“The Force binds the galaxy together.” ~ Obi-Wan Kenobi in the movie Star Wars (1977)
A galaxy is a cluster of star systems and stellar remnants, swirling in an interstellar mixture of gas, dust, and massive matter.
“The structures in our present universe are the outcome of more than 10 billion years of evolution. Slight irregularities imprinted at very early eras led to increasing contrasts in the density from place to place, until overdense regions evolved into bound structures.” ~ English astrophysicist Martin Rees
We do not know when galaxies emerged. The 1st galaxies we are aware of coalesced by 13.57 BYA. There were already mature galaxies with billions of stars 12.3 BYA.
(That galaxies existed only 250 million years after the supposed Big Bang strongly indicates that the standard cosmological model is bogus, as there is no astrophysical explanation for such rapid galactic evolution.)
“The number of galaxies is much bigger than anyone would have guessed. And the real number could be even higher.” ~ English astrophysicist Christopher Conselice
There are now ~4 trillion (4,000,000,000,000) galaxies in the universe; roughly half light and half dark. Each light galaxy may contain millions or even billions of stars. Almost all visible star systems have planets.
Within a few billion years of galactic formation, there were 10 times as many galaxies as there are today. Cosmic evolution reduced the number of galaxies through extensive merging.
To this day, mysterious filaments of galactic attraction thread the universe in an invisible gravitational web. Galaxies form along these filaments, with massive black holes as their hearts. The gravitational influence of filaments entices molecular hydrogen gas to coalesce, and so permits star formation. Galaxies run on gas.
Acting as a black backdrop to the glittering cosmopolitan cosmos, dark galaxies are conjectured to be as plentiful as the light variety. Some are utterly devoid of stars; others have a relative few. Black holes and gravitational filaments corral dense gas globules that shed no light. Little is known about the ecologies of galaxies, light or dark.
“Equipped with his 5 senses, man explores the universe around him and calls the adventure science.” ~ Edwin Hubble
Astronomers have traditionally classified galaxies by how they look. Edwin Hubble developed his galaxy morphology in 1926. The Hubble sequence, still used today, has 3 galaxy classes: ellipticals, spirals, and lenticulars.
Elliptical galaxies appear as featureless ellipses of light.
Spiral galaxies have a central concentration of stars – a galactic bulge – with arms forming a spiral structure. How fat the bulge is depends upon how rapidly the galaxy is spinning. 70% of the galaxies near the Milky Way are spiral.
Lenticulars have a bright central bulge, surrounded by a thinner disk, but without the spiraling effect.
Hubble also defined 2 classes of irregular galaxies outside the Hubble sequence: one of star clusters without a central bulge, and another smoother configuration with an asymmetric appearance.
New galactic types are still being found. 300 million light-years away is a galaxy with the same mass as the Milky Way, but with only 1% of the star shine.
“That’s just something we never knew could happen.” ~ Dutch astronomer Pieter van Dokkum in 2016
A galaxy’s visual morphology reflects the dynamics of its formation and evolution. Galaxies form a spiral pattern out from a central core via density waves: oscillations in the galactic gravitational field that sashays stars back and forth. Galactic structures are frequently shaped by tidal interactions with other galaxies.
Before describing the importance of black holes and quasars in galactic formation and dynamics, a brief digression into the history of astrophysics.
In the late 18th century, English natural philosopher and geologist John Michell and French mathematician and astronomer Pierre-Simon Laplace contemplated the prospect of an object with gravity too strong for light to escape: a black hole.
German physicist Karl Schwarzschild mathematically conjectured simple black holes in 1915, the same year Einstein introduced general relativity. The Schwarzschild radius is the size of the event horizon for a simplified abstraction of black holes: massive, non-rotating, and spherically symmetric objects. A black hole’s event horizon defines the rim of no return for matter/energy, as the gravitational pull approaches infinity.
Einstein was pleasantly surprised to learn of Schwarzschild’s exact solutions for general relativity’s field equations, as he could only produce an approximate solution.
Whereas Einstein had used a rectangular coordinate system to approximate the gravitational field near the black hole mathematical construct, Schwarzschild developed a polar, spherical coordinate system, which afforded more elegant mathematical expression.
(Schwarzschild’s triumphal equations were created while he was in the German army during World War I. Schwarzschild was suffering from a painful autoimmune disease (pemphigus) which he developed while at the Russian front, yet he managed to write 3 outstanding physics papers in 1915: 2 on relativity theory, and 1 on quantum theory. Schwarzschild died the following year.)
