A Chart of ACRONYMS for most of the equipment, devices, telescopes, organizations and related COSMIC topics is provided for all previous parts including this one, PART 7. The ACRONYM is provided so it can be used to simplify the text and identify the PART where it was introduced in case someone wants to return to that discussion.
THE YOUNG STARS
For the first time, astronomers, using the combined capabilities of the CHANDRA X-RAY OBERVATORY, (CXO), an X-Ray emission detector, and the HUBBLE SPACE TELESCOPE (HST), an optical telescope, and the SPITZER SPACE TELESCOPE, (SST), for infrared emissions, have imaged young stars outside the MILKY WAY GALAXY. (Astronomy, September 2013, p. 74)
The stars of interest belong to a cluster designated NGC 602. Most objects are given a catalogue number of some sort for identification purposes, generally the first two or three letters refer to a catalogue name. The NATIONAL GENERAL CATALOGUE (NGC) is one often referred to, and all of its objects are prefixed with the NGC letters and then the objects number in the Catalogue. (Murdin pp. 248-249, 255) Other catalogues and lists will be mentioned from time to time. The most common one is named after Charles Messier, they are the M-series, who in 1784 listed 103 nebulous objects, later many were found to be objects outside our galaxy, and gave them a M-number. (Murden p. 248; Whitney p. 60)
NGC 602 is a recently born nebula and star cluster that lies in the so-called "Wing" of the SMALL MAGELLANIC CLOUD (SMC), one of the small satellite galaxies near the MILKY WAY, part of the LOCAL GROUP of galaxies and objects. (van den Bergh pp. 142-143) Looking at the image, which looks like a burst soap bubble, there is, in the center, a cluster of very bright blue new stars. The radiation pressure from these intensely hot stars has created a shock front which has ionized the gas of the bubble causing it to glow and expand out ward like a balloon, to form a very large irregular circle or broken bubble of colored gases. The bubble or object is a nebula and is listed as N90. There are many of these birthing areas for stars. Their study enables one to interpret what is being found at great distances.
The image they obtained is a unique multi-wavelength image , combing the results of all three of the large instruments. Eventually, in such tasks, they will now be able to add the capability of the sub-millimeter telescopes, such as ALMA, to get detail data on the hydrogen clouds and streams in such a system, and for additional information they will use other specialized telescopes and detectors. In the meantime, they have produced an extraordinary image provided on page 74 of the magazine ASTRONOMY, for September 2013.
The HST results from optical emissions are shown on the image of the nebula, or bubble, in red, green and blue, helping to outline the nearly spherical structure of the nebula. The CXO, or X-Ray emissions detected are shown on the image in purple and fill the inside of the bubble and surround the newly born bright stars. Recall that the radiation pressure created a shock front that has expanded the bubble and causing the inside and outside of the nebula to glow. The SMC infrared emissions show up on the image as red features, streams of gas the shock front is pushing outward and folding up and packing the gas on the rim areas.
It is the cluster of bright new stars in the center of the nebula that is the source of the new X-Ray discovery. The star cluster and its surrounding nebula lie in the Wing, a wisp of stars and nebulosity, that connects the SMC to the Magellanic Bridge of stars and a stream of neutral hydrogen between the SMC and the LARGE MAGELLANIC CLOUD, (LMC), (van den Bergh pp. 92-94; 137-138), all caught up in the tugging of the gigantic MILKY WAY GALAXY, which is gravitationally pulling the small galaxies, streaming its stars and sucking them into the arms of the spiral galaxy. In time the two small galaxies will lose their identity and vanish into the giant Milky Way as streams of stars. The stars are so far apart there will be few if any collisions. (Astronomy, p. 74, September, 2013) One stream of stars is not too far from earth.
THE MILKY WAY- A BARRED SPIRAL GALAXY WITH A BIG BLACK HOLE
The MILKY WAY, our galaxy, our residence in the universe, is a barred spiral structure. Instead of a nearly circular dense area of stars around a massive black hole, the circular are or center, is elongated to form a sort of bar. Most of the spiral arms originate at the ends of the bar, the bar creates a more massive core of a galaxy and is much greater in density and collection of stars. For decades astronomers believed the Milky Way Galaxy was a garden-variety spiral galaxy with a nearly spherical central area. But the last four years have changed things. Since 2009, a team led by Ed Churchwell and Robert Benjamin of the University of Wisconsin investigated the galaxy with the SPITZER SPACE TELESCOPE (SST). Starting in 2003, the team have mapped the galaxy accurately for the first time, revealing that the MILKY WAY is a barred spiral of type SBc. (Eicher p. 9) For years the slowly accumulating work of Dutch astronomers was piecing the together the nearby portions of the spiral arms of Sagittarius, and Perseus, and in between them the Orion-Cygnus spiral in which the sun is located. The main spiral arms are less than 5000 light years wide. (Murdin p. 67) I was using some of the early released data in my classes, but a fully developed picture had not as yet been completed. It would be ten more years before detail would be compiled to provide a clearer picture and image of our magnificent BARRED SPIRAL GALAXY . See the image provided.
