47. EXPANDING UNIVERSE

The future of the universe is a continuous and intriguent question, sofar without any definitive answer. But there many models giving more or less acceptable solutions.
The "collapsing model": which requires a strong density, much higher than the critical density, leading to a "big crunch", but that is in contradiction with all the data.
The "pure matter model" : requiring sufficient real matter in the universe, what certainly is not the case, it should lead to a rather constant expansion of the universe.
The "cosmological constant model": Einsteins' idea, based on the famous"vacuümenergy", it leads to a constant accelerated expansion of the universe. It means a more and more empty universe expanding for ever, an anathema for astronomers.
The "quintessence model":
The essential feature of this theory is the supposed dynamic of the quintessence field, in fact a quantumfield (scalarfield), what gives an acceptable explanation both for the inflation and the evolution of the universe, particularly for the fast expansion over the last billions years, including a solution for the difference in measured and calculated density. Anyhow, the theory requires the questionable Dark Energy (= vacuüm energy).
Another consequence of the theory is that there will be an ending to the condensation of matter, that is the creation of new stars and starsystems, the density of matter will continuously decrease and maybe the acceleration of the expansion will increase. But it is also possible be that with a declining quintessencefield new forms of radiation and dustforming evolve in creating and expanding “bubbles” of “empty space”, of which the envelopes absorb still more energy, what then can be the cause of the formation of new forms of protons and neutrons and perhaps, finally, stars and starsystems and perhaps life.
A nice predictive theory, but yet with many suppositions still to be proved.

46. EXPANDING UNIVERSE

All authors have as an established pattern always the Big Bang model assimilated in their theories. That model also comprises the Inflation theorie, the theory supposing a very fast expansion of the universe (within 10^-35 sec). In principle every cosmologist accepts that model.
It is worthwhile to underline that the idea many people have about the Big Bang, namely an explosion of dust in space from a specific point or something like that, is absolutely wrong:
What was before the Big Bang is unknown, but it is clear that the notion of time in the Planck - period (10^-44 sec) does not have any meaning, it is leading to a singularity at t = 0, where all quantities get infinite values, which is a horror for scientists.
To explain the situation in that first period there is a search for a theory coupling or integrating quantummechanics and relativity theory for which indeed stringtheory is the most promising at the moment.
In the model of the Big Bang after the creation of the universe, space and the distribution of matter therein is stricly bound: because of the tremendous high energy with very high temperatures there is no difference between fundamental particles, they have no mass and are converted in each other without problems. Just after a “phase transition”, to compare with condensation of vapour by decreasing temperature, massive particles are created with mass clotting together by gravitation forces. The inflationary expansion of the system with stars and galaxies means an expansion of space itself. The average density in space decreases and the distribution of matter forms no limitation to that space. In an “explosion” the fastest particles are moving to an empty space, in the Big Bang model particles fill space in an uniform way and expansion takes place from each point of that space. The expansion had little influence on the dimensions of galaxies and clusters, which were bound by gravitation, the space between the matter-objects has simply increased, to compare with plumcake: during baking the raisin dough will rise, there is no movement of the raisins with respect to the dough, yet distances between raisins increase because of the movement of the dough, the speed of the raisins with respect to each other is directly related to the quantity of dough between them.
Space expands “in the nothingness”, in the mean time material conglomerates are created, moving compulsary.
But as said before the Big Bang model involves also the "INFLATION" process: on the expected expansion a superfast expansion is superimposed.
The inflation theory implies that scalarfields cause the expansion in a very early phase of space evolution after the start of the Big Bang, in such a way that it may be considered to be an “explosion” (but is is not!) in a fraction of a second, that is within 10^-34 sec., resulting in an increase in size of 10^30!
Within the Planck-time: 10^-44 s, there was a situation that we still do not know or understand, A time t = 0 cannot physically exist because the infinite values physical quantities will get. An dark time so, of which the stringtheory states on the basis of mathematical considerations that you cannot even enter there, you simply will be sent back at the border, to say it that way, the sign of various quantities simply switches.
But let us assume a start with a very dense plasma at a very high temperature and a homogeneous radiation-dominated universe of unimaginable small size, which indicates that there is high, temperature-dependent potential-energy density, that large that it suggests a negative pressure, leading in a more or less natural way to a fast expansion.
During that expansion the potential energy decreases, transferring energy to the system.
Later on when matter is formed, temperature variations cause gravitational variations in matter density, from which in the long run objects are created nowadays observed by us on the firmament.
After the inflationperiod, that is after ~ 10^-35 s, there is the period of primordial nucleosynthesis, when from the original soup of elementary particles (quarks, gluons, electrons, etc.) protons and neutrons are formed, followed by the formation of the nucleï of light elements (He, Li, H), but then we are already a 100.000 year further in time, it is the time of “decoupling” or “recombination”. Radiation is yet hardly scattered and the photons get free way that is: maximum kinetic energy, the universe is “optically thin”. After this “last scattering” the CMB-RADIATION starts, the cosmic microwave backgound radiation.