Einstein considered black holes purely a mathematical construct. He did not think that black holes could actually form. Following Einstein’s lead, mainstream physicists disregarded all results to the contrary, though a minority maintained that black holes were possible. It was not until the close of the 1960s that consensus conviction turned toward acceptance that black holes existed.
Via quantum mechanics, not general relativity, English theoretical physicist Stephen Hawking predicted in 1974 that black holes must emit radiation (Hawking radiation), though at a temperature inversely proportional to the mass of the black hole.
“There is no escape from a black hole in classical theory, but quantum theory enables energy and information to escape.” ~ Stephen Hawking
30 years later, Hawking had convinced himself that black holes do not exist. Hawking’s repudiation stemmed from a paradoxical conundrum.
The equivalence principle of relativity assumes that the laws of physics are identical everywhere. Someone falling into a black hole would feel the same as if floating free in space, at least until ripped apart by gravitational intensity.
At the quantum level, approaching a singularity would be very energetic, with excited particles bustling about. Someone entering the event horizon would be fried to a crisp by sizzling subatomics.
Such a quantum firewall poses serious problems. It violates the relativity axiom of equivalence. And it breaks the mathematical symmetry of quantum theory.
So, Hawking proposed that a black hole isn’t really a black hole. Instead, it is a cosmological shredder, which merely mangles matter before releasing it; an utterly unsupported hypothesis.
“A different resolution of the paradox is proposed, namely that gravitational collapse produces apparent horizons but no event horizons behind which information is lost.” ~ Stephen Hawking, concerned about the cosmic integrity of information
By trading an event horizon for one which is only apparent, Hawking’s proposal attempts to leave both relativity and quantum theories intact. Instead, it denies what a black hole must be.
A black body is an idealized object that absorbs all incident electromagnetic radiation. The only consummate black bodies are black holes.
Black bodies at a uniform temperature emit an electromagnetic signature termed black-body radiation. The radiation from a black body depends only on the body’s temperature.
In 1879 Jožef Stefan mathematically stated the law pertaining to radiant energy after considering the mathematical relation between temperature and radiation in black bodies. With this equation, Stefan was able to make the first approximate estimate of the temperature of the Sun’s surface.
At the atomic and molecular level, radiation typically exerts a positive pressure. As an energy source, radiation temporarily charges particles. This is known as the Stark shift.
The Stark shift of black-body radiation is roughly proportional to the 4th power of the black body’s temperature. The hotter the body, the higher the shift.
Stark shifts induced by black-body radiation can combine, creating an attractive force that overwhelms the repulsive radiation pressure. Despite outgoing radiative energy flow, a hot black body can attract nearby neutral molecular matter rather than repel it. This attraction happens because radiated atomic matter can be drawn to a higher radiation intensity; in this instance, a hot black body.
Up to a point, the hotter the body, the stronger the attraction. But, above a few thousand degrees Kelvin, attraction turns to repulsion. The attractive force of black-body radiation rapidly decays with distance: to the 3rd power. The force of transition is stronger for small bodies.
The attractive black-body force of a black hole the size of a dust grain at 100K is much stronger than its puny gravitational tug. In contrast, a large, hot black hole relies upon its gravitational pull. By virtue of their tiny black bodies, minute black holes take advantage of their black-body allure to get a head start on growth.
“The black holes of Nature are the most perfect macroscopic objects there are in the universe: the only elements in their construction are our concepts of space and time.” ~ Indian astrophysicist Subramanyan Chandrasekhar
A black hole is a cosmic singularity of no return once within, past the event horizon that defines entrance into a black hole.
“The event horizon is not a physical barrier.” ~ Scottish astrophysicist Paul McNamara
Most matter drawn into a black hole is spun off before it reaches the event horizon. This expelled energy flow is termed a quasar when the emitted radiation is luminous (light and infrared warmth being the only spectral range of radiation celebrated by humanity).
A black hole grows as matter is absorbed. However logical that seems, how it happens is not known. The mystery emanates from the nature of the singularity. A black hole is literally a perfectly spherical hole in the universe – spacetime simply ceases to exist.
It is bizarre that these infinite voids provide for the gyre of existence by anchoring galaxies and driving their dynamics. As Lao Tzu stated: what is not makes what is useful.
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“Black holes and their host galaxies coevolve, with the feedback from the black hole inducing star formation.” ~ Israeli astronomer Benny Trakhtenbrot et al
Small density fluctuations in the early universe led to perturbations that sprouted in the fertile ground of gravity. These grew to the point that they disconnected from the global expansion of the universe. Such centers became self-gravitating; forming halos within which gas condensed to form stars, black holes, and galaxies.
