Black Holes Manage Galactic Growth

Using a new computer model of galaxy formation, researchers have shown that growing black holes release a blast of energy that fundamentally regulates galaxy evolution and black hole growth itself. The model explains for the first time observed phenomena and promises to deliver deeper insights into our understanding of galaxy formation and the role of black holes throughout cosmic history, according to its creators. Published in the Feb. 10 issue of Nature, the results were generated by Carnegie Mellon University astrophysicist Tiziana Di Matteo and her colleagues while at the Max Planck Institut fur Astrophysik in Germany. Di Matteo?s collaborators include Volker Springel at Max-Planck Institut for Astrophysics and Lars Hernquist at Harvard University.
“In recent years, scientists have begun to appreciate that the total mass of stars in today?s galaxies corresponds directly to the size of a galaxy?s black hole, but until now, no one could account for this observed relationship,” said Di Matteo, assistant professor of physics at Carnegie Mellon. “Using our simulations has given us a completely new way to explore this problem.”

The key to the researchers? breakthrough was incorporating calculations for black hole dynamics into a computational model of galaxy formation.

As galaxies formed in the early universe, they likely contained small black holes at their centers. In the standard scenario of galaxy formation, galaxies grow by coming together with one another by the pull of gravity. In the process, the black holes at their center merge together and quickly grow to reach their observed masses of a billion times that of the Sun; hence, they are called supermassive black holes. Also at the time of merger, the majority of stars form from available gas. Today?s galaxies and their central black holes must be the result of a series of such events.

Di Matteo and her colleagues simulated the collision of two nascent galaxies and found that when the two galaxies came together, their two supermassive black holes merged and initially consumed the surrounding gas. But this activity was self-limiting. As the remnant galaxy?s supermassive black hole sucked up gas, it powered a luminescent state called a quasar. The quasar energized the surrounding gas to such a level that it was blown away from the vicinity of the supermassive black hole to the outside of the galaxy. Without nearby gas, the galaxy?s supermassive black hole could not “eat” to sustain itself and became dormant. At the same time, gas was no longer available to form any more stars.

“We?ve discovered that the energy released by black holes during a quasar phase powers a strong wind that prevents material from falling into the black hole,” Springel said. “This process inhibits further black hole growth and shuts off the quasar, just as star formation stops inside a galaxy. As a result, the black hole mass and the mass of stars in a galaxy are closely linked. Our results also explain for the first time why the quasar lifetime is such a short phase compared to the life of a galaxy.”

In their simulations, Di Matteo, Springel and Hernquist found that the black holes in small galaxies self-limit their growth more effectively than in those in larger galaxies. A smaller galaxy contains smaller amounts of gas so that a small amount of energy from the black hole can quickly blow this gas away. In a large galaxy, the black hole can reach a greater size before its surrounding gas is energized enough to stop falling in. With their gas quickly spent, smaller galaxies make fewer stars. With a longer-lived pool of gas, larger galaxies make more stars. These findings match the observed relation between black hole size and the total mass of stars in galaxies.

“Our simulations demonstrate that self-regulation can quantitatively account for observed facts associated with black holes and galaxies,” said Hernquist, professor and chair of astronomy in Harvard?s Faculty of Arts and Sciences. “It provides an explanation for the origin of the quasar lifetime and should allow us to understand why quasars were more plentiful in the early universe than they are today.”

“With these computations, we now see that black holes must have an enormous impact on the way galaxies form and evolve,” Di Matteo said. “The successes obtained so far will allow us to implement these models within larger simulated universes, so that we can understand how large populations of black holes and galaxies influence each other in a cosmological context.”

The team ran their simulations with the extensive computing resources of the Center for Parallel Astrophysical Computing at the Harvard-Smithsonian Center for Astrophysics and at the Rechenzentrum der Max-Planck-Gesellschaft in Garching.

Original Source: Max Planck Institute News Release

What Did Galileo See?

A replica of the earliest surviving telescope attributed to Galileo Galilei, on display at the Griffith Observatory. Credit: Wikipedia Commons/Mike Dunn

By the time Galileo took eye to eyepiece in Padua Italy in 1609, he had already begun a life-long quest to understand the natural world around him. At his father’s behest, Gailieo gave up his youthful aspirations to join the Camaldolese Order as a monk and began training in medicine. Before completing his medical studies however, Galileo’s strong interest in the laws of nature (along with a little intercession by one of his teachers in mathematics) overcame his fathers insistence and he embraced mathematics.

Over the next quarter century Galileo made numerous investigations into the mechanics of motion and weight. Early on he was intrigued by Archimedes investigations into specific gravity and published a work entitled: “La Balancitta” (or “The Little Weight”). Galileo’s bent was as scientific as mathematical, he suggested methods of testing the behavior of falling bodies using inclined planes. (Although it is unlikely that he ever dropped objects from the famed “Leaning Tower of Pisa”.)

By the year 1609 Galileo had spent nearly two decades ensconced as a lecturer on mathematics and physical sciences at the University of Padua. He is said to have described this period as one of the most personally fulfilling years of his life. But the quiet joys of teaching and raising a family of three children were poised for change. And that change came in the form of a fateful letter describing a spyglass demonstrated by a Dutchman visiting Venice (located some 40 kms west of the university).

