Category: Astronomy

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

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

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

Ghostly haloes of dark matter as heavy as the earth and as large as our solar system were the first structures to form in the universe, according to new calculations from scientists at the University of Zurich, published in this week’s issue of Nature.

Our own galaxy still contains quadrillions of these halos with one expected to pass by Earth every few thousand years, leaving a bright, detectable trail of gamma rays in its wake, the scientists say. Day to day, countless random dark matter particles rain down upon the Earth and through our bodies undetected.

“These dark matter haloes were the gravitational ‘glue’ that attracted ordinary matter, eventually enabling stars and galaxies to form,” said Prof. Ben Moore of the Institute for Theoretical Physics at the University of Zurich, a co-author on the Nature report. “These structures, the building blocks of all we see today, started forming early, only about 20 million years after the big bang.”

Dark matter comprises over 80 percent of the mass of the universe, yet its nature is unknown. It seems to be intrinsically different from the atoms that make up matter all around us. Dark matter has never been detected directly; its presence is inferred through its gravitational influence on ordinary matter.

The Zurich scientists based their calculation on the leading candidate for dark matter, a theoretical particle called a neutralino, thought to have been created in the big bang. Their results entailed several months of number crunching on the zBox, a new supercomputer designed and built at the University of Zurich by Moore and Drs. Joachim Stadel and Juerg Diemand, co-authors on the report.

?Until 20 million years after the big bang, the universe was nearly smooth and homogenous?, Moore said. But slight imbalances in the matter distribution allowed gravity to create the familiar structure that we see today. Regions of higher mass density attracted more matter, and regions of lower density lost matter. Dark matter creates gravitational wells in space and ordinary matter flows into them. Galaxies and stars started to form as a result about 500 million years after the big bang, whereas the universe is 13.7 billion years old.

Using the zBox supercomputer that harnessed the power of 300 Athlon processors, the team calculated how neutralinos created in the big bang would evolve over time. The neutralino has long been a favoured candidate for “cold dark matter,” which means it does not move fast and can clump together to create a gravitational well. The neutralino has not yet been detected. This is a proposed “supersymmetric” particle, part of a theory that attempts to rectify inconsistencies in the standard model of elementary particles.

For the past two decades scientists have believed that neutralinos could form massive dark matter haloes and envelope entire galaxies today. What has emerged from the Zurich team’s zBox supercomputer calculation are three new and salient facts: Earth-mass haloes formed first; these structures have extremely dense cores enabling quadrillions to have survived the ages in our galaxy; also these “miniature” dark matter haloes move through their host galaxies and interact with ordinary matter as they pass by. It is even possible that these haloes could perturb the Oort cometary cloud far beyond Pluto and send debris through our solar system.

?Detection of these neutralino haloes is difficult but possible?, the team said. The halos are constantly emitting gamma rays, the highest-energy form of light, which are produced when neutralinos collide and self-annihilate.

“A passing halo in our lifetime (should we be so lucky), would be close enough for us to easily see a bright trail of gamma rays,” said Diemand, now at the University of California at Santa Cruz.

The best chance to detect neutralinos, however, is in galactic centres, where the density of dark matter is the highest, or in the centres of these migrating Earth-mass neutralino haloes. Denser regions will provide a greater chance of neutralino collisions and thus more gamma rays. “This would still be difficult to detect, like trying to see the light of a single candle placed on Pluto,” said Diemand.

NASA’s GLAST mission, planned for launch in 2007, will be capable of detecting these signals if they exist. Ground-based gamma-ray observatories such as VERITAS or MAGIC might also be able to detect gamma rays from neutralino interactions. In the next few years the Large Hadron Collider at CERN in Switzerland will confirm or rule out the concepts of supersymmetry.

Images and computer animations of a neutralino halo and early structure in the universe based on computer simulations are available at http://www.nbody.net

Albert Einstein and Erwin Schr?dinger were amongst the previous professors working at the Institute for Theoretical Physics at the University of Zurich, who made substantial contributions to our understanding of the origin of the universe and quantum mechanics. The year 2005 is the centenary of Einstein’s most remarkable work in quantum physics and relativity. In 1905 Einstein earned his doctorate from the University of Zurich and published three science-changing papers.

