Swarms Of Small, Faint Galaxies Illuminated The Ancient Universe!

Starlit galaxies were born in the very ancient Cosmos, and they began to illuminate it less than a billion years after its Big Bang birth almost 14 billion years ago. The prevailing theory of galaxy formation suggests that the most ancient galaxies were only a small fraction of the size of our own large, mature, barred-spiral Galaxy, the Milky Way–but they were just as brilliant, because they were vigorously giving birth to a myriad of searing-hot, active, sparkling baby stars. In July 2014, a team of astronomers studying the behavior of the Universe shortly after the Big Bang, reported that they have made a surprising observation: their research suggests that the properties of the ancient Universe were determined by the smallest and faintest galaxies. The team reports their findings in a paper published on July 7, 2014 in the journal Monthly Notices of the Royal Astronomical Society.

Most astronomers think that the Cosmos was fully re-ionized approximately one billion years after the Big Bang. Ionization is the process by which an atom acquires a negative or positive charge as the result of either the loss or the gain of electrons. About 200 million years after the Universe’s Big Bang beginning, ultraviolet (UV) radiation emitted by the first generation of stars began to split neutral hydrogen into negatively charged electrons and positively charged protons. It took another 800 million years for this process to be completed all over the ancient Cosmos. This epoch of re-ionization heralded the last major alteration in the Universe’s supply of gas, and it remains ionized to this very day–more than 12 billion years later!

However, astronomers are not in general agreement about which of the various types of galaxies, dancing around in the early Universe, proved to be the primary player in this great, and very ancient Cosmic drama. Most astronomers have focused on the larger galaxies dwelling in the early Universe. However, the new study conducted by researchers at the Georgia Institute of Technology and the San Diego Computer Center, both located in the United States, suggests that scientific studies should not dismiss the possible influence of the smallest galactic denizens of our Cosmos, as well.

The astronomers used new supercomputer simulations to show how the smallest, dimmest galaxies dwelling in the ancient Cosmos may have made it what it is today. These petite galaxies, even though they were approximately 30 times tinier in size and 1000 times smaller in mass than our Milky Way Galaxy–contributed as much as 30 percent of the blasts of UV light during this ancient process.

Earlier studies ignored these faint, tiny dwarf galaxies, assuming that they were unable to give birth to fiery baby stars. This is because it was believed that the UV light from nearby larger galaxies was too powerful and, as a result, suppressed their smaller neighbors’ star-forming abilities.

“It turns out these dwarf galaxies did form stars, usually in one burst, around 500 million years after the Big Bang. The galaxies were small, but so plentiful that they contributed a significant fraction of UV light in the re-ionization process,” explained Dr. John Wise in a July 7, 2014 Royal Astronomical Society (RAS) in London Press Release. Dr. Wise, who led the new study, is of the Georgia Institute of Technology.

Dazzling!

Most galaxies inhabit groups or clusters, with groups being quite a bit smaller than clusters. Clusters and superclusters of galaxies are the largest structures known to dwell in the Cosmos, and they are frequently made up of literally hundreds to thousands of separate galactic constituents all bound together by gravity–thus forming the densest component of the large-scale structure of the Universe. Our Milky Way, for example, is a constituent of the Local Group along with about 40 other galaxies. In turn, our Local Group is located near the edge of the Virgo Cluster, whose core is situated 50 million light-years from us! The star-fired galaxies of our Cosmos trace out the enormous, massive, and mysterious web-like tendrils of the Cosmic Web. These web-like tendrils are made up of bizarre, transparent dark matter, which is of unknown composition. However, the weird stuff is probably there, and it is thought to be made up of some as yet undiscovered, exotic particles that do not interact with light–which is why it is transparent and, therefore, invisible. The luminous galaxies that swarm together in groups and clusters outline this transparent Cosmic Web, tracing out for the prying eyes of curious astronomers–with their wonderful light–that which cannot be seen.

The prevailing theory of galactic formation, playfully termed the bottom up theory, indicates that large galaxies were rare in the early Universe, and that galaxies only eventually reached their mature, majestic sizes as the result of many mergers between smaller, amorphous protogalactic blobs dancing around long ago. Therefore, the extremely brilliant, relatively tiny early galactic structures served as the “seeds” of the large, mature galaxies that inhabit our Universe today–such as our own Milky Way.

Imagine the ancient scene of floating clouds of primordial opaque gases colliding with each other, and then merging along the enormous, heavy tendrils of the transparent, mysterious dark matter of the great Cosmic Web. Even though scientists do not know the identity of the exotic particles that compose the dark matter, it is strongly suspected that it is not composed of the atoms that make up the so-called “ordinary” matter that we are familiar with–the stuff of stars, planets, and people–literally all of the elements listed in the Periodic Table. In fact, so-called “ordinary” atomic matter–baryonic matter–accounts for less than 5 percent of the mass-energy of the Cosmos. The weird and mysterious dark matter is far more abundant, and it accounts for about 27 percent of the mass-energy of the Cosmos, while the even more bizarre and puzzling dark energy composes a whopping 70 percent of the Universe! Dark energy is a baffling substance, probably a property of Space itself, that is causing the Universe to accelerate in its expansion. Because the so-called “ordinary” atomic matter–that Earthlings are so familiar with–constitutes such a relatively small portion of the Cosmos, calling it “ordinary” is somewhat misleading. This runt of the Cosmic litter is, in fact, both very rare and very special in the Cosmic scheme of things. Atomic elements heavier than hydrogen and helium–both born in the Big Bang–were all manufactured in the searing-hot nuclear-fusing hearts of the Universe’s stars! Atomic matter is not “merely” stardust–it is the stuff of life itself. Atomic matter, a precious rarity, brought our Universe to life!