Based on a scant description of the spyglass workings, Galileo concluded that its main principle was that of refraction. Obtaining “off-the-shelf” lenses normally for spectacle use, he soon possessed a 4x instrument and it wasn’t long thereafter that he had personally ground a lens set and crafted a telescope of twice that magnification. By the Spring of 1610, Galileo had published the first telescopic “observing reports” describing denizens of the night sky. And in that report (Sidereus Nuncius – The Starry Messenger) Galileo himself lists a few of his most startling discoveries:

“With the aid of this new instrument one looks upon the face of the Moon, the expanse of the Milky Way, innumerable fixed stars, faint nebulosities and asterisms, and the four wandering stars attending Jupiter never before seen.”-1

Recognizing the significance of these discoveries Galileo goes on to say:

“Great things embodying the spirit of truth based on observation and contemplation of nature do I propose in this short treatise. Large, I say, and for the clarification of truth, based on an innovation never heard throughout the centuries, and finally I extoll the instrument by which means these same things have been revealed to our perception.”

There can be no doubt that Galileo’s early adoption of the recently invented spyglass for astronomical purposes marked a major departure toward the way we now view the world. For before Galileo’s era the heavens and the Earth were not in accord. The bulk of the thinking going on prior to Galileo was scholastic in nature. Truth depended on the words of the ancients – words which carried greater weight of authority than natural law and behavior. It was the era of faith – not science – that Galileo was born into. But his observations built a bridge between Terrum et Coelum. Earth and sky became part of a single natural order. The telescope could demonstrate to anyone with an open mind that there was more to all things than could be conceived of by the great minds of the past. Nature had begun to instruct the hearts and minds of humanity…

But let us speak no more of Earth-shaking events. What did Galileo actually see in the early months of the year 1610?

Lacking a background in Latin is no hindrance to furthering our investigation, for “the Starry Messenger” himself left many fine sketches (a few which are seen in the above composite image).

Of course, any amateur astronomer of the today can do no better than to begin with the Moon. Using a telescope is no easy matter. Sweeping the sky unsteadily at high magnifications to find anything in the heavens can be very frustrating to the neophyte to our High Art and Science. Of course, Galileo’s first telescope was very low power and this simplified things. But his later instruments always included a second smaller “finder scope” to simplify astro-navigation. Here are some of Galileo’s descriptions of the Moon:

“Most beautiful and admirable is it to see the Moon’s luminous form,… At nearly thirty diameters – some 900 times greater in region – anyone can perceive that the Moon is not covered with a smooth and uniform surface but in fact reveals great mountainous shelves, deep cavities, and gorges just like those of the Earth.”

Even during the winter the Milky Way can be seen – a faint gossamer of light attending Cassiopeia and Perseus to the north then plummeting south east of Orion – the Hunter, into Monoceros – the Unicorn. Again The Starry Messenger speaks:

“Moreover let us not underestimate the questions surrounding the Milky Way. For it has revealed to the senses its essence (through the turning of our instrument upon it). And in so doing out of its cloudy substance numerous stars are called forth.”

But in terms of Galileo’s own estimation his observations of the four Jupiterean satellites evoked the greatest of significances:

“By far and exceeding every other wonder, and mainly promoted for the contemplation of all astronomers and philosophers, is the discovery of four wandering stars. For I propose that they – like Venus and Mercury around the Sun – have revolutions around a conspicuous star among the known wanderers. And in their lesser wanderings they may precede the greater – sometimes before it and sometimes after – never going beyond some pre-determined limits.”

Galileo also went on to detect sun spots and the phases of Venus. The Venusian phases, in particular conclusively demonstrated the heliocentrism conceived by Copernicus and mathematically described by Johan Kepler of Galileo’s own time and correspondence.

Of course Galileo was large enough in his perception to realize that these few initial discoveries were but only the beginnings of a beginning for the telescope as an instrument and astronomy as a whole for he goes on to say:

“Perhaps other miraculous things from both myself and others will be discovered in the future aided by this instrument…”

Galileo was wrong – there was no “perhaps” about it…

-1 This and later quotations ascribed to Galileo are re-interpretations of an Italian to English Babelfish translation of Siderius Nuncius by the author.

About The Author:
Inspired by the early 1900’s masterpiece: “The Sky Through Three, Four, and Five Inch Telescopes”, Jeff Barbour got a start in astronomy and space science at the age of seven. Currently Jeff devotes much of his time observing the heavens and maintaining the website Astro.Geekjoy.

Mini Solar System Around a Brown Dwarf

Moons circle planets, and planets circle stars. Now, astronomers have learned that planets may also circle celestial bodies almost as small as planets.

NASA’s Spitzer Space Telescope has spotted a dusty disk of planet-building material around an extraordinarily low-mass brown dwarf, or “failed star.” The brown dwarf, called OTS 44, is only 15 times the mass of Jupiter. Previously, the smallest brown dwarf known to host a planet-forming disk was 25 to 30 times more massive than Jupiter.

The finding will ultimately help astronomers better understand how and where planets — including rocky ones resembling our own — form.

“There may be a host of miniature solar systems out there, in which planets orbit brown dwarfs,” said Dr. Kevin Luhman, lead author of the new study from the Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass. “This leads to all sorts of new questions, like ‘Could life exist on such planets?’ or ‘What do you call a planet circling a planet-sized body? A moon or a planet?'”

Brown dwarfs are something of misfits in the astronomy world. These cool orbs of gas have been called both failed stars and super planets. Like planets, they lack the mass to ignite and produce starlight. Like stars, they are often found alone in space, with no parent body to orbit.

“In this case, we are seeing the ingredients for planets around a brown dwarf near the dividing line between planets and stars. This raises the tantalizing possibility of planet formation around objects that themselves have planetary masses,” said Dr. Giovanni Fazio, an astronomer at the Harvard Smithsonian Center for Astrophysics and a co-author of the new study.

