Tour of the Invisible Universe

For the Tour of the Invisible Universe (Activity 4 in the Invisible Universe GEMS Teacher's Guide), the best way to display the images is by color computer display with a videoprojector or directly on-screen. As promised in the "What You Need" section on page 58 of the teacher guide, we provide an electronic file in PDF format that can be used with Adobe Acrobat Reader here. (If you are unable to download the 1.5 MB file, links to the images are also provided below.)

Once you open the file in Adobe Acrobat, choose "Full Screen" in the "View" menu, and the image will appear maximum size with an elegant black background. Use the arrow keys on your computer to scroll through as you present the pages. When you're done, just press the "esc" key to exit.

As referenced in the text in the sidebar at the top of page 59, the following is for teachers who would like to present more detailed information during the the "Tour of the Universe" than that outlined in the tour narration cards on pages 63 through 66 of the guide. The information can be added to that provided on the narration cards. By exploring the source pages for the images you can find further information regarding the images and their subjects, providing for as detailed a discussion as your students demand. Selecting any of the smaller images below will open a larger version of that same image. Selecting the link will take you to the page where the image was originally posted.

1. Moon
2. Sun
3. Jupiter
4. Great Nebula in Orion (M42)
5. Cat’s Eye Nebula (NGC6543)
6. Crab Nebula
7. Globular Cluster (M15)
8. Supernova 1987A
9. The Whirlpool Galaxy (M51)
10. Black Hole Causes Jet in Galaxy M87
11. Gamma-ray Burst (GRB991216)
12. The Early Universe


1. Moon–Distance: 380,000 km (240,000 miles)

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This color image of the Moon was taken by the Galileo spacecraft at 9:35 a.m. PST Dec. 9, 1990, at a range of about 350,000 miles. The color composite uses monochrome images taken through violet, red, and near-infrared filters. The concentric, circular Orientale basin, 600 miles across, is near the center; the near side is to the right, the far side to the left. At the upper right is the large, dark Oceanus Procellarum; below it is the smaller Mare Humorum. These, like the small dark Mare Orientale in the center of the basin, formed over 3 billion years ago as basaltic lava flows. At the lower left, among the southern cratered highlands of the far side, is the South-Pole-Aitken basin, similar to Orientale but twice as great in diameter and much older and more degraded by cratering and weathering. The cratered highlands of the near and far sides and the Maria are covered with scattered bright, young ray craters.

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The Midcourse Space Experiment (MSX) satellite had a spectacular view of the lunar eclipse of Jan 10, 1997 from Earth orbit, with the Moon completely immersed in the Earth’s shadow. Its onboard infrared telescope, was used to repeatedly image the Moon during the eclipse. The bright spots correspond to the warm areas on the lunar surface, dark areas are cooler. The brightest spot below and left of center is the crater Tycho, the dark region at the upper right is the Mare Crisium. The series of SPIRIT III images allow the determination of cooling curves for geologically different areas, exploring the physical properties of the Moon’s surface. Eclipsed Moon in Infrared Credit: DCATT Team, MSX Project, BMDO.

2. Sun–Distance: about 150,000,000 km (93,000,000 miles)

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Image Source: This image no longer available on-line.

Sunspots can be seen to rotate across the surface of the Sun, revealing that our Sun spins, completing a rotation about every 28 days. The Exploratorium website has an excellent section on sunspots at

See also for more links as well as some solar observatory websites:
* Amateur Solar Observatory --
* Big Bear --
* Birmingham Solar Oscillations Network --
* Mees Solar Observatory
* Mt. Wilson Observatory 150-ft Solar Tower --
* National Solar Observatory --
* SOHO (NASA-European Space Agency Solar Heliospheric Observatory):

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The infrared image shows granulation in the Sun’s surface. Granulation is evidence of upward and downward currents of gas (convection currents) within the Sun. While visible ligth images show sunspots well, IR images show prominences, which look like tongues of flame sticking out of the edge of the Sun. They are very different from flames that we are familiar with on Earth.

