Astrophysical Directions by Michael Erlewine

 

 

In Astrophysical Directions
Introduction Coordinate Systems The Solar System The Solar Neighborhood The Galaxy Galactic Objects The Fixed Stars Star Clusters & Nebulae Non-Visual Astronomy External Galaxies Finder-Lists, etc.
Non-Visual Astronomy

 

  If Eyes Could See ...

  Introduction to Radio Sky

  Source Listings

  Radio Sources

  Pulsars

  Quasars

  Seyfert Galaxies

  X-ray

  Infrared

 

If Eyes Could See

The picture represents a panoramic view of how the sky would appear if our eyes were sensitive to radio waves rather than to light. Such a sight would go a long ways toward persuading astrologers as to the existence of preferential directions in space. While 'bright' discrete radio sources do stand out, the overpowering sense received from such a view is of the shape or body of our galaxy. There is no mistaking the galactic plane and the very heart, the center of the galaxy. It abounds with light. We could renew our sense of cosmic direction almost any night of the year by just walking outside.

 

Radio Map

 

Why we cannot see at visual frequencies the great light of the galactic center (GC) is very simple. At visual wavelengths, great clouds of relatively near dust intervene and block our view of the GC and of much of the galactic plane. These dark clouds, in general, prevent us from seeing more than a few kiloparsecs in any direction along the galactic plane. If we could see our galaxy from the vantage point of a neighboring galaxy, such as Andromeda, the center would appear filled with light.

Radio and infrared waves are able to bend around the particles of dust and to reach us. Only in recent years has it been possible to really "see" the actual center and structure of our galaxy. The radio maps of the heavens shown on these pages bring out the basic shape, body, and "aura" of our galaxy. Our dependence upon the EYE and optical frequencies results in an idea of the heavens as filled with an infinite number of points of light or stars, but otherwise relatively empty of form. The stars are 'set' in space, but most of us do not have much sense or feel for the fabric or matrix in which these stars are set. This shape becomes clear in radio maps and it is obvious that the great galaxy is the mother and home of the countless stars within it. Radio maps reveal that whole areas of the sky are filled with more light than others and that this light is graded, with a concentration toward the galactic plane and, of course, the galactic nucleus.

Until about 40 years ago, our knowledge of the cosmos outside the sphere of the Earth came almost entirely from the light we could collect with large mirrors and lenses. In fact "light" meant to us the eye and the visual part of the electromagnetic spectrum. The atmosphere surrounding the Earth is largely opaque (blocks) to most parts of the electromagnetic spectrum, although there are several transparent regions through which we may receive light and thus "look" out into space. These have been termed "windows," and the two most important windows are the optical and radio bands of the light spectrum. If we compare these two windows to the sound spectrum, the radio window represents a ten-octave span, while the optical window represents a little less than a single octave! There are several other bands of relative transparency in the Infrared range through which appear an almost entirely different set of stars and constellations. In fact, the range of energy between the extremes of the electromagnetic spectrum is so great that very different techniques have evolved for their study.

The atmosphere of the Earth serves to shield the Earth from much of the radiation reaching it from outer space, with the exception of the two windows in the visual and radio frequencies. In recent years man has removed the entire concept of windows by bypassing the atmosphere through the means of balloons, rockets, and other space vehicles. Beyond our atmosphere, the entire range of the "light" spectrum is wide open to our reception. In our lifetimes, we have experienced not only a fantastic increase in receptivity of light but have made active outreach beyond the atmosphere and Earth itself. We have stepped beyond ourselves into the space beyond and into ideas outside our imagination but a few years ago.

 

The Kinds of Light

 

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Introduction to Radio Sky

The map shown below was furnished through the courtesy of the Ohio State Radio Observatory.

 

Map

How are these different kinds of light generated? Radio waves, the longest waves, are generated by oscillating electric currents. The Short Wave or Microwave has a wavelength similar to that of sound through air. Infrared radiation (such as a hot stove) is produced by heated solids or the molecular vibrations and rotations in gases and liquids. Visible radiation is produced by rearrangements of the outer electrons in atoms. Ultra-violet light immediately joins the visible spectrum. X-rays have wavelengths of the approximate size of atoms and originate in the rearrangement of the innermost electrons in atoms. The gamma rays (?-rays) are the electromagnetic waves of highest frequency (and thus the shortest wavelength) and originate in the rearrangement of the particles within the atomic nucleus itself. Each of these different portions of the light spectrum presents a different view of our universe.