Note to editors: The innovative supercomputer designed by Joachim Stadel and Ben Moore is a cube of 300 Athlon processors interconnected by a two-dimensional high-speed network from Dolphin/SCI and cooled by a patented airflow system. Refer to http://krone.physik.unizh.ch/~stadel/zBox/ for more details. Stadel, who led the project, noted: “It was a daunting task assembling a world-class supercomputer from thousands of components, but when it was completed it was the fastest in Switzerland and the world’s highest density supercomputer. The parallel simulation code we use splits up the calculation by distributing separate parts of the model universe to different processors.”

Original Source: Institute for Theoretical Physics ? University of Zurich News Release

The centre of our galaxy has been known for years to host a black hole, a ‘super-massive’ yet very quiet one. New observations with Integral, ESA’s gamma-ray observatory, have now revealed that 350 years ago the black hole was much more active, releasing a million times more energy than at present. Scientists expect that it will become active again in the future.

Most galaxies harbour a super-massive black hole in their centre, weighing a million or even a thousand million times more than our Sun.

Our galaxy too, the Milky Way, hosts a super-massive black hole at its centre. Astronomers call it Sgr A* (pronounced ‘Sagittarius A star’) from its position in the southern constellation Sagittarius, ‘the archer’.

In spite of its enormous mass of more than a million suns, Sgr A* appears today as a quiet and harmless black hole. However, a new investigation with ESA’s gamma-ray observatory Integral has revealed that in the past Sgr A* has been much more active. Data clearly show that it interacted violently with its surroundings, releasing almost a million times as much energy than it does today.

This result has been obtained by a international team of scientists led by Dr Mikhail Revnivtsev (Space Research Institute, Moscow, Russia, and Max Planck Institute for Astrophysics, Garching, Germany). As Revnivtsev explains, “About 350 years ago, the region around Sgr A* was literally swamped in a tide of gamma rays.”

This gamma-ray radiation is a direct consequence of Sgr A*’s past activity, in which gas and matter trapped by the hole’s gravity are crushed and heated until they radiate X-rays and gamma rays, just before disappearing below the ‘event horizon’ – the point of no return from which even light cannot escape.

The team were able to unveil the history of Sgr A* thanks to a cloud of molecular hydrogen gas, called Sgr B2 and located about 350 light-years away from it, which acts as a living record of the hectic black hole’s past.

Because of its distance from the black hole, Sgr B2 is only now being exposed to the gamma rays emitted by Sgr A* 350 years ago, during one of its ‘high’ states. This powerful radiation is absorbed and then re-emitted by the gas in Sgr B2, but this process leaves behind an unmistakable signature.

“We are now seeing an echo from a sort of natural mirror near the galactic centre – the giant cloud Sgr B2 simply reflects gamma rays emitted by Sgr A* in the past,” says Revnivtsev. The flash was so powerful that the cloud became fluorescent in the X-rays and was even seen with X-ray telescopes before Integral. However, by showing how high-energy radiation is reflected and reprocessed by the cloud, Integral allowed scientists to reconstruct for the first time the hectic past of Sgr A*.

The high state or ‘activity’ of black holes is closely linked to the way in which they grow in size. Super-massive black holes are not born so big but, thanks to their tremendous gravitational pull, they grow over time by sucking up the gas and matter around them. When the matter is finally swallowed, a burst of X-rays and gamma rays results. The more voracious a black hole, the stronger the radiation that erupts from it.

The new Integral discovery solves the mystery of the emission from super-massive but weak black holes, such as Sgr A*. Scientists already suspected that such weak black holes should be numerous in the Universe, but they were unable to tell how much energy and of which type they emit. “Just a few years ago we could only imagine a result like this,” Revnivtsev says. “But thanks to Integral, we now know it!”

As for the duration of the latest high state of Sgr A*, 350 years ago, Revnivtsev and his team have evidence that it must have lasted at least ten years and probably much longer. The team also expect that Sgr A* will become bright again in the foreseeable future. Detecting the next burst would provide much needed information about the duty cycle of super-massive black holes.

