Clusters and superclusters of starlit galaxies are the largest structures known to exist in the observable Universe, and they are frequently made up of hundreds to thousands of separate galactic constituents all bound together by gravity. The observable, or visible, Universe is that relatively “small” region of the entire vast Cosmos that we are able to observe–the rest of our unimaginably enormous Universe lies far beyond the reach of our visibility, because the light traveling to us from remote objects, inhabiting those faraway regions, has not had time to reach us since the inflationary Big Bang birth of the Universe almost 14 billion years ago. Galactic clusters and superclusters form the densest component of the large-scale structure of the Universe, but their mysterious formation history is not well understood. In October 2014, astronomers announced that they have used the APEX telescope to probe an enormous galaxy cluster that is forming in the ancient Universe, and that their observations have shown that much of the star-birth occurring is not only veiled by dust, but also happening in surprising and unexpected places. This is the first time that a complete census of star-birth in such an object has been possible.
The APEX telescope is a collaboration between the Max Planck Institute for Radio Astronomy (MPIfR) in Germany, the Onsala Space Observatory (OSO) in Sweden, and the European Southern Observatory (ESO).
The Spiderweb Galaxy–more formally known by the colorless name of MRC 1138-262–and its surrounding environment have been observed for the past two decades, using ESO as well as other telescopes. This particular galaxy is the large central galaxy of the Spiderweb Galaxy Cluster –commonly considered by astronomers to be one of the best examples of a protocluster in the process of construction–which, in this case, occurred more than ten billion years ago! The Spiderweb Cluster is composed of dozens of galaxies in the midst of merging–and forming a multitude of new stellar sparklers!
However, Dr. Helmut Dannerbauer, of the University of Vienna in Austria, and his colleagues strongly suspected that what was known of the saga of the Spiderweb was incomplete. They wanted to investigate the “dark side” of star-birth and discover how much of the star formation occurring in the Spiderweb Galaxy Cluster was hidden from view behind a heavy, obscuring veil of dust.
The team of astronomers used the LABOCA camera on the APEX telescope in Chile to make 40 hours of observations of the Spiderweb Cluster at millimeter wavelengths. Millimeter wavelengths of light are sufficiently long to peer right through most of the thick, veiling, obscuring dust clouds. LABOCA has a wide field and is an ideal instrument for this survey.
Dr. Carlos De Breuck, who is APEX project scientist at ESO, and a co-author of the paper, explained in an October 15, 2014 ESO Press Release that “This is one of the deepest observations ever made with APEX and pushes the technology to its limits–as well as the endurance of the staff working at the high-altitude APEX site, 5050 meters above sea level.
Clusters Of Starlit Galaxies
A multitude of brilliant, fiery stars set fire to the more than 100 billion galaxies that inhabit our observable region of the Cosmos. Most galaxies are situated in groups or clusters, with clusters being considerably larger than groups. Our own Galaxy, the large starlit barred-spiral Milky Way, is a lovely and majestic constituent of the Local Group that hosts more than 40 galaxies. Our Local Group, in turn, is situated near the outermost rim of the Virgo Cluster of galaxies, whose enormous, glowing heart is 50 million light-years from Earth. The starry galaxies that dance in our Universe trace out enormous, massive, and very mysterious web-like filaments that are composed of weird and transparent dark matter–whose identity is still unknown. However, scientists strongly suspect that the dark matter is made up of some as yet mysterious and undiscovered exotic non-atomic particles that do not interact with light, or any other form of electromagnetic radiation, and are therefore transparent and invisible. The multitude of sparkling starlit galaxies, that swarm around together in groups and clusters, have brilliantly set this invisible Cosmic Web on fire, tracing out for the prying eyes of curious observers that which otherwise would not be seen.
The starlit galaxies ignited a very long time ago, and began to light up the primordial Cosmos less than a billion years after the Big Bang. The most widely accepted theory of galactic formation among astronomers is playfully termed the “bottom up” model, which basically suggests that large, majestic galaxies–such as our own Milky Way–were uncommon in the early Universe, and that large galaxies only eventually attained their more mature sizes as a result of ancient mergers between smaller protogalactic blobs. The earliest galaxies were only approximately one-tenth the size of our Galaxy–but they were just as brilliantly lit up. This is because they were furiously giving birth to searing-hot, fiery, sparkling baby stars. These relatively small, but very luminous, ancient galactic structures, served as the precious “seeds” from which the large, mature galaxies–observed today–emerged.