In the center of our barred spiral is the 6 million solar masses Black Hole, called Sagittarius A*, it was first imaged by CHANDRA and NASA/MIT/PSU more than ten years ago, and among the sources carrying the image was that of Melia. (Melia p. 123) Sagittarius A*, now considered our Black Hole, appears in that early image as a circular white dot created by the emission of X-ray and heat generated activity in the central region. There are eight additional white dots on the image. One, about a fourth the size of the Black Hole dot, is only about a diameter (of the Black Hole dot) distance to the right from the Black Hole. The eight other objects and the Black Hole are embedded in a large gaseous mass about the size of ten diameter distances of the Black Hole. The gaseous mass is irregular and globular and is red in this early image, and therefore somewhat cooler than the Black Hole. The gaseous mass is being drawn out and around the black hole, preliminary data on this aspect seems to indicate the Black Hole is about ready to dine on the gas. A huge panorama of a Black Hole in the act of sucking in by gravity a mass of matter is going to be stunning to watch and watch it they are. The inner region or center of our galaxy containing these objects is about 10 light years across and radiates X-ray. This energy, because the gas and objects are heated to millions of degrees by shock waves from supernova explosions and colliding winds from the young massive stars in orbit around the black hole, lights up the whole region. Some 15 to 20 stars surround and circle in distorted orbits around the BLACK HOLE and produce energy and light winds that collide and form a tessellated pattern of gas condensations, some of which are captured, or are going to be, by the Black Hole and subsequently accrete toward it. Several of the wind-producing stars are visible to the right of images taken of the BLACK HOLE. (Melia p. 126) The rotation in different orbits of these near- by stars will eventually become so distorted and elliptical by the gravity pull of the Black Hole that they will someday be on the menu as a snack or major course for the BLACK HOLE. On the 16 of September 2001,Nature published an announcement at a press conference in Washington D.C., that Fred Baganoff and his collaborators had monitored an event by CHANDRA . There was an unusual flurry of activity coming from the direction of Sagittarius A*, our Black Hole. It was over in a couple of hours, but while it lasted, about 45 times as many X-rays were being emitted per second by the Black Hole, and being detected, than when the Black Hole was quiet. During the flare of radiation, the X-ray output dropped abruptly by nearly five times in less than 10 minutes and then recovered almost as quickly. An abrupt change in the X-ray emission of Sagittarius A* over 10 minutes means that the compressed, hot, radiating gas could not have been distributed over a region larger than the distance between the Earth and the Sun, the distance traversed by a light beam during that interval. This gave essential information on how large the Black Hole is and what space it occupies. (Melia pp. 148-149) The radius of Sagittarius A*s event horizon is only about 10 times smaller. It had enjoyed a quick snack, mostly of gas. It places the mass of 6 million solar masses into a region the size of a sphere less than the distance from the earth to the sun, a sort of ten second radius. This would mean the Black Hole occupies a region at most 20 times larger than that predicted for our black hole by general relativity. This indicated that future high-energy missions, such as intended for the MICROARSECOND X-RAY IMAGING MISSION (MAXIM), with an ultimate resolution 3 million times better than of CHANDRA, and other future instruments would be able to probe the nature of space and time at mere threads above the event horizon of a giant black hole. (Melia pp. 146-148) Black Holes can now be recognized, measured and their mass determined anywhere. Whenever it feasted on gas or stars there would a scream of resistance and then of obliteration as the consumption took place. Besides the massive black hole in the center of galaxy, there are nearly 50 other small black holes throughout the galaxy due to star collapse and there may be a smaller companion black hole near the center area.
In its fatal progress from the point of capture by the Black Hole, the gas, debris, plasma or small or larger star, is compressed l million billion times. As it crosses from one level of high density to the next during its descent, which is cannot resist, its temperature correspondingly rises. By the time it has reached the final layer just before disappearing through the membrane of no return, its temperature will have risen to 100 billion degrees or more, that is 10 million times hotter than the surface of the Sun. That is why they see a glow surrounding Sagittarius A*, and why its size changes with color as the temperature of the object on the menu rises. The closer it gets, the more energetic is the radiation it produces, meaning that the object emits bluer and bluer light as it approaches its devourer, or tomb. What happens to it then is open for debate! (Melia p. 126) The inner two light years or center of the Galaxy is a very hot and active place. In addition to CHANDRA, Most of this early data was collected by COMPTON GAMMA-RAY OBSERVATORY (CGRO), which could detect gamma-rays flowing freely over very long distances. It did for gamma-ray astronomy what the HST did for optical and infrared astronomy. It obtained images sensing radiation with more than 40 million times the energy of visible light. Now light produced by some of the most exotic and mysterious objects in the universe can be detected and thus, observed. (Melia p. 29) CGRO was a bus sized detector which provided a look at the gamma-ray universe, it plunged into the Pacific Ocean during the summer of 2000. It is now or will be, replaced by a whole series of more sensitive instruments. The study of results is on-going, when received they will be summarized and included in future web site entries.