We should realize that albeit that the original universe was very strong curved (three-dimensionally, the time-coordinate is usually not involved, but is certainly also curved!), we just see today a very, very small part of its “horizon”, such a small piece is suggesting a very flat spacetime compared with the related part of the original universe. (imagine the inflation of a balloon!).

45. FIRST STARS

The first stars may have 
lighted up the cosmos 
within 200 to 400 million 
years after the Big Bang, 
and then clustered together 
into what later became 
galaxies .

On November 2, 2005, a team of astronomers (including Alexander Kashlinsky, Richard G. Arendt, John Mather, and S. Harvey Moseley) using NASA's Spitzer Space Telescope announced the detection of near-infrared light that may radiated from the the very first stars and/or from hot gas falling into the first black holes more than 13 billion years ago . Based at NASA's Goddard Space Flight Center, the team captured a diffuse glow of infrared light six-months apart in Constellation Draco after the removal of light attributed to stars, galaxies, and artifacts of telescopic observation. The resulting near-infrared image shows a field of merging blobs of light that may have beem radiated by extremely massive Population III stars and/or superheated gas near black hole horizons within 200 to 400 million years after the Big Bang. Such a strong signal was detected that the first stars are deduced to be very massive stars, much bigger than those seen today. They may have been hundreds of times as massive as Sol, burning out in just a few million years but emitting vast amounts of ultraviolet radiation which was stretched out as the Universe expanded, leaving an infrared signature.

44. THE MICROWAVE SKY

The Microwave Sky
WMAP has produced a new, more detailed picture of the infant universe. Colors indicate "warmer" (red) and "cooler" (blue) spots. This new information helps to pinpoint when the first stars formed and provides new clues about events that transpired in the first trillionth of a second of the universe.


The CMB Angular Spectrum



The "angular spectrum" of the fluctuations in the WMAP full-sky map. This shows the relative brightness of the "spots" in the map vs. the size of the spots. The shape of this curve contain a wealth of information about the history the universe.

There is a "black" period between the inflation process and the start of CMB - radiation (see article 46). We call that period "DARK AGES", the period where stars and systems were born. Fortunately there is a very poor radiation: "spin-radiation" , in the radio-frequency region with some cm's wavelength, which is stretched by the expansion up to some hundreds of meters. That radiation can yet be used to investigate that period, albeit that we need antenna's of kilometers length!.
The expansion goes on and on, even in an accelerated way since the last ~ 7 billion years!
For stopping the expansion of the universe dark matter is not the answer, (if dark matter should consist of normally matter formed from elements it can only exist in very short supply, otherwise the limit of the critical mass will be severely exceeded). If we take all observed resp. calculated stardust and dark matter (as defined in article 37) together, then it is still only a fraction of the critical mass necessary, less than 30%.
Therefore there must be another source of density compensating for the great deficiency in required density. That is the reason for the introduction of the notion “DARK ENERGY”, an energy being “invisible” but contributing to the density of the universe in order to reach the critical density (energy = mass!) . That energy is not just fantasy, it comes out that when it is added as extra mass to the universe to explain the now observed ever increasing expansion it fills up exactly the 70% deficiency in density.