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The image in our tour is from the YOHKOH spacecraft. For more on Yokoh mission, see

3. Jupiter–Distance: about 400,000,000 km (250,000,000 miles)

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The Red Spot is the largest known storm in the Solar System. With a diameter of 15,400 miles, it is almost twice the size of the entire Earth and one-sixth the diameter of Jupiter itself. Unlike a low-pressure hurricane in the Caribbean Sea, however, the Red Spot rotates in a counterclockwise direction in the southern hemisphere, showing that it is a high-pressure system.

The long lifetime of the Red Spot may be due to the fact that Jupiter is mainly a gaseous planet. It possibly has liquid layers but lacks a solid surface, which would dissipate the storm's energy, much as happens when a hurricane makes landfall on the Earth. However, the Red Spot does change its shape, size, and color, sometimes dramatically. Such changes are demonstrated in high-resolution Wide Field and Planetary Cameras 1 & 2 images of Jupiter obtained by NASA's Hubble Space Telescope, which can be found at [original image: 9929a.jpg] by the Hubble Heritage Project team.

Astronomers study weather phenomena on other planets in order to gain a greater understanding of our own Earth's climate. Lacking a solid surface, Jupiter provides us with a laboratory experiment for observing weather phenomena under very different conditions than those prevailing on Earth. This knowledge can also be applied to places in the Earth's atmosphere that are over deep oceans, making them more similar to Jupiter's deep atmosphere.

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The bright central region is due to thermal radiation from Jupiter’s atmosphere. The bright features beyond the disk are due to radiation emitted by fast moving electrons trapped in Jupiter’s magnetic field. This radiation is mainly concentrated along Jupiter’s magnetic equator, but is also at higher magnetic latitudes as seen by the two "horns". From the US National Radio Astronomy Observatory.

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4. Great Nebula in Orion–Distance: 1,400 light years

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The Great Nebula in Orion is the finest example of a diffuse nebula in the sky and one of the most beautiful objects one can see, even in a relatively small telescope. It is a vast cloud of glowing gases, mostly hydrogen, of immensity beyond comprehension, and birthplace of stars.

Tennyson, often called "The Poet of Science," said this of the Great Nebula:

"…A single misty star
Which is the second in a line of stars
That seem a sword beneath a belt of three,
I never gazed upon it but I dreamt
Of some vast charm concluded in that star
To make fame nothing…"

"…regions of lucid matter taking form,
Brushes of fire, hazy gleams,
Clusters and beds of worlds, and bee-like swarms
Of suns and starry streams…"

From Merlin and Vivien.

Closeup images by Hubble Space telescope show especially dense clouds of molecular hydrogen gas (two atoms of hydrogen in each molecule) and dust that are shaped by a flood of ultraviolet light from hot, massive newborn stars. This process is called "photoevaporation." This ultraviolet light is also responsible for illuminating the convoluted surfaces and ghostly streamers of gas that highlight the three-dimensional nature of the clouds.

As parts of the nebula is slowly eroded away by the ultraviolet light, small globules of denser gas buried within the nebula are uncovered. These globules have been dubbed "EGGs," an acronym for "Evaporating Gaseous Globules," forming inside at least some of the EGGs are embryonic stars -- stars that abruptly stop growing when the EGGs are uncovered and they are separated from the larger reservoir of gas from which they were drawing mass. Eventually, the stars themselves emerge from the EGGs as the EGGs themselves succumb to photoevaporation.

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The familiar winter sky constellation Orion takes on a spectacular guise in the infrared, as seen in this false-color image constructed from data collected by IRAS--the Infrared Astronomical Satellite. The warmest features, e.g. the stars, are brightest. This emission is coded blue. The interstellar dust is cooler (coded green and red).

The bright yellow region in the lower right of the picture is the Sword of Orion, containing the Great Orion Nebula (M42 and M43). Above it to the left is the nebulosity around the belt star Zeta Orionis which contains the often photographed Horsehead Nebula (barely visible as a small indentation on the right side). Higher and to the left is M78, a reflection nebula. The Rosette Nebula is the brightest object near the left margin of the picture.