A Black Hole really seems like a hole in space. Most Black Holes form when the core of a massive star collapses crushing itself into oblivion. Black Holes come in different sizes. The smallest has a mass about three times that of the sun. Every galaxy will have many of these small ones. The biggest one discovered so far was M87 with its immense mass equivalent to 6 billion solar masses. The big black holes at the centers of galaxies probably form by swallowing enormous amounts of gas and stars over time. One of NASA's spacecraft, confirming at least 50, has found thousands of Black Hole candidates in the MILKY WAY and other areas within the MILKY WAY may host many more. The nearest one of the small Black Holes is about 1,600 light years away. But not near enough to do much damage. They represent the remnants of collapsed massive stars. (Aguilar p. 114) The debris they leave behind host the heavy elements necessary for an earth.
Galaxies are being classified in some detail, and as more data is obtained from the dozens of new and future instruments, their classification will change. An early classification is provided by Ferris with excellent images as examples of each type. (Ferris pp. 81, Fig. 7) He charted four categories: l. ELLIPTICAL GALAXIES, from circular to elongated; EO to E5; 2. SO GALAXIES, SO to SBO; 3. SPIRAL GALAXIES, Sa to Sd; 4. BARRED SPIRAL GALAXIES, SBa to SBd. Our galaxy falls in category 4. A Barred Spiral, type SBc. Refinements made on this early classification, which goes back to E. Hubble, will be provided as galactic systems are discussed in future entries to this Web Site. Images that are similar to our galaxy with the development of a bar, ...include such spirals as M101-NGC5457 p. 82 Fig. 45; NGC3992 p. 92 Fig 53; M83- NGC5236 p. 94 Fig. 56, (Ferris pp. 81-94) , and many more.
Unlike a pure spiral, such as Ferris had imaged, that approximates our galaxy (Ferris p. 82 Fig 454) we now know that the Milk Way is a barred spiral with two arms, and four prominent spurs, of type SBc. (Eicher p. 9; Ferrris p. 81) The Milky Way is a highly flattened disk, due to the rapid symmetric rotation about an axis perpendicular to the plane, and embedded in a tenuous, more or less spherical halo, or corona, of very low luminous stars, gas, and other objects, that stretches out with a diameter in excess of 400,000 light years. (Bok p. 35) The spiral arms are outlined by O and B type stars and by bright and dark nebulae. At the center of the disk is a dense nucleus, composed mostly of older stars, but about 100 light years thick in the central plane . Lindblad and Oort recognized the rotation of the galaxy as early as 1926. Given the present age of the universe of nearly 14 billion years, the galaxy may have rotated at least five times. The sun may have made its first trip around the galaxy, and the earth may be on its fifth the trip. See below for more on the Milky Way.
The sun is moving around the galaxy at about 220 kilometers per second, (Bok p. 152) following the path of the yellow circle shown on the map of the MILKY WAY GALAXY . The yellow circle also defines the HABITABLE ZONE, which is a narrow zone less than 5,000 light years either way of the yellow line. Planets in that zone would, if they get nearer to the center of the galaxy, the radiation would be too much, and if they were too far out it would be too cold. Life as we know it is confined to this HABITABLE ZONE. More primitive life forms may exist in extreme conditions closer to the center or farther out, but as will be observed in future PARTS to this series, the parameters for life as we know it are very restrained and proscribed.
