Gravitational Redshift Explained

Everyone who has studied elementary science is quite aware of Albert Einstein’s general theory of relativity and how gravity affects light.  All observations made by astronomers and astrophysicists are made due to light emitted from galaxies, stars and all other objects in space.

Astrophysicists at the Niels Bohr Institute’s Dark Cosmology Centre have now been able to measure how light is affected by gravity as it exits galaxy clusters.  The observations have, once again, confirmed Einstein’s famous theory of relativity.

According to the institute’s news release, observations of a great distance are due to measurements of redshift, an occurrence that transpires when the wavelength of light from faraway galaxies moves towards the red with larger distance.

The redshift provides the observer with information of how much the universe has expanded from when the light left until it was measured on our planet.  Also, Einstein’s theory suggests that the light and the redshift is affected by gravity from large objects in the galaxy clusters and leads to a gravitational redshift of the light.

Gravitational light has never before been measured on a cosmological scale.

“It is really wonderful. We live in an era with the technological ability to actually measure such phenomena as cosmological gravitational redshift,” said Radek Wotjak, an astrophysicist at the University of Copenhagen’s Dark Cosmology Centre and lead author of the paper.

Alongside researchers Steen Hansen and Jens Hjorth, Wotjak collected light data and measurements from more than 8,000 galaxy clusters.

“We could measure small differences in the redshift of the galaxies and see that the light from galaxies in the middle of a cluster had to ‘crawl’ out through the gravitational field, while it was easier for the light from the outlying galaxies to emerge.”

The next step for scientists will be to measure the entire galaxy cluster’s total mass to arrive at its gravitational feat.  However, researchers could find evidence of theoretical dark matter and dark energy – two theories that scientists are still unaware of, except of its mass and gravity – that could be contributing factors to the gravitational redshift.

“Now the general theory of relativity has been tested on a cosmological scale and this confirms that the general theory of relativity works and that means that there is a strong indication for the presence of dark energy,” added Wotjak.

Results of the research have been published in the Sept. 29 edition of the esteemed journal Nature.