1997 October 19
The Heart Of NGC 4261
Credit: H. Ford and L. Ferrarese, (Johns Hopkins), W. Jaffe, (Leiden), NASA
What evil lurks in the hearts of galaxies? This Hubble Space Telescope picture of the center of the nearby elliptical galaxy NGC 4261 tells one dramatic tale. The gas and dust in this disk are swirling into what is almost certainly a massive black hole. The disk is probably what remains of a smaller galaxy that fell in hundreds of millions of years ago. Collisions like this may be a common way of creating such active galactic nuclei as quasars. Strangely, the center of this fiery whirlpool is offset from the exact center of the galaxy - for a reason that for now remains an astronomical mystery.
The Heart Of NGC 4261
Credit: H. Ford and L. Ferrarese, (Johns Hopkins), W. Jaffe, (Leiden), NASA
What evil lurks in the hearts of galaxies? This Hubble Space Telescope picture of the center of the nearby elliptical galaxy NGC 4261 tells one dramatic tale. The gas and dust in this disk are swirling into what is almost certainly a massive black hole. The disk is probably what remains of a smaller galaxy that fell in hundreds of millions of years ago. Collisions like this may be a common way of creating such active galactic nuclei as quasars. Strangely, the center of this fiery whirlpool is offset from the exact center of the galaxy - for a reason that for now remains an astronomical mystery.
1997 October 20
Spiral Eddies On Planet Earth
Credit: STS 41G Crew, NASA
Can you identify this stellar nebula? How many light-years from Earth did you say? Looking like a twisting cloud of gas and dust between the stars this wispy nebulosity is actually close by - a spiral eddy formed near the North Atlantic Gulf Stream off the East coast of the US. Tens of miles across, spiral eddies are an ocean current phenomenon discovered by observations from manned spacecraft. Imaged by the Challenger space shuttle crew during the STS 41G mission this eddy is dramatically visible due to the low sun angle and strong reflection of sunlight. The reflection is caused by a very thin biologically produced oily film on the surface of the swirling water. Prior to STS 41G these eddies were thought to be rare but are now understood to be a significant dynamic feature of ocean currents. However, no good explanation of their origin or persistence exists.
Spiral Eddies On Planet Earth
Credit: STS 41G Crew, NASA
Can you identify this stellar nebula? How many light-years from Earth did you say? Looking like a twisting cloud of gas and dust between the stars this wispy nebulosity is actually close by - a spiral eddy formed near the North Atlantic Gulf Stream off the East coast of the US. Tens of miles across, spiral eddies are an ocean current phenomenon discovered by observations from manned spacecraft. Imaged by the Challenger space shuttle crew during the STS 41G mission this eddy is dramatically visible due to the low sun angle and strong reflection of sunlight. The reflection is caused by a very thin biologically produced oily film on the surface of the swirling water. Prior to STS 41G these eddies were thought to be rare but are now understood to be a significant dynamic feature of ocean currents. However, no good explanation of their origin or persistence exists.
1997 October 21
The Butterfly Planetary Nebula
Credit & Copyright: J. H. Hora & W. B. Latter (U. Hawaii), 2.2-m Telescope, Mauna Kea
As stars age, they throw off their outer layers. Sometimes a highly symmetric gaseous planetary nebula is created, as is the case in M2-9, also called the Butterfly. Most planetary nebulae show this bipolar appearance, although some appear nearly spherical. An unusual characteristic of the Butterfly is that spots on the "wings" appear to have moved slightly over the years. The above picture was taken in three bands of infrared light and computationally shifted into the visible. Much remains unknown about planetary nebulae, including why some appear symmetric, what creates the knots of emission (some known as FLIERS), and how exactly stars create them.