DESCRIPTION OF THE MILKY WAY AND IMAGE
As one can see on the MAP of the MILKY WAY GALAXY , our galaxy has a strong central bar, called the LONG BAR, emanating from the hub of the galaxy, which then gives rise to two prominent spiral arms: One is the Perseus Arm coming off the southwest (lower left) end of the LONG BAR. Most maps, images and so forth are generally oriented with North at the top. In the case of the universe, North is arbitrary and merely permits us to organize activities and observations by defining a point of observation and direction or orientation of those observations. Look close at the Perseus Arm, it splits with a small forked arm curving inside the arm closer to the LONG BAR, it is called 3b. Orion-Cygnus, generally named after stars or constellations, or nearby nebula that are in the arm. The Perseus Arm continues out to an area, near its end, of old red stars. Some of the red patches on the MAP are huge nebula and birthing areas for new stars; some only a million years old. So the arm tells us something about the age of the spiral development . There will be more complete discussion of the Perseus and other Arms in a future presentation and how they were mapped. Note that at the northeast end of the Long Bar the most important arm or spiral, named Scutum- Centaurus, it also originates from and at the end of the LONG BAR. It then circles out and around nearly 360 degrees, its band of stars and nebula somewhat wider, about five light years wide, than the Perseus Arm. The 2b. Orion-Cygnus spur splits off of the Perseus half way around the wrap of Perseus and fades to fewer stellar objects beyond where our SUN is located. Recent work on the location of our SUN, not shown in this picture of the Galaxy, shows more stars in a line arcing back to the PERSEUS arm, forming a definite arm between the Sagittarius Arm and the Perseus Arm called the LOCAL ARM. (Astronomy October 2013 p. 18) They are constantly working on the Galaxy and this picture will change in the future as even more detail is obtained. But it is the best now available and an immense improvement over the earlier understanding of our galaxy. In the SUN's orbit around the galaxy it passes through four or more arms of the spiral. A great deal more will be said about this in future PARTS. The 2a. Carina- Sagittarius arm is a tiny arm or string of stellar object, originating between the Perseus and the southwest end of the Long Bar, it circles around between the Orion- Cygnus Spur and extends out in a long stream of stellar objects fading out south or on the bottom, outside the 2. Scutum Centaurus Arm. Another spur is linked to the Perseus arm a quarter of the way around its wrap and extends outside the Perseus Arm to the vicinity of 1a. New Outer Arm. It extends for a long distance as a stream of stellar objects to an area west and beyond the l. Perseus, northwestern extension. Another small and thinly populated arm, the la. Norma originates nearer the northeast end of the LONG BAR and circles around between the l. Perseus major arm and the denser 2. Scutum-Centaures arm. There is a unique feature in the 1a Outer arm, note in the southeast or lower right the strange Y looking feature, a zwego (yoked) feature that zigs to the left with a small arm and very low density stream of stars extending outward and may, as studied further, link up with the extension of the 2 Scutum-Centaurus Arm. (Eicher p. 9)
The solar system lies conveniently tucked into the edge of the Orion-Cygnus Spur, the LOCAL ARM, some 27, 700 light years from the center of our galaxy. (Bok p. 152) The overall diameter of the galaxy's bright visible disk is more than 120,000 light years. Inside the galaxy's nucleus lies a dormant supermassive black hole, discussed above and below. (Eicher p. 9)
ACTION AT THE HEART OF THE MILKY WAY
Observations made by the EUROPEAN SOUTERN OBDSERVATORY VERY LARGE TELESCOPE (ESOVLT), in Chile, were made available and presented on17 July 2013. An immense gas cloud several times the mass of Earth has started its death spiral around the supermassive Black Hole at the heart of the Milky Way. The gas cloud, called G2, (Gas clouds in the center area are numbered) is swinging and stretching around the Black Hole. Extreme gravitational forces are expected to rip apart the cloud in the coming months . (go.nature .com/3kpqzj) (Cosmic Gas Guzzler, Nature Vol. 499, 25 July 2013) There such events or action in the center of the galaxy occurring every year or so. (Whitney p. 285)
SUPERMASSIVE BLACK HOLES
There is a correlation between a supermassive black hole's mass and the stellar content of its host galaxy's bulge. In some galaxies, such as spirals, the bulge is smaller, round and confined to the center, while giant elliptical galaxies are essentially all bulge. Elliptical galaxies seldom have a Black Hole, they can be much larger in size than spirals, some are as large as to have a population of ten thousand million stars. They are seldom ever round, mostly distorted spheres. (Ferris p. 97) There are several ways to measure the amount of stars in the bulges of galaxies. l. Measure the light from the stars. 2. Determine the mass of the bulge, because it is mostly stars. 3. Measure the speed of the random motions of stars due to the bulge's gravitational attractions, called the velocity dispersion," which has the tightest correlation." They have taken and plotted the relationship of mass and stellar relationships and this correlation seems to correlate well. But by whatever method, the more stars in a galaxy, the larger the black hole. This correlation may be due to "quasar feedback." In the model, when galaxies merge, and they merge all the time, our galaxy is the results of numerous mergers, the evidence is piling up on events with streams of stars throughout the galaxy exhibiting features that could only be the results of mergers. Mergers were probably much more so in the early history of the universe when everything was closer together.
The larger central black hole swallows a lot of gas, as the material funnels toward the black hole, as described herein, friction and radiative processes cause it to glow as a bright "quasar." The quasar (quasi-stellar object) shines until its powerful winds and jets heat up and/or expel all the gas in the galaxy. Gas is the main substance from which new stars are created, if driven from the galaxy by whatever means, then the galaxy can't make any new stars or feed the black hole. then the black hole stops growing until it, if it can, by gravitational attraction draw in distant stars from the bulge of the galaxy. Without food for its maintenance, the Black Hole will eventually evaporate through the expenditure of its mass in generating gravity field forces and magnetic fields energy dissipation. Black holes are smaller than expected based in some galaxies based on the amount of stars in their bulges. In the model the present interpretation is that such a galaxy may never have gone through a quasar phase. (David Irvin page 34, Astronomy September, 2013) But, as they continue to study the evolution and development of galaxies from the earliest events of the BB that led to star formation and then primitive galaxies they will develop a clearer picture of the whole scheme of things and answer more questions.
