Skip to main content

Scientists look to the skies to estimate how fast the universe is expanding

This image of the Cherenkov Telescope Array illustrates all three classes of the 99 telescopes planned for the southern hemisphere at ESO’s Paranal Observatory, as viewed from the center of the array. CTAO/M-A. Besel/IAC (G.P. Diaz)/ESO

The Hubble Constant is one of the most important concepts in astronomy. It describes how fast the universe is expanding, which has implications for the age and future development of the universe.

Many different figures have been presented for the constant over the years, based on different data analyses. A recent estimate based on data from the Hubble Space Telescope found the constant to be in the region of 74 kilometers per second per megaparsec. That means that for every megaparsec of distance (a megaparsec is approximately 3.26 million light-years) that an object is away from you, its velocity would appear to increase by 74 kilometers per second.

Related Videos

Now, a new paper has used a different technique to estimate the constant and found a slightly slower rate of expansion of 67.5 kilometers per second per megaparsec. To find the constant, the team looked at the interactions between gamma rays, which are a highly energetic form of electromagnetic radiation, and the background light fog of the universe, called the extragalactic background light (EBL). As the gamma rays move through the EBL, they are absorbed and attenuated.

The scientists studied the rate of attenuation to figure out how far the gamma rays had traveled. If they were highly attenuated, they must have traveled further, indicating faster expansion. If they were less attenuated, the expansion must be slower. They collected data using the Fermi Gamma-ray Space Telescope and Imaging Atmospheric Cherenkov Telescopes, like those in the Cherenkov Telescope Array pictured above.

“Cosmology is about understanding the evolution of our universe — how it evolved in the past, what it is doing now and what will happen in the future,” co-author Marco Ajello, an associate professor in the Clemson University department of physics and astronomy, said in a statement. “Our knowledge rests on a number of parameters — including the Hubble Constant — that we strive to measure as precisely as possible. In this paper, our team analyzed data obtained from both orbiting and ground-based telescopes to come up with one of the newest measurements yet of how quickly the universe is expanding.”

The findings are published in the Astrophysical Journal.

Editors' Recommendations

James Webb researcher on how telescope will investigate exoplanet atmospheres
This artist’s conception shows the fully unfolded James Webb Space Telescope in space.

When the James Webb Space Telescope begins science operations this summer, it will be used to investigate a wide variety of astronomical objects, from supermassive black holes to distant galaxies. One of Webb's big scientific goals is to learn more about exoplanets, or planets outside our solar system, and in particular to look at exoplanet atmospheres. It is extremely difficult to tell whether an exoplanet has an atmosphere or what that atmosphere might be composed of using current telescopes, but Webb's sensitive instruments will be able to detect these atmospheres and learn more about distant planets -- potentially even finding habitable worlds.

One of the researchers who will be using Webb to analyze exoplanet atmospheres, Knicole Colón, Webb's deputy project scientist for exoplanet science, has shared more about this work in a recent NASA blog post:

Read more
James Webb Space Telescope has gone cold, but that’s good
The James Webb Space Telescope.

Almost four months after launch, the James Webb Space Telescope has just taken a big step toward making its first observations of deep space.

The $10 billion mission -- a joint effort involving NASA, the European Space Agency, and the Canadian Space Agency -- is on a quest to find out more about the origins of the universe while at the same time searching for distant planets that may support life.

Read more
Largest comet ever seen is coming our way, but don’t worry
A comet zipping through the universe.

Astronomers have confirmed that a comet first spotted by the Hubble Space Telescope is the largest ever identified.

With a nucleus around 80 miles across, the comet, named C/2014 UN271 (Bernardinelli-Bernstein), is larger than Rhode Island, according to NASA, which shared news of Hubble’s discovery on Tuesday, April 12. It's also 20 miles wider than the previously largest-known comet, which held the record for 20 years.

Read more