The Butterfly Planetary Nebula
Credit & Copyright: J. H. Hora & W. B. Latter (U. Hawaii), 2.2-m Telescope, Mauna Kea
As stars age, they throw off their outer layers. Sometimes a highly symmetric gaseous planetary nebula is created, as is the case in M2-9, also called the Butterfly. Most planetary nebulae show this bipolar appearance, although some appear nearly spherical. An unusual characteristic of the Butterfly is that spots on the "wings" appear to have moved slightly over the years. The above picture was taken in three bands of infrared light and computationally shifted into the visible. Much remains unknown about planetary nebulae, including why some appear symmetric, what creates the knots of emission (some known as FLIERS), and how exactly stars create them.
1997 October 22
The Antennae Galaxies
B. Whitmore (STScI), F. Schweizer (DTM), NASA
A ground-based telescopic view (left) of the collision between the galaxies NGC4038 and NGC4039 reveals long arcing insect-like "antennae" of luminous matter flung from the scene of the accident. Investigators using the Hubble Space Telescope to sift through the cosmic wreckage near the two galaxy cores have recently announced the discovery of over a thousand bright young clusters of stars - the result of a burst of star formation triggered by the collision. The green outline shows the area covered by the higher resolution Hubble image (right). At the distance of the Antennae galaxies (about 63 million light-years), a pixel in this image corresponds to about 15 light-years. Dust clouds around the two galactic nuclei give them a dimmed and reddened appearance while the massive, hot, young stars of the newly formed clusters are blue. How do colliding galaxies evolve with time? Determining the ages of star clusters formed in galaxy collisions can provide significant clues. The Antennae galaxies are seen in the southerly constellation Corvus.
The Antennae Galaxies
B. Whitmore (STScI), F. Schweizer (DTM), NASA
A ground-based telescopic view (left) of the collision between the galaxies NGC4038 and NGC4039 reveals long arcing insect-like "antennae" of luminous matter flung from the scene of the accident. Investigators using the Hubble Space Telescope to sift through the cosmic wreckage near the two galaxy cores have recently announced the discovery of over a thousand bright young clusters of stars - the result of a burst of star formation triggered by the collision. The green outline shows the area covered by the higher resolution Hubble image (right). At the distance of the Antennae galaxies (about 63 million light-years), a pixel in this image corresponds to about 15 light-years. Dust clouds around the two galactic nuclei give them a dimmed and reddened appearance while the massive, hot, young stars of the newly formed clusters are blue. How do colliding galaxies evolve with time? Determining the ages of star clusters formed in galaxy collisions can provide significant clues. The Antennae galaxies are seen in the southerly constellation Corvus.
1997 October 23
Echos of Supernova 1987A
Credit: Anglo-Australian Telescope photograph by David Malin
Copyright: Anglo-Australian Telescope Board
Can you find Supernova 1987a? It's not hard - it occurred in the center of the bulls-eye pattern. Although this stellar detonation was seen more than a decade ago, light from it continues to bounce off nearby interstellar dust and be reflected to us. These two rings are thus echoes of the powerful supernova. As time goes on, these echoes appear to expand outward from the center. The above image was created by subtracting a picture taken before 1987, from a picture taken after.
Echos of Supernova 1987A
Credit: Anglo-Australian Telescope photograph by David Malin
Copyright: Anglo-Australian Telescope Board
Can you find Supernova 1987a? It's not hard - it occurred in the center of the bulls-eye pattern. Although this stellar detonation was seen more than a decade ago, light from it continues to bounce off nearby interstellar dust and be reflected to us. These two rings are thus echoes of the powerful supernova. As time goes on, these echoes appear to expand outward from the center. The above image was created by subtracting a picture taken before 1987, from a picture taken after.
1997 October 24
Moving Echoes Around SN 1987A
Credit: J. Krist (STScI) et al., WFPC2, HST, NASA
Yesterday's image highlighted reflective rings of light emitted by a supernova explosion. Today's pictures, taken over a year apart, highlight how these echoes are seen to move over time. Visible on the left of each picture is part of a reflective ring, an existing dust cloud momentarily illuminated by the light of Supernova 1987A. Note how the nebulosity reflecting the most light occurs farther to the left in the lower photograph. If you look closely, you can see the actual location of SN 1987A itself on the right of each photograph: it appears in the center of a small yellowish ring. The apparent motion and brightness of these echoes help astronomers understand the abundance and distribution of interstellar nebulae in the LMC galaxy, where the stellar explosion occurred.