Black holes have peppered the cosmos since its salad days. They were abundant in the early universe; swapping the beginning of something for a gaping maw of nothing. These seeds of nothingness grew by consuming whatever fell into their path.
One black hole has a mass 12 billion times that of the Sun, accreting surrounding substance at the maximum rate afforded by the laws of physics. This black hole had an awesome girth 12.92 bya, only 900 million years after the supposed Big Bang. Other contemporaneous monstrous black holes have been found. Astrophysicists have no explanation for how such massive black holes were possible so early in the cosmos’ supposed history.
“We expected as we looked further back into time that the black holes would be smaller and smaller because they hadn’t had as much time to grow.” ~ American astrophysicist Rob Simcoe
The existence of massive black holes just hundreds of millions of years after the Big Bang strongly indicates that the conventional dating of this universe’s birth is wrong. The cosmos must be much older.
Black holes were the nursery in which early galaxies grew up; both a great attractor and generator of galaxy-making material. Black holes were more massive relative to their respective galaxies when the universe was young.
Besides the intense implosion of a massive gas cloud, a black hole can form after a supernova explosion, with the remnants collapsing, forming a forceful gravitational pull that sucks in surrounding mass in an ongoing accretion process.
Black holes are everywhere and come in all sizes. Some are swollen to 50 billion times the mass of the Sun.
A massive black hole is a gyre, gaining girth and power while emitting energetic streams that may stretch for millions of light-years. A star coming close to a supermassive black hole may be ripped apart by the hole’s tidal pull, with stellar debris spun off as a quasar.
There is an ancient quasar at the edge of the observable universe that appears to be 12.9 billion years old, powered by a black hole of 2 billion solar masses. The quasar emits 60 trillion times the light of the Sun.
“This enhancement of star formation by outflows would have been even more important in a younger universe, where dense clumps of gas were much more common.” ~ Australian astrophysicist Stanislav Shabala
Black holes typically account for 0.1% of a galaxy’s mass, but one has been observed that is a whopping 14% of galactic girth.
A spinning black hole draws matter that rotates around it. On the way to a black hole, incoming material picks up its pace. In the competition between speed and gravity, speed wins. Over 99% of the matter drawn to black holes is ejected.
Feasting makes a black hole faster. The larger the black hole, the quicker its spin. A supermassive black hole at the center of a nearby galaxy has been clocked at 1.08 billion kilometers per hour: close to the speed of light. Black holes continuously spew cosmic rays, the most energetic radiation in the universe.
Galaxies and black holes have grown in tandem throughout cosmic history. There is a correlation between the mass of a galaxy’s central black hole and the velocity of stars in its galaxy. All the galaxies near the Milky Way have about 700 times more mass in their stellar bulges than deposited in their black holes, irrespective of the galaxy’s size. This appears to be an evolved situation.
The Milky Way grew by capturing dwarf galaxies which had originally formed from black holes. The galactic merger process can result in a dwarf black hole recoiling rather than merging with the massive black hole at the heart of the Milky Way. More often, galaxies are joined as their black holes interact.
When black holes encounter one another, they dance together for a while in a close embrace. The footfalls of black hole ballet are gravitational waves that ripple spacetime itself. These waves carry for untold light-years, creating a web of galactic interactions. Eventually, the black holes merge into one – their mutual gravitational attraction irresistible.
Black holes are not confined to being center stage in the galaxy. Galaxies may have millions of black holes roaming about, each with the mass of anywhere from 1,000 to 100,000 suns, swallowing anything in their path, shaping galactic dynamics. There an estimated 400 million black holes in the Milky Way galaxy.
While black holes often engender galactic formation, they can also slowly suffocate galaxies. The spin of a black hole determines what role it plays in the galaxy about it.
“The lives of galaxies and their supermassive black holes are inextricably intertwined.” ~ American astrophysicists Timothy Heckman & Guinevere Kauffmann
As matter is sucked toward a black hole, a disk of infalling gas and dust forms around the rim. On the journey inwards, owing to quantum effects, incoming debris emits large amounts of X-ray and ultraviolet radiation; radiation so strong that it diverts part of the inflow. This causes strong outflowing winds, with velocities up to several hundreds of kilometers per second.
