Biggest 3D map of the universe yet

A slice through the largest 3-D map of the universe to date. Quasars are in red and nearer galaxies in yellow. Image by Anand Raichoor and SDSS.

Astronomers from the Sloan Digital Sky Survey (SDSS) said on May 18, 2017 that they’ve created the largest and most detailed three-dimensional map of the universe to date, using bright quasars as reference points. The team used the 2.5-meter telescope at the Apache Point Observatory in New Mexico to make their map, and they relied on the extreme brightness of quasars, which can be seen across vast distances of intergalactic space.

Originally called quasi-stellar radio sources (“qua-s-r-s”), quasars today are thought to be young galaxies containing central supermassive black holes. The holes are pictured as “active,” that is, actively swallowing material and surrounded by large accretion disks. As a supermassive black hole swallows material from its surrounding galaxy, temperatures in its accretion disk increase, creating a quasar that is extremely bright, sometimes brighter than its home galaxy. Many galaxies in our universe are known to contain black holes, but nearby ones – such as the black hole at the center of our own Milky Way galaxy – tend to be more quiescent.

Active supermassive black holes appear common in the early universe, though, making quasars the perfect reference points for creating the largest map yet of our universe.

Here’s one of the many images taken by the SDSS as part of its 3-D map of the universe. This image shows Stephan’s Quintet, which is a group of 5 galaxies. NGC 7319, on the right in this image, harbors a bright quasar near its center. Image via SDSS.

This work is part of the Sloan Digital Sky Survey’s project called eBOSS, which stands for Extended Baryon Oscillation Spectroscopic Survey. Over eBOSS’s first two years, astronomers measured accurate three-dimensional positions for more than 147,000 quasars.

It was these measurements that were used to create the new map.

But these astronomers didn’t just want to map the universe. They also want to understand how our universe has expanded since the Big Bang. To do so, they studied what are called baryon acoustic oscillations (BAOs). Their statement explained:

BAOs are the present-day imprint of sound waves which traveled through the early universe, when it was much hotter and denser than the universe we see today. But when the universe was 380,000 years old, conditions changed suddenly and the sound waves became ‘frozen’ in place. These frozen waves are left imprinted in the three-dimensional structure of the universe we see today.

Baryon acoustic oscillations (BAOs) are used to help astronomers comprehend intergalactic distances in expanding space and time. Image via Chris Blake and Same Moorfield/ SDSS.

Scientists understand the concept of BAOs very well. Present-day BAOs are a “stretched out” version of early universe BAOs. The size of BAOs measured today can therefore be used to probe expanding space. Pauline Zarrouk, a PhD student at the Irfu/CEA, University Paris-Saclay, who worked with the BAOs in this study, said:

You have meters for small units of length, kilometers or miles for distances between cities, and we have the BAO scale for distances between galaxies and quasars in cosmology.

SDSS’s eBOSS project is designed to map the universe when it was between 3 and 8 billion years old. Astronomers hope it will reveal more about dark energy. Image via Dana Berry / SkyWorks Digital Inc/ SDSS collaboration.

The results of the study are consistent with what most modern astronomers believe about the universe. That is, their statement said:

The results of the new study confirm the standard model of cosmology that researchers have built over the last 20 years. In this standard model, the universe follows the predictions of Einstein’s General Theory of Relativity — but includes components whose effects we can measure, but whose causes we do not understand. Along with the ordinary matter that makes up stars and galaxies, the [standard model calls for the universe to include] dark matter – invisible yet still affected by gravity – and a mysterious component called ‘dark energy.’ Dark energy is the dominant component at the present time, and it has special properties that cause the expansion of the universe to speed up.

Astronomers from SDSS believe that eBOSS will help in discovering more about dark energy.

Bottom line: Astronomers from the Sloan Digital Sky Survey (SDSS) have created the largest three-dimensional map of the universe to date using bright quasars as reference points.

Browse through the SDSS data.

May 30, 2017

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