Most of the visually bright stars of Orion are not prominent in the infrared. However, Betelgeuse can be easily seen in the upper center of the picture as a blue-white dot (the faint tail is an instrumental artifact). The large ring to the right of Betelgeuse is the remnant of a supernova explosion, centered around the star Lambda Orionis. These rings are quite common in the IRAS sky. Another one, fainter and larger, can be seen in the lower left quadrant of the image.

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To see the whole Orion Nebula region in X-ray see:

This X-ray image, shows about a thousand X-ray emitting young stars in the Orion Nebula star cluster. The X rays are produced in the multimillion degree upper atmospheres of these stars. At a distance of about 1800 light years, this cluster is the closest massive star forming region to Earth. It is well-known in the night sky because it illuminates the Orion Nebula. The region shown in this image is about 10 light years across. The bright stars in the center are part of the Trapezium, an association of very young stars with ages less than a million years. The dark vertical and horizontal lines, and the streaks from the brightest stars are instrument effects.

The Orion Trapezium cluster is a group of very young stars concentrated in a region only 1.5 light years across at the core of the Orion Nebula star cluster. The Trapezium cluster offers a prime view into a stellar nursery. It is composed of stars with a median age of around 300,000 years, and at a distance of 1400 light years, is one of the nearest star-forming regions to Earth. The Chandra X-ray Observatory identified X-ray emission from individual stars in the Trapezium for the first time and found that almost all of their upper atmospheres, or coronas, are much hotter than expected. Chandra also detected several stars that are still surrounded by protoplanetary disks, for example the blue object on the lower left.

Chandra X-ray Observatory ACIS Image (Credit: NASA/MIT/N.Schulz et al.)

5. The "Cat’s Eye" Nebula (NGC6543)–Distance: 3,000 light years

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The Cat's Eye Nebula is in the class of nebulae known as Planetary Nebulae, which are associated with dying stars. The name "planetary nebula" is very misleading, since they have almost nothing to do with planets. The name was given to this class of nebula by early observers who used telescopes in which the disk-shaped planetary nebulae resembled planets. A planetary nebula is actually tunnels of gas cast off by a dying red giant star over a period of thousands of years. The dying central star, which ultimately becomes a white dwarf star, can sometimes be seen in the center of the planetary nebula.

Perhaps the most famous example of a planetary nebula is the Ring Nebula (M57) which is about a light-year in diameter, and located some 2,000 light-years from Earth in the direction of the constellation Lyra. See a Hubble Space Telescope view of M57, at 00000. Look for the colors that represent three different chemical elements: helium (blue), oxygen (green), and nitrogen (red).

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A planetary nebula forms when a dying red giant star puffs off its outer layer, leaving behind a hot central core. Scale: Images are 30 arcsec a side.

6. Crab Nebula (M1)–Distance: 6,500 light years

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Located about 6,500 light-years from Earth in the direction of the constellation Taurus, the Crab Nebula is the remnant of a star that began its life with about 10 times the mass of our own Sun. Such a massive star consumes its nuclear fuel so rapidly that it lives only some 50 million years before exploding as a supernova. For the Crab star, the end came on July 4, 1054. The explosion was witnessed as a naked-eye "Guest Star" by Chinese astronomers. Some researchers believe it is also depicted in rock paintings of Native Americans in the southwestern United States.

The spinning pulsar heats its surroundings, creating the ghostly diffuse bluish-green glowing gas cloud in its vicinity, including a blue arc just to the right of the neutron star. The colorful network of filaments is the material from the outer layers of the star that was expelled during the explosion and is now expanding outward at high speed, approaching some 300 miles per second. The pulsar has about 1.4 times the mass of the Sun, but jammed into an object only about 10 miles in diameter. This incredible object, a "neutron star," is even more remarkable because it spins on its axis 30 times a second.

NASA’s Hubble Space Telescope (HST) zoomed in on the center of the Crab to reveal its structure with unprecedented detail. See:

The HST Crab Nebula image was obtained by Hubble’s Wide Field and Planetary Camera 2 in 1995. Images taken with five different color filters have been combined to construct this false-color picture. Resembling an abstract painting by Jackson Pollack, the image shows ragged shreds of gas that are expanding away from the explosion site at over 3 million miles per hour. The core of the star has survived the explosion as a "pulsar," visible in the Hubble image.

