The Clemson team is working together to form one of the fundamental laws of the cosmos.
Wielding state-of-the-art technologies and techniques, a group of Clemson University astrophysicists have added a novel approach to the calculation of one of the major laws of the universe.
In a paper published on Friday, November 8, 2019, in The Astrophysical Journal Clemson scientists Marco Ajello, Abhishek Desai, Lea Marcotulli and Dieter Hartmann 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 has changed in the past, what it does today and what will happen in the future," said Ajello, an associate professor in the department of physics and astronomy of the College of Science. "Our knowledge rests on a number of parameters – including the Hubble Constant – that we try to measure as accurately as possible. In this paper, our team analyzed data obtained from both orbiting and base -based telescopes to produce one of the latest measurements of how fast the universe is expanding. ”
The concept of an expanding universe was advanced by American astronomer Edwin Hubble (1889-1953), which was named for in the Hubble Space Telescope In the early 20th [19459014Hubblebecameoneofthefirstastronomerstodeterminethattheuniversewasmadeupofmanygalaxiesresearchledtohismostfamousdiscovery:thatgalaxiesmoveateachotheratarateproportionaltotheirdistance
Hubble originally estimated an expansion rate of 500 kilometers per second per megaparsec, with a megaparsec equivalent of about 3.26 million light years. Hubble concluded that a galaxy two megaparsecs away from our galaxy would have moved twice as fast as a galaxy only a megaparsec. This estimate is known as the Hubble Constant, which has been proven for the first time that the universe is expanding. Astronomers have been trying again – with mixed results – ever since.
With the help of skyrocketing technologies, astronomers have measurements that differ greatly from Hubble's original calculations – slowing the rate of expansion to between 50 and 100 kilometers per second per megaparsec. And in the last decade, ultra-sophisticated instruments, such as the Planck satellite, have increased the accuracy of Hubble's original measurements in somewhat dramatic fashion.
"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 Ajello
In a paper entitled "A New Measurement of Hubble Constant and Matter Contents of the Universe using Extragalactic Background Light-Gamma Ray Attenuation," the collaboration team adopted the latest gamma-ray emission data from the Fermi Gamma-ray Space Telescope and Cherenkov Atmospheric Imaging Telescopes to infer their estimates from extragalactic background light models. The approach of this novel led to a measurement of approximately 67.5 kilometers per second per megaparsec.
Rays of ray are the most energetic form of light. Extragalactic (EBL) background light is a cosmic fog made up of all the ultraviolet, visible and infrared light emitted by the stars or from the dust around them. When gamma rays and EBL interact, they leave behind a noticeable imprint – a gradual loss of flow – that scientists study in developing their hypothesis.
"The astronomical community invests enormous amounts of money and resources in the production of precision cosmology in all its various parameters, including the Hubble Constant," says Dieter Hartmann, a professor of physics and astronomy. "Our understanding of basic requirements defines the universe as we know it today. As our understanding of laws becomes more accurate, our definition of the universe becomes more accurate, leading to new ones. perspective and discovery. ”
A common analogy of the expansion of the universe is a balloon with places, in each place representing a galaxy. When the balloon explodes, places spread and farther apart.
"Some suggest that the balloon will expand at a certain point and then collapse again," said Desai, an assistant who heads the physics and astronomy department. "But the most popular belief is that the universe will continue to expand as far as everything is left without light. At this point, the universe will suffer a cold death. But it doesn't worry us. If this happened, it would be trillions of years from now. ”
But if the balloon is exactly that, what is it, exactly, that it blows?
"Essentials – the stars, the planets, even us – are just a small part of the overall composition of the universe," Ajello explains. "Most of the universe is made up of dark energy and dark matter. And we believe dark energy is & # 39; blowing the balloon. & # 39; Dark energy is pushing things away from each other." Gravity, which attracts objects to each other, is the stronger force at the local level, so it's not that some galaxies continue to run. But at cosmic distances, the dark energy is the dominant force. ”Radek Wojtak of the University of Copenhagen; Justin Finke 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 Vaidehi Paliya, a former postdoctoral researcher in the Ajello group in Clemson now at the Deutsches Elektronen-Synchrotron in Zeuthen, Germany.
"It's great that we use gamma rays to study cosmology. Our approach allows us to use an independent approach – a new method that is independent – to measure the fundamental properties of the universe," says Dominguez , who is also a former postdoctoral researcher in Ajello's group. "Our results show the maturity reached in the last decade by the relatively recent field of high-energy astrophysics. The analysis we developed paves the way for better measurements in the future using the Cherenkov Telescope Array, which if which is still in development and will be the most ambitious set of high-energy ground-based telescopes. "
Many of the same methods used in the present paper relate to previous work performed of Ajello and his counterparts. In an earlier project, which appeared in the journal Science, Ajello and his team were able to measure all the star lights emitted in the history of the universe.
"What we do know is that gamma-ray photons from the extragalactic travel of the universe travel to Earth, where they can be absorbed by interacting with photons from the starlight," says Ajello. "The rate of contact depends on the length of their journey to the universe. And the length of their journey depends on the expansion. If the expansion is low, they travel a small distance. If the expansion is large, they travel very large. distance. So the amount of absorption we measure depends entirely on the value of the Hubble Constant. What we did was turn it around and use it to force the rate of expansion of the universe. ”
Reference:" A New Hubble Measurement Constant and Matter Contents of the Universe Using Extragalactic Background Light γ-Ray Attenuation "by A. Domínguez, R. Wojtak, J. Finke, M. Ajello, K. Helgason, F. Prada, A. Desai, V. Paliya, L Marcotulli and DH Hartmann, November 8, 2019, The Astrophysical Journal .
DOI: 10.3847 / 1538-4357 / ab4a0e