Another new way to measure distance in the universe: acoustic baryon oscillations

Measuring cosmic distances is quite challenging, thanks to the fact that we live in a relativistic universe. When astronomers observe distant objects, they are not only looking across space, but also looking into the past. In addition, the universe has been expanding since its birth in the Big Bang, and this expansion is accelerating. Astronomers usually rely on one of two methods of measuring cosmic distances (known as the cosmic distance ladder). On the one hand, astronomers rely on measurements of the cosmic microwave background (CMB) redshift to determine cosmic distances.

Conversely, they will rely on local observations using parallax measurements, variable stars, and supernovae. Unfortunately, there is a discrepancy between the redshift measurements of the CMB and the local measurements, leading to what is known as the Hubble tension. To address this, a team of astronomers from several Chinese universities and the University of Cordoba conducted a two-year statistical analysis of a million galaxies. Hence, they developed a new technique based on Baryon Acoustic Oscillations (BAO) to determine distances with a greater degree of accuracy.

The team included Kun Xu, a graduate researcher at Shanghai Jiao Tong University (SJTU) and the Institute for Computational Cosmology (ICC) at Durham University; Yipeng Jing, Professor at the Tsung-Dao Lee Institute and Shanghai Key Laboratory for Particle Physics and Cosmology at SJTU; and Zhongbo Zhao, deputy director of the National Astronomical Observatories (NAO-CAS), Chinese Academy of Sciences, University of China (UCAS), and Frontiers Institute in Astronomy and Astrophysics (IFAA). They were joined by Antonio J. Cuesta, associate professor of physics at the University of Cordoba. The paper describing their findings recently appeared in the journal Nature Astronomy.

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Baryon sonic oscillations, first shown in 2005, are one of the few traces of the Big Bang that can still be detected in the universe (like CMB radiation). During the first 380,000 years after the Big Bang, these waves propagated through matter so hot that it behaved like a fluid, like ripples across a pond. As the universe expanded and cooled over the next 500 million years, these waves became effectively “time-frozen”. Since the exact duration of these waves is known, they are very useful for measuring cosmic distances based on the distance between galaxies.

Detecting BAOs and quantifying them is crucial to accurately mapping the universe to objects billions of light-years (cosmic distances) away. In their study, the team used statistical methods to examine nearly a million galaxies contained in Data Release XII (DR12) of BOSS CMASS samples, as well as older Dark Energy Analysis Instrument (DESI) imaging surveys. . This allowed them to obtain accurate information about the elliptical shape of galaxies and the density around them.

This was important because the gravitational pull of neighboring galaxies usually stretches galaxies to the point where they are relatively close together. But in some places across the universe, this effect is not as severe. When examining all the data collected, they found that their method showed where the BAOs could be found. As Professor Cuesta stated in a University of Córdoba press release:

“It is at those points, where galaxies are not pointing where they should, that statistics tell us that baryon acoustic oscillations occur, because these waves also act as gravitational pulls. The first practical application this study can offer is to locate galaxies more precisely, And the separation between it and the Earth, but in a way, we’re also staring back.

An illustration of the concept of BAOs, which were imprinted in the early universe and can still be seen today in surveys such as BOSS. Credit: Chris Blake/Sam Moorfield

Combined with other methods on the cosmic scale, this independent technique could help solve one of the most troubling issues in modern cosmology. Getting accurate estimates of cosmic distances will open new doors in astronomy, including how the universe has expanded over time. This could lead to a revolutionary insight into the physics that govern the universe, possibly solving questions about the existence and role of dark matter and dark energy – two of the greatest mysteries in modern astronomy.

They could also reveal that our concepts of how gravity behaves on the largest scales (as described in general relativity) require some revision, potentially leading to the adoption of alternative models such as modified Newtonian dynamics (MOND).

Further reading: Yorick alert, nature

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