Original Source: ESA News Release

It wasn’t too long ago (13.7 billion years by some accounts) that a rather significant cosmological event occured. We speak of course, of the Big Bang. Cosmologists tell us that at one time there was no universe as we know it. Whatever existed before that time was null and void – beyond all conception. Why? Well there are a couple answers to that question – the philosophic answer for instance: Because before the universe took form there was nothing to conceive of, with, or even about. But there’s also a scientific answer and that answer comes down to this: Before the Big Bang there was no space-time continuum – the immaterial medium through which all things energy and matter move.

Once the space-time continuum popped into existence, one of the most moving of things to take form were the units of light physicists call “photons”. The scientific notion of photons begins with the fact that these elementary particles of energy display two seemingly contradictory behaviors: One behavior has to do with how they act as members of a group (in a wavefront) and the other relates to how they behave in isolation (as discrete particles). An individual photon may be thought of as a packet of waves cork-screwing rapidly through space. Each packet is an oscillation along two perpendicular axes of force – the electrical and the magnetic. Because light is an oscillation, wave-particles interact with each other. One way of understanding the dual-nature of light is to realize that wave after wave of photons affect our telescopes – but individual photons are absorbed by the neurons in our eyes.

The very first photons travelling through the space-time continuum were extremely powerful. As a group, they were incredibly intense. As individuals, each vibrated at an extraordinary rate. The light of these primordial photons quickly illuminated the rapidly expanding limits of the youthful universe. Light was everywhere – but matter was yet to be seen.

As the universe expanded, primordial light lost in both frequency and intensity. This occured as the original photons spread themselves thinner and thinner across an ever-expanding space. Today, the first light of creation still echos around the cosmos. This is seen as cosmic background radiation. And that particular type radiation is no more visible to the eye as the waves within a microwave oven.

Primordial light is NOT the radiation we see today. Primordial radiation has red-shifted to the very low end of the electromagnetic spectrum. This occured as the universe expanded from what may have originally been no larger than a single atom to the point where our grandest instruments have yet to find any limit whatsoever. Knowing that primordial light is now so ternuous makes it necessary to look elsewhere to account for the kind of light visible to our eyes and optical telescopes.

Stars (such as our Sun) exist because space-time does more than simply transmit light as waves. Somehow – still unexplained^-1 – space-time causes matter too. And one thing distinguishing light from matter is that matter has “mass” while light has none.

Because of mass, matter displays two main properties: Inertia and gravity. Inertia may be thought of as resistence to change. Basically matter is “lazy” and just keeps doing whatever it’s been doing – unless acted upon something outside itself. Early in the formation of the universe, the main thing overcoming matter’s lazyness was light. Under the influence of radiation pressure, primordial matter (mostly hydrogen gas) got “organized”.

Following light’s prodding, something inside matter took over – that subtle behavior we call “gravity”. Gravitation has been described as a “distortion of the space-time continuum”. Such distortions occur wherever mass is found. Because matter has mass, space curves. It is this curve that causes matter and light to move in ways elucidated early on in the twentieth century by Albert Einstein. Each and every little atom of matter causes a tiny “micro-distortion” in space-time^-2. And when enough micro-distortions come together things can happen in a big way.

And what happened was the formation of the first stars. No ordinary stars these – but super-massive giants living very fast lives and coming to very, very spectacular ends. At those ends, these stars collapsed in on themselves (under the weight of all that mass) generating tremendous shock waves of such intensity as to fuse entirely new elements out of older ones. As a result, space-time became suffused with all the many types of matter (atoms) making up the universe today.

Today, two types of atomic matter now exists: Primordial and something we might call “star-stuff”. Whether primordial or stellar in origin, atomic matter makes up all things touched and seen. Atoms have properties and behaviors: Inertia, gravity, extension in space, and density. They can also have electrical charge (if ionized) and participate in chemical reactions (to form molecules of tremendous sophistication and complexity). All matter we do see is based on a fundamental pattern established long-ago by those primordial atoms mysteriously created after the Big Bang. This pattern is founded on two fundamental units of electrical charge: The proton and the electron – each having mass and capable of doing those things mass is liable to.

But not all matter follows the hydrogen prototype exactly. One difference is that newer generation atoms have electrically-balanced neutrons as well as positively-charged protons in their nuclei. But even stranger is a type of matter (dark matter) that doesn’t interact with light at all. And furthermore (just to keep things symmetric), there may be a type of energy (vacuum energy) that doesn’t take the form of photons – acting more like a “gentle pressure” causing the universe to expand with a momentum not orignally supplied by the Big-Bang.