We can't see it with any of our instruments as yet. We don't know what it is. Dark Matter is the largest cosmic mystery we have to solve. It plays an inordinately large role in cosmology today. Theorists given to making the most of information being gathered but realizing that at any time revealing new information could change everything-and it does, put the best interpretation they can into the Standard Theory, the LAMBA COLD DARK MATTER MODEL (LCDM, see PART 4, p. 2 and PART 8), the possibility that the mysterious MASS called DARK MATTER, constitutes about 85 % of the mass of the universe. The best estimate for the moment is that this mysterious mass also constitutes 26.8 % of the universe's total energy. Understanding and identifying the early forms of energy are going to play an important part in defining the Creation event (CE). It will be interesting to see how these numbers hold up. At any given moment in any science, the best estimate is made and then efforts focus on how to confirm them or change them. Until they are crystallized as part of a law, theories do not have the dignity of being a fact.
Ordinary matter is composed of protons, neutrons, an d electrons, the stuff out of which stars, planets, buildings, bacteria and people are made. When the energy, temperature and pressure of the initial event was so high matter could not form and until it cooled down to permit initial matter, quarks and sub- atomic particles, that make up the protons and neutrons of today. That is the period of time that theorists are trying to get a handle on and some instruments now operating and new ones being built that will explore that interval in the history of the BB. In the future there will be discussions about what is considered plausible for that period of time until matter, as we now know it, formed. That matter accounts for only 4.9 % of the entire cosmos on the balance sheet of the content of the cosmos. (Kelly p. 46)
As galaxies were recognized in the 1930's it was also realized that galaxies and galaxy clusters would fly apart unless some form of concealed mass supplied added gravitational "glue" to hold them together. Speculation on what that '"glue" was has been going on for eighty years. The concealed or unseen mass was called Dark Matter. Now cosmologists and astronomers, scientists in general, ascribe an even grander role to DARK MATTER: It provides form to the visible universe and serves as a kind of unseen scaffolding or lattice, upon which the luminous celestial entities, stars, star cluster, galaxies, galaxy clusters and galaxy super-clusters are aligned and supported, like a string of lights at Christmas time, in the distance we presume there must be a wire or line they are attached or a tree or something they are hanging on, even if we cannot make it out. (Nadis p. 44) It is there! But what is it?
Detailed supercomputer simulations, guided by the most extensive galaxy surveys conducted over the past decades, and there has been more than 20 of them, (See Chart of LARGE SCALE STRUCTURE SURVEYS), suggest that the universe assumes the form of a vast network, referred to as the "cosmic web," composed of thread-like filaments that extend tens or hundreds of millions of light years. These filaments branch off in different directions, intersecting in places, called nodes, where clusters containing hundreds or thousands of galaxies are situated. The filaments act as giant channels that direct DARK MATTER, hot gas, even whole galaxies, drawn by the tug of gravity, toward dense galaxy clusters. For the time being these are regarded as the key structural elements in the cosmos. (see the GALAXY SURVEY MAP) Astronomers think the majority of DARK MATTER, is confined to these filaments. They realize that DARK MATTER is also resident somehow in galaxies and galaxy clusters. So, how do astronomers ever get direct confirmation that this elaborate filament foundation really exists. The surveys certainly show the arrangements of the clusters of galaxies and they are linked by some kind of connecting feature, so why and how are they congregated that way and can their history and development be unraveled? Theorists pondering the questions had tentatively concluded that the observational challenges were beyond technology current at that time. In the latter half of 2012, two independent teams of astronomers did the seemingly impossible. they found persuasive evidence of dark matter filaments in separate patches of the sky. Suddenly the idea that a hidden netting permeates our cosmos trapping normal matter some- what like a spider web traps unsuspecting insects, seemed a lot less fanciful and a lot more compelling. They got excited by certain features turning up on images of the survey.
COLD DARK MATTER
In 1984, the idea of filamentary structure rested on a theory called COLD DARK MATTER (CDM), which has held reasonably well since it was introduced. This model is COLD, because it consists of particles that move relatively slowly compared to the speed of light and DARK, because this inferred mass does not, as far as can now be detected, emit, absorb, or reflect any form of radiation, and no one knows what these particles are. While there are various ideas regarding the particles none are confirmed and none may be correct. A central premise of CDM is that this mass dictates structure formation in the universe. Perhaps slower material can clump more easily to form structure. Dark Matter seems to provide the footing, whereas normal matter merely follows its distribution.