The universe has been created from a very hot and dense “prehistoric soup”, a plasma of electrons and positrons, of various sorts neutrino’s with their antiparticles and of protons and neutrons. Photons were strongly bound, escaping was not possible, but fluctuations in density occur, that is “quantum noise”. When the temperature decreased by super-fast expansion of the universe, those fluctuations were isolated and blown up into inhomogeneous areas of various densities, where gravitational forces had the final word at last.
The masses in the inhomogenities were enormous, equal to stars or even galaxies. So 300.000 - 400.000 year after the inflationperiod, when the temperature has dropped to about 3000 K, the original fluctuations became all “frozen" in as anisotropies, that is: photons therein had no longer any pressure effect, they are no more bound, moving more or less free through space after their last scattering.
Those free photons give a radiation phenomenon: the CMB : COSMIC MICROWAVE BACKGROUND - radiation, which presents the temperature differences between small areas on the firmament against a continuous background. The temperature differences are “frozen” acoustic oscillations, mathematically expressed in a “powerspectrum”, (see figure).
The first large-scale measurements of CMB by the Cobe-satellite show a very homogeneous universe, with many small spots of just a bit higher or lower temperature (1 on 100.000!) from which finally the larger structures in the present day cosmos were formed, such as galaxies.
The intensity of light emitted as CMB-radiation shows an frequency distribution analogous to the spectrum of light, that is emitted by a black box with T = 2.7 Kelvin. That spectrum has a wavelength distribution with a peak at ~ 2 mm.
Be aware of the fact that the CMB - radiation has shifted from the highfrequency area (gamma-rays) to the microwave area today by the expansion of the universe during 13 billion years.

CMB - radiation is everywhere present in the universe, so also around ourself: about 1% of the noise on T.V. - screens is determined by that.
Those areas with different temperatures form also the basis of the matter in the present day universe: stars and galaxies, because it is supposed that the resulting density-anisotropies grew by gravitation forces to the objects now observed by us.
This proces of gravitational attraction, causing the accretion of matter around the original small fluctuations, forming still larger structures, is called: the “gravitational instability model” for the formation of the structure of the universe.

43. SUPERRNOVA TYPES

A supernova is a stellar explosion which produces an extremely bright object that fades to invisibility over weeks or months. A supernova may briefly overshine its entire galaxy, It would take bilions of years for the sun to produce the energy output of an ordinary Type II supernova. There are at least two possible routes to their formation. A massive star may cease to generate "fusion energy" from fusing the nuclei of atoms in its core and collapse under the force of its own gravity to form a neutron star or black hole. It is the Type II supernova.
Alternatively a white dwarf star may accumulate material from a companion star until it nears its "Chandrasekhar limit" ( 1.2 - 1.4 sunmasses), then it undergoes runaway nuclear fusion in its interior, completely disrupting it. This the Type I supernova.

TYPE I Supernova:
This type is the brightest kind of supernovae. The companion star is often a red giant. The process is sometimes called: "stellar cannibalism": the white dwarf soak up the outer layers of the red giant, increasing its mass, raising the temperature near the center. At some point carbon fusion is born causing within a period of only a few seconds the integral temperature to raise to billions of degrees. Then the star explodes violently, releasing a shockwave while matter is ejected at speeds of 5 - 20.000 km/sec (3 % of the light speed). The energy released in the explosion increases the luminosity up to
~ 5 x 10^9 times brighter than the sun, that's what we observe then.

TYPE II sueprnova:
Stars much more massive, typically more then eight solar masses, evolve in more complex fashions. First hydrogen is fused into helium, releasing energy which heats the core providing pressure against gravitation forces. The very high core mass stimulates further contraction as hydrogen is exhausted, inducing helium fusion, carbon fusion and fusing to progessively heavier elements. In between the core collapses further until iron is produced, the most stable atoms in nature, resulting in no more temperature raising, no more counterpressure and a density in the core of more than one million kg per cm3! This happens within seconds. Because of the enormous mass the star core collapses by gravitation, an unstoppable implosion, and a neutron star remains. Once the collapse stops, the infalling matter from the surrounding layers rebounds, producing a shockwave that propagates outwards causing the outer layers to explode.