The results were presented today at the Planet Formation and Detection meeting at the Aspen Center for Physics, Aspen, Colo., and will be published in the Feb. 10th issue of The Astrophysical Journal Letters.

Planet-forming, or protoplanetary, disks are the precursors to planets. Astronomers speculate that the disk circling OTS 44 has enough mass to make a small gas giant planet and a few Earth-sized, rocky ones. This begs the question: Could a habitable planet like Earth sustain life around a brown dwarf?

“If life did exist in this system, it would have to constantly adjust to the dwindling temperatures of a brown dwarf,” said Luhman. “For liquid water to be present, the planet would have to be much closer to the brown dwarf than Earth is to our Sun.”

“It’s exciting to speculate about the possibilities for life in such as system, of course at this point we are only beginning to understand the unusual circumstances under which planets arise,” he added.

Brown dwarfs are rare and difficult to study due to their dim light. Though astronomers recently reported what may be the first-ever image of a planet around a brown dwarf called 2M1207, not much is understood about the planet-formation process around these odd balls of gas. Less is understood about low-mass brown dwarfs, of which only a handful are known.

OTS 44 was first discovered about six months ago by Luhman and his colleagues using the Gemini Observatory in Chile. The object is located 500 light-years away in the Chamaeleon constellation. Later, the team used Spitzer’s highly sensitive infrared eyes to see the dim glow of OTS 44’s dusty disk. These observations took only 20 seconds. Longer searches with Spitzer could reveal disks around brown dwarfs below 10 Jupiter masses.

Other authors of this study include Dr. Paola D’Alessia of the Universidad Nacional Autonoma de Mexico; and Drs. Nuria Calvet, Lori Allen, Lee Hartmann, Thomas Megeath and Philip Myers of the Harvard-Smithsonian Center for Astrophysics.

NASA’s Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate, Washington, D.C. Science operations are conducted at the Spitzer Science Center, Pasadena, Calif. JPL is a division of Caltech. The infrared array camera, which spotted the protoplanetary disk around OTS 44, was built by NASA Goddard Space Flight Center, Greenbelt, Md.; its development was led by Fazio.

Original Source: Spitzer News Release

This Star is Leaving Our Galaxy

Using the MMT Observatory in Tucson, AZ, astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA) are the first to report the discovery of a star leaving our galaxy, speeding along at over 1.5 million miles per hour. This incredible speed likely resulted from a close encounter with the Milky Way’s central black hole, which flung the star outward like a stone from a slingshot. So strong was the event that the speedy star eventually will be lost altogether, traveling alone in the blackness of intergalactic space.

“We have never before seen a star moving fast enough to completely escape the confines of our galaxy,” said co-discoverer Warren Brown (CfA). “We’re tempted to call it the outcast star because it was forcefully tossed from its home.”

The star, catalogued as SDSS J090745.0+24507, once had a companion star. However, a close pass by the supermassive black hole at the galaxy’s center trapped the companion into orbit while the speedster was violently flung out. Astronomer Jack Hills proposed this scenario in 1998, and the discovery of the first expelled star seems to confirm it.

“Only the powerful gravity of a very massive black hole could propel a star with enough force to exit our galaxy,” explained Brown.

While the star’s speed offers one clue to its origin, its path offers another. By measuring its line-of-sight velocity, it suggests that the star is moving almost directly away from the galactic center. “It’s like standing curbside watching a baseball fly out of the park,” said Brown.

Its composition and age provide additional proof of the star’s history. The fastest star contains many elements heavier than hydrogen and helium, which astronomers collectively call metals. “Because this is a metal-rich star, we believe that it recently came from a star-forming region like that in the galactic center,” said Brown. Less than 80 million years were needed for the star to reach its current location, which is consistent with its estimated age.

The star is traveling twice as fast as galactic escape velocity, meaning that the Milky Way’s gravity will not be able to hold onto it. Like a space probe launched from Earth, this star was launched from the galactic center onto a never-ending outward journey. It faces a lonely future as it leaves our galaxy, never to return.

Brown’s co-authors on the paper announcing this find are Margaret J. Geller, Scott J. Kenyon and Michael J. Kurtz (Smithsonian Astrophysical Observatory). This study will be published in an upcoming issue of The Astrophysical Journal.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Original Source: CfA News Release

Galaxies Might Exist Without Stars

Fitted with its new compound eye on the heavens, the National Science Foundation’s (NSF) Arecibo Observatory telescope, the world’s largest and most sensitive single-dish radio telescope, early tomorrow morning begins a years-long survey of distant galaxies, perhaps discovering elusive “dark galaxies” — galaxies that are devoid of stars.

Astronomers at Arecibo Observatory hope the new sky survey will result in a comprehensive census of galaxies out to a distance of 800 million light years from our galaxy, the Milky Way, in nearly one-sixth of the sky — or some 7,000 square degrees.

The search, conducted by an international team of students and scholars, is the first of a series of large-scale Arecibo surveys that will take advantage of a the telescope’s new instrument, installed last year, called ALFA (for Arecibo L-Band Feed Array). The device is essentially a seven-pixel camera with unprecedented sensitivity for making radio pictures of the sky, allowing astronomers to collect data about seven times faster than at present. The project has been dubbed ALFALFA, for Arecibo Legacy Fast Alfa Survey.

“Fast” does not refer to the time necessary to carry out the survey, which will require thousand hours of telescope time and a few years to complete, but rather to the observing technique, which consists in fast sweeps of broad swaths of sky.