ASTROPHYSICS REDSHIFT SURVEY
The first CENTER FOR ASTROPHYSICS REDSHIFT SURVEY (CFARS), with the technology then available, made a survey, which ran from 1977 to1982, of large scale observations. The ongoing ten year old Sloan Digital Sky Survey has greatly expanded these observations. These, and other surveys, revealed as we now know that galaxies are not randomly splayed out across the sky, but instead follow a web like pattern. Although many astronomers have been engaged in the effort to map galaxy distribution and understand galaxy formation, but only a handful are intent on seeing the dark matter web to which the galaxies adhere. Highly capable infrared space observatories yield great harvests of data deep in the infrared. The INFRARED ASTRONOMICAL SATELLITE, (IRAS), which began operations in 1983, harvested 10,000,000 far-infrared sources in its all-sky scanning survey, bringing the study on galaxies, dust-shrouded quasars, and debris disks around stars, into focus. Ten years later ESA'S's INFRARED SPACE OBSERVATORY (ISO) added deeper levels of mapping and spectroscopy, with results still appearing in the literature. Then steps were taken with deep-infrared astronomy. That was ten years ago, equipment planned then has been constructed, used and replaced with newer more sensitive instruments on the planning board. (Keel pp. 216-217) These included CHANDRA X-RAY OBSERVATORY (CXO), the 60-centemiter SPACE INFRARED TELESCOPE FACILITY (SIRTF), with its INFRARED ARRAY CAMERA (IRAC), and the GREAT OBSERVATORIES ORIGINS DEEP SURVEY , (GOODS), but more importantly, what was being added were the dramatically improved sensitive detectors. Some are now operational, others are planned for the next ten years, beginning with the fall of 2013 into the 2020's. These instruments and improvements on others, are crucial in tracing the cosmic star-formation history. Astronomers are determined to get answers. And they are getting them. As noted above, future studies of the universe will employ combinations of equipment and technologies to investigate various objects and substances that occupy the void. There will be massive collaborations between individuals, institutions and countries.
GRAVITATIONAL LENSING AND DARK MATTER
One technique being used to discern the underlying structure has been the use of weak gravitational lensing. This method takes advantage of Dark matter's gravitational influence. The general theory of relativity of Einstein states that any object with mass bends space and time around it. Heavier objects warp space-time more than lighter ones. So, if Dark Matter filaments lay between a distant galaxy and a telescope or detector, the filament's concentration of mass would bend the light coming from a more distant galaxy and the result and image would appear slightly distorted. The individual distortion for a galaxy would be too small to tell anything about the object that is doing the lensing. This approach is called weak gravitation lensing because an astronomer would have to look at the minute distortions in hundreds of thousands of galaxies, analyzing them statistically to get some inkling as to how mass is distributed within the lens or filament itself. The measurement is difficult. Even though filaments are extremely massive overall, they also are thinly spread, having a much lower mass density than the clusters to which they connect. When the sought after signal lies near the limits of detection, astronomers sometimes can be fooled into thinking they see things that may not be there. Two such observations in 1998 were discounted.
Undeterred, Jorg Dietrich of the University Observatory in Munich in Germany picked an exceptionally good place to look for a filament so he sifted through known pairs of massive clusters and found that only half a dozen were reasonable candidates for having any observable filaments. One these was a super cluster which included ABELL 223 NORTH, ABELL 223 SOUTH, and ABELL 222, which lie just below the equator in the southern sky. In the 1950's George Abell catalogued the most prominent clusters, observable at that time, according to their apparent richness and estimated distance. (Coles p. 73) The ABELL super cluster appeared to have a special geometry, two portions of the clusters connected by a filament, looking like a dumbbell. The filament, or connecting thread, between the two galactic clusters has a density of 100 trillion solar masses. (Nadis p. 48) It is immense. If the dumbbell is aligned so one can see its full length, then the filament will appear very diffused. Rotate the dumbbell and the filament will become more compact and the distortion from gravitation lensing will become greater. Light traveling to us from galaxies behind the filament therefore would have to pass through more mass accentuating the lensing effect. This was the case for THE ABELL CLUSTER. The clusters are less than 10 million light years apart, that would be the length of the filament, and are 60 million light years away. Again, light traveling to us from galaxies behind the filament would have to pass through more mass, accentuating the lensing effect. Dietrich's team managed to get the EUROPEAN SPACE AGENCY'S, (ESA) XMM NEWTON SPACE TELESCOPE, to make X-ray observations of the cluster pair. They observed a bridge of hot gas between these clusters. The X-ray data provided evidence of an underlying FILAMENTARY STRUCTURE, that was what they were looking for, and added incentive to see what weak gravitational lensing might reveal. The collaborators drew on archival data, which had been stored, untouched, since 2001, obtained from the 8.2-METER SUBARU TELESCOPE (ST), in Hawaii and scrutinized the subtle distortions in more than 40,000 background galaxies. (Nadis p. 46)
Previous investigators had not properly distinguished between distortion due to gravitation lensing and those due to imperfect detection technology. A study of many galaxies over a large swath of the sky requires multi Charge-Coupled Devices (CCD) detectors, but if the plane that formed when they were laid out was not perfectly flat, there would be tiny misalignments of the detectors and this would give optical distortions. Because they could not achieve such a perfect plane they had to make separate corrections, which had not been done before. After making these adjustments the team analyzed the combined distortion patterns from the thousands of galaxies in the survey and were able to determine the mass distributed within the filament connecting or bridging the ABELL CLUSTER. They were able to compute the filaments total mass at about 200 trillion times the Sun's mass. (Nadis p. 48) This was no small cluster and no small filament to make the barbell appearance.
