The first galaxies were born long before there were observers on Earth to gaze with curiosity up into the mysterious night sky that was filled with the frantic fireworks of blazing distant stars. The primeval galaxies were relatively small amorphous structures at the dawn of this era of galactic buildup, but these shapeless blobs eventually merged with one another to form ever larger and larger galaxies. The first generation of small galaxies was likely well in place about 400 million years after the hot Big Bang birth of the Universe about 13.8 billion years ago, and this building up process is thought to have continued until the Universe was approximately two billion years old. In September 2016, astronomers announced that NASA’s infrared Spitzer Space Telescope–on the hunt for the Universe’s most ancient galaxies–has wrapped up its observations for the Frontier Fields project. This successful project combined the power of the trio of NASA’s Great Observatories–Spitzer, the Hubble Space Telescope (HST), and the Chandra X-ray Observatory–to go as far back in Space and Time as current technology will permit.
The Frontiers Field program, officially named the Hubble Deep Fields Initiative 2012, was designed to advance scientific knowledge of ancient galactic formation by observing very remote galaxies in blank fields with the aid of gravitational lensing in order to study the “faintest galaxies in the distant Universe.”
Even with the best telescopes available today, it is difficult to acquire a sufficient amount of light from the very first galaxies, that are situated billions of light-years away, in order to learn much about them beyond their approximate distance from Earth. However, astrophysicists on the hunt for the first generation of galaxies have a remarkable tool to help them in their chase–a little gift from nature to aid them in their observations. The gravity exerted by massive, foreground galaxy clusters bends and magnifies the light emanating from distant, background objects–creating “cosmic zoom lenses”.
This lensing effect was proposed by Albert Einstein in his Theory of General Relativity (1915) when he came to the realization that light from a background object can be warped by the gravity of an object in the foreground. According to General Relativity, the presence of matter (energy density) can bend, warp, and curve Spacetime. As a result, the path of a wandering beam of light will be deflected, and in many cases it can be described by analogy to the distortion of light by (glass) lenses in optics. The traveling light that is deflected is not only visible light–the light that we can see–but more generally any form of electromagnetic radiation. As a result of this lensing, light beams that would have otherwise not reached observers on Earth are bent from their paths and towards the observer. There are different regimes: strong lensing, weak lensing, and microlensing. The variations between these three regimes depend on the positions of the observer, the source, and the lens–and the mass and shape of the foreground lensing object itself, which determines the amount of light that is deflected, as well as where it will travel. Traveling light can also be bent away from the observer.
The Birth Of Galaxies In Our Cosmic Wonderland
The billions of galaxies that we can observe today ignited with the brilliant light of the first stars very long ago–less than a billion years after the Big Bang. When the first galaxies began to take shape, our primordial Universe was brimming with a mysterious mist composed of pristine hydrogen gas. However, when the first luminous objects were born in the Cosmos, their fabulous, flowing light cleared away that very ancient mist and caused the Universe to become transparent to ultraviolet light. Scientists term this primordial era reionization–but little is known about those ancient first galaxies, and until recently they had only been observed as faint blobs bobbing around in the most distant regions of the observable Universe. The observable Universe is that relatively small domain of the entire unimaginably vast Cosmos that we are able to observe. This is because the light that is wandering towards us from domains beyond our cosmological horizon has not had enough time to reach us since the Big Bang as a result of the expansion of Spacetime.
In astronomy long ago is the same as far away. The closer to us that a shining object is in Space, the more recent it is in Time. The galaxies of our Universe usually dwell in groups or clusters, with clusters being considerably larger than groups. In fact, clusters of galaxies are some of the most immense structures known to inhabit the Cosmos–and they very often contain hundreds to thousands of individual galaxies, all bound together by the irresistible lure of their mutual gravitation. Our own Galaxy, the Milky Way, is a large barred-spiral–a whirling starlit pin-wheel in Spacetime. Our Milky Way is a member of the Local Group of galaxies that plays host to more than 40 separate galactic constituents. Our Local Group, in turn, is located near the outer limits of the Virgo Cluster of galaxies, whose big, hot, and brilliant heart is about 50 million light-years away from our Solar System. The glittering, starlit galaxies inhabiting our Universe outline with their lovely light the massive, immense, and mysterious web-like filaments of the Cosmic Web that are thought to be composed of exotic, invisible, and ghostly dark matter–the identity of which is unknown. Scientists strongly suspect that the dark matter is made up of exotic non-atomic particles that do not interact with light–or any other form electromagnetic radiation–which is why it is a transparent and invisible phantom-like substance inhabiting Space and Time. The galaxies that shine with the light of a glittering myriad of dancing stars, that bob around together within galactic groups and clusters, light up this ghostly Cosmic Web, and outline with their light that which otherwise could not be observed.