In that ancient time, long before the first generation of stars blasted the Universe with their light, opaque clouds, primarily made up of hydrogen, swarmed together along the heavy tendrils of the transparent dark matter. The most massive portions of the dark matter snared these floating clouds of pristine gas with gravitational snatching claws. Dark matter does not interact with baryonic matter or electromagnetic radiation–except through the force of gravity! However, because it does interact with baryonic matter gravitationally, and because it bends, warps, magnifies and distorts light (gravitational lensing), it reveals its eerie, ghostly presence. Gravitational lensing is a prediction of Albert Einstein’s Theory of General Relativity, and it postulates that gravity can warp light and, therefore, have lens-like effects.

The invisible dark matter gravitationally snatched floating clouds of primordial gases, and these ancient pools of captured gas became the nurseries of the first stars to light up the dark Cosmos. The captured gas clouds pooled together like strange pearls within the transparent halos made of dark matter. The blobs of gas then floated down, down, down into the very hearts of these invisible, transparent halos, and were then strung out like beads on this immense, weird Cosmic Web of darkness.

Indeed, most scientists think that the first galaxies to dance around the ancient Universe were opaque, dark, shapeless blobs of gas, collecting silently and ghost-like within the strange and exotic hearts of dark matter halos–and that these bizarre halos pulled in the first generation of sparkling, dazzling infant stars, with their mighty gravitational pull. The sparkling new stars, and the primordial gas clouds glowing with intense heat, lit up what was previously a dark and desolate expanse.

Relentlessly, the swirling, wild sea of ancient gases and the weird, mysterious, phantom-like dark matter flowed throughout the ancient Universe, mixing together to form the now familiar and distinct structures that can be observed today. The more massive portions of dark matter composing the great Cosmic Web flowed through the ancient Universe, becoming the “seeds” from which primordial galaxies were born and evolved. The gravitational grip of those ancient “seeds” ultimately snatched up the ancient gases and pulled them together into ever tighter and tighter blobs. Structures of differing sizes began to form, depending on the mass of the dark matter “seed.” If the “seed” was relatively light in weight, only a small protogalactic blob was born from the gas. However, if the “seed” was heavy, a large protogalactic blob formed. These blobs swarmed together gravitationally, and then met together to form clusters. The protogalaxies, both large and small, swarmed like bees around a pool of sweet and sticky honey, and they interacted with one another gravitationally, snatching at one another, and creating ever-larger and larger structures that grew into the huge, majestic galaxies that we know today. Like masses of dough being smacked together by a pastry chef to make a loaf of bread, the protogalaxies smacked into one another to lam bang dai hoc ever-larger masses. The ancient Universe was crowded–it was considerably smaller than what it is today. Therefore, the amorphous protogalaxies were in relatively close proximity and– as a result–they often bumped into one another and merged together to form increasingly larger structures!

Swarms Of Small, Faint Galaxies Illuminate The Ancient Universe

The team’s supercomputer simulations modeled the traveling UV light, emanating from the first stars, as it wandered through the gas floating around within the galaxies as they formed. They discovered that the fraction of ionizing photons zipping away into the Space between galaxies was about 50 percent in small galaxies (weighing over 10 million times the mass of our Sun)–however, it was a comparatively small 5 percent in larger galaxies (weighing approximately 30 million times the mass of our Sun). The higher fraction, combined with their much greater abundance, is precisely the reason why the faintest, tiniest galaxies may have played a critical part in the re-ionization of the ancient Universe.

“It’s very hard for UV light to escape galaxies because of the dense gas that fills them. In small galaxies, there’s less gas between stars, making it easier for UV light to escape because it isn’t absorbed as quickly. Plus, supernova explosions can open up channels more easily in these tiny galaxies in which UV light can escape,” Dr. Wise explained in the July 7, 2014 RAS Press Release.

The team’s supercomputer simulation results suggest a gradual timeline that traces the progress of the ancient re-ionization over the passage of hundreds of millions of years. Approximately 300 million years after the Big Bang, the Cosmos was about 20 percent ionized. It was 50 percent ionized at about 550 million years! The simulated Cosmos became completely ionized at 860 million years after the Big Bang.

“That such small galaxies could contribute so much to the re-ionization is a real surprise. Once again, the supercomputer is teaching us something new and unexpected; something that will need to be factored into future studies of re-ionization,” explained Dr. Michael Norman in the July 7, 2014 RAS Press Release. Dr. Norman, of the University of California, San Diego, is one of the co-authors of the study.

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