Event 4

13 billion years ago

The Milky Way, with our Sun's location
This is an image of the Milky Way, with our Sun’s location.
Credit: Image is used courtesy of NASA/JPL-Caltech/R. Hurt (SSC)

Stars, attracted to other stars by gravity, formed clusters that developed into gigantic spinning discs called galaxies that are usually spiral-shaped (like our own Milky Way) or more elliptical (football-shaped), possibly formed by the merging of two galaxies or more. It is believed that the first galaxies formed around 13 billion years ago, and the Milky Way may be this old. It now appears that most, if not all, galaxies contain a supermassive black hole at their center, and there is a growing suspicion that these galaxies and black holes may be necessarily linked.

Andromeda Galaxy
This is an image of the Andromeda Galaxy, the nearest large galaxy to our own galaxy, the Milky Way. It is a compilation of several images gathered by the Galaxy Evolution Explorer (GALEX).
Credit: Image is used courtesy of NASA/JPL/California Institute of Technology

The overall size of galaxies appears to stay the same, but it is now known that galaxies are moving away from each other over time. What is more, this expansion appears to have started speeding up about 7.5 billion years ago. The further away a galaxy is, the faster it tends to be moving away from us, so that the most distant galaxies are moving away from us at velocities faster than the speed of light!


As we peer deeper into space with powerful telescopes, we are gazing back in time as well, closer and closer to the origins of the universe. The Hubble telescopes’ “Deep Space” image of a very small portion of the sky shows very early galaxies forming, and observations of space allow us to estimate the total number of galaxies in the universe.


Our Milky Way is one of perhaps 100 billion galaxies, each containing, on average, 100 billion stars. Our sun is one of these stars in one of these galaxies. Dust clouds (nebula) from exploded stars in galaxies were the nurseries for new star and planet formation, including our own solar system, which formed around 4.5 billion years ago (when the universe was already over 9 billion years old).





An article from the New Scientist about the collision of galaxies, including a computer simulation comprised of the photographs taken in space and depicting the collision of the two galaxies:

An informational site from NASA about stars and galaxies:

Searching for the first galaxies, a YouTube video about the Evolution of the Universe:  structure and galaxy formation



Loeb, Abraham and Steven R. Furlanetto. The First Galaxies In The Universe. Princeton NJ: Princeton University Press. 2013.

Mather, John C. and John Boslough. The Very First Light: The True Inside Story of the Scientific Journey Back to the Dawn of the Universe. New York: Basic Books. 2008.

May, Brian, Patrick Moore, and Chris Lintott. BANG! The Complete History of the Universe. Baltimore: Johns Hopkins University Press. 2008.

Murdin, Paul. Secrets of the Universe: How We Discovered the Cosmos. Chicago: University of Chicago Press. 2009.

Ronan, Colin A. Universe: The Cosmos Explained. London: Quantum Publishing. 2007.


Cosmic Voyage. Narrated by Morgan Freeman. IMAX and Warner Brothers. 2002.

Origins: Fourteen Billion Years of Cosmic Evolution. NOVA, WGBH, Boston Video. 2004. Hosted by Neil deGrasse Tyson.

The Universe. The History Channel. (A multi-year television series).

Understanding the Universe: Introduction to Astronomy. The Teaching Company. 2007. (96 presentations by Alex Filippenko).

Universe: A Journey from Earth to the Edge of the Cosmos. Quercus. 2008.

Comments are closed.