42. SUPERNOVA IN ACTION

August 30, 2006
X-Ray Burst Leads Scientists to See Supernova in Action
By David Biello
A star in a galaxy about 440 million light-years away released in a few seconds more energy than the sun will over the course of its entire lifetime, according to observations made on February 18. A high-energy jet of x-rays shot out from the doomed star's core and was captured by the Burst Alert Telescope on NASA's Swift satellite. The satellite relayed the information to astronomers on the ground, and within days a wide array of telescopes turned to the exploding object.
Meanwhile the other telescopes on Swift continued to observe the unusually long-lived burst; it lasted more than 30 minutes compared with other examples that flared up for only milliseconds. As the x-rays faded away, the star itself exploded in a spectacular supernova -- shown in the before (l) and after (r) images above -- the first such supernova to be observed from start to finish.
This supernova was half as bright as those typically preceded by such a burst, despite its emanating from a star 20 times as massive as the sun
Usually these events are not detected until after the supernova has brightened substantially. On this occasion, they were able to study the remarkable event in all its glory from the very beginning.

41. SUPERNOVAE

Astronomers using the NASA Hubble Space Telescope's Advanced Camera
for Surveys (ACS) have found two supernovae that exploded so long
ago they provide new clues about the accelerating universe and its
mysterious "dark energy." The supernovae are approximately 5 and
8 billion light-years from Earth. The farther one exploded so long ago the universe may still have been decelerating under its own gravity.


Type Ia supernovae are believed to be white dwarf stars that pull in
gas from an orbiting companion star. The white dwarf siphons off
mass until it hits a critical point where a thermonuclear "burning"
wave of oxygen, carbon, and heavier elements immolates the star in
a few seconds. The physics of the explosions is so similar from star
to star that all Type Ia supernovae glow at a predictable peak
brightness. This makes them reliable objects for calibrating vast
intergalactic distances

Information from studies of Type Ia supernovae confronted
astronomers about five years ago with the stunning, unexpected
revelation that galaxies appeared to be moving away from each other
at an ever-increasing speed. They have attributed this accelerating
expansion to a mysterious factor known as dark energy that is
believed to permeate the universe

Continued studies of supernovae will allow us to uncover the full
history of the universal expansion

40. DARK ENERGY AND SUPERNOVAE

Before discussing the expansion of the universe we should know what DARK ENERGY is, and also being aware of the importance of the observation of SUPER NOVAE , which are a very important sort of "stars", telling us about the history of the universe. Therefore the following articles will first give more information on Supernovae before we start telling about the expansion of the universe.

Scientists using NASA's Hubble Space Telescope have discovered that dark energy is not a new constituent of space, but rather has been present for most of the universe's history. Dark energy is a mysterious repulsive force that causes the universe to expand at an increasing rate. Investigators used Hubble to find that dark energy was already boosting the expansion rate of the universe as long as nine billion years ago. This picture of dark energy is consistent with Albert Einstein's prediction of nearly a century ago that a repulsive form of gravity emanates from empty space. Data from Hubble provides supporting evidence to help astrophysicists to understand the nature of dark energy. This will allow them to begin ruling out some competing explanations that predict that the strength of dark energy changes over time.

Researchers also have found that the class of ancient exploding stars, or supernovae, used to measure the expansion of space today look remarkably similar to those that exploded nine billion years ago and are just now being seen by Hubble. This important finding gives additional credibility to the use of these supernovae for tracking the cosmic expansion over most of the universe's lifetime. Supernovae provide reliable measurements because their intrinsic brightness is well understood. They are therefore reliable distance markers, allowing astronomers to determine how far away they are from Earth.
The snapshots above, taken by Hubble reveal five supernovae and their host galaxies. The arrows in the top row of images point to the supernovae. The bottom row shows the host galaxies before or after the stars exploded. The supernovae exploded between 3.5 and 10 billion years ago.