The survey is supported by the National Astronomy and Ionosphere Center (NAIC) at Cornell University, Ithaca, N.Y., which manages the Arecibo Observatory for the NSF. In addition, support is being provided through research grants from the NSF and the Brinson Foundation to the project’s leader, Cornell professor of astronomy Riccardo Giovanelli, and to Martha Haynes, a Goldwin Smith Professor of Astronomy at Cornell.

Giovanelli explains that ALFA operates at radio frequencies near 1420 MegaHertz (MHz), a frequency range that includes a spectral line emitted by neutral atomic hydrogen, the most abundant element in the universe. ALFA detects this signature of hydrogen, which hopefully signals the presence of an undiscovered galaxy. Nearly every previous sky survey has been of optically, infrared- or X-ray-selected galaxies.

ALFALFA will be six times more sensitive — meaning that it will go much deeper in distance — than the only previous hydrogen wide-field survey carried out in Australia in the late 1990s. “What has made ALFALFA possible is the completion of the Gregorian upgrade to the Arecibo telescope in 1997, which allowed feed arrays to be placed in the telescope focal plane and expanded the instantaneous frequency coverage of the telescope,” he says.

Besides providing a comprehensive census of the gaseous content of the near universe, ALFALFA will explore galaxies in groups and clusters and investigate the efficiency by which galaxies convert gas into stars. What particularly intrigues astronomers is that ALFALFA could determine whether gas-rich systems of low mass that have not been able to convert their cosmic material into stars — the so-called dark galaxies — actually exist. Because these galaxies, being starless, are optically inert, it is hoped that they can be detected by their hydrogen signature.

The galaxy survey is feasible now because ALFA lets the telescope see seven spots — seven pixels — on the sky at once, greatly reducing the time needed to make all-sky surveys. The Australian-built detector, on the 305-meter (1,000-foot) diameter Arecibo radio telescope, provides the imaging speed and sensitivity that astronomers will need for their search.

Robert Brown, the NAIC’s director, said that a significant fraction of the Arecibo telescope time in the next few years will be devoted to extensive surveys with the ALFA array, such as ALFALFA. The new survey consortium consists of 38 scientists from 10 countries, including the United States, France, the United Kingdom, Italy, Spain, Israel, Argentina, Chile, Russia and the Ukraine.

Several of the members are graduate students who will base their Ph.D. theses on ALFALFA data. Among them are Cornell graduate students Brian Kent, Sabrina Stierwalt and Amelie Saintonge.

Says Giovanelli: “My one and only paper published in an engineering journal proposed the construction of a feed array at the upgraded Arecibo telescope to carry out hydrogen line surveys of the sky. It took 15 years of waiting, but I am finally going to do the experiment.”

Original Source: Cornell News Release

Upper Limit on Star Mass

New research from the University of Michigan shows that there may be an upper limit to the mass of a star, somewhere around 120 to 200 times bigger than our sun.

The sun is the closest star to Earth and therefore looks very big to us, but compared to other stars in the Milky Way, it?s considered a low-mass star. Knowing that there may be a limit to a star?s mass answers a fundamental question, but raises a raft of other issues about what limits their mass, said Sally Oey, assistant professor of astronomy.

The study is the first to determine the stellar upper mass limit by examining a wide range of star clusters, said Oey (rhymes with chewy). In the paper, ?Statistical Confirmation of a Stellar Upper Mass Limit,? Oey and colleague C.J. Clarke, from the Institute of Astronomy at Cambridge, England, compared historical data on 12 OB associations, large aggregates of hundreds to several thousands of young stars.

The paper will appear in the Feb. 10 edition of the Astrophysical Journal Letters.

Other studies have suggested an upper mass limit of about the same size, but had looked at only one cluster. ?Ours has more statistical significance because we were able to use many clusters,? Oey said.

Oey and Clarke looked at star clusters in the Milky Way, our galaxy, and in the Magellanic Clouds, the brightest satellite galaxies, because they are close enough to enable seeing individual stars and making measurements, Oey said.

?If you looked at any of the clusters, you?ll see roughly the same ratio of big to little stars,? Oey said. Based on the size and number of stars, the probability of finding stars above a certain mass dropped significantly at 120-200 solar masses, Oey said.

The question of mass is an important one because it relates to basic star formation, Oey said. ?My African violets won?t grow any bigger now because their roots are totally taking up the maximum room in the pot,? she said. ?If I repotted them they would grow larger. Are the stars maxed out because the parent clouds are limiting them, or because, like a whale in the sea, there?s something else physical about stars themselves that limits the size?

?The question about why stars have the masses that they do is fundamental, and our lack of understanding shows that we really don?t know some basics of how stars form.?

The biggest stars put out huge amounts of energy by exploding when they die or by releasing ultraviolet radiation during the star?s normal life. That puts tremendous energy into the interstellar medium, which in turn leads to evolutionary activity like renewed star formation and the conversion of gas into stars.

?If you have more stars and energy in the interstellar medium it means more evolutionary activity,? Oey said. ?It stirs things up.?

Original Source: University of Michigan News Release

Where Did the Modern Telescope Come From?

If you think about it, it was just a matter of time before the first telescope was invented. People have been fascinated by crystals for millenia. Many crystals – quartz for instance – are completely transparent. Others – rubies – absorb some frequencies of light and pass others. Shaping crystals into spheres can be done by cleaving, tumbling, and polishing – this removes sharp edges and rounds the surface. Dissecting a crystal begins with finding a flaw. Creating a half-sphere – or crystal segment – creates two different surfaces. Light is gathered by the convex frontface and projected toward a point of convergence by the planar backface. Because crystal segments have severe curves, the point of focus may be very close to the crystal itself. Due to short focal lengths, crystal segments make better microscopes than telescopes.