In the HST picture, look for various colors that arise from different chemical elements in the expanding gas, including hydrogen (orange), nitrogen (red), sulfur (pink), and oxygen (green). The shades of color represent variations in the temperature and density of the gas, as well as changes in the elemental composition. These chemical elements, some of them newly created during the evolution and explosion of the star and now blasted back into space, will eventually be incorporated into new stars and planets. Astronomers believe that the chemical elements in the Earth and even in our own bodies, such as carbon, oxygen, and iron, were made in other exploding stars billions of years ago.

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For an excellent discussion of the Crab Nebula in IR and other wavelengths, see the SIRTF mission web page:

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This picture by the recently launched Chandra X-Ray Observatory shows new details of the nebula's center in X-ray light, yielding important clues to how the neutron star powers the nebula. Visible are rings of high-energy particles that are being flung outward near light-speed from the center, and powerful jets emerging from the poles. Astrophysicists continue to study and learn from this unusual engine which continually transfers 30 million times more power than lightning at nearly perfect efficiency.

7. Globular Star Cluster M15–Distance: 34,000 light years


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This stellar swarm is M15, one of the147 known globular star clusters in the Milky Way galaxy. M15 contains hundreds of thousands of stars, all held together by their mutual gravitational attraction. Globular clusters are particularly useful for studying stellar evolution, since all of the stars in the cluster have the same age (about 15 billion years), but cover a range of stellar masses. Every star visible in this image is either more highly evolved than, or in a few rare cases more massive than, our own Sun.

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Image Source:
Chandra X-ray Observatory Center
Harvard-Smithsonian Center for Astrophysics

Chandra's image of a puzzling X-ray source in the globular star cluster M15 shows that it is not one neutron star binary system, but two neutron star binary systems that appear so close together (2.7 seconds of arc) that they were indistinguishable with previous X-ray telescopes. In the 1970's astronomers discovered one neutron star binary system in M15, called 4U2127, with the Uhuru X-ray satellite. Subsequent data from X-ray telescopes indicated that the neutron star itself was not directly visible in X-ray light because it was hidden by an accretion disk of hot matter swirling from a companion star onto the neutron star. This picture was put into doubt when the Japanese Ginga X-ray satellite saw luminous X-ray bursts from the region in 1990. The length of the burst and other light characteristics implied that the surface of the neutron star was directly visible, in contradiction with earlier observations.

Chandra observations solved this mystery. The source could exhibit two contradictory modes of behavior because 4U2127 is not one source, but two: one whose neutron star is hidden by an accretion disk (on the left in the image), and one (right) where occasional X-ray outbursts reveal another neutron star's surface.

The broader implication of the Chandra discovery is that binary star systems with a neutron star orbiting a normal star may be common in globular clusters. Previously, and inexplicably, astronomers had never seen more than one of these neutron star binaries in any one globular cluster–a tight spherical region that can contain a million stars or more.

8. Supernova 1987A–Distance: 168,000 light years

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Glittering stars and wisps of gas create a breathtaking backdrop for the self-destruction of a massive star, called supernova 1987A, in the Large Magellanic Cloud, a nearby galaxy. Astronomers in the Southern hemisphere witnessed the brilliant explosion of this star on Feb. 23, 1987. In this NASA Hubble Space Telescope (HST) image, the supernova remnant, surrounded by inner and outer rings of material, is set in a forest of ethereal, diffuse clouds of gas.

This three-color HST image is composed of several pictures of the supernova and its neighboring region taken with the HST Wide Field and Planetary Camera 2 in Sept. 1994, Feb. 1996 and July1997. The many bright blue stars nearby the supernova are massive stars, each more than six times heftier than our Sun. With ages of about 12 million years old, they are members of the same generation of stars as the star that went supernova. The presence of bright gas clouds is another sign of the youth of this region, which still appears to be a fertile breeding ground for new stars. In a few years the supernova’s fast moving material will sweep the inner ring with full force, heating and exciting its gas, and will produce a new series of cosmic fireworks that will offer a striking view for more than a decade.