39. DARK MATTER PROOF

Hubble sees the graceful dance of two interacting galaxies
30-October-2007 Two galaxies perform an intricate dance in this new Hubble Space Telescope image. The galaxies, containing a vast number of stars, swing past each other in a graceful performance choreographed by gravity.A pair of galaxies, known collectively as Arp 87, is one of hundreds of interacting and merging galaxies known in our nearby Universe.
The resolution in the Hubble image shows exquisite detail and fine structure that was not observable when Arp 87 was first catalogued in the 1960ís.
The two main players comprising Arp 87 are NGC 3808 on the right (the larger of the two galaxies) and its companion NGC 3808A on the left. NGC 3808 is a nearly face-on spiral galaxy with a bright ring of star formation and several prominent dust arms. Stars, gas, and dust flow
from NGC 3808, forming an enveloping arm around its companion. NGC 3808A is a spiral galaxy seen edge-on and is surrounded by a rotating ring that contains stars and interstellar gas clouds. The ring is situated perpendicular to the plane of the host galaxy disk and is called a
ìpolar ring.îAs seen in other mergers similar to Arp 87, the corkscrew shape of the tidal material or bridge of shared matter between the two galaxies suggests that some stars and gas drawn from the larger galaxy have been caught in the gravitational pull of the smaller one.
The shapes of both galaxies have been distorted by their gravitational interaction with one another.
(News Release Number: STScl - 2007-36
Image credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA))

Such collisions gives us the possibility to study the famous, but mysterious "Dark Matter".

Is dark matter really existing?
Yes,it is!
This composite image shows the galaxy cluster 1E 0657-56, also known as the "bullet cluster." This cluster was formed after the collision of two large clusters of galaxies, the most energetic event known in the universe since the Big Bang.

These observations provide the strongest evidence yet that most of the matter in the universe is dark.
In galaxy clusters, the normal matter, like the atoms that make up the stars, planets, and everything on Earth, is primarily in the form of hot gas and stars. The mass of the hot gas between the galaxies is far greater than the mass of the stars in all of the galaxies. This normal matter is bound in the cluster by the gravity of an even greater mass of dark matter. Without dark matter, which is invisible and can only be detected through its gravity, the fast-moving galaxies and the hot gas would quickly fly apart.

This image is not a real photo, it is a computer simulation. The blue areas in this image show where astronomers find most of the mass in the clusters (mostly dark matter!!). The concentration of mass is determined using the effect of so-called gravitational lensing, where light from the distant objects is distorted by intervening matter. Most of the matter in the clusters (blue) is clearly separate from the normal matter and gaseous clouds (pink), giving direct evidence that nearly all of the matter in the clusters is dark.
The hot gas (pink) in this collision was slowed by a drag force, similar to air resistance. In contrast, the dark matter was not slowed by the impact, because it does not interact directly with itself or the gas except through gravity. This produced the separation of the dark and normal matter seen in the data. If hot gas was the most massive component in the clusters, as proposed by alternative gravity theories, such a separation would not have been seen. Instead, dark matter is required.
This really is a beautiful proof of the existance of DARK MATTER !!

38. STARDUST 2

Undersea corral? Enchanted castles? Space serpents? These eerie, dark pillar-like structures are actually columns of cool interstellar hydrogen gas and dust that are also incubators for new stars. The pillars protrude from the interior wall of a dark molecular cloud like stalagmites from the floor of a cavern. They are part of the "Eagle Nebula" a nearby star-forming region 7,000 light-years away in the constellation Serpens. The pillars are in some ways akin to buttes in the desert, where basalt and other dense rock have protected a region from erosion, while the surrounding landscape has been worn away over millennia. In this celestial case, it is especially dense clouds of molecular hydrogen gas (two atoms of hydrogen in each molecule) and dust that have survived longer than their surroundings in the face of a flood of ultraviolet
light from hot, massive newborn stars (off the top edge of the picture). The tallest pillar (left) is about a light-year long from base to tip. As the pillars themselves are slowly eroded away by the ultraviolet light, small globules of even denser gas buried within the pillars are uncovered.
The picture was taken on April 1, 1995 with the Hubble Space Telescope Wide Field and Planetary Camera 2. The color image is constructed from three separate images taken in the light of emission from different types of atoms. Red shows emission from singly-ionized sulfur atoms. Green shows emission from hydrogen. Blue shows light emitted by doubly- ionized oxygen atoms.
But don't think it is just a little "object", actually it is a very, very little part of an immense composition of clouds! See the picture below!

