctoral researcher in the Ajello group. "Our results show the maturity reached in the last decade by the relatively recent field of high-energy astrophysics. The analysis we have developed paves the way for better measurements in the future with the help of the Cherenkov telescope, which is still under development and will be the most ambitious array of terrestrial high-energy telescopes. "

The same techniques used in this document are related to previous work carried out by Ajello and his colleagues. In an earlier project that appeared in Science magazine, Ajello and his team were able to measure all the starlight ever radiated in the history of the universe. "

" What we do know is that photons of gamma rays from extralactic sources travel to the Universe to Earth, where they can be absorbed by interacting with photons from starlight, Aiello said. "The speed of interaction depends on the length of travel in the universe. And the length they travel depends on the extension. If the extension is low, they travel a short distance. If the extension is large, they travel a very long distance. So the amount of absorption we measured was very much dependent on the value of the Hubble constant. What we did was reverse this and use it to limit the speed of expansion of the universe.

Reference: A New Measurement of Hubble Permanent and Material Content in the Universe Using Extragalactic Background Light γ-Reduction Damping by A. Dominguez, R. Wojtak, J. Finke, M. Aelo, K. Helgason, F. Prada, A. Desai, V. Palia, L. Marcotuli, and D. H. Hartman, November 8, 2019, Astrophysical Journal .
doi: 10.3847 / 1538-4357 / ab4a0e


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