If we examine the heavens through the longer radio waves (several meters) the 'reading' we get is of a universe alive with radiant fog or haze in almost all directions. As we move to receivers of higher radio frequencies, certain shapes and forms begin to emerge or stand out from the general fog. The haze is thicker and more radiant in the direction of the galactic plane and is most bright at the galactic nucleus. The plane of our galaxy appears as a glowing archway across the sky. If we further increase the frequency, we can penetrate or see deeper through the fog and discover some discrete features. Now we find extended sources of radiation and at still higher frequencies point sources or 'radio stars' begin to show up that shine (at these frequencies) more bright than any other objects in the heavens, yet never seen by the human eye. At yet higher frequencies, we reach the Visual level of radiation, where bright point sources or stars are the main objects resolved. Beyond the visual window are the ultra-high frequencies of the x-ray and gamma ray wavelengths. These waves shine right through much of what we would call matter and indicate the sites of cataclysmic events and massive outpourings of energy beyond our comprehension.

 

Radio Map

 

Radio Map

 

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Source Listing

By far the greatest amount of radio energy reaching the Earth comes from the galactic plane and in particular, the center of our galaxy. In addition to these vast extended radio regions, many thousands of discrete or point sources of radio emission have been detected. These may be divided into three major qroups:

  • Objects within our solar system.
  • Objects within our galaxy.
  • Extragalactic objects.

 

Objects within our solar system.

Radio emission has been detected from the quiet and the disturbed Sun (flares, etc.), the Moon, Mercury, Venus, Mars, Jupiter and Saturn. Jupiter appears to radiate as both a thermal and non-thermal source.

 

Radio emission from within our galaxy

Emission within our galaxy, aside from background emission, consists of several types:

(A) Supernovae Remnants:
The most intense discrete radio source Cassiopeia A -- a non-thermal source. Cassiopeia A is believed to be the remains or remnant of a supernova detonation around the year 1700 A.D. (SN II type). The first identification of a radio source with an optical object other than the Sun was the strong non-thermal Taurus A with the Crab Nebula -- another remnant of a supernova explosion in A.D. 1054 (SN I type). Other strong non-thermal sources include Puppis A and the Tycho and Kepler supernovae remnants.

(B) Ionized hydrogen Clouds:
The interstellar hydrogen in our galaxy tends to be distributed in vast clouds. When a hot star is in or near one of these clouds, its ultra-violet radiation tends to ionize the cloud and causes it to emit (thermal) continuum radiation. The young and hot O and B stars are often the exciting sources. Well-known examples of thermal -hydrogen (H II) cloud radio sources are the Orion and Rosette nebulae, the Cygnus X source, and the North American, Omega, and Lagoon Nebulae.

(C) Neutral Hydrogen (21cm) Emission:
One of the more important results of radio astronomy has been the detection of 21-cm emission in the clouds of neutral hydrogen that occurs in the spiral arms of the galaxy. A tendency in the hydrogen atom toward a lower energy state results in the emission of radiation at a wavelength of 21 cm. Radio astronomers can detect this radiation and the resulting maps have provided us with the first real ppicture of the spiral arm structure of the galaxy.

(D) Flare Stars:
Radio emission has been detected from certain red dwarf stars that show occasional sudden increases in optical brightness or flares. Some of these stars are among those listed in the section on flare stars given elsewhere.

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Extragalactic Radio Sources

The space beyond our galaxy contains billions of-other galaxies and some of these are strong emitters at radio wavelengths. Extra-galactic radio sources are often divided into two groups: "normal" galaxies and "radio" galaxies. The great Andromeda galaxy (M.3,I) is an example of a normal radio galaxy as are the Large and Small Magellanic Clouds. Our own galaxy is also normal at radio wavelengths with an output of less than 1022 watts.

The so-called "radio" galaxies have a power output of a very different order. The second strongest radio source is Cygnus A (Cas A is the first),a remote galaxy located some 184 Mpc. in distance from our Sun, with a radio output of some 1038 watts! In the words of radio astronomy pioneer John D. Kraus: "The tremendous magnitude of Cygnus A's power may take on more significance if we note that the radio wave energy radiated by Cygnus A in just one millionth of one second is sufficient to supply all of the world's electric power requirements for all purposes (light, heat, mechanical work, etc.) at a million times the present rate for the next 10 million years." That is hot stuff!