It wasn’t the crystal segment – but the lens of glass – that made modern telescopes possible. Convex lenses came out of glass ground in a way to correct far-sighted vision. Although both spectacles and crystal segments are convex, far-sighted lenses have less severe curves. Rays of light are only slightly bent from the parallel. Because of this, the point where the image takes form is much farther away from the lens. This creates image scale large enough for detailed human inspection.

The first use of lenses to augment sight can be traced back to the Middle East of the 11th century. An Arabian text (Opticae Thesaurus written by scientist-mathematician Al-hazen) notes that segments of crystal balls could be used to magnify small objects. In the late 13th century, an English monk (possibly referencing Roger Bacon’s Perspectiva of 1267) is said to have created the first practical near-focus spectacles to aid in reading the Bible. It wasn’t until 1440 when Nicholas of Cusa ground the first lens to correct near-sightedness -1. And it would be another four centuries before defects in lens shape itself (astigmatism) would be aided by a set of spectacles. (This was accomplished by the British astronomer George Airy in 1827 some 220 years after another – more famous astronomer – Johann Kepler first accurately described the effect of lenses on light.)

The earliest telescopes took form just after spectacle grinding became well-established as a means to correct both myopia and presbyopia. Because far-sighted lenses are convex, they make good “collectors” of light. A convex lens takes parallel beams from the distance and bends them to a common point of focus. This creates a virtual image in space – one that can be inspected more closely using a second lens. The virtue of a collecting lens is twofold: It combines light together (increasing its intensity) – and amplifies image scale – both to a degree potentially far greater than the eye alone is capable of.

Concave lenses (used to correct near-sightedness) splay light outward and make things appear smaller to the eye. A concave lens can increase the focal length of the eye whenever the eye’s own system (fixed cornea and morphing lens) falls short of focusing an image on the retina. Concave lenses make good eyepieces because they enable the eye to more closely inspect the virtual image cast by a convex lens. This is possible because convergent rays from a collecting lens are refracted toward the parallel by a concave lens. The effect is to show a nearby virtual image as though at a great distance. A single concave lens allows the eye lens to relax as if focused on infinity.

Combining convex and concave lenses was just a matter of time. We can imagine the very first occasion occurring as children toyed with the lens-grinder’s toil of the day – or possibly when the optician felt called to inspect one lens using another. Such an experience must have seemed almost magical: A distant tower instantly looms as if approached at the end of a long stroll; unrecognizable figures are suddenly seen to be close friends; natural boundaries – such as canals or rivers – are leapt over as though Mercury’s own wings were attached to the heals…

Once the telescope came to be, two new optical problems presented themselves. Light collecting lenses create curved virtual images. That curve is slightly “bowl-shaped” with the bottom turned toward the observer. This of course is just the opposite of how the eye itself sees the world. For the eye sees things as though arrayed on a great sphere whose center lies on the retina. So something had to be done to draw perimeter rays back toward the eye. This problem was partially resolved by astronomer Christiaan Huygens in the 1650’s. He did this by combining several lenses together as a unit. The use of two lenses brought more of the peripheral rays from a collecting lens toward the parallel. Huygen’s new eyepiece effectively flattened the image and allowed the eye to achieve focus across a wider field of view. But that field would still induce claustrophobia in most observers of today!

The final problem was more intractable – refracting lenses bend light based on wavelength or frequency. The greater the frequency, the more a particular color of light is bent. For this reason, objects displaying light of various colors (polychromatic light) are not seen at the same point of focus across the electro-magnetic spectrum. Basically lenses act in ways similar to prisms – creating a spread of colors, each with its own unique focal point.

Galileo’s first telescope only solved the problem of getting an eye close enough to magnify the virtual image. His instrument was composed of two lenses separable by a controlled distance to set focus. The objective lens had a less severe curve to collect light and bring it to various points of focus depending on color-frequency. The smaller lens – possessed of a more severe curve of shorter focal length – allowed Galileo’s observing eye to get close enough to the image to see magnified detail.

But Galileo’s scope could only be brought to focus near the middle of the eyepiece field of view. And focus could only be set based on the dominant color emitted or reflected by whatever Galileo was viewing at the time. Galileo usually observed bright studies – like the Moon, Venus, and Jupiter – using an aperture stop and took some pride in having come up with the idea!

Christiaan Huygens created the first – Huygenian – eyepiece after the time of Galileo. This eyepiece consists of two plano-convex lenses facing the collecting lens – not a single concave lens. The focal plane of the two lenses lies between the objective and eye lens elements. The use of two lenses flattened the curve of the image – but only over a score or so degrees of apparent field of view. Since Huygen’s time, eyepieces have become much more sophisticated. Beginning with this original concept of multiplicity, today’s eyepieces can add another half-dozen or so optical elements rearranged in both shape and position. Amateur astronomers can now purchase eyepieces off the shelf giving reasonably flat fields exceeding 80 degrees in apparent diameter-2.

The third problem – that of chromatically tinged multi-color images – was not solved in telescopy until a working reflector telescope was designed and constructed by Sir Isaac Newton in the 1670’s. That telescope eliminated the collecting lens altogether – though it still required the use of a refractory eyepiece (which contributes far less to “false color” than the objective does).