This majestic view taken by NASA's Spitzer Space Telescope tells an untold story of life and death in the above mentioned Eagle nebula, an industrious star-making factory located 7,000 light-years away. The image shows the region's entire network of turbulent clouds and newborn stars in infrared light. The color green denotes cooler towers and fields of dust, including the three famous space pillars, dubbed the "Pillars of Creation," which were photographed by NASA's Hubble Space Telescope in 1995 (right of center).
But it is the color red that speaks of the drama taking place in this region. Red represents hotter dust thought to have been warmed by the explosion of a massive star about 8,000 to 9,000 years ago. Since light from the Eagle nebula takes 7,000 years to reach us, this "supernova" explosion would have appeared as an oddly bright star in our skies about 1,000 to 2,000 years ago.
According to astronomers' estimations, the explosion's blast wave would have spread outward and toppled the three pillars about 6,000 years ago (which means we wouldn't witness the destruction for another 1,000 years or so). The blast wave would have crumbled the mighty towers, exposing newborn stars that were buried inside, and triggering the birth of new ones.


This photo shows the famous "Horsehead Nebula", which is situated in the Orion molecular cloud complex. The distance to the region is about 1400 light-years (430 pc).
This beautiful colour image was produced from three images.
There is obviously a wealth of detail, and scientific information can be derived from the colours shown in this photo. Three predominant colours are seen in the image: red from the hydrogen (H-alpha) emission from the HII region; brown for the foreground obscuring dust; and blue-green for scattered starlight.
The blue-green regions of the Horsehead Nebula correspond to regions not shadowed from the light from the stars in the H II region to the top of the picture and scatter stellar radiation towards the observer; these are thus `mountains' of dust. The Horse's `mane' is an area in which there is less dust along the line-of-sight and the background (H-alpha) emission from ionized hydrogen atoms can be seen through the foreground dust.
At this high resolution image the Horsehead appears very chaotic with many wisps and filaments and diffuse dust. At the top of the figure there is a bright rim separating the dust from the HII region. This is an `ionization front' where the ionizing photons from the HII region are moving into the cloud, destroying the dust and the molecules and heating and ionizing the gas.
Such structures are only temporary as they are being constantly eroded by the expanding region of ionized gas and are destroyed on timescales of typically a few thousand years. The Horsehead as we see it today will therefore not last forever and minute changes will become observable as the time passes.

37. STARDUST

It is true that looking to the Milky Way on a cloudness night you still will see black smudges, as if there are many interruptions. But that is the result of a lot of dust clouds, “stardust” as it is named, filling the emptiness a bit.
What’s that: stardust?
We should distinguish between gasses, stardust and dark matter if speaking of clouds in space.
Gasses consists of atoms and/or molecules.
Stardust consists of very small molecular structures of the order of 1 to .001 micron.
Dark matter enclose matter particles not radiating light or very little particles as neutrino’s but also minor black holes, but for the main part perhaps unknown exotic particles. So in fact all what has a certain mass but always extreme dim. The most important feature of dark matter is that it must necessarily contribute to the gravitation but without any mutual attraction what means no pressure effects as in a gas. The reason for supposing such matter is that e.g. movements of stars in galaxies can not be explained by gravitation from centres of mass or other visible objects, so other sources of gravitation are necessary.

Eta Carinae, located 10,000 light-years from Earth, was once the second brightest star in the sky. It is so massive, more than 100 times the mass of our Sun, it can barely hold itself together. Over the years, it has brightened and faded as material has shot away from its surface. Some astronomers think Eta Carinae might die in a supernova blast within our lifetime.
Eta Carinae's home, the Carina Nebula, is also quite big, stretching across 200 light-years of space. This colossal cloud of gas and dust not only gave birth to Eta Carinae, but also to a handful of slightly less massive sibling stars. When massive stars like these are born, they rapidly begin to shred to pieces the very cloud that nurtured them, forcing gas and dust to clump together and collapse into new stars. The process continues to spread outward, triggering successive generations of fewer and fewer stars. Our own Sun may have grown up in a similar environment.

36. SOMBRERO GALAXY

Our own galaxy should have been formed like this magnificent edge-on picture of the Sombrero Galaxy, having the size of the Milky Way. At a distance of 28 million ly and 82.000 ly wide it can be found in the constellation VIRGO. It is one of the larges Hubble mosaics ever assembled, the team took six pictures of the galaxy and then stitched them together to create the final composite image.The photo reveales a myriad of stars in a pancake-shaped disk as wel as a glowing central bulge of stars.

