A Map of the Universe

FAS Astronomers Blog, Volume 30, Number 15.

Earlier this year (2022), I posted an article about the history of the universe. I followed with a second article about the shape and future of the universe.

The universe is big (really big). Estimates place the diameter of the visible universe at 92 billion light years. It has also been around for a very long time (some 13.8 billion years). But have you ever wanted to see a definitive map of the universe showing its structure far back in time?

Well wait no more! Two astronomers at Johns Hopkins University (Brice Ménard and Nikita Shtarkman) just published a map of the observable universe. The map is a small slice of the night sky showing around 200,000 galaxies and quasars. Staring with our Milky Way galaxy, the map allows you “see out into the universe.” Because light travels at a finite speed (300,000 km/sec) we are also seeing back in time.

This is the view as we look out into the universe and back into time. Each of these points are galaxies (not stars) with hundreds of billions of stars each. The above image is one of several available to download (see Download | Poster). However, you can also scroll through the universe (see Explore the Map). All this is available at https://mapoftheuniverse.net/.

Within the first billion years, we see the spiral galaxies shown in blue. These galaxies have a structure similar to the Milky Way with large spiral arms and a bright center. They are found in filaments of galactic clusters separated by voids.

Another billion years takes us to the realm of elliptical galaxies shown in yellow. These galaxies have less of a structure than the spiral galaxies. However, they are brighter and are visible farther out.

The next four billion years shows the elliptical galaxies, but with a reddish hue. The universe is expanding, and the light that reaches us is stretched out and shifted to the red end of the electromagnetic spectrum. This is due to the Doppler Shift of light. Light from objects moving toward us is compressed (blue shift), while light from objects moving away from us is stretched out (red shift).

At close to 8 billion years to 11 billion years, individual galaxies are too faint to be observed, however we can see Quasars. These are extremely bright objects, which were discovered back in the 1950s. Initially referred to as “quasi-stellar objects”, they were a huge mystery for many years. Eventually, it was discovered that most galaxies have super massive black holes at their center. Quasars are streams of highly energetic material resulting from material falling into these black holes as they were forming.

At 11 billion years, we see a few red shifted quasars. Then there is a void called the “dark ages” when, before stars and galaxies formed, the universe was filled with neutral hydrogen gas.

Eventually, at 13.7 billion years, we reach the Cosmic Microwave Background (CMB), which is the radiation left over from 380,000 years after the big bang when the universe cooled enough so that light could escape and first travel through the universe.

Regrettably, we can’t see any farther back. Prior to the CMB the universe was too hot, which prevented light from escaping. This obscures our view of the earlier universe all the way back to the Big Bang.

Sloan Digital Sky Survey

This map isn’t just a drawing. It includes actual images of these galaxies and quasars. The images were taken by the Solan Digital Sky Survey (SDSS) over a period of 15 years using a 2.5-meter telescope located in New Mexico (Apache Point Observatory).

CMB and the Planck Satellite

Arno Penzias and Robert Wilson first observed the Cosmic Microwave Background back in 1965. Initially, it was seen to be uniform (at least to one part in 100,000). However, over time, three satellites (COBE, WMAP, and Planck) observed and measured the CMB discovering the faint temperature differences from which the large-scale universe evolved. The image in the map is from the Planck satellite.

Red Shift (z)

In addition to the look back time, the map shows something called the red shift (z). This is a measure of how much light is stretched as we look farther and farther back into the universe. Technically, the red shift is z = (λ_o – λ_e)/λ_e = v/c, where λ_o is the observed wavelength, λ_e the emitted wavelength of an object, v the receding velocity, and c the speed of light.

Selected Sources and Further Reading

Jill Rosen. “This New Interactive Map Lets You Scroll Through The Universe.” HUB, Johns Hopkins University. https://hub.jhu.edu/2022/11/17/interactive-universe-map/

B. Menard and N. Shtarkman. “New Interactive Map Offers Scroll Through Universe.” Johns Hopkins University/YouTube. November 17, 2022. https://youtu.be/Oekma9SZMMI

“Map of the observable Universe.” Johns Hopkins University. (Accessed November 21, 2022). https://mapoftheuniverse.net/

“Sloan Digital Sky Survey.” Alfred P. Sloan Foundation. (Accessed November 21, 2022). https://sloan.org/programs/research/sloan-digital-sky-survey

Liz Kruesi. “Decoding the cosmic microwave background.” Astronomy. August 2018 Issue. July 27, 2018. https://www.astronomy.com/magazine/2018/07/decoding-the-cosmic-microwave-background

Andy Briggs. “What is a quasar?” EarthSky. February 28, 2021. https://earthsky.org/astronomy-essentials/definition-what-is-a-quasar/

Ethan Siegel. “Ask Ethan: How do we know the universe is 13.8 billion years old?” Big Think. October 22, 2021. https://bigthink.com/starts-with-a-bang/universe-13-8-billion-years/