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The Supernova 1987A shock wave is evident in this radio telescope image also.

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This false-color image from the Chandra X-ray Observatory reveals a one light-year diameter ring of hot, ten million degree plasma. It is one of the most detailed X-ray images of the expanding blast wave from supernova 1987A (SN1987A). Superposed on this image are white contour lines which outline the innermost optical ring as seen by the Hubble Space Telescope. The composite picture clearly shows that the X-ray emitting shocked material lies just inside the optical ring. In fact, the X-ray emission seems to peak (whitest color) close to where the optical emission peaks (closely spaced contours), a persuasive demonstration that the optical light is produced as the blast wave plows into surrounding material.

What will SN1987A look like in the future? According to a popular model, in coming years the expanding supernova blast wave should hit and light up even more material while the violent impacts send reverse shocks back towards the site of the explosion and light up the ejected stellar debris. In any event, astronomers will watch eagerly from a ringside seat as a new supernova remnant emerges.

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9. The Whirlpool Galaxy (M51)–Distance: 37 million light years

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See also

The famous Whirlpool galaxy M51 was one of Charles Messier's original discoveries: He discovered it on October 13, 1773, when observing a comet, and described it as a "very faint nebula, without stars" which is difficult to see. Its companion, NGC 5195, was discovered in 1781 by his friend, Pierre Méchain, so that it is mentioned in his 1784 catalog: `It is double, each has a bright center, which are separated 4'35". The two "atmospheres" touch each other, the one is even fainter than the other.' NGC 5195 was assigned an own number by William Herschel: H I.186.

This galaxy was the first one where the spiral structure was discovered, in spring 1845 by Lord Rosse, who made a very careful and acurate painting. Therefore, M51 is sometimes referenced as Rosse's Galaxy or Lord Rosse's "Question Mark" - he is cited with this name (see, e.g., NED).

According to our present understanding, the pronounced spiral structure is a result of M51's current encounter with its neighbor, NGC 5195. Due to this interaction, the gas in the galaxy was disturbed and compressed in some regions, resulting in the formation of new young stars. As is common in galactic encounters, spiral structure is preferably induced in the more massive galaxy.

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Two-Micron All-Sky Survey (2MASS)

The near-infrared (NIR) image was obtained by the Two-Micron All-Sky Survey (2MASS), an ongoing effort to map the entire sky at J-band (1.25 microns), H-band (1.65 microns) and K-band (2.17 microns) wavelengths. The 2MASS survey is led by the University of Massachusetts, with all data and images processed at Caltech's Infrared Processing and Analysis Center (IPAC). The survey utilizes two nearly identical 1.3-meter diameter telescopes located on Mount Hopkins (Arizona) and on Cerro Tololo (Chile). Exposure times are 7.8 seconds.

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ESA's Infrared Space observaotry (ISO)

The nearby Whirlpool Galaxy, M51, was ISO's "first light" target on 28 November, when the telescope was opened to the sky. The infrared image shows regions of star formation along the galaxy's spiral arms and on either side of the nucleus.

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InfraRed Astronomical Satellite(IRAS)

The far-infrared image was obtained with the InfraRed Astronomical Satellite (IRAS) in 1983. This was the first space-borne infrared astronomy satellite, and was an international collaboration between the US, the Netherlands and the UK. IRAS mapped nearly the entire sky at four wavelengths, including 60 microns (millionths of a meter) and 100 microns in the far-infrared. Since infrared detector technology was still relatively immature at the time of this path-breaking mission, the spatial resolution for the mid-IR images is rather modest. The IRAS detectors were rectangular in shape, and had relatively large fields of view (about 1.5 arcmin wide and 4.7 arcmin long at 60 microns, and 3 arcmin by 5 arcmin at 100 microns). The far-IR images depicted in the Museum resulted from high-resolution processing, in which sky coverage and sophisticated mathematical algorithms combine to yield effective resolutions of better than 1 arcmin. The odd elliptical shape of many mid-infrared emission peaks is a consequence of the underlying rectangular detectors used by IRAS.

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image Source:
National Radio Astronomy Observatory Very Large Array (VLA)
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Image Source: No longer available on line.

