Photons being blueshifted when crossing evolving voids?

In summary, the phenomenon of photons being blueshifted when crossing evolving voids refers to the increase in energy and frequency of light as it moves through regions of lower gravitational potential. This effect occurs due to the expansion of the universe and the dynamics of cosmic voids, which are large areas with fewer galaxies. As photons travel towards these voids, their wavelength shortens, resulting in a blueshift, indicating that they have gained energy. This process has implications for our understanding of cosmic structure and the behavior of light in a dynamic universe.
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Photons being blueshifted when crossing voids due to Rees-Sciama effect...?
I was reading this paper (https://academic.oup.com/mnras/article/288/2/387/960778) where they analysed how CMB radiation is affected by evolving voids in an expanding spacetime (particularly through the Rees-Sciama effect and the integrated Sachs-Wolfe effect).

This effect predicts that photons crossing well potentials would be blueshifted and the ones crossing voids would be redshifted. However, in this paper (and some others: https://arxiv.org/abs/astro-ph/0612347, https://pure.port.ac.uk/ws/portalfiles/portal/6034571/Alvise_Raccanelli_Thesis.pdf) the authors indicate that there can be a partial cancellation of the redshift of photons crossing the voids (or said in another way, that growing voids can blueshift photons).

My question is:

Can there be cases where the photons crossing the voids have a total net blueshift as they get out of them?
 

FAQ: Photons being blueshifted when crossing evolving voids?

What does it mean for photons to be blueshifted when crossing evolving voids?

Blueshifting of photons refers to the increase in their frequency and energy as they move through a gravitational potential, such as an evolving void. An evolving void is a region of space with a lower-than-average density of matter, which changes over time. As photons enter these voids, the gravitational potential decreases, causing them to gain energy and thus become blueshifted.

How do evolving voids affect the cosmic microwave background (CMB) radiation?

Evolving voids can cause subtle distortions in the CMB radiation through a process known as the Integrated Sachs-Wolfe (ISW) effect. As CMB photons traverse these voids, they can be blueshifted due to the changing gravitational potential. This results in slight temperature anisotropies in the CMB, which can be observed and used to study the large-scale structure of the universe.

Why is the study of photon blueshifting in evolving voids important for cosmology?

Studying photon blueshifting in evolving voids helps cosmologists understand the distribution and evolution of large-scale structures in the universe, such as voids, filaments, and clusters. This information is crucial for testing models of cosmic evolution, dark energy, and the overall geometry of the universe.

Can the blueshifting of photons in evolving voids be directly observed?

Direct observation of individual photon blueshifting in evolving voids is challenging due to the subtlety of the effect. However, the cumulative impact on the CMB and large-scale structure surveys can be measured. By analyzing these data, scientists can infer the presence and properties of evolving voids and their influence on photon behavior.

What role does dark energy play in the blueshifting of photons in evolving voids?

Dark energy, which is responsible for the accelerated expansion of the universe, affects the rate at which voids evolve. As voids expand and their gravitational potential changes, the impact on photon blueshifting can provide insights into the nature and properties of dark energy. By studying these effects, scientists aim to better understand how dark energy influences the large-scale structure of the universe.

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