Now they had to figure out how much of the total was ordinary matter and how much was DARK MATTER. From the XMM-NEWTON data they obtained the X-ray luminosity of the hot filament gas. Luminosity is proportional to the square of the gas's density, so the team determined that hot gas constitutes no more than 9 % of the filament's mass. Stars and galaxies might contribute another 5-10 % of the mass, but between 81 and 95 % is DARK MATTER. The proportions were what the Standard Model called for. (Nadis p. 47) But they would need refinement and confirmation. Jorg Dietrich and his six co-authors published their results, after a three year review of the data, on line in NATURE July 4, 2012. They had observed and established a lensing signal, but also hot gas emissions, there was an over-density of everything in the same place, there they were -DARK MATTER, HOT GAS, GALAXIES. At least Dietrich was confident that it was real. Nick Kaiser of the University of Hawaii, a pioneer in probing dark matter's distribution through weak lensing, is also impressed, "calling the measurements difficult and clean. Detecting the filement was a "technological tour de force."" (Kaiser in Nadis p.48). In this area of observation some things were coming together, so it seems.
But of the cosmic web or filament and node structure is as vast and extensive as the observations are suggesting and theorists purporting it to be, meaning the DARK MATTER filaments and nodes should be ubiquitous, so others with the present and future instruments should be making comparable observations. In October 1012, Mathilde Jauzac of the LABORATOIRE d'ASTROPHYSIQUE de MARSEILLE (LAM) and the University of KwaZulu-Natal in South Africa and a team of eight co-authors published their find of another DARK MATTER filament. This one extends some 60 million light-years from the core of THE GALAXY MACS J0717.5+3745M, a massive cluster consisting of more than a thousand galaxies, a globular cluster, with at least three close-by associated clusters. (Nadis p. 48 with Ebeling's images) They are unlike the dumbbell style of the earlier observations. The MACS J0717 tendril does not appear to connect to another cluster, but the filament connects to something, involving the three nearby clusters (Nodes). Here the density is very low. As one moves away from the nodes where the clusters are immense, the density becomes so diffuse that they lose the filament and don't know exactly where it goes. They relied on high-resolution images of the cluster and its environs from the HUBBLE SPACE TELESCOPE and the SUBRU TELESCOPE, and the CANADA-FRANCE-HAWAII TELESCOPE, (CFHT).
"We didn't set out originally to look for a filament. We just wanted to make a mass measurement and couldn't help notice huge strings or streams of reddish galaxies sticking out." (Ebling in Nadis p. 48) They collected images of the cluster, they relied on gravitational lensing measurements to map the extent of the protruding filament and determined that it too is mostly composed of DARK MATTER, rather than luminous, matter. (Nadis p. 48) Now as observers visit similar regions there should be a proliferation of finds.
The filaments run between two clusters and other times where the filament is leading away it just goes out, but with clusters, nothing is static so they do not think it as a problem to see a cluster with something sticking out and not being able to trace that thread to the next cluster. Future observations by more sensitive instruments may make a difference. But one has to take into consideration, as Ebeling points out, that the observations now observed correspond to different periods of the evolution of large-scale clusters and their linking filaments of DARK MATTER. There could be a thin stream of galaxies or even bands of stars, extending out to make the link with another cluster. What they are recording now is what was there a long time ago. By now, the ABELL dumbbell, or pair, could have already merged into a single cluster, the MACS may well merge with a cluster pair, but we may never know. Ebeling's agenda now is to attach himself along with several colleagues, to the HST FRONTIER FIELD PROGRAM (HSTFFP) that intends to investigate three other galaxy clusters that have been glanced at, during the next couple of years, and depending on results, another two suspect clusters after that, "The purpose of this study is to focus on the cluster cores, not to search for filaments, but we'd like to look around the neighborhood if at all possible." (Ebeling in Nadis p. 49) And with new instruments it will be possible. In time results of work in progress now and in the immediate future will become available, they will be summarized in future entries to this web site. There are going to be a lot of PARTS to this series.