Meanwhile early attempts to fix the refractor were to simply make them longer. Scopes to 140 feet in length were devised. None had especially exorbitant lens diameters. Such spindly dynasaurs required a truly adventurous observer to use – but did “tone down” the color problem.

Despite eliminating color error, early reflectors had problems too. Newton’s scope used a spherically ground speculum mirror. Compared to the aluminum coating of modern reflector mirrors, speculum is a weak performer. At roughly three-quarters the light gathering ability of aluminum, speculum loses about one magnitude in light grasp. Thus the six-inch instrument devised by Newton behaved more like a contemporary 4 inch model. But this is not what made Newton’s instrument hard to sell, it simply provided very poor image quality. And this was due to the use of that spherically ground primary mirror.

Newton’s mirror did not bring all rays of light to common focus. The fault didn’t lay with the speculum – it lay with the shape of the mirror which – if extended 360 degrees – would make a complete circle. Such a mirror is incapable of bringing central light beams to the same point of focus as those nearer the rim. It wasn’t until 1740 when Scotland’s John Short corrected this problem (for on-axis light) by parabolizing the mirror. Short accomplished this in a very practical manner: Since parallel rays nearer the center of a spherical mirror overshoot marginal rays, why not just deepen the center and rein them in?

It wasn’t until the 1850’s that silver replaced speculum as the mirror surface of choice. Of course the more than 1000 parabolic reflectors fabricated by John Short all had speculum mirrors. And silver, like speculum, loses reflectivity rather quickly over time to oxidation. By 1930, the first professional telescopes were being coated with more durable and reflective aluminum. Despite this improvement, small reflectors bring less light to focus than refractors of comparable aperture.

Meanwhile, refractors evolved too. During John Short’s time, opticians figured out something Newton had not – how to get red and green light to merge at a common point of focus by refraction. This was first accomplished by Chester Moor Hall in 1725 and rediscovered a quarter century later by John Dolland. Hall and Dolland combined two different lenses – one convex and other concave. Each consisted of a different glass type (crown and flint) refracting light differently (based on refractive indices). The convex lens of crown glass did the immediate task of collecting light of all colors. This bent photons inward. The negative lens splayed the converging beam slightly outward. Where the positive lens caused red light to overshoot focus, the negative lens caused red to undershoot. Red and green blended and the eye saw yellow. The result was the achromatic refractor telescope – a type favored by many amateur astronomers today for inexpensive, small aperture, wide-field, but – in shorter focal ratios – less than ideal image quality use.

It wasn’t until the mid-nineteenth century that opticians managed to get blue-violet to join red and green at focus. That development initially came out of the use of exotic materials (flourite) as an element in the doublet objectives of high-powered optical microscopes – not telescopes. Three element telescope designs using standard glass types – triplets – solved the problem as well some forty years later (just before the twentieth-century).

Today’s amateur astronomers can choose from a wide assortment of scope types and manufacturers. There is no one scope for all skies, eyes, and celestial studies. Issues of field flatness (particularly with fast Newtonian telescopes), and hefty optical tubes (associated with large refractors) have been addressed by new optical configurations developed in the 1930’s. Instrument types – such as the SCT (Schmidt-Cassegrain telescope) and MCT (Maksutov-Cassegrain telescope) plus newton-esque Schmidt and Maksutov variants and oblique reflectors – are now manufactured in the USA and throughout the world. Each scope type developed to address some valid concern or another related to scope size, bulk, field flatness, image quality, contrast, cost, and portability.

Meanwhile refractors have taken center stage among optophiles – folks wanting the highest possible image quality irrespective of other constraints. Fully apochromatic (color-corrected) refractors provide some of the most stunning images available for optical, photographic, and CCD imaging use. But alas, such models are limited to smaller apertures due to significantly higher costs of materials (exotic low-dispersion crystals & glass), manufacture (up to six optical surfaces must be shaped) and greater load bearing requirements (due to heavy disks of glass).

All of today’s variety in scope types began with the discovery that two lenses of unequal curvature could be held up to the eye to transport human perception over great distances. Like many great technological advances, the modern astronomical telescope emerged out of three fundamental ingredients: Necessity, imagination, and a growing understanding of the way energy and matter interact.

So where did the modern astronomical telescope come from? Certainly the telescope went through a long period of constant improvement. But perhaps, just perhaps, the telescope is at essence a gift of the Universe itself exulting in profound admiration through human eyes, hearts, and minds…

-1 Questions exist as to who first created spectacles correcting far- and near-sighted vsion. It is unlikely that Abu Ali al-Hasan Ibn al-Haitham or Roger Bacon ever used a lens in this way. Confusing the issue of provenance is the question of how spectacles were actually worn. It is likely that the first visual aid was simply held to the eye as a monocle – necessity taking over from there. But would such a primitive method be historically recounted as “the origin of the spectacle”?

-2 The ability of a particular eyepiece to compensate for a necessarily curved virtual image is limited fundamentally by effective focal ratio and scope archetecture. Thus telescopes whose focal length are many times their aperture present less of an instantaneous curve at the “image plane”. Meanwhile scopes that refract light initially (catadioptics as well as refractors) have the advantage of better handling off-axis light. Both factors increase the radius of curvature of the projected image and simplify the eyepiece’s task of presenting a flat field to the eye.

About The Author:
Inspired by the early 1900’s masterpiece: “The Sky Through Three, Four, and Five Inch Telescopes”, Jeff Barbour got a start in astronomy and space science at the age of seven. Currently Jeff devotes much of his time observing the heavens and maintaining the website Astro.Geekjoy.

