The Universe Today

Another new way to measure distance in the universe: Baryon Acoustic Oscillations

Measuring cosmic distances is the biggest challenge thanks to the fact that we live in a parallel Universe. When astronomers see distant objects, they are not just looking into space but back in time. In addition, the cosmos has been expanding since its birth in the Big Bang, and that expansion is accelerating. Astronomers rely on one of two methods of measuring cosmic distances (known as the Cosmic Distance Ladder). On the other hand, astronomers rely on redshift measurements of the Cosmic Microwave Background (CMB) to determine cosmological distances.

On the other hand, they will rely on spatial 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 meet this, a team of astronomers from several Chinese universities and the University of Cordoba conducted a two-year statistical analysis of one million galaxies. Since then, they have developed a new technique that relies 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 Center for Computational Cosmology (ICC) at Durham University; Yipeng Jing, professor at the Tsung-Dao Lee Institute and Shanghai Key Laboratory of Particle Physics and Cosmology at SJTU; and Gong-Bo Zhao, Deputy Director of National Astronomy Observatories (NAO-CAS), University of Chinese Academy of Sciences (UCAS), and Institute for Frontiers in Astronomy and Astrophysics (IFAA). They were joined by Antonio J. Cuesta, associate professor of physics at the University of Cordoba. A paper detailing their findings has appeared in the journal Natural Astronomy.

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Baryon Acoustic Oscillations, which were first demonstrated in 2005, are one of the few forms of the Big Bang that can be detected in the cosmos (like the CMB). In the first 380,000 years after the Big Bang, these waves propagated through material so hot that it behaved like a liquid, like waves from a lake. As the Universe expanded and cooled over the next 500 million years, these waves became frozen over time. Since the exact timing of these waves is known, they are very useful for measuring cosmic distances based on the separation between galaxies.

Detecting BAOs and determining their size is essential to accurately map the Universe to objects billions of light years away (cosmological distance). For their study, the team used statistical methods to evaluate nearly a million galaxies contained in the twelfth data release (DR12) from the Baryon Oscillation Spectroscopic Survey (BOSS) samples of CMASS, combined with the Dak Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys. . This allowed them to obtain accurate information about the ellipticity of the galaxies and the mass of the surrounding galaxies.

This was important as the gravitational pull of neighboring galaxies tends to pull galaxies closer to each other. But elsewhere in the Universe, this effect is not so great. After reviewing all the combined data, they found that their method shows where BAO can be found. As Prof. Cuesta said at the University of Cordoba in a press release:

“It is in those places, where galaxies can point where they should be, where the statistics tell us that Baryon Acoustic Oscillations exist, since these waves also act as gravitational attractors. The first possible application of this study is to accurately establish the location of galaxies, and the separation between them and Earth, but, in a way, we also look into the past.”

A conceptual diagram of BAOs, printed in the early Universe and still seen today in research such as BOSS. Credit: Chris Blake/Sam Moorfield

Combined with other methods on the Cosmic Ladder, this independent technique can help solve one of the most pressing problems in modern cosmology. Getting an accurate estimate of cosmic distance will open new doors in astronomy, including how the Universe has expanded over time. This could lead to a revolutionary understanding of the physics that governs the cosmos, which could solve questions about the existence and role of Dark Matter and Dark Energy – two of the biggest mysteries in modern astronomy.

They may reveal that our ideas about how gravity behaves on the largest scales (as defined by General Relativity) require some revision, perhaps leading to the adoption of other models such as Modified Newtonian Dynamics (MOND).

Further Reading: EurekAlert, Nature

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