In the ancient Universe, opaque clouds of hydrogen gas bumped into one another and then merged along the massive and enormous dark matter filaments of the Cosmic Web. The Cosmic Web got its name because some cosmologists think that this enormous structure hauntingly resembles a strange web woven by a huge hidden spider. Even though it is still not known what the dark matter really is, it is likely not composed of “ordinary” atomic matter–which is the type of matter that makes up our familiar world, and accounts for all of the elements listed in the Periodic Table. Atomic matter is the stuff of stars, planets, moons, and people.
The currently most favored model for galactic formation proposes that large galaxies like our own Milky Way were rare in the ancient Universe. According to this model, the large galaxies that we observe today eventually attained their more mature and impressive sizes when small primeval protogalactic blobs bumped into one another in the ancient Cosmos, and ultimately merged together to create ever larger and larger galactic structures.
There was an era, when our Universe was young, that existed long before the first generation of stars had been born to light up the dark Cosmos with their fabulous fires. Opaque clouds of hydrogen gas gathered together along the transparent filaments of the Cosmic Web, that were spun from the exotic dark matter. The heavier blobs of the dark matter snared clouds of gas with the irresistible grip of their gravity. In the dark Universe, these pristine blobs of hydrogen gas became the exotic cradles of the very first generation of stars. The gravity of the Cosmic Web grabbed its atomic prey until the trapped clouds of hydrogen gas formed pools of blackness within the transparent halos of dark matter within the Cosmic Web. The blobs of gas then floated down into the hearts of these invisible halos, and strung themselves out like dewdrops on the web of an unseen spider. The very first galaxies are generally believed to have pulled in the first generation of sparkling infant stars with their snatching gravitational hooks. The newborn stars and extremely hot and glaring gas at last lit up what was before a vast swath of blackness.
Gradually, as time went by, the swirling sea of ancient gases and the exotic dark matter converged together and created the structures that are seen in our Universe today. Within the heavy filaments of the enormous Cosmic Web, areas of greater than average density served as the “seeds” from which the galaxies were born and eventually evolved. The “seeds” pulled the hydrogen gas into ever tighter and tighter knots. In this way, depending on the size of the dark matter halo, structures of differing sizes began to take shape. The protogalaxies, of varying sizes, swarmed together in the universal twilight of ancient Space and Time–colliding with each other and ultimately merging to become the large, majestic, star-blazing galaxies like our Milky Way. Our Universe is expanding, and because of this it was considerably smaller during this ancient era than it is today. As a result, the shapeless protogalaxies frequently bumped into one another and stuck together because of the powerful force of their mutual gravitational attraction–forming increasingly larger structures.
Where Primeval Galaxies Play Hide And Seek!
The Frontier Fields observations have stared at the Cosmos through the most powerful “cosmic zoom lenses” available by peering at six of the most massive galaxy clusters known. These gravitational lenses can magnify extremely small background galaxies by as much as a factor of one hundred. With Spitzer’s freshly acquired Frontier Fields data, along with data obtained from HST and Chandra, astronomers will be able to attain a greater understanding about the earliest galaxies.
“Spitzer has finished its Frontier Fields observations and we are very excited to get all of this data out to the astronomical community,” commented Dr. Peter Capak in a September 28, 2016 NASA Jet Propulsion Laboratory (JPL) Press Release. Dr. Capak is a research scientist with the NASA/JPL Spitzer Science Center at the California Institute of Technology (Caltech) in Pasadena California, and the Spitzer lead for the Frontier Fields project.