In the primordial Cosmos, opaque clouds of gas merged together along the extremely massive and immense filaments of the mysterious, exotic dark matter, that weave the strange Cosmic Web throughout Space and Time. Even though scientists do not know what exotic particles make up the dark matter, they do realize that it is not made up of “ordinary” atomic matter that composes the stuff of stars, planets, moons, people, and all of the elements of the familiar Periodic Table of the Elements. Indeed, so-called “ordinary” atomic matter, or baryonic matter, accounts for a mere 4% or so of the mass-energy of the Cosmos.
In that dark era, long before the first stars were born to cast their brilliant fires into the swath of blackness that was the primordial Cosmos, opaque clouds of pristine hydrogen gas converged together along the massive filaments of transparent dark matter. The densest regions of the dark matter hoisted in the pristine clouds of gas by way of relentless gravitational tugs. The dark matter does not interact with atomic matter or electromagnetic radiation except through gravity. Because dark matter does exert a gravitational effect, it warps, distorts, and bends light (gravitational lensing), thus revealing its ghostly presence, letting observers know that it is really there! Gravitational lensing is a phenomenon suggested by Albert Einstein in his Theory of General Relativity (1915), when he realized that gravity could warp light and therefore exert lens-like effects.
The merciless, mysterious, magnificent dark matter snatched up the clouds of pristine hydrogen gas floating around in the primordial Cosmos. These pools of captured ancient gas became the nurseries for the first batch of sparkling stars to ignite the Universe. The powerful gravity of the Cosmic Web tugged and tugged on its prey, until the captured clouds–composed primarily of pristine hydrogen–formed blobs like black pearls within the transparent halos of the strange dark matter. The black blobs of pristine gas floated down, down, down into the centers of these transparent halos, and were strung out on the mysterious, wonderful, vast Cosmic spider’s web.
Lazily, relentlessly, the floating swarm of primordial, pristine gases and the ghostly, weird dark matter, spread throughout the primordial Universe, merging together to form the familiar structures that observers see today. These very ancient structures danced together, interacting gravitationally, and began to cluster together. The primordial protogalaxies, of all sizes, swarmed together like fireflies in the vastness of Spacetime. They were the building-blocks of mature galaxies that were born when halos of dark matter collapsed under their own heavy weight. The protogalaxies smacked together, like bits of clay in the small hands of a playful toddler, and then stuck together to create ever larger and larger amorphous structures. The ancient Cosmos was considerably smaller than what it is today. Therefore, the amorphous protogalaxies were relatively close to one another and, as a result, frequently bumped into one another and merged to create bigger things.
The Strange Construction Secrets Of A Mega Star City
The APEX observations showed that there were approximately four times as many sources dwelling within the area of the Spiderweb compared to the surrounding sky. By carefully comparing the newly obtained data with complementary observations, conducted at varying wavelengths, the team of astronomers confirmed that many of these sources were located at the same distance as the galaxy cluster itself and, therefore, must be components of the forming cluster.
“The new APEX observations add the final piece needed to create a complete census of all inhabitants of this mega star city. These galaxies are in the process of formation so, rather like a construction site on Earth, they are very dusty,” Dr. Dannerbauer explained in the October 15, 2014 ESO Press Release.
But there was a big surprise in store for the astronomers when they discovered where the newly discovered star-birth was occurring. They were expecting to to find this star-birthing region taking place on the large filaments connecting galaxies. However, they found something else! What they found was that star-birth was primarily concentrated in a single, lone region–and that this region is not even on the central Spiderweb Galaxy in the forming protocluster!
“We aimed to find the hidden star formation in the Spiderweb Cluster–and succeeded–but we unearthed a new mystery in the process; it was not where we expected! The mega city is developing asymetrically,” Dr. Dannerbauer said in the ESO Press Release.
In order to continue uncovering the strange construction secrets of the Spiderweb Cluster additional observations are necessary—so that scientists can study the mysterious dusty regions in greater detail.