But let’s get back to the stuff we can see…

In relationship to light, matter can be opaque or transparent – it can absorb or refract light. Light can pass into matter, through matter, reflect off matter, or be absorbed by matter. When light passes into matter, light slows – while its frequency increases. When light reflects, the path it takes changes. When light is absorbed, electrons are stimulated potentially leading to new molecular combinations. But even more significantly, when light passes through matter – even without absorption – atoms and molecules vibrate the space-time continuum and because of this, light can be stepped down in frequency. We see, because something called “light” interacts with something called “matter” in something called “the space-time continuum”.

In addition to describing the gravitational effects of matter on space-time, Einstein performed an extremely elegant investigation into the influence of light associated with the photo-electric effect. Before Einstein, physicists believed lights’ capacity to affect matter was based primarily on “intensity”. But the photo-electric effect showed that light effected electrons on the basis of frequency as well. Thus red light – regardless of intensity – fails to dislodge electrons in metals, while even very low levels of violet light stimulate measurable electrical currents. Clearly the rate at which light vibrates has a power all its own.

Einstein’s investigation into the photo-electric effect contributed mightily to what later became known as quantum mechanics. For physicists soon learned that atoms are selective about what frequencies of light they will absorb. Meanwhile it was also discovered that electrons were the key to all quantum absorption – a key related to properties such as one electrons relationships to others and with the nucleus of the atom.

So now we come to our second point: Selective absorption and emission of photons by electrons does not explain the continuous spread of frequencies seen when examining light through our instruments^-3.

What can explain it then?

One answer: The “stepping-down” principle associated with the refraction and absorption of light.

Common glass – such as in the windows of our homes – is transparent to visible light. Glass however reflects most infrared light and absorbs ultraviolet. When visible light enters a room, it is absorbed by furniture, rugs etc. These items convert part of the light to heat – or infrared radiation. This infrared radiation is trapped by the glass and the room heats up. Meanwhile glass itself is opaque to ultraviolet. Light emitted by the Sun in the ultraviolet is mostly absorbed by the atmosphere – but some non-ionizing ultraviolet manages to get through. Ultraviolet light is converted to heat by glass in the same way furnishings absorb and re-radiate visible light.

How does all this relate to the presence of visible light in the Universe?

Within the Sun, high energy photons (invisible light from the perimeter of the solar core) irradiate the solar mantle beneath the photosphere. The mantle converts these rays to “heat” by absorption – but this particular “heat” is of a frequency well beyond our capacity to see. The mantle then sets up convective currents carrying heat outward toward the photosphere while also emitting lesser-energized – but still invisible – photons. The resulting “heat” and “light” passes to the solar photosphere. In the photosphere (“the sphere of visible light”) atoms are “heated” by convection and stimulated through refraction to vibrate at a rate slow enough to give off visible light. And it is this principle that accounts for the visible light emitted by stars which are – by far – the most significant source of light seen throughout the cosmos.

So – from a certain perspective, we can say that the “refractive index” of the Sun’s photosphere is the means by which invisible light is converted into visible light. In this case however, we invoke the idea that the refractive index of the photosphere is so high that high energy rays are bent to the point of absorption. When this occurs lower frequency waves are spawned radiating as a form of heat peceptible to the eye and not simply warm to the touch…

And with all this understanding beneath our intellectual feet, we can now answer our question: The light we see today is the primordial light of creation. But it is light that materialized some few hundreds of thousands of years after the Big Bang. Later that materialized light came together under the influence of gravity as great condensed orbs. These orbs then developed powerful alchemical furnaces de-materializing matter into light invisible. Later – through refraction and absorption – light invisible was rendered visible to the eye by rite of passage through those great “lenses of luminosity” we call the stars…

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^-1 How all things cosmological transpired in detail is probably the major area of astronomical research today and will take physicists – with their “atom-smashers”, astronomers – with their telescopes, mathematicians – with their number-crunching super-computers (and pencils!) and cosmologists – with their subtle understanding of the early years of the universe – to puzzle the whole thing through.
^-2
In a sense matter may simply be a distortion of the space-time continuum – but we are a long way from understanding that continuum in all its properties and behaviors.