DARK ENERGY SURVEY (DES)
Jorg Dietrich, for his part, is anxiously awaiting results from the DARK ENERGY SURVEY (DES), set to begin during 2013, using the 4-meter VICTOR M. BLANCO TELESCOPE (VMBT), in Chile, which astronomers expect will see some 100,000 clusters, with thousands of galaxies in each cluster, most of which are not currently known. "This is the first time we are doing a survey of this scale in the Southern Hemisphere, where people haven't looked systematically before, and we're bound to turn up good places to look for filaments." (Dietrich in Nadis p. 49) In fact they are counting on finding them to advance the study of DARK ENERGY.
SUMMARY OF GALAXY SURVEYS 1932-2008
Maps of the general pattern of galactic clustering on the sky require systematic surveys of galaxies but avoiding getting too close to the galactic plane because of observational difficulties posed by interstellar dust within our Galaxy. The first survey of galaxies were initiated by Shapley and Ames in 1932 which catalogued 1250 galaxies. This was the first strong indicator of galaxy clustering. Later Zwicky accumulated a sample of 5,000 galaxies with the PALOMAR SKY SURVEY, (PSS). Then Shane and Wirtanen in 1967 made enormous strides resulting in the famous LICK MAP OF GALAXIES (LMG) , which showed a million galaxies and clear evidence of clustering in the form of filamentary patterns, large clusters and regions of very low density, and extensive voids. Progress continued with the AUTOMATIC PLATE-MEASURING MACHINE (APMM) and COSMOS, cataloguing two million galaxies in 1990. The HARVARD-SMITHSONIAN CENTER for ASTROPHYSICS (CfA) survey, made three dimension cut through the galaxies of the Zwicky catalogue. A large-scale map of the galaxy distribution was obtained by the QUEEN MAP, DURHAM, OXFORD and TORONTO (QDOT) team, including use of IRS for infrared detection, which contained 10,000 galaxies. Then with the advent of multi-fiber spectroscopic devices the LAS CAMPANAS REDSHIFT SURVEY, (LCRS) survey contained 25,000 galaxies, it was available in 1996. (see LCRS SURVEY MAP A survey of 250,000 galaxies using the APM data and the ANGLO-AUSTRALIAN TELESCOPE, (AAT), which was completed in 2002 and their data became available by a British-Australian consortium). In the US, the SLOAN DIGITAL SKY SURVEY, (SDSS) measured millions of galaxies finding that galaxies not only clustered, but that the clusters also clustered. With the so called SHAPLEY CONCENTRATIONS, (SC) in between the large clusters arranged around huge voids. (Coles pp. 73-75) Now the great SUPPER COMA CLUSTER and the great GALAXY WALL have been added to the mix. They have a problem of trying to explain the ascending clustering aspects of the cosmos and voids of all sizes some 500 million light years across, in the context of the expanding universe. (Coles pp. 75) The next 10 years will be very exciting.
ESA EUCLID AND DARK MATTER AND DARK ENERGY
ESA'S EUCLID, with NASA contributing, is a space telescope that will offer resolutions comparable to HST but over a far wider field of view--covering 15,000 square degrees, or roughly one-third of the sky, during its survey project--making it an ideal instrument for gravitational lensing measurement in general and searching for DARK MATTER FILAMENTS, (DMF) in particular. EUCLID is scheduled for launch in 2020. During the interim Dietrich will be involved in the DARK ENERGY SURVEY (DES), that will keep he and others busy for years. (Nadis p. 49) For many astronomers and cosmologists, penetrating the cosmos to the degree they wish will necessarily await the completion of instrument construction now in progress, or soon to be.
DARK ENERGY SURVEY (DES)
The DARK ENERGY SURVEY (DES), is scheduled to begin in September 2013. One of its objectives is to catalog some 300 million galaxies. Another objective the teams of observers will be engaged in will be to detect and study the shearing effects of weak gravitational lensing in the galactic clusters and galaxy data. Also, they expect DES will go on a filament hunt to find 100,000 galaxy clusters, and thus shed light on the DMF'S connecting them. (Nadis p. 49) All of this to understand more about DARK ENERGY and DARK MATTER. These DARKS will be discussed in future PARTS of this series. See below.
THE CONTENT OF THE UNIVERSE
Last spring, the ESA PLANK SPACECRAFT completed its ultra precise 15-month survey and census of the composition of the universe. (Powell p. 90) From the results Roen Kelly has compiled the most recent summary of the content of the universe. As noted above, just 4.9 % of the universe is ordinary matter which makes up most of what we are aware of, see and are made of, like stars, trees, bugs, bacteria and people. The rest of the universe is made up of the two DARKS. DARK MATTER, a form of mass that interacts via gravity but doesn't emit, absorb, or reflect light, it is 26.9 %, and DARK ENERGY, a mysterious something that opposes gravity, it makes up 68.3 % of the universe. (Kelly p. 46) These numbers will be updated as they change.
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