An even better image of M51 in X-ray is at

The popular pair of interacting galaxies known as the Whirlpool is imaged here at high energies by the orbiting Chandra X-ray Observatory. Still turning in a remarkable performance, over 80 glittering x-ray stars are present in the Chandra image data from the region. The number of luminous x-ray sources, likely neutron star and black hole binary systems within the confines of M51, is unusually high for normal spiral or elliptical galaxies and suggests this cosmic whirlpool has experienced intense bursts of massive star formation. The bright cores of both galaxies, NGC 5194 and NGC 5195 (right and left respectively), also exhibit high-energy activity in this false-color x-ray picture showing a diffuse glow from multi-million degree gas. An expanded view of the region near the core of NGC 5194 reveals x-rays from a supernova remnant, the debris from a spectacular stellar explosion, first detected by earthbound astronomers in 1994.

10. Jet in Galaxy M87–Distance: 50 million light years

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Hubble Space Telescope

Astronomers using the Hubble telescope have found seemingly conclusive evidence for a massive black hole in the center of the giant elliptical galaxy M87, located 50 million light-years from Earth in the constellation Virgo. Earlier observations suggested that the black hole was present, but they were not decisive.

This observation provides very strong support for the existence of gravitationally collapsed objects, which were predicted 80 years ago by Albert Einstein's general theory of relativity. This image shows a spiral-shaped disk of hot gas in the core of M87. Hubble measurements indicate that the disk's rapid rotation is strong evidence that it contains a massive black hole. A black hole is so massive and compact that nothing can escape its gravitational pull, not even light.

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Image Source:
Chandra X-ray Observatory Center
Harvard-Smithsonian Center for Astrophysics

NASA's Chandra X-ray Observatory has given astronomers their most detailed look to date at the X-ray jet blasting out of the nucleus of M87, a giant elliptical galaxy 50 million light years away in the constellation Virgo. The X-ray image of the jet reveals an irregular, knotty structure similar to that detected by radio telescopes and the Hubble Space Telescope. At the extreme left of the image, the bright galactic nucleus harboring a supermassive black hole shines. The jet is thought to be produced by strong electromagnetic forces created by matter swirling toward the supermassive black hole. These forces pull gas and magnetic fields away from the black hole along its axis of rotation in a narrow jet. Inside the jet, shock waves produce high-energy electrons that spiral around the magnetic field and radiate by the "synchrotron" process, creating the observed radio, optical and X-ray knots. Synchrotron radiation is caused by high-speed charged particles, such as electrons, emitting radiation as they are accelerated in a magnetic field.

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National Radio Astronomy Observatory Very Large Array (VLA)
An excellent link for further research is

At the center of M87, material being drawn inward by the strong gravitation of the black hole is formed into a rapidly-spinning flat disk, called an accretion disk. The subatomic particles are thought to be pushed outward from the poles of this disk. Scientists believe that magnetic fields in the disk are twisted tightly as the disk spins and then channel the electrically-charged particles into a pair of narrow jets.

M87 is one of the nearest jet-emitting galaxies and its strong radio emission made it an excellent target for radio telescopes. Both radio observations with the VLBA and optical observations with the Hubble Space Telescope have measured the motions of concentrations of material in M87's jets, and have shown the material to be moving at apparent speeds greater than that of light. This "superluminal" motion is a geometric illusion created by material moving nearly, but under, the speed of light, but in a direction somewhat toward the Earth.

M87 also is known by radio astronomers as Virgo A, the strongest emitter of radio waves in the constellation Virgo. The galaxy was discovered by the French astronomer Charles Messier in 1781. The jet was first seen in 1918 by Lick Observatory astronomer Heber Curtis, who described it as "a curious straight ray." The galaxy's radio emission was first observed by Australian astronomers in 1948/49. M87 is the largest of thousands of galaxies in the Virgo Cluster of galaxies.

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Hubble Space Telescope

11. Gamma Ray Burst 991216–Distance: several billion light years


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"The energy released by this burst in its first few seconds staggers the imagination," said Caltech professor Shrinivas Kulkarni, one of the two principal investigators on the Hubble Space Telescope team that captured this image. The burst appears to have released several hundred times more energy than an exploding star, called a supernova, until now the most energetic phenomenon in the universe known to scientists.