Moving Echoes Around SN 1987A
Credit: J. Krist (STScI) et al., WFPC2, HST, NASA
Yesterday's image highlighted reflective rings of light emitted by a supernova explosion. Today's pictures, taken over a year apart, highlight how these echoes are seen to move over time. Visible on the left of each picture is part of a reflective ring, an existing dust cloud momentarily illuminated by the light of Supernova 1987A. Note how the nebulosity reflecting the most light occurs farther to the left in the lower photograph. If you look closely, you can see the actual location of SN 1987A itself on the right of each photograph: it appears in the center of a small yellowish ring. The apparent motion and brightness of these echoes help astronomers understand the abundance and distribution of interstellar nebulae in the LMC galaxy, where the stellar explosion occurred.
1997 October 25
Orion's Horsehead Nebula
Credit & Copyright: D. Malin (AAO), AATB, ROE, UKS Telescope
The Horsehead Nebula is one of the most famous nebulae on the sky. It is visible as the black indentation to the red emission nebula seen just to the right of center of the above photograph. The bright star near the center is located in the belt of the familiar constellation of Orion. The horse-head feature is dark because it is really an opaque dust cloud which lies in front of the bright red emission nebula. Like clouds in Earth's atmosphere, this cosmic cloud has assumed a recognizable shape by chance. After many thousands of years, the internal motions of the cloud will alter its appearance. The emission nebula's red color is caused by electrons recombining with protons to form hydrogen atoms. Also visible in the picture are blue reflection nebulae, which preferentially reflect the blue light from nearby stars.
Orion's Horsehead Nebula
Credit & Copyright: D. Malin (AAO), AATB, ROE, UKS Telescope
The Horsehead Nebula is one of the most famous nebulae on the sky. It is visible as the black indentation to the red emission nebula seen just to the right of center of the above photograph. The bright star near the center is located in the belt of the familiar constellation of Orion. The horse-head feature is dark because it is really an opaque dust cloud which lies in front of the bright red emission nebula. Like clouds in Earth's atmosphere, this cosmic cloud has assumed a recognizable shape by chance. After many thousands of years, the internal motions of the cloud will alter its appearance. The emission nebula's red color is caused by electrons recombining with protons to form hydrogen atoms. Also visible in the picture are blue reflection nebulae, which preferentially reflect the blue light from nearby stars.
1997 October 26
Welcome to Planet Earth
Apollo 17 Crew, NASA
Welcome to Planet Earth, the third planet from a star named the Sun. The Earth is shaped like a sphere and composed mostly of rock. Over 70 percent of the Earth's surface is water. The planet has a relatively thin atmosphere composed mostly of nitrogen and oxygen. Earth has a single large Moon which is about 1/4 of its diameter and, from the planet's surface, is seen to have almost exactly the same angular size as the Sun. With its abundance of liquid water, Earth supports a large variety of life forms, including potentially intelligent species such as dolphins and humans. Please enjoy your stay on Planet Earth.
Welcome to Planet Earth
Apollo 17 Crew, NASA
Welcome to Planet Earth, the third planet from a star named the Sun. The Earth is shaped like a sphere and composed mostly of rock. Over 70 percent of the Earth's surface is water. The planet has a relatively thin atmosphere composed mostly of nitrogen and oxygen. Earth has a single large Moon which is about 1/4 of its diameter and, from the planet's surface, is seen to have almost exactly the same angular size as the Sun. With its abundance of liquid water, Earth supports a large variety of life forms, including potentially intelligent species such as dolphins and humans. Please enjoy your stay on Planet Earth.