^-3 The Sun and all luminous sources of light do display dark absorption and bright emission bands of very narrow frequencies. These of course, are the various Fraunhofer lines related to quantum mechanical properties associated with transition states of electrons associated with specific atoms and molecules.

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.

For decades, scientists have observed that Regulus, the brightest star in the constellation Leo, spins much faster than the sun. But thanks to a powerful new telescopic array, astronomers now know with unprecedented clarity what that means to this massive celestial body.

A group of astronomers, led by Hal McAlister, director of Georgia State University’s Center for High Angular Resolution Astronomy, have used the center’s array of telescopes to detect for the first time Regulus’ rotationally induced distortions. Scientists have measured the size and shape of the star, the temperature difference between its polar and equatorial regions, and the orientation of its spin axis. The researchers’ observations of Regulus represent the first scientific output from the CHARA array, which became routinely operational in early 2004.

Most stars rotate sedately about their spin axes, McAlister says. The sun, for example, completes a full rotation in about 24 days, which means its equatorial spin speed is roughly 4,500 miles per hour. Regulus’ equatorial spin speed is nearly 700,000 miles per hour and its diameter is about five times greater than the sun’s. Regulus also bulges conspicuously at its equator, a stellar rarity.

Regulus’ centrifugal force causes it to expand so that its equatorial diameter is one-third larger than its polar diameter. In fact, if Regulus were rotating about 10 percent faster, its outward centrifugal force would exceed the inward pull of gravity and the star would fly apart, says McAlister, CHARA’s director and Regents Professor of Astronomy at Georgia State.

Because of its distorted shape, Regulus, a single star, exhibits what is known as “gravity darkening” ? the star becomes brighter at its poles than at its equator — a phenomenon previously only detected in binary stars. According to McAlister, the darkening occurs because Regulus is colder at its equator than at its poles. Regulus’ equatorial bulge diminishes the pull of gravity at the equator, which causes the temperature there to decrease. CHARA researchers have found that the temperature at Regulus’ poles is 15,100 degrees Celsius, while the equator’s temperature is only 10,000 Celsius. The temperature variation causes the star to be about five times brighter at its poles than at its equator. Regulus’ surface is so hot that the star is actually nearly 350 times more luminous than the sun.

CHARA researchers discovered another oddity when they determined the orientation of the star’s spin axis, says McAlister.

“We’re looking at the star essentially equator-on, and the spin axis is tilted about 86 degrees from the north direction in the sky,” he says. “But, curiously enough, the star is moving through space in the same direction its pole is pointing. Regulus is moving like an enormous spinning bullet through space. We have no idea why this is the case.”

Astronomers viewed Regulus using CHARA’s telescopes for six weeks last spring to obtain interferometric data that, combined with spectroscopic measurements and theoretical models, created a picture of the star that reveals the effects of its incredibly fast spin. The results will be published this spring in The Astrophysical Journal.

The CHARA array, located atop Mt. Wilson in southern California, is among a handful of new “super” instruments composed of multiple telescopes optically linked to function as a single telescope of enormous size. The array consists of six telescopes, each containing a light-collecting mirror one meter in diameter. The telescopes are arranged in the shape of a “Y,” with the outermost telescopes located about 200 meters from the center of the array.

A precise combination of the light from the individual telescopes allows the CHARA array to behave as if it were a single telescope with a mirror 330 meters across. The array can’t show very faint objects detected by telescopes such as the giant 10-meter Keck telescopes in Hawaii, but scientists can see details in brighter objects nearly 100 times sharper than those obtainable using the Keck array. Working at infrared wavelengths, the CHARA array can see details as small as 0.0005 arcseconds. (One arcsecond is 1/3,600 of a degree, equivalent to the angular size of a dime seen from a distance of 2.3 miles.) In addition to Georgia State researchers, the CHARA team includes collaborators from the National Optical Astronomy Observatories in Tucson, Ariz., and NASA’s Michelson Science Center at the California Institute of Technology in Pasadena.

The CHARA array was constructed with funding from the National Science Foundation, Georgia State, the W. M. Keck Foundation, and the David and Lucile Packard Foundation. The NSF also has awarded funds for ongoing research at the CHARA array.

