Scientists Further Refine How Quickly the Universe Is Expanding

With the help of skyrocketing technologies, astronomers came up with measurements that differed significantly from Hubble’s original calculations for the Hubble Constant. (Image: Wikimedia ; .2.0)
With the help of skyrocketing technologies, astronomers came up with measurements that differed significantly from Hubble’s original calculations for the Hubble Constant. (Image: Wikimedia ; .2.0)

Wielding state-of-the-art technologies and techniques, a team of Clemson University astrophysicists has added a novel approach to quantifying one of the most fundamental laws of the universe.

In a paper published in The Astrophysical Journal, Clemson scientists Marco Ajello, Abhishek Desai, Lea Marcotulli, and Dieter Hartmann have collaborated with six other scientists around the world to devise a new measurement of the Hubble Constant, the unit of measure used to describe the rate of expansion of the universe.

 

Clemson scientists Marco Ajello, Abhishek Desai, Lea Marcotulli and Dieter Hartmann have collaborated with six other scientists around the world to devise a new measurement of the Hubble Constant. (Image: Jim Melvin / College of Science)

Clemson scientists Marco Ajello, Abhishek Desai, Lea Marcotulli, and Dieter Hartmann have collaborated with six other scientists around the world to devise a new measurement of the Hubble Constant. (Image: Jim Melvin / College of Science)

Ajello, an associate professor in the College of Science’s department of physics and astronomy, said:

The concept of an expanding universe was advanced by the American astronomer Edwin Hubble (1889-1953), who is the namesake for the Hubble Space Telescope. In the early 20th century, Hubble became one of the first astronomers to deduce that the universe was composed of multiple galaxies. His subsequent research led to his most renowned discovery — that galaxies were moving away from each other at a speed in proportion to their distance.

Hubble originally estimated the expansion rate to be 500 kilometers per second per megaparsec, with a megaparsec being equivalent to about 3.26 million light-years. Hubble concluded that a galaxy two megaparsecs away from our galaxy was receding twice as fast as a galaxy only one megaparsec away. This estimate became known as the Hubble Constant, which proved for the first time that the universe was expanding. Astronomers have been recalibrating it — with mixed results — ever since.

With the help of skyrocketing technologies, astronomers came up with measurements that differed significantly from Hubble’s original calculations — slowing the expansion rate down to between 50 and 100 kilometers per second per megaparsec. And in the past decade, ultra-sophisticated instruments, such as the Planck satellite, have increased the precision of Hubble’s original measurements in relatively dramatic fashion.

In a paper titled A New Measurement of the Hubble Constant and Matter Content of the Universe using Extragalactic Background Light-Gamma Ray Attenuation, the collaborative team compared the latest gamma-ray attenuation data from the Fermi Gamma-ray Space Telescope and Imaging Atmospheric Cherenkov Telescopes to devise their estimates from extragalactic background light models. This novel strategy led to a measurement of approximately 67.5 kilometers per second per megaparsec.

The team’s analysis paves the way for better measurements in the future using telescopes from the Cherenkov Telescope Array. (Image: courtesy of Daniel López/IAC)

The team’s analysis paves the way for better measurements in the future using telescopes from the Cherenkov Telescope Array. (Image: courtesy of Daniel López/IAC)

 

Gamma rays are the most energetic form of light. Extragalactic background light (EBL) is a cosmic fog composed of all the ultraviolet, visible, and infrared light emitted by stars or from dust in their vicinity. When gamma rays and EBL interact, they leave an observable imprint — a gradual loss of flow — that the scientists were able to analyze in formulating their hypothesis.

Dieter Hartmann, a professor in physics and astronomy, said:

A common analogy of the expansion of the universe is a balloon dotted with spots, with each spot representing a galaxy. When the balloon is blown up, the spots spread farther and farther apart. Desai, a graduate research assistant in the department of physics and astronomy, said:

But if the balloon analogy is accurate, what is it, exactly, that is blowing up the balloon? Ajello explained:

The other contributing authors are lead author Alberto Dominguez of the Complutense University of Madrid; 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 Ajello’s group at Clemson who is now at Deutsches Elektronen-Synchrotron in Zeuthen, Germany.

Dominguez, who is also a former postdoctoral researcher in Ajello’s group, said:

Many of the same techniques used in the current paper correlate to previous work conducted by Ajello and his counterparts. In an earlier project, which appeared in the journal Science, Ajello and his team were able to measure all of the starlight ever emitted in the history of the universe. Ajello said:

Provided by: Jim Melvin, Clemson University [Note: Materials may be edited for content and length.]

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