1997 October 27
Closeup of Antennae Galaxy Collision
Credit: B. Whitmore (STScI), F. Schweizer (DTM), NASA
It's a clash of the titans. Two galaxies are squaring off in Corvus and here are the latest pictures. When two galaxies collide, however, the stars that compose them usually do not. This is because galaxies are mostly empty space and, however bright, stars only take up only a small amount of that space. But during the slow, hundred million year collision, one galaxy can rip the other apart gravitationally, and dust and gas common to both galaxies does collide. In the above wreckage, dark dust pillars mark massive molecular clouds, which are being compressed during the galactic encounter, causing the rapid birth of millions of stars.
Closeup of Antennae Galaxy Collision
Credit: B. Whitmore (STScI), F. Schweizer (DTM), NASA
It's a clash of the titans. Two galaxies are squaring off in Corvus and here are the latest pictures. When two galaxies collide, however, the stars that compose them usually do not. This is because galaxies are mostly empty space and, however bright, stars only take up only a small amount of that space. But during the slow, hundred million year collision, one galaxy can rip the other apart gravitationally, and dust and gas common to both galaxies does collide. In the above wreckage, dark dust pillars mark massive molecular clouds, which are being compressed during the galactic encounter, causing the rapid birth of millions of stars.
1997 October 28
Rafting for Solar Neutrinos
Credit: Super-Kamiokande Collaboration, Japan
Where have all the neutrinos gone? A long time passing since this question was first asked (decades) as increasingly larger and more diverse detectors sensitive to neutrinos from our Sun have found fewer than expected. But why? Above, scientists check the equipment surrounding a huge tank of extremely pure water from the Super-Kamiokande experiment in Japan, designed to detect colliding neutrinos. Large detectors are needed because the neutrino is an elementary particle that goes right through practically everything. Reasons for the lack of solar neutrinos may include a more complex theory for electroweak interactions than currently in use. Future results from detectors like Super-Kamiokande may help us know more.
Rafting for Solar Neutrinos
Credit: Super-Kamiokande Collaboration, Japan
Where have all the neutrinos gone? A long time passing since this question was first asked (decades) as increasingly larger and more diverse detectors sensitive to neutrinos from our Sun have found fewer than expected. But why? Above, scientists check the equipment surrounding a huge tank of extremely pure water from the Super-Kamiokande experiment in Japan, designed to detect colliding neutrinos. Large detectors are needed because the neutrino is an elementary particle that goes right through practically everything. Reasons for the lack of solar neutrinos may include a more complex theory for electroweak interactions than currently in use. Future results from detectors like Super-Kamiokande may help us know more.
1997 October 29
Stereo Saturn
Credit: Voyager Project, LPI, JPL, NASA
Get out your red/blue glasses and launch yourself into this stereo picture of Saturn! The picture is actually composed from two images recorded weeks apart by the Voyager 2 spacecraft during its visit to the Saturnian System in August of 1981. Traveling at about 35,000 miles per hour, the spacecraft's changing viewpoint from one image to the next produced this exaggerated but pleasing stereo effect. Saturn is the second largest planet in the Solar System, after Jupiter. Its spectacular ring system is so wide that it would span the space between the Earth and Moon. Although they look solid here, Saturn's Rings consist of individually orbiting bits of ice and rock ranging in size from grains of sand to barn-sized boulders.
Stereo Saturn
Credit: Voyager Project, LPI, JPL, NASA
Get out your red/blue glasses and launch yourself into this stereo picture of Saturn! The picture is actually composed from two images recorded weeks apart by the Voyager 2 spacecraft during its visit to the Saturnian System in August of 1981. Traveling at about 35,000 miles per hour, the spacecraft's changing viewpoint from one image to the next produced this exaggerated but pleasing stereo effect. Saturn is the second largest planet in the Solar System, after Jupiter. Its spectacular ring system is so wide that it would span the space between the Earth and Moon. Although they look solid here, Saturn's Rings consist of individually orbiting bits of ice and rock ranging in size from grains of sand to barn-sized boulders.