Outflowing jets from massive black holes engender star formation by plowing through galactic gas, thereby creating hot gas filaments, the raw material from which stars form. A black hole’s energetic jet causes a supersonic shock wave on a gas cloud in its path, heating and compressing the gas.
The shock wave ionizes the gas cloud: stripping electrons from the gaseous atoms. After the shock wave subsides, the ions recombine, emitting radiation, which takes energy out of the cloud. This cooling effect causes the gas cloud to contract further. When the knot of gas reaches a critical density, it collapses to form a star.
“Quasars are immensely bright. From the central point in a galaxy, they emit as much energy as thousands of giant galaxies from a region as tiny as the solar system.” ~ American astrophysicist Robert Antonucci
Quasars are the shiny companions to black holes. Powered by regurgitation from supermassive black holes, quasars appear as stunningly bright, distant stars. More than 200,000 quasars have been spotted. Quasars are powered by both the spin toward the black hole and the rotation of the black hole itself.
A quasar’s brightness corresponds to how much matter a black hole is consuming. When black hole intake slackens, the light goes out and black hole output is downgraded in human esteem. A typical quasar only lasts a few hundred million years.
Quasars are not always solely outflow. 1 out of 10,000 quasars feed the black hole from which they are formed. How that happens is not understood.
Quasars appear linked in a cosmic web of filaments and clumps in the vast voids where galaxies are scarce. The dynamics of large quasar group formation remain a mystery.
“Some of the quasars’ rotation axes are aligned with each other, despite the fact that these quasars are separated by billions of light-years.” ~ Belgian cosmologist Damien Hutsemékers
While the cause of disparate quasar alignment is uncertain, it is a clear indication of synchronism on a vast cosmic scale.
“The alignments hint that there is a missing ingredient in our current models of the cosmos.” ~ Belgian astrophysicist Dominique Sluse
The Milky Way
The Milky Way formed 13.2 BYA. Our galaxy is now a stellar spiral disk with 4 major arms and 2 dozen smaller ones. The Milky Way’s present shape is a product of its evolution, which continues. The Milky Way is a gyre of streaming debris, replenished by gas cloud encounters, and consuming satellite galaxies which are drawn to it. So far, the Milky Way has devoured 15 other galaxies.
The Milky Way is at least 200,000 light-years in diameter, with over 400 billion stars, and at least 640 billion planets, cumulatively weighing in at 1.54 trillion suns.
Like the planet Tatooine in the Star Wars movies, many millions of Milky Way planets orbit 2 stars.
“We used to think that the Earth might be unique in our galaxy. But now it seems that there are literally billions of planets with masses similar to Earth orbiting stars in the Milky Way.” ~ German astronomer Daniel Kubas
The Milky Way spins at 250 kilometers per second. 1 revolution takes 240 million years.
At the center of the Milky Way lies a ponderous, barely spinning black hole, equivalent to 4 million solar masses. The black hole continues to accrete matter and energy: constantly snacking on hot gas. This central black hole is surrounded by a well-ordered magnetic field that regulates the flow of material into it.
The Milky Way and its neighbor, the Andromeda galaxy, are reckoned to be halfway through their life cycle, with some 4 billion years left. That estimate does not account for a continuing influx of new matter that keeps galaxies dynamic.
The Milky Way and Andromeda are encircled by a ring of 12 large galaxies ~24 million light-years (mly) across. All these galaxies lie on a sheet that is 34 mly across, but only 1.5 mly thick.
Somewhat analogous to the atmosphere of a planet, galaxies such as the Milky Way have halo clouds of hydrogen gas and other incidental matter. These clouds are not evenly distributed, but cluster as residue from star formation.
Massive stars age quickly. Within a few million years, their stellar wind sheds matter, as a prelude to exploding as supernovae, spraying their contents into a cloud which forms galactic halos.
Cloud matter gets recycled back into the galaxy, seeding it with the fuel to trigger another burst of star system births. Galactic fuel clouds can also drift in from other galaxies along a gravitational filament.
These influxes are simply a continuation of the dynamics by which the Milky Way came to be. While matter accretion is one route to growing a galaxy, about 25% of the star clusters in the Milky Way immigrated from other galaxies.
Many of the stars in the halo that surrounds the Milky Way travel in groups. These small star clusters spend most of their time outside the disk-like structure that gives the Milky Way its name. They are the remnants of small galaxies that were cannibalized by the Milky Way.
A star cluster carries from 100,000 to a million stars. The Milky Way has swallowed up to 6 dwarf galaxies on its journey so far. There are hundreds, if not thousands, of small satellite galaxies swarming around the Milky Way.