"For about one or two seconds, this burst was as luminous as all the rest of the entire universe," said Caltech professor George Djorgovski, the other principal investigator on the team. Finding such large energy release over such a brief period of time is unprecedented in astronomy, except for the big bang itself. "In a region about a hundred miles across, the burst created conditions like those in the early universe, about one millisecond (1/1,000 of a second) after the big bang," said Djorgovski.

Gamma-ray bursts are mysterious flashes of high-energy radiation that appear from random directions in space and typically last a few seconds. They were first discovered by U.S. Air Force Vela satellites in the 1960s. Since then, numerous theories of their origin have been proposed, but the causes of gamma-ray bursts remain unknown. NASA’s Compton Gamma-Ray Observatory (CGRO) satellite detected several thousand bursts in its 9-year lifetime. Swift will detect hundreds more following its launch in 2003.

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Chandra X-ray Observatory HETG/ACIS (Credit: NASA/CNR/L.Piro et al)

This gamma-ray burst exploded roughly 8 billion years ago. An international team of researchers used the Chandra X-ray Observatory to detect never-before-seen properties in the X-ray afterglow of a gamma-ray burst (GRB). GRBs are mysterious blasts of high-energy radiation, believed to be the most powerful explosions in the Universe. Chandra’s latest discovery of iron in the ejected material surrounding GRB991216 strengthens the case for a "hypernova" model for GRBs. In this theory, GRBs are caused by massive stars that collapse under their own weight, releasing gigantic amounts of energy.

12. The Early Universe: Hubble Deep Field

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Hubble Space Telescope (HST)

Several hundred never before seen galaxies are visible in this "deepest-ever" view of the universe, called the Hubble Deep Field, made with NASA’s Hubble Space Telescope. Besides the classical spiral and elliptical shaped galaxies, there is a bewildering variety of other galaxy shapes and colors that are important clues to understanding the evolution of the universe. Some of the galaxies may have formed less that one billion years after the Big Bang. Representing a narrow "keyhole" view all the way to the visible horizon of the universe, the Hubble Deep Field image covers a speck of sky 1/30th the diameter of the full Moon. About 25% of the entire Hubble Deep Field is shown here.

This is so narrow, just a few foreground stars in our Milky Way galaxy are visible and are vastly outnumbered by the menagerie of far more distant galaxies, some nearly as faint as 30th magnitude, or nearly four billion times fainter than the limits of human vision. (The relatively bright object with diffraction spikes just left of center may be a 20th magnitude star.) Though the field is a very small sample of sky area it is considered representative of the typical distribution of galaxies in space because the universe, statistically, looks the same in all directions.

The image was assembled from many separate exposures (342 frames total were taken, 276 have been fully processed to date and used for this picture) with the Wide Field and Planetary Camera 2 (WFPC2), for ten consecutive days between December 18 to 28, 1995. This picture is from one of three wide-field CCD (Charged Coupled Device) detectors on the WFPC2.

This "true-color" view was assembled from separate images taken in blue, red, and infrared light. By combining these separate images into a single color picture, astronomers will be able to infer — at least statistically — the distance, age, and composition of galaxies in the field. Bluer objects contain young stars and/or are relatively close, while redder objects contain older stellar populations and/or are farther away.

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Chandra X-Ray Observatory ACIS Image; (Credit: Optical: NASA/HST, X-ray: NASA/PSU)

This image shows the results of the first long-duration (approx. 46 hour) X-ray survey of the Hubble Deep Field North. Chandra detected X rays from six of the galaxies in the field. The X-ray emitting objects discovered are a distant galaxy thought to contain a central giant black hole, three elliptically shaped galaxies, an extremely red distant galaxy, and a nearby spiral galaxy. A surprise result that must be studied further is the lack of X rays from some of the extremely luminous submillimeter galaxies at huge distances (over 10 billion light years) from earth. The Chandra results raise questions about the current theories used to explain the high energy output of these objects.

Scale: Image is 1 arcmin on a side.

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