1997 October 30
3-D View Of Jupiter's Clouds
Credit: Galileo Project, JPL, NASA
Every day is a cloudy day on Jupiter, the Solar System's reigning gas giant. This 3-dimensional visualization presents a simplified model view from between Jovian cloud decks based on imaging and spectral data recorded by the Galileo spacecraft. The separation between the cloud layers and the height variations have been exaggerated. The upper cloud layer is haze a few tens of miles thick. Heights in the lower cloud layers have been color coded; light bluish clouds are high and thin, reddish clouds are low, and white clouds are high and thick. Streaks in the lower layer suggestively lead to a dark blue area, a relatively clear, dry region similar to the site where Galileo's atmospheric probe made the first entry into a gas giant planet's atmosphere on December 7th, 1995.
3-D View Of Jupiter's Clouds
Credit: Galileo Project, JPL, NASA
Every day is a cloudy day on Jupiter, the Solar System's reigning gas giant. This 3-dimensional visualization presents a simplified model view from between Jovian cloud decks based on imaging and spectral data recorded by the Galileo spacecraft. The separation between the cloud layers and the height variations have been exaggerated. The upper cloud layer is haze a few tens of miles thick. Heights in the lower cloud layers have been color coded; light bluish clouds are high and thin, reddish clouds are low, and white clouds are high and thick. Streaks in the lower layer suggestively lead to a dark blue area, a relatively clear, dry region similar to the site where Galileo's atmospheric probe made the first entry into a gas giant planet's atmosphere on December 7th, 1995.
1997 October 31
Haunting Mars
Credit: MGS Project, JPL, NASA
This Halloween, the news about Mars is good news - Mars Global Surveyor will resume aerobraking into a mapping orbit around the haunting red planet. Wide angle cameras onboard the spacecraft recently recorded this shadowy image of Olympus Mons, the Solar System's largest volcano, from an altitude of over 100 miles. The summit depression or caldera of Olympus Mons is about 40 miles across and 15 miles above the Martian surface. On Halloween Night in 1938, Mars also made the news when Orson Welles' radio theatre adaptation of H.G. Wells' "War of the Worlds" - a fictional account of invaders from Mars - was dramatized as a live news report. The performance was so convincing it tricked some listeners, but most who heard the broadcast felt it was a treat. Have a happy and safe Halloween!
Haunting Mars
Credit: MGS Project, JPL, NASA
This Halloween, the news about Mars is good news - Mars Global Surveyor will resume aerobraking into a mapping orbit around the haunting red planet. Wide angle cameras onboard the spacecraft recently recorded this shadowy image of Olympus Mons, the Solar System's largest volcano, from an altitude of over 100 miles. The summit depression or caldera of Olympus Mons is about 40 miles across and 15 miles above the Martian surface. On Halloween Night in 1938, Mars also made the news when Orson Welles' radio theatre adaptation of H.G. Wells' "War of the Worlds" - a fictional account of invaders from Mars - was dramatized as a live news report. The performance was so convincing it tricked some listeners, but most who heard the broadcast felt it was a treat. Have a happy and safe Halloween!
1997 November 1
M31: The Andromeda Galaxy
Credit & Copyright: Jason Ware
Andromeda is the nearest major galaxy to our own Milky Way Galaxy. Our Galaxy is thought to look much like Andromeda. Together these two galaxies dominate the Local Group of galaxies. The diffuse light from Andromeda is caused by the hundreds of billions of stars that compose it. The several distinct stars that surround Andromeda's image are actually stars in our Galaxy that are well in front of the background object. Andromeda is frequently referred to as M31 since it is the 31st object on Messier's list of diffuse sky objects. M31 is so distant it takes about 2 million years for light to reach us from there. Much about M31 remains unknown, including why the center contains two nuclei.
M31: The Andromeda Galaxy
Credit & Copyright: Jason Ware
Andromeda is the nearest major galaxy to our own Milky Way Galaxy. Our Galaxy is thought to look much like Andromeda. Together these two galaxies dominate the Local Group of galaxies. The diffuse light from Andromeda is caused by the hundreds of billions of stars that compose it. The several distinct stars that surround Andromeda's image are actually stars in our Galaxy that are well in front of the background object. Andromeda is frequently referred to as M31 since it is the 31st object on Messier's list of diffuse sky objects. M31 is so distant it takes about 2 million years for light to reach us from there. Much about M31 remains unknown, including why the center contains two nuclei.
