[video] Scientists measure the expansion history of our Universe

DESI’s largest 3D map unlocks some secrets of dark matter.

An international team of some 900 scientists from 70 institutions who are working with the Dark Energy Spectroscopic Instrument (DESI) has made the largest and most detailed 3D map of our Universe to date, which reveals an astonishing structure of cosmos.

For the first time, utilizing 5,000 tiny robots in a mountaintop telescope, the researchers have measured the expansion history of the Universe by capturing light from distant objects as far as 9-11 billion years ago, with a precision better than 1%. This precision offers powerful insights into dark energy's role in the universe's accelerating expansion.

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The team said in a study published by Harvard University that initial results confirm the basics of the Lambda CDM model, which includes cold dark matter and dark energy. Some findings suggest that dark energy evolves over time. 

According to the Lambda CDM model, both matter and dark energy shape how the Universe expands, albeit in opposite directions. Matter and dark matter slow the expansion down, while dark energy speeds it up. The amount of each influences how our universe evolves.

DESI uses Baryon Acoustic Oscillations (BAO) as a cosmic ruler to measure distances and the Universe's expansion rate.

This technique involves analyzing patterns in galaxy clustering that originated from early cosmic pressure waves.

“We’ve measured the expansion history over this huge range of cosmic time with a precision that surpasses all of the previous BAO surveys combined,” Hee-Jong Seo, a professor at Ohio University and the co-leader of DESI’s BAO analysis was quoted as saying.

However, to study even more distant parts of the universe, DESI uses quasars and the Lyman-alpha forest technique to map intergalactic gas and measure the expansion. Using galaxies to measure the expansion history and better understand dark energy is one technique, but it can only reach so far. At a certain point, light from typical galaxies was too faint, so astronomers turned to 450,000 quasars, extremely distant, bright galactic cores with black holes at their centers.

After five years of surveys, they plan to update the 3D map now up to 3 million quasars and 37 million galaxies.

By measuring the size of these BAO bubbles, the study’s authors can determine distances to the matter responsible for this extremely faint pattern on the sky. Mapping the BAO bubbles both near and far lets researchers slice the data into chunks, measuring how fast the universe was expanding at each time in its past and modeling how dark energy affects that expansion.

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Measured by observations of relatively nearby galaxies, scientists have determined that the Universe expands at a rate of 73-74 kilometers per second, while the cosmic microwave background approach (Lambda) puts that rate at 67-68 kilometers per second.

DESI, which builds upon a huge amount of data from previous papers on similar topics, is conceived to investigate this discrepancy among others. 

It is funded by the U.S. Department of Energy Office of Science and is hosted at the NSF's Kitt Peak National Observatory.

SciTech Daily published a visualization of the map.

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