35. DISTRIBUTION OF GALAXIES

We know that the universe is filled up with clusters and superclusters like that of our own galaxy, the Milky Way, and its companions, containing billions and billions and billions of stars and much more!! Nevertheless here again: here is emptiness as well! It is estimated that the intergalactic distances in a cluster of galaxies is of the order of 10^24 cm = 10^6 lightyear!
Michael Strauss of the Princeton University constructed a map of far remote galaxies and it appeared that they were distributed in a very homogeneous way The whole projected surface of the sky has been covered with it, an effect of the two-dimensional reproduction, in reality the mutual distances were on average a million lightyear.

Space is really unimaginable empty, albeit that we have to be cautious with such statements: astronomers responsible for tthe Hubble-telescope just took it as read because of Christmas and oriented their telescope to an according to their opinion empty part of space and let it gone its way, all measuring. On New Years day, after 240 hours measuring, they went to the telescope interested in the results. It appeared that the picture was filled completely with more than thousand galaxies. If that would be valid for the whole universe, there should be more than 50 billion galaxies! Hubble had proved that the boundary of the universe lies very much farther than previously assumed and such a statement is still valid.

An empty universum it seems, but it does not mean that there is no mutual contact, for as already said about our Milky Way, starsystems can absorb other systems, being fully integrated. Collisions between galaxies occur continuously, of which the image above is a nice example. What happens then is giantic, an enormous intensive integration process characterized by the creation of many new stars, Such a process takes billions of years before finally one single, more massive, galaxy results.
The image shows two colliding galaxies in the constellation CANIS MAJOR at a distance of 140 million ly being completely integrated within a 500 million years.

Below a picture of one of the largest galaxies in the universum: the SPIDERWEB GALAXY (constellation HYDRA) on a distance of 10,6 billion ly from earth. In the middle of the "web" there is a very large black hole that captures its victims - smaller galaxies of the size of our Milky Way - in an inescapable net of gravitation. Hundreds of galaxies in this cluster at distances of hundredthousands ly and speeds up to hundreds km/sec. are absorbed by this "black widow".

34. A CHOICE OF ASTRONOMIES

The introduction showed the possibilities we have to get information about the stars and galaxies by observing objects at wavelengths other than those of visible light. Here follows another example:
Four views of the Andromeda Galaxy M31, at different wavelengths give an impression of he power of "multispectral astronomy". By visible light (4) the galaxy appears as a spiral, disk-like aggregation of stars with as bright central bulge.
Infra-red rays (5) come from the galaxy's dust clouds and cool stars, and the rings colour-coded yellow may show where new stars are forming. In radio emissions at 21 centimeters (6) the central bulge disappears. Instead what we see is the galaxy's outlying stock of hydrogen gas, which approaches us (blue) or recedes (red) as the whole galaxy rotates in a clockwise fashion. The fourth view is a close-up of the central region of the galaxy as seen by X - rays (7). Two of the scattered sources registered by the European EXOSAT satellite have flared up since the same region was observed by the American EINSTEIN satellite a few years arlier.

33. THE LOCAL GROUP

The Local Group is the group of galaxies that includes our galaxy, the Milky Way. The group comprises over 30 galaxies, with its gravitational center located somewhere between the Milky Way and the Andromeda Galaxy
The two closest galaxies to the Milky Way are called the Magellanic Clouds, which may be viewed as satellite galaxies to the Milky Way at a distance of a little less than 200,000 light years.
They are only visible in the Southern Hemisphere, but can easily be seen by the naked-eye and their brightest stars can be seen with binoculars. They are irregular galaxies and are much smaller than the Milky Way. Below the Large Cloud and a more accurate detail of it showing that is not exactly a "cloud".




Two galaxies are visible to the naked-eye in the Northern Hemisphere. The Andromeda Galaxy (M31) is a great spiral galaxy much like our own at a distance of about 3 million light years. This galaxy and the Milky Way are approaching each other with a speed of 119 km/sec and will collide with each other within 6.3 billion years.


The other galaxy of the local group that is visible to the naked eye is the spiral M33 in Triangulum at a distance comparable to that of Andromeda. It too is a spiral galaxy, but it is smaller than Andromeda and therefore is harder to see.


The Local Group moves with a speed of 600 km/sc to a point in space which is called: the"GREAT ATTRACTOR" in the constellation "HYDRA"