The dwarf galaxy Sagittarius has smacked into the Milky Way several times. In an early encounter, 80% to 90% of its mass was stripped from Sagittarius. This set off a cascade of instabilities that resulted in the formation of the spiral arms in the Milky Way, along with ringlike structures on the galaxy’s outskirts. Sagittarius strikes again 10 million years from now, fated to slap the southern face of the Milky Way disk.
Milky Way vitality was flagging until 5 BYA, when its star population suddenly burgeoned. Half of all the Milky Way’s stars were produced during this period.
Like most galaxies, the Milky Way has had a calamitous evolution. 100 mya, the Milky Way was banged by a smaller galaxy (not Sagittarius). Like a gong, the Milky Way reverberates from that encounter, and will continue to do so for the next 100 million years.
The Milky Way’s spinning galactic disk is warped, bowing to immense gravitational dynamics. Gravitational effects shape the structure of the cosmos.
2 satellite galaxies – the Magellanic Clouds – orbit the Milky Way. Their gravitational tug distorts the galactic disk.
2.5 billion years from now, one of those satellite galaxies will collide with the Milky Way, infusing the Milky Way with more stellar material and altering its shape.
For all the drama that has beset the galaxy in its evolution, the major arms of the Milky Way are uncommonly symmetrical. The Milky Way may be a rare beauty in spiral galaxies.
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To put it mildly, the Milky Way is on the move. Our home galaxy is coursing through the cosmos at 2.15 million kilometers per hour. (Please fasten your seat-belt and observe the “no smoking” sign.)
The Shapely Supercluster is a galactic concentration 650 million light-years away that exerts a powerful pull on the Milky Way. That is not the whole story of why the Milky Way is bustling at such ferocious speed.
Behind the Milky Way, on the far side of the constellation Lacerta (the lizard), is a relative void. This vast patch of nada has a striking dearth of galaxies compared to the rest of the cosmic neighborhood. But somehow it is exerting a repulsive force, pushing the Milky Way on its way.
“The Shapley attractor is really pulling, but then almost 180º in the other direction is a region devoid of galaxies, and this region is repelling us. So, we have a pull from one side and a push from the other. It’s a story of love and hate, attraction and repulsion.” ~ Israeli cosmologist Yehuda Hoffman
“Galaxy formation history may be telling us something about the places in the universe where life can form.’ ~ Swedish astrophysicist Kambiz Fathi
At different scales, accretion disks of dust and gas are the cradles of galaxies, stars, and planets. Accretion disks are common because the coalescing force of gravitation is offset by angular momentum, forming a disk.
The growth of galaxies in the early universe was vigorous. Within just 3 billion years of galactic formation, there were already thousands of galaxy clusters.
The nascent universe was much smaller. Star density was 10 times greater than today. Each galaxy cluster contained hundreds of thousands of galaxies. Some were massive galaxies, with several hundred billion stars, formed by collisions of smaller galaxies.
Most of the earliest galaxies were elliptical, having many stars, but insufficient dust and gas to fuel organic expansion. The most massive galaxies are giant ellipticals.
The mass of a galaxy directly relates to the mass of its central black hole. Mass determines how fast a galaxy spins. Spin slows as a galaxy grows.
“Regardless of whether a galaxy is very big or very small, if you could sit on the extreme edge of its disk as it spins, it would take you about a billion years to go all the way round.” ~ American astrophysicist Gerhardt Meurer
Just 3 billion years after galaxies got going there were already spent elliptical galaxies: no longer forming new stars. In contrast, spiral galaxies, like the Milky Way, contain much material for star formation.
Young galaxies furiously create stars. The more gas a galaxy has, the more sparkling stars are ignited. A galaxy’s magnetic field nudges huge clouds of gas and dust into pregnant concentrations that give birth to stars.
“Through self-excitation, a magnetic field is created from virtually nothing, whereby the complex movement of the conductive plasma serves as an energy source.” ~ German physicist Frank Stefani
Massive cosmic magnetic fields pervade the universe and persist for billions of years. Small-scale fluctuations of astrophysical plasma create large-scale, persistent magnetic fields which shape the material dynamics of galaxies. Like rivers of energy, plasmas flow in a certain direction. There are also plasmatic counter-streams.
Like water, plasmas have abiding internal structures which have been observed during star formation and star death. Supernovas are tremendous plasma producers.