A paper published in the journal Astronomy & Astrophysics presented the entire catalog data for two of the six galaxy clusters studied by the Frontier Fields: Abell 2744–nicknamed Pandora’s Cluster–and MACS J0416, both situated approximately four billion light years from Earth. The other galaxy clusters chosen for Frontier Fields are RXC J2248, MACS J1149, MACS J0717, and Abell 370.
Astronomers will sift through the Frontier Fields catalogs for the smallest, faintest-lensed objects, many of which should prove to be the most remote galaxies ever detected. The current record-holder is a galaxy dubbed GN-z11, that was reported in March 2016 by HST scientists. GN-z11 is an astonishing 13.4 billion light-years from Earth, which makes it only a few hundred million years younger than the Universe itself. The discovery of this very distant galaxy did not require gravitational lenses because it is an outlying extraordinarily bright object for its era. With the magnification boost bestowed by gravitational lenses, the Frontier Fields project will enable eager astronomers to observe typical objects that existed incredibly long ago and far away. These new observations are expected to provide a more complete and accurate portrait of the Universe’s most ancient galaxies.
Astronomers want to attain a better comprehension of how these primordial galaxies were born, and how their myriad of magnficent, searing-hot, and brilliant stars have enriched the galaxies with the precious chemical elements that they manufactured in their nuclear-fusing stellar hearts. The only atomic elements born in the Big Bang were hydrogen, helium, and traces of lithium and beryllium. All of the other atomic elements were fused in the hot, nuclear-fusing furnaces of the Universe’s billions and billions of stars. The iron in your blood, the water that you drink, the calcium in your bones, the oxygen that your breathe, and the carbon that is the basis of life on our planet, were all manufactured within the hearts of stars. We are such stuff as stars are made of. We would not be here if the stars did not exist. We are stardust.
In order to learn more about the birth and evolution of the most ancient galaxies in the Universe, which are extremely faint, astronomers must collect as much light as possible across a wide range of frequencies. With sufficient light from these primeval galaxies, astronomers can then perform spectroscopy, teasing out important details concerning the stars’ environments, temperatures, and compositions by studying the signatures of the chemical elements that reveal their tattle-tale imprints in the light.
“With the Frontier Fields approach the most remote and faintest galaxies are made bright enough for us to start to say some definite things about them, such as their star formation histories,” Dr. Capak continued to explain.
Because the Universe has expanded over the almost 14 billion years of its existence, light traveling from extremely remote objects has been stretched out–or redshifted–as it travels towards us from very far away. Optical light sent forth by fiery stars in the gravitational-lensed, background galaxies observed in Frontier Fields has therefore been redshifted into infrared wavelengths. Spitzer can use this infrared light to determine the population sizes of stars in a galaxy, which in turn provides valuable clues to the mystery surrounding the galaxy’s mass. Combining the light observed by Spitzer and the HST enables astronomers to identify galaxies located at the very edge of the observable Universe.
In the meantime, HST scans the Frontier Fields galaxy clusters in optical and near-infrared light, which has redshifted from ultraviolet light on its long and treacherous travels to Earth. Chandra‘s task is to observe the foreground galaxy clusters in high-energy X-rays hurled out by black holes and ambient searing-hot gas. With the help of Spitzer, the space telescopes measure the masses of the galaxy clusters, also taking into account their invisible but, nevertheless, abundant quantities of dark matter. The determination of the clusters’ overall mass is an important step in quantifying the distortion and magnification they produce on background galaxies of interest. Multi-wavelength results pertaining to the MACS J0416 and MACS J0717 clusters were published in October 2015 and February 2016. These results also brought in radio wave observations from the Karl G. Jansky Very Large Array (VLA) that were able to observe star-birthing regions that would otherwise be hidden by obscuring dust and gas.
The Frontier Fields project has inspired astronomers involved in the collaboration to look forward to the future when they will be able to peer deeper into the distant Universe using the upcoming James Webb Space Telescope, scheduled to launch in 2018.
Dr. Lisa Storrie-Lombardi, of the Spitzer Science Center and the Frontier Fields project, said in the September 28, 2016 JPL Press Release that “The Frontier Fields has been an entirely community-led project, which is different from the way many projects of this magnitude are typically pursued. People have gotten together and really embraced Frontier Fields.“