Original Source: Georgia State University

Thanks to the powerful new high-contrast camera installed at the Very Large Telescope, photos have been obtained of a low-mass companion very close to a star. This has allowed astronomers to measure directly the mass of a young, very low mass object for the first time.

The object, more than 100 times fainter than its host star, is still 93 times as massive as Jupiter. And it appears to be almost twice as heavy as theory predicts it to be.

This discovery therefore suggests that, due to errors in the models, astronomers may have overestimated the number of young “brown dwarfs” and “free floating” extrasolar planets.

A winning combination
A star can be characterised by many parameters. But one is of uttermost importance: its mass. It is the mass of a star that will decide its fate. It is thus no surprise that astronomers are keen to obtain a precise measure of this parameter.

This is however not an easy task, especially for the least massive ones, those at the border between stars and brown dwarf objects. Brown dwarfs, or “failed stars”, are objects which are up to 75 times more massive than Jupiter, too small for major nuclear fusion processes to have ignited in its interior.

To determine the mass of a star, astronomers generally look at the motion of stars in a binary system. And then apply the same method that allows determining the mass of the Earth, knowing the distance of the Moon and the time it takes for its satellite to complete one full orbit (the so-called “Kepler’s Third Law”). In the same way, they have also measured the mass of the Sun by knowing the Earth-Sun distance and the time – one year – it takes our planet to make a tour around the Sun.

The problem with low-mass objects is that they are very faint and will often be hidden in the glare of the brighter star they orbit, also when viewed in large telescopes.

Astronomers have however found ways to overcome this difficulty. For this, they rely on a combination of a well-considered observational strategy with state-of-the-art instruments.

High contrast camera
First, astronomers searching for very low mass objects look at young nearby stars because low-mass companion objects will be brightest while they are young, before they contract and cool off.

In this particular case, an international team of astronomers [1] led by Laird Close (Steward Observatory, University of Arizona), studied the star AB Doradus A (AB Dor A). This star is located about 48 light-years away and is “only” 50 million years old. Because the position in the sky of AB Dor A “wobbles”, due to the gravitational pull of a star-like object, it was believed since the early 1990s that AB Dor A must have a low-mass companion.

To photograph this companion and obtain a comprehensive set of data about it, Close and his colleagues used a novel instrument on the European Southern Observatory’s Very Large Telescope. This new high-contrast adaptive optics camera, the NACO Simultaneous Differential Imager, or NACO SDI [2], was specifically developed by Laird Close and Rainer Lenzen (Max-Planck-Institute for Astronomy in Heidelberg, Germany) for hunting extrasolar planets. The SDI camera enhances the ability of the VLT and its adaptive optics system to detect faint companions that would normally be lost in the glare of the primary star.

A world premiere
Turning this camera towards AB Dor A in February 2004, they were able for the first time to image a companion so faint – 120 times fainter than its star – and so near its star.

Says Markus Hartung (ESO), member of the team: “This world premiere was only possible because of the unique capabilities of the NACO SDI instrument on the VLT. In fact, the Hubble Space Telescope tried but failed to detect the companion, as it was too faint and too close to the glare of the primary star.”

The tiny distance between the star and the faint companion (0.156 arcsec) is the same as the width of a one Euro coin (2.3 cm) when seen 20 km away. The companion, called AB Dor C, was seen at a distance of 2.3 times the mean distance between the Earth and the Sun. It completes a cycle around its host star in 11.75 years on a rather eccentric orbit.

Using the companion’s exact location, along with the star’s known ‘wobble’, the astronomers could then accurately determine the companion’s mass. The object, more than 100 times fainter than its close primary star, has one tenth of the mass of its host star, i.e., it is 93 times more massive than Jupiter. It is thus slightly above the brown dwarf limit.

Using NACO on the VLT, the astronomers further observed AB Dor C at near infrared wavelengths to measure its temperature and luminosity.

“We were surprised to find that the companion was 400 degrees (Celsius) cooler and 2.5 times fainter than the most recent models predict for an object of this mass,” Close said.

“Theory predicts that this low-mass, cool object would be about 50 Jupiter masses. But theory is incorrect: this object is indeed between 88 to 98 Jupiter masses.”

These new findings therefore challenge current ideas about the brown dwarf population and the possible existence of widely publicized “free-floating” extrasolar planets.