1997 November 2
White Dwarf Stars Cool
Credit: H. Richer (UBC), NASA
Diminutive by stellar standards, white dwarf stars are also intensely hot ... but they are cooling. No longer do their interior nuclear fires burn, so they will continue to cool until they fade away. This Hubble Space Telescope image covers a small region near the center of a globular cluster known as M4. Here, researchers have discovered a large concentration of white dwarf stars (circled above). This was expected - low mass stars, including the Sun, are believed to evolve to the white dwarf stage. Studying how these stars cool could lead to a better understanding of their ages, of the age of their parent globular cluster, and even the age of our universe!
White Dwarf Stars Cool
Credit: H. Richer (UBC), NASA
Diminutive by stellar standards, white dwarf stars are also intensely hot ... but they are cooling. No longer do their interior nuclear fires burn, so they will continue to cool until they fade away. This Hubble Space Telescope image covers a small region near the center of a globular cluster known as M4. Here, researchers have discovered a large concentration of white dwarf stars (circled above). This was expected - low mass stars, including the Sun, are believed to evolve to the white dwarf stage. Studying how these stars cool could lead to a better understanding of their ages, of the age of their parent globular cluster, and even the age of our universe!
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1997 November 3
Irregular Moons Discovered Around Uranus
Credit: B. Gladman (CITA) et al., Hale 5-meter Telescope, Palomar Obs.
Where did these two irregular moons of Uranus originate? Last week two previously undiscovered moons of the distant gas planet were confirmed, the first in irregular orbits. All fifteen previously known moons of Uranus are 'regular', circling near the planet's equator. Most of these were discovered by the passing Voyager 2 spacecraft in 1986. These newly discovered moons are thought to be odd-shaped and about 100 km across. They are considered irregular, though, because they orbit in odd directions and far from Uranus. If Uranus' irregular moons have the same origin as those orbiting Jupiter, Saturn, and Neptune, then they were probably caught from orbits around the Sun. Moons like this are discovered by their motion. One of these moons is shown above as the circled point of light moving from left to right. (To stop the movie from repeating, click "stop" on most browsers.)
Irregular Moons Discovered Around Uranus
Credit: B. Gladman (CITA) et al., Hale 5-meter Telescope, Palomar Obs.
Where did these two irregular moons of Uranus originate? Last week two previously undiscovered moons of the distant gas planet were confirmed, the first in irregular orbits. All fifteen previously known moons of Uranus are 'regular', circling near the planet's equator. Most of these were discovered by the passing Voyager 2 spacecraft in 1986. These newly discovered moons are thought to be odd-shaped and about 100 km across. They are considered irregular, though, because they orbit in odd directions and far from Uranus. If Uranus' irregular moons have the same origin as those orbiting Jupiter, Saturn, and Neptune, then they were probably caught from orbits around the Sun. Moons like this are discovered by their motion. One of these moons is shown above as the circled point of light moving from left to right. (To stop the movie from repeating, click "stop" on most browsers.)
1997 November 4
Blue Stragglers in Globular Clusters
Credit: M. Shara (STScI), R.A. Safer (Villanova), M. Livio (STScI), WFPC2, HST, NASA
This old dog is doing new tricks. On the left is ancient globular cluster 47 Tucanae which formed many billions of years ago. On the right is a closeup of its dense stellar center by the Hubble Space Telescope, released last week. Circled are mysterious stars called "blue stragglers." Stars as bright and blue as blue stragglers live short lives, much shorter than the age of the host globular cluster itself. But this contradicts evidence that globular cluster stars formed all at once. Although this problem has been known for almost 50 years, a mass and spin rate for a blue straggler was first published last Saturday. This new information indicates that BSS 19 was rejuvenated by two orbiting stars slowly coalescing , and not by a dramatic collision.