Swift is Now Fully Operational

The Swift satellite’s Ultraviolet/Optical Telescope (UVOT) has seen first light, capturing an image of the Pinwheel Galaxy, long loved by amateur astronomers as the “perfect” face-on spiral galaxy. The UVOT now remains poised to observe its first gamma-ray burst and the Swift observatory, launched into Earth orbit in November 2004, is now fully operational.

Swift is a NASA-led mission dedicated to the gamma-ray burst mystery. These random and fleeting explosions likely signal the birth of black holes. With the UVOT turned on, Swift now is fully operational. Swift’s two other instruments — the Burst Alert Telescope (BAT) and the X-ray Telescope (XRT) — were turned on over the past several weeks and have been snapping up gamma-ray bursts ever since.

“After many years of effort building the UVOT, it was exciting to point it toward the famous Pinwheel Galaxy, M101,” said Peter Roming, UVOT Lead Scientist at Penn State. “The ultraviolet wavelengths in particular reveal regions of star formation in the galaxy’s wispy spiral arms. But more than a pretty image, this first-light observation is a test of the UVOT’s capabilities.”

Swift’s three telescopes work in unison. The BAT detects gamma-ray bursts and autonomously turns the satellite in seconds to bring the burst within view of the XRT and the UVOT, which provide detailed follow-up observations of the burst afterglow. Although the burst itself is gone within seconds, scientists can study the afterglow for clues about the origin and nature of the burst, much like detectives at a crime scene.

The UVOT serves several important functions. First, it will pinpoint the gamma-ray burst location a few minutes after the BAT detection. The XRT provides a burst position within a 1- to-2-arcsecond range. The UVOT will provide sub-arcsecond precision, a spot on the sky far smaller than the eye of a needle at arm’s length. This information is then relayed to scientists at observatories around the world so that they can view the afterglow with other telescopes.

As the name applies, the UVOT captures the optical and ultraviolet component of the fading burst afterglow. “The ‘big gun’ optical observatories such as Hubble, Keck, and VLT have provided useful data over the years, but only for the later portion of the afterglow,” said Keith Mason, the U.K. UVOT Lead at University College London?s Mullard Space Science Laboratory. “The UVOT isn’t as powerful as these observatories, but has the advantage of observing from the very dark skies of space. Moreover, it will start observing the burst afterglow within minutes, as opposed to the day-long or week-long lag times inherent with heavily used observatories. The bulk of the afterglow fades within hours.”

The ultraviolet portion will be particularly revealing, said Roming. “We know nearly nothing about the ultraviolet part of a gamma-ray burst afterglow,” he said. “This is because the atmosphere blocks most ultraviolet rays from reaching telescopes on Earth, and there have been few ultraviolet telescopes in orbit. We simply haven’t yet reached a burst fast enough with a UV telescope.”

The UVOT’s imaging capability will enable scientists to understand the shape of the afterglow as it evolves and fades. The telescope’s spectral capability will enable detailed analysis of the dynamics of the afterglow, such as the temperature, velocity, and direction of material ejected in the explosion.

The UVOT also will help scientists determine the distance to the closer gamma-ray bursts, within a redshift of 4, which corresponds to a distance of about 11 billion light years. The XRT will determine distances to more distant bursts.

Scientists hope to use the UVOT and XRT to observe the afterglow of short bursts, less than two seconds long. Such afterglows have not yet been seen; it is not clear if they fade fast or simply don’t exist. Some scientists think there are at least two kinds of gamma-ray bursts: longer ones (more than two seconds) that generate afterglows and that seem to be caused by massive star explosions, and shorter ones that may be caused by mergers of black holes or neutron stars. The UVOT and XRT will help to rule out various theories and scenarios.

The UVOT is a 30-centimeter telescope with intensified CCD detectors and is similar to an instrument on the European Space Agency’s XMM-Newton mission. The UVOT is as sensitive as a four-meter optical ground-based telescope. The UVOT’s day-to-day observations, however, will look nothing like M101. Distant and faint gamma-ray burst afterglows will appear as tiny smudges of light even to the powerful UVOT. The UVOT is a joint product of Penn State and the Mullard Space Science Laboratory.

Swift is a medium-class explorer mission managed by NASA Goddard. Swift is a NASA mission with participation of the Italian Space Agency and the Particle Physics and Astronomy Research Council in the United Kingdom. It was built in collaboration with national laboratories, universities and international partners, including Penn State University in Pennsylvania, U.S.A.; Los Alamos National Laboratory in New Mexico, U.S.A.; Sonoma State University in California, U.S.A.; the University of Leicester in Leicester, England; the Mullard Space Science Laboratory in Dorking, England; the Brera Observatory of the University of Milan in Italy; and the ASI Science Data Center in Rome, Italy.

Original Source: Eberly College of Science News Release

Pluto and Charon Could Have Formed Together

The evolution of Kuiper Belt objects, Pluto and its lone moon Charon may have something in common with Earth and our single Moon: a giant impact in the distant past.

Dr. Robin Canup, assistant director of Southwest Research Institute’s? (SwRI) Department of Space Studies, argues for such an origin for the Pluto-Charon pair in an article for the January 28 issue of the journal Science.

Canup, who currently is a visiting professor at the California Institute of Technology, has worked extensively on a similar “giant collision” scenario to explain the Moon’s origin.

In both the Earth-Moon and Pluto-Charon cases, Canup’s smooth particle hydrodynamic simulations depict an origin in which a large, oblique collision with the growing planet produced its satellite and provided the current planet-moon system with its angular momentum.