Some other strong radio galaxies include Virgo A, Perseus , Centaurus A, Fornax A and Hercules A. Included elsewhere is a list of the stronger of the known radio sources within and without the galaxy. Some attempt has been made to indicate the nature of the radiating object in the notes column. The column marked "flux" will provide the reader with some idea as to the relative strength of the various radio sources. The values listed (under flux) are for 1400 Mhz, with the exception of those marked with an asterisk which are for 178 Mhz. The reader should keep in mind that some of these objects are very remote, while others are within out galaxy. The bibliography at the end of this series lists some of the source catalogs for these objects and readers are referred to the excellent book by John D. Kraus, Radio Astronomy, for further details.

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Pulsars

In the late summer of 1967 radio astronomers detected some very unusual signals consisting of short pulses of radio noise arriving at approximately one second intervals. It was at first thought that perhaps a secret Solviet space satellite had been detected, but it was soon clear that the mysterious pulsating radio source came from among the very remote fixed stars. Detailed study proved the source to be extremely precise and regular, more regular than anything ever observed in nature. The next theory was that we had detected signals from an 'alien' spacecraft or distant planet. By the spring of 1,968, three additional pulsating radio sources had been discovered and today over 100 such sources are known. In all cases, the periods of pulsation are extremely regular (note the number of decimal places listed in the table), with periods ranging from 1/30 of a second for the fastest to just over three seconds for the slowest.

Today it is considered a fact that pulsars (as these objects came to be called) are the final remains of ancient supernovae explosions, rapidly rotating neutron stars. These neutron stars (see section on Birth of Stars) have intense magnetic fields and radiation streaming out of the north and south magnetic poles and can account for the properties of pulsars, if high-speed rotation is assumed. One of the fastest pulsars (the Crab Nebula) his been observed flashing pulses of visible light on and off 30 times each second. The fastest and therefore youngest of the pulsars have been found at the sites of supernova detonations and it is known that these objects have high velocities. Astronomers therefore assume that the longer period (older) pulsars may have moved far from their original sites at the heart of a superhova. Pulsars are galactic objects of powerful intensity and extreme regularity. The column in the listing, "Period," will give you an idea of the degree of regularity for these objects.

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Quasars

The Black Hole may have captured the imagination of the general public as the most intriguing of the many new astrophysical concepts, but it is the Quasar (Quasi-stellar Object) that has most puzzled astronomers.

In 1960, optical astronomers found a star-like object at the position given for the radio source 3C 48 (Third Cambridge Catalog). The star-like object appeared as a 16th magnitude star whose spectrum exhibited broad emission lines that could not be identified. In addition, the object emitted far more radiation in the ultra-violet than an ordinary star and its brightness varied by more than 40% in a year. 3C 48 was thought to be some kind of radio-emitting star located in our galaxy.

In early 1963 another radio source, 3C 273, was identified with a star-like object even brighter than 3C 48, only this time it was recognized that most of the puzzling lines in its spectrum could be explained as the Balmer series of Hydrogen lines shifted in wavelength toward the red -- a red shift. In other words, this suggested that this new class of objects were cosmological (very distant) in origin, rather than members of our galaxy.

What puzzled astronomers was that optical photographs of these objects showed them to be pinpoints of light (with no extended envelopes of emission), which might suggest spiral-arms, and thus galaxies. The redshift (distance indicator) associated with normal external galAxi6s was in the case of these new objects very much larger. Here were what appeared to be stars that apparently were objects at more extreme distances than any external galaxy ever discovered. And that was only the beginning!

The term "Quasi-stellar Objects" was coined and thus the nick-name Quasars, The mystery of these objects deepened. The problem was that if the distance of these objects corresponded to their redshift, then they were thousands of millions of light years away. The fact that we could pick up any kind of radio signal from such distant objects suggested that they were enormously powerful radiators of energy, beyond anything we had known. As a final straw, astronomers had to consider that these remote objects possessed variability! Lets explain why this was so very hard for astronomers to digest:

It is a fundamental astronomical concept that very distant objects are so enormous (large diameters) that they could not possibly show any variations over time scales that human beings might ever measure. For instance, a distant galaxy might be some 50,000 light years in diameter. If it suffered a profound explosion within itself, this information (travelling at the speed of light) would take several tens of thousands of years to illuminate the entire galaxy in question, too long to catch our notice. Yet the first quasar whose redshift was measured (3C 273) showed variability from year to year for over eighty years. Astounding! Any object that varies on a time scale of a single year cannot be much larger than a light year in size. At the proposed distance for quasars, this would indicate that a tiny source was emitting more light and energy than an entire galaxy of stars! Subsequently quasars have been discovered that vary over a period of months and even days.