Blue Stragglers in Globular Clusters
Credit: M. Shara (STScI), R.A. Safer (Villanova), M. Livio (STScI), WFPC2, HST, NASA
This old dog is doing new tricks. On the left is ancient globular cluster 47 Tucanae which formed many billions of years ago. On the right is a closeup of its dense stellar center by the Hubble Space Telescope, released last week. Circled are mysterious stars called "blue stragglers." Stars as bright and blue as blue stragglers live short lives, much shorter than the age of the host globular cluster itself. But this contradicts evidence that globular cluster stars formed all at once. Although this problem has been known for almost 50 years, a mass and spin rate for a blue straggler was first published last Saturday. This new information indicates that BSS 19 was rejuvenated by two orbiting stars slowly coalescing , and not by a dramatic collision.
1997 November 5
The Milky Way's Gamma-Ray Halo
Credit: D. Dixon (UCR), D. Hartmann (Clemson), E. Kolaczyk (U. Chicago), NASA
Our Milky Way galaxy appears to be surrounded by a halo of gamma rays. Gamma rays are the most energetic form of electromagnetic radiation, with more than a hundred thousand times the energy of visible light, but known gamma-ray sources don't account for the diffuse distribution of this high-energy glow. This surprising result is based on data from the EGRET instrument onboard the Compton Gamma Ray Observatory. In this false color all-sky image centered on the Milky Way, the brown and green regions indicate brighter, known sources of gamma-rays. The galactic center and plane clearly standout as do some distant galaxies seen near the top and bottom of the picture. The dim, blue regions above and below the plane correspond to our Galaxy's unexpected gamma-ray halo. What causes the halo? Future gamma-ray telescopes could solve this mystery. However, the excitement has already inspired tantalizing speculation about the solution including; collisions of low energy photons with high-energy cosmic rays, high energy electrons accelerated by a previous burst of Milky Way star formation, and exotic interacting particles which make up Dark Matter.
The Milky Way's Gamma-Ray Halo
Credit: D. Dixon (UCR), D. Hartmann (Clemson), E. Kolaczyk (U. Chicago), NASA
Our Milky Way galaxy appears to be surrounded by a halo of gamma rays. Gamma rays are the most energetic form of electromagnetic radiation, with more than a hundred thousand times the energy of visible light, but known gamma-ray sources don't account for the diffuse distribution of this high-energy glow. This surprising result is based on data from the EGRET instrument onboard the Compton Gamma Ray Observatory. In this false color all-sky image centered on the Milky Way, the brown and green regions indicate brighter, known sources of gamma-rays. The galactic center and plane clearly standout as do some distant galaxies seen near the top and bottom of the picture. The dim, blue regions above and below the plane correspond to our Galaxy's unexpected gamma-ray halo. What causes the halo? Future gamma-ray telescopes could solve this mystery. However, the excitement has already inspired tantalizing speculation about the solution including; collisions of low energy photons with high-energy cosmic rays, high energy electrons accelerated by a previous burst of Milky Way star formation, and exotic interacting particles which make up Dark Matter.
1997 November 6
The Magnetic Carpet Of The Sun
Credit: SOHO Consortium, ESA, NASA
The Sun has a magnetic carpet. Its visible surface appears to be carpeted with tens of thousands of magnetic north and south poles joined by looping field lines which extend outward into the Solar Corona. Recently, researchers have revealed maps of large numbers of these small magnetic concentrations produced using data and images from the space-based SOHO observatory. The above computer generated sunscape highlights these effects, with white and black field lines drawn in joining regions of strong magnetism. A close-up of the Solar surface is illustrated in the inset. These small magnetic regions emerge, fragment, drift, and disappear over periods of only 40 hours or so. Their origin is mystifying and their dynamic behavior is difficult to reconcile with present theories of rotationally driven large-scale Solar Magnetism. Is some unknown process at work? Possibly, but the source of this mystery may well be the solution to another -- the long standing mystery of why the outer Solar Corona is over 100 times hotter than the sun's visible surface! The SOHO data reveal that energy released as these loops break apart and interact seems to be heating the coronal plasma.