While the Moon has only about 1 percent of the mass of Earth, Charon accounts for a much larger 10 to 15 percent of Pluto’s total mass. Canup’s simulations suggest that a proportionally much larger impactor – one nearly as large as Pluto itself – was responsible for Charon, and that the satellite likely formed intact as a direct result of the collision.

According to Canup, a collision in the early Kuiper Belt – a disk of comet-like objects orbiting in the outer solar system beyond Neptune – could have given rise to a planet and satellite with relative sizes and angular rotation characteristics consistent with those of the Pluto-Charon pair. The colliding objects would have been about 1,600 to 2,000 kilometers in diameter, or each about half the size of the Earth’s Moon.

“This work suggests that despite their many differences, our Earth and the tiny, distant Pluto may share a key element in their formation histories. This provides further support for the emerging view that stochastic impact events may have played an important role in shaping final planetary properties in the early solar system,” said Canup.

The “giant impact” theory was first proposed in the mid-1970s to explain how the Moon formed, and a similar mode of origin was suggested for Pluto and Charon in the early 1980s. Canup’s simulations are the first to successfully model such an event for the Pluto-Charon pair.

Simulations published by Canup and a colleague in Nature in 2001 showed that a single impact by a Mars-sized object in the late stages of Earth’s formation could account for the iron-depleted Moon and the masses and angular momentum of the Earth-Moon system.

This was the first model to simultaneously explain these characteristics without requiring that the Earth-Moon system be substantially modified after the lunar forming impact.

This research was supported by the National Science Foundation under grant no. AST0307933.

Original Source: SwRI News Release

Biggest Stars Make the Biggest Magnets

Astronomy is a science of extremes–the biggest, the hottest, and the most massive. Today, astrophysicist Bryan Gaensler (Harvard-Smithsonian Center for Astrophysics) and colleagues announced that they have linked two of astronomy’s extremes, showing that some of the biggest stars in the cosmos become the strongest magnets when they die.

“The source of these very powerful magnetic objects has been a mystery since the first one was discovered in 1998. Now, we think we have solved that mystery,” says Gaensler.

The astronomers base their conclusions on data taken with CSIRO’s Australia Telescope Compact Array and Parkes radio telescope in eastern Australia.

A magnetar is an exotic kind of neutron star–a city-sized ball of neutrons created when a massive star’s core collapses at the end of its lifetime. A magnetar typically possesses a magnetic field more than one quadrillion times (one followed by 15 zeroes) stronger than the earth’s magnetic field. If a magnetar were located halfway to the moon, it could wipe the data from every credit card on earth.

Magnetars spit out bursts of high-energy X-rays or gamma rays. Normal pulsars emit beams of low-energy radio waves. Only about 10 magnetars are known, while astronomers have found more than 1500 pulsars.

“Both radio pulsars and magnetars tend to be found in the same regions of the Milky Way, in areas where stars have recently exploded as supernovae,” explains Gaensler. “The question has been: if they are located in similar places and are born in similar ways, then why are they so different?”

Previous research has hinted that the mass of the original, progenitor star might be the key. Recent papers by Eikenberry et al (2004) and Figer et al (2005) have suggested this connection, based on finding magnetars in clusters of massive stars.

“Astronomers used to think that really massive stars formed black holes when they died,” says Dr Simon Johnston (CSIRO Australia Telescope National Facility). “But in the past few years we’ve realized that some of these stars could form pulsars, because they go on a rapid weight-loss program before they explode as supernovae.”

These stars lose a lot of mass by blowing it off in winds that are like the sun’s solar wind, but much stronger. This loss would allow a very massive star to form a pulsar when it died.

To test this idea, Gaensler and his team investigated a magnetar called 1E 1048.1-5937, located approximately 9,000 light-years away in the constellation Carina. For clues about the original star, they studied the hydrogen gas lying around the magnetar, using data gathered by CSIRO’s Australia Telescope Compact Array radio telescope and its 64-m Parkes radio telescope.

By analyzing a map of neutral hydrogen gas, the team located a striking hole surrounding the magnetar. “The evidence points to this hole being a bubble carved out by the wind that flowed from the original star,” says Naomi McClure-Griffiths (CSIRO Australia Telescope National Facility), one of the researchers who made the map. The characteristics of the hole indicate that the progenitor star must have been about 30 to 40 times the mass of the sun.

Another clue to the pulsar/magnetar difference may lie in how fast neutron stars are spinning when they form. Gaensler and his team suggest that heavy stars will form neutron stars spinning at up to 500-1000 times per second. Such rapid rotation should power a dynamo and generate superstrong magnetic fields. `Normal’ neutron stars are born spinning at only 50-100 times per second, preventing the dynamo from working and leaving them with a magnetic field 1000 times weaker, says Gaensler.

“A magnetar goes through a cosmic extreme makeover and ends up very different from its less exotic radio pulsar cousins,” he says.

If magnetars are indeed born from massive stars, then one can predict what their birth rate should be, compared to that of radio pulsars.

“Magnetars are the rare `white tigers’ of stellar astrophysics,” says Gaensler. “We estimate that the magnetar birth rate will be only about a tenth that of normal pulsars. Since magnetars are also short-lived, the ten we have already discovered may be almost all that are out there to be found.”

The team’s result will be published in an upcoming issue of The Astrophysical Journal Letters.

This press release is being issued in conjunction with CSIRO’s Australia Telescope National Facility.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Original Source: CfA News Release