The year 1989 will be remembered for a number of memorable events:
Student protesters in Peking's Tiananmen Square were massacred by the Chinese government, a terrifying 6.9 California earthquake cancelled the third game of the 1989 "Battle of the Bay" World Series between the Giants and the As, gargantuan Hurricane Hugo slammed into the southeastern coast of the USA resulting in 100,000 homeless Americans, and NASA's Voyager spacecraft revealed dramatic upclose views of the outer planets.
But one 1989 event, that had a profound impact on our understanding of the cosmos, received very little news coverage at the time; it was the chance discovery of the largest known structure in the universe, a cosmic superstructure known as the Great Wall of Galaxies. This wall or sheet of stellar matter in deep space is located 200-300 million light years from Earth.
American astronomers M.J. Geller and J.P. Huchra co-discovered the now famous Great Wall in 1989 while mining astronomical data collected earlier in the 1980s; they did it as part of their final work on Harvard University's long-running CfA Redshift Survey.
The goal of the Harvard redshift survey, which started in 1977 and ended in the 1982, was to measure the speeds, or redshifts, of distance galaxies flying away from our perspective here on Earth. The astronomers' chance discovery of a superstructure or vast wall of galaxies still reverberates into 21st century astronomy.
The Great Wall, like a vast galactic quilt, measures 500 million light years long by 200 light years wide and 15 million years 'thick'. The human mind boggles at such a scale.
"...Astronomers have been haunted by a sense that the universe is controlled by forces they don't understand. And now comes a striking confirmation: The Great Wall," said Geller after the discovery.
The Great Wall has frustrated astronomers ever since 1989 because it is an anomaly. It also contrasts with vast intergalactic voids, so-called space deserts, such as the 'Desert of Bootes'. Several clumps (walls or sheets) and voids (deserts nearly devoid of stellar objects) were also discovered by Harvard redshift survey teams.
Here's the rub: According to Big Bang science, the universe should be homogeneous-that is, it should be smooth with an even or uniform distribution of galaxies. But the discovery of superstructures like the the Great Wall and voids presents astronomers with an inhomogeneous universe that doesn't quite fit the whiteboard math model.
"Great Walls are definitely anomalous," J.P. Huchra, remarked. "My view is that there is something fundamentally wrong in our approach to understanding such large-scale structures-some key piece of the puzzle that we're missing."
According to the latest thinking regarding the evolution of the universe, superstructures or clumps of galaxies form along spider-like webs of invisible dark matter. It is believed that dark matter (technically known as non-baryonic matter not comprised of baryon particles like normal matter) determines the structure of the universe.
Dark matter gravitationally attracts normal or baryonic matter to it; this creates the clumping of galaxies we see-think 'clumping' clay cat litter and you'll get the picture of cosmic clumps and voids.
Normal or baryonic matter-the stuff you and I are made of-clumps along dark matter lines to form galaxies which then clump together more to form superstructures such as the Great Wall.
What's in the Sky: On Friday, Nov. 19, why not take the Seeing Stars' Twilight Challenge: Scan for the planet Mercury with binoculars. Look very low in the southwest 20-30 minutes after local sunset time. Mars is close to 2 degrees to Mercury's upper right. A good place to see the two planets is from a high mountain pass such as Appalachian Gap (if the road is open). Let us know what you see: firstname.lastname@example.org.
Lou Varricchio. M.Sc., was a senior science writer at the NASA Ames Research Center in California. He is also a producer of public radio and television programs about space science. He is a member of the NASA-JPL Solar System Ambassador program in Vermont. He received the U.S. Air Force Auxiliary's Civil Air Patrol's Gen. Charles E. "Chuck" Yeager Aerospace Education Achievement Award in 2009.