The Magnetic Carpet Of The Sun
Credit: SOHO Consortium, ESA, NASA
The Sun has a magnetic carpet. Its visible surface appears to be carpeted with tens of thousands of magnetic north and south poles joined by looping field lines which extend outward into the Solar Corona. Recently, researchers have revealed maps of large numbers of these small magnetic concentrations produced using data and images from the space-based SOHO observatory. The above computer generated sunscape highlights these effects, with white and black field lines drawn in joining regions of strong magnetism. A close-up of the Solar surface is illustrated in the inset. These small magnetic regions emerge, fragment, drift, and disappear over periods of only 40 hours or so. Their origin is mystifying and their dynamic behavior is difficult to reconcile with present theories of rotationally driven large-scale Solar Magnetism. Is some unknown process at work? Possibly, but the source of this mystery may well be the solution to another -- the long standing mystery of why the outer Solar Corona is over 100 times hotter than the sun's visible surface! The SOHO data reveal that energy released as these loops break apart and interact seems to be heating the coronal plasma.
1997 November 7
Evidence for Frame Dragging Black Holes
Drawing Credit & Copyright: J. Bergeron, Sky & Telescope Magazine
Gravity can do more than floor you. According to recent measurements of a star system thought to contain a black hole, it can spin you too. This effect, called frame-dragging, is most prominent near massive, fast spinning objects. Now, a team led by W. Cui (MIT) has used the orbiting Rossi X-ray Timing Explorer to search for it near a system thought to contain a black hole. Cui's team claim that matter in this system gets caught up and spun around the black hole at just the rate expected from frame-dragging. Such discoveries help scientists better understand gravity itself.
Evidence for Frame Dragging Black Holes
Drawing Credit & Copyright: J. Bergeron, Sky & Telescope Magazine
Gravity can do more than floor you. According to recent measurements of a star system thought to contain a black hole, it can spin you too. This effect, called frame-dragging, is most prominent near massive, fast spinning objects. Now, a team led by W. Cui (MIT) has used the orbiting Rossi X-ray Timing Explorer to search for it near a system thought to contain a black hole. Cui's team claim that matter in this system gets caught up and spun around the black hole at just the rate expected from frame-dragging. Such discoveries help scientists better understand gravity itself.
1997 November 8
Aristarchus' Unbelievable Discoveries
Credit: Space Shuttle Columbia, STS58, NASA
Here lived one of the greatest thinkers in human history. Aristarchus lived on the Greek island of Samos, a small island in the center of the above picture that can be identified with a good map. Aristarchus, who lived from 310 BC to 230 BC, postulated that the planets orbited the Sun - not the Earth -- over a thousand years before Copernicus and Galileo made similar arguments. Aristarchus used clear logic to estimate the size of the Earth, the size and distance to our Moon, the size and distance to our Sun, then he even deduced that the points of light we see at night are not dots painted on some celestial sphere but stars like our Sun at enormous distances. Aristarchus' discoveries remained truly unbelievable to the people of his time but stand today as pillars of deductive reasoning.
Aristarchus' Unbelievable Discoveries
Credit: Space Shuttle Columbia, STS58, NASA
Here lived one of the greatest thinkers in human history. Aristarchus lived on the Greek island of Samos, a small island in the center of the above picture that can be identified with a good map. Aristarchus, who lived from 310 BC to 230 BC, postulated that the planets orbited the Sun - not the Earth -- over a thousand years before Copernicus and Galileo made similar arguments. Aristarchus used clear logic to estimate the size of the Earth, the size and distance to our Moon, the size and distance to our Sun, then he even deduced that the points of light we see at night are not dots painted on some celestial sphere but stars like our Sun at enormous distances. Aristarchus' discoveries remained truly unbelievable to the people of his time but stand today as pillars of deductive reasoning.