Whatever is responsible for the enormous energy output ii quasars must be small and massive -- perhaps with a mass as large as 10 million Suns. One of the side effects of these discoveries was that optical and radio astronomers could come together in mutual awe and wonder for the first time. Previous to quasars, there had been no joint project between these two very different kinds of astronomers.

The radio astronomers had not sprung from the midst of established optical astronomy, but had gathered together from several other disciplines, not previously associated with the "educated" circle of astronomers, such as radio hardware personnel. In fact many of the early papers on radio astronomy exist only in the purple ink of the "spirit" duplicator process, rather than offset printing, much less sewn signatures. Astrologers today find themselves in much the same positions that radio astronomers were in several decades ago: entering the established order from the fringe, rather than from the center.

A long and interesting controversy arose among astronomers as to the nature of quasars. Many felt that quasars might be more near and smaller objects engaged in an intense gravitational struggle, causing the shift in spectra toward the red, and so on. Today it is (more or less) generally accepted that quasars are objects located at cosmological distances, rather than near distances. Many astronomers feel that quasars are members of a group that includes the Seyfert galaxies, N galaxies, and BL Lacertae objects. Quasars have been found to emit radiation at almost all frequencies, including the x-ray. Quasars are brighter at increasing wavelengths and their radiation is partially plane polarized. This suggests that the source of energy is synchroton radiation, which is emitted by high-energy electrons spiraling around the lines of force in a magnetic field. It is currently being suggested that the ultimate source of such great energy as we find in quasars must be the black hole and that these objects must either already be black holes or will become such in a very short time.

It is also interesting to note that if quasars are indeed very remote objects, we see in them the universe, as it was a very long, long time ago, not long after the so-called beginning.

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Seyfert Galaxies

Seyfert Galaxies are a small class of galaxies (spirals) that have very small, intensely bright nuclei, whose broad emission lines (in spectrograms) indicate that the atoms present are in a very high state of-activity. They are powerful emitters of radio energy and several emit an enormous amount of energy in the infrared. They also emit in the ultraviolet.

The emission lines in Seyfert galaxies have only modest red shifts. The very compact nuclei observed in these galaxies indicate that the gases in them are in a high state of excitation and are traveling at high speed in clouds and filaments. It is now believed that the intense outbursts of energy observed in Seyfert galaxies may be normal to all galaxies and that even our own galaxy may experience such a renewal, from time to time.

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X-ray

X-ray emission coming from the heavens was detected in the early 1960's by means of special detectors flown outside the Earth's atmosphere in rockets or satellites. By 1974, a total of 161 x-ray sources had been examined and cataloged. X-rays are high-energy emission in the region of the spectrum from about 1 to 140 Angstrom units, which is above the visual region. Most x-ray sources are strong, point like, and show a distinct concentration toward the galactic plane, an indication that they are members of the galaxy.

In 1966, the strongest x-ray source (Scorpio X-1) was identified optically with a faint blue star-like object that looked like an old nova. It had been known that old novas are close binary systems in which one of the stars is a white dwarf. Such binary systems involved a transfer of matter from the normal star to the white dwarf, leading to an explosion in the outermost envelope of the white-dwarf nova. With the discovery of Sco X-1, it was suggested that the x-ray sources were binaries and that x-rays were being emitted by a hot cloud around the white dwarf, consisting of matter captured from the normal companion star. Other suggestions for the phenomenon were a neutron star and a black hole.

A black hole is a star that hat collapsed under gravitational pressure to such a small radius that the tendency toward further collapse exceeds the velocity of light itself, with the result that light emitted from the object cannot get out. As the star suffers internal collapse, the intensity of gravity above its surface causes space-time to fold over the star, which vanishes from the universe, leaving a very highly warped region or "hole" in an otherwise flat area of space. The idea that any force can be greater than the speed of light has frightened and intrigued the modern mind and the literature -surrounding the black hole reads like a science-fiction novel. The vocabulary surrounding the black hole phenomenon represents some of the most fascinating terms to emerge in our lifetimes. For example:

At the center of a black hole is the SINGULARITY, a point of infinite pressure, density, and curvature. At the edge of a black hole is the EVENT HORIZON, a one-way surface from which there is no escape, once it is crossed. Great speculation exists concerning what may happen if an object falls into one of these gravitational vortices. At first astrophysicists decided that an object unfortunate enough to be drawn through the event horizon would simply be crushed beyond imagination when it came to the singularity, and that was that. Further speculation was able to demonstrate that this was not the only possibility and ways began to be found to avoid the singularity. It was felt that if the singularity could be avoided that the traveler would emerge, perhaps in another universe than our own or in a different part of our own universe or a different time.