Plasmas also pulse on a galactic scale. The coherent self-organizing of plasma among seeming chaos produces the energetic seeds from which galaxies and star systems are born.
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A massive black hole forms and builds a galaxy from its quasar emissions. The mass of a black hole in a galaxy’s center typically ranges between a million and a billion times that of the Sun.
Galactic formation dynamics act as a thermal gyre: pulling in dense, cold gas, and ejecting hot gas back into intergalactic space. A galaxy ends up with a fraction of the raw material it processes.
Galaxies grow from the inside out. Most galaxies have a bulge at their center, as does the Milky Way.
Black hole growth and star formation typically go together. If the nearby environment of a black hole is gas poor, gas accretion is slow. Radiation emission is correspondingly low.
Black holes at the heart of a galaxy not only spin, they also move across their host galaxy, altering galactic dynamics. The speed at which a black hole spins distinctively affects the spacetime around it: another factor in the gyre of a black hole.
Galactic gyres follow fluid dynamics, with viscosity something of a mystery. The level and nature of turbulence determine what stays and what flies away. In a galactic butterfly effect, small disturbances can affect stabilities and mass transfers at a much larger scale.
The structures and sizes of galaxies vary. Galaxy range from dwarfs of 10 million (107) stars to giants with a hundred trillion (1014) stellar lights.
Galaxies typically spread from 1,000 to 100,000 parsecs in diameter, separated by millions of parsecs (megaparsecs) of intergalactic space. The space between galaxies is a tenuous gas, with less than 1 atom per cubic meter.
A parsec is an astronomical length unit: about 3.26 light-years, just under 31 trillion (3.1 x 1013) kilometers (km). A light-year is ~9.461 trillion km: how far light can travel in a vacuum in 1 Julian year (365.25 days).
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“Big galaxies are crashing into other big galaxies to make even bigger galaxies.” ~ American astrophysicist Adam Bolton
Galaxies are attracted to each other under the influence of their gravity. Galaxies may collide, merge, or pass through each other. Large galaxies grow by absorbing smaller ones.
Even with no major collisions, the interstellar medium of gas and dust interact, triggering bursts of star formation. Collisions gas up galaxies, further triggering star birth bursts.
Stellar collisions can severely distort the galaxies involved, forming oddly shaped galactic artifacts, such as tail-like structures. Stellar orbits about a galaxy can be thrown off course.
Relatively passive pass-throughs between galaxies can leave lasting connections. Tendrils of cold hydrogen gas can be pulled from one galaxy toward another, creating a tenuous bridge between the two.
“The cosmic web formed very early in the history of the universe, starting with small initial fluctuations in the primordial universe.” ~ American astrophysicist Behnam Darvish
Galaxies are not isolated. They are instead interactively distributed via a cosmic web of gravitational filaments.
“The filaments are like bridges connecting the denser regions in the cosmic web.” ~ Behnam Darvish
Where intergalactic gravitational filaments meet are dense galactic clusters of galaxies, which began as modest fluctuations away from homogeneity. Galaxy distribution ultimately reflects subtle variations in the early universe.
These galactic filaments are themselves dynamic gyres, growing as tendrils, sprouting new galaxies in a variety of formations and with different growth patterns. By this, galaxies are organized in a hierarchy of associations.
Filaments engender interaction between galaxies, thereby enhancing star formation. This dynamic began early and continues today.
“Galaxies flow in currents, swirl in eddies and collect in pools.” ~ German cosmologist Noam Libeskind & Canadian astronomer Brent Tully
Clusters of galaxies form superclusters comprising tens of thousands of individual galaxies. Superclusters fit into galactic sheets and filaments that fly through the immense voids that comprise 90% of the volume of the universe.
Galactic superclusters are the largest known arrangements in the universe. Even larger structures are suspected.
The Milky Way lies within the Laniakea supercluster, which encompasses 100,000 galaxies stretched out over 160 megaparsecs (520 million light-years). Laniakea weighs roughly 1017 (a hundred quadrillion) solar masses; 100,000 times that of the Milky Way.
Laniakea is an elaborately organized gyre. Within it, galaxies flow inwards toward a gravitational valley called the Great Attractor. Laniakea is Hawaiian for “immeasurable heaven”; an oddly inapt name in that the supercluster has an approximate measure and is a relatively small part of a much larger universe.
Large Quasar Groups
As quasars are the bright half of galactic formation (black holes being the shadowy opposite), astronomers refer to an oversized galactic cluster as a large quasar group. Owing to the dynamics of black hole affiliation, quasars tend to clump together.