It has been written that the black hole is connected through a tunnel called a "worm hole" to a "white hole" where the material gushes forth once again in re-birth and new life. All of these concepts are presented through very complex mathematics. Whatever the truth may be, the discovery of the black hole and gravitational physics in general has carried scientists to the brink of the known and threatens to plunge them into what may amount to a basic renewal similar to that induced through the Einstein theory of relativity.

Several x-ray binary star systems found to date may contain a black hole as one of their components. The only, more or less, official black hole is the x-ray source Cygnus X-1 (#101 in the x-ray list) located at 13° degrees of Aquarius on the ecliptic. It is now considered that black holes may be very common in the universe and that they are required or regular members rather than oddballs. Speculation ranges from black holes the size of a pinhead in existence to their being a black hole at the center of our galaxy. It has been suggested that globular clusters may contain black holes. More about some of the other super-dense stellar remains is given in the section on stellar evolution.

X-ray astronomy is experiencing rapid growth similar to that of high-energy particle physics in the 1960's. New data pouring in from orbiting x-ray satellites will help to revolutionize our knowledge of physics through a variety of ongoing research that includes (1) an understanding of how plasma behaves at temperatures of billions of degrees when immersed in magnetic fields millions of times stronger than any on the Earth, (2) the measurements of neutron star masses, (3) sources of rapidly repeating x-ray bursters, (4) x-ray polarimetry, and (4) more details on the various black hole candidates.

We can expect detailed x-ray maps of our own and other galaxies to become available in the next few years. The gamma-ray astronomy (at even higher frequencies) is just now getting to the point of locating discrete sources and the coming years will see this branch of non-optical astronomy providing us with its unique perspective. However we choose to view the emergence of the non-optical astronomy, it has changed forever our way of viewing ourselves and our universe and has extended our window into space (in both directions) until what we now have is a panorama of light.

It is a good question what all of this means to the counseling astrologer. Some general thoughts would have to include: greater tolerance of the range of human genius extending from the more 'feeling' or radio regions of the spectrum through the visual or conscious-mind regions to the x-ray or super-conscious levels of experience. It is a general tenet of many astrologers that there is a coincidence of new discoveries and ideas with a change of consciousness or life-perspective. If this is so, then we are changing now like we have never changed in the history of time, as we have recorded it. It has been my experience that these non-optical sources check out in the traditional astrological interpretative ways, i.e. by Sun/Earth axis, conjunctions, aspects, etc.

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Infrared

Infrared radiation is below the visible spectrum (longer wavelengths), but above the radio portion of the spectrum. Infrared is considered to occur between wavelengths of 1 micron and 1 millimeter. Absorption by gases such as water vapor, carbon dioxide, and ozone prevent us from ground-based study of infrared (IF) except through a few 'windows'.

Our body and the entire world radiate at IF wavelengths and the problem facing infrared astronomers has been described as "comparable to that of an optical astronomer working in a lighted dome with a luminescent telescope." The objects of infrared study are cool, dim, and in general this means either stars that are dying (cooling off) or those stars that are just now forming and have not begun to radiate at visible frequencies: proto-stars.

Only a small fraction of the 6000-odd stars visible to the naked eye are prominent at IF wavelengths and an entire new set of constellations appear. Infrared radiation has been detected from the Sun, Moon, and several planets, in particular, Jupiter. Beyond the solar system, IF radiation has been associated with a great many red-faint stars, planetary nebulae, the galactic center, and other galaxies, in particular, the Seyfert galaxies.

The most interesting IF research involves attempts to discover the very young proto-stars in the vast dust complexes that are known to be the birth places of stellar bodies. The great Orion Nebula has received much attention, and astronomers believe stars are condensing and forming in these dark clouds at the present time. Infrared astronomy is quite young at the present time.

 

 

© Copyright © 1997 Michael Erlewine

 

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