Indeed, if young objects hitherto identified as brown dwarfs are twice as massive as was thought, many must rather be low-mass stars. And objects recently identified as “free-floating” planets are in turn likely to be low-mass brown dwarfs.

For Close and his colleagues, “this discovery will force astronomers to rethink what masses of the smallest objects produced in nature really are.”

More information
The work presented here appears as a Letter in the January 20 issue of Nature (“A dynamical calibration of the mass-luminosity relation at very low stellar masses and young ages” by L. Close et al.).

Notes
[1]: The team is composed of Laird M. Close, Eric Nielsen, Eric E. Mamajek and Beth Biller (Steward Observatory, University of Arizona, Tucson, USA), Rainer Lenzen and Wolfgang Brandner (Max-Planck Institut for Astronomie, Heidelberg, Germany), Jose C. Guirado (University of Valencia, Spain), and Markus Hartung and Chris Lidman (ESO-Chile).

[2]: The NACO SDI camera is a unique type of camera using adaptive optics, which removes the blurring effects of Earth’s atmosphere to produce extremely sharp images. SDI splits light from a single star into four identical images, then passes the resulting beams through four slightly different (methane-sensitive) filters. When the filtered light beams hit the camera’s detector array, astronomers can subtract the images so the bright star disappears, revealing a fainter, cooler object otherwise hidden in the star’s scattered light halo (“glare”). Unique images of Saturn’s satellite Titan obtained earlier with NACO SDI were published in ESO PR 09/04.

Original Source: ESO News Release

Image credit: Jason Ware
Amateur astronomy isn’t for everyone. But unlike other interests, it could be! After all, there’s plenty of sky to go around. And to enjoy the sky doesn’t take much. To start, just the power of human sight and the ability to “keep looking up”.

Appreciating the night sky and its numerous denizens is akin to enjoying any great work of art. Anyone captive to a painting by Van Gogh, statue by Roden, sonata by Beethoven, play by Shakespeare, or poem by Tennyson, can certainly appreciate a constellation wrought by nature’s sculpting hand. So like such great works of art, a fine appreciation of the night sky can be cultivated. Yet unlike such works, there is something far more primordial and immediately evocative about the heavens – a thing that defies any need for profound study or inculturation by others.

While it is true that some ingenious devices (such as the quadrant) were developed early on in the history of astronomy, it wasn’t until the time of Galileo (the early 17th century) that astronomers began probing the universe in detail. Before that time, the human eye placed such constraints on what could be seen that all we knew of the heavens was limited to two large bright bodies (Sun and Moon), numerous faint lights (the fixed stars and infrequent novae), and an intermediate group (the planets and occasional comets). Using instruments such as the quadrant (for position), and waterclock (for time), it became possible to predict the movements of all such bodies. And it was prediction – not understanding – that drove observation using the human eye alone.

Ultimately it was the telescope that made discovery – rather than measurement – the driving force behind the science of astronomy. For without the telescope, the Universe would be a far smaller place and populated by far, far fewer things. Consider that at 2.3 million light-years, the most distant celestial object visible unaided – the Great Galaxy of Andromeda – could never have been so-named at all. In fact, it might not have even received its older name: The Great Nebula in Andromeda. First noted in the 10th century text “Book of Fixed Stars”, sharp-eyed Abd-al-Rahman Al Sufi described the Great Galaxy as “a little cloud”. And that – without the telescope – is all we would ever have seen of this:

Because of the telescope, we now know far more about Sun, Moon, planets, comets, and stars than simply where they might be found in the sky. We understand that our Sun is a nearby star and that our Earth, the planets, and those “harbingers of doom” – the comets – are all part of a solar system. We have detected other such stellar systems beyond our own. We know we live in a galaxy that – from a distance of two million light-years – would appear much like M31 ^-1. We have determined that several billion years hence, our galaxy and M31 will embrace spiral arms. And we recognize that the Universe is extraordinary in its vastness, diversity, beauty, and harmony of inter-connectedness.

We know all this because we possess the telescope – and similar instruments – that can sound the depths of the cosmos across numerous octaves of spectral vibrancy.

But it all begins with the human eye…

The working of the human eye is based on three of the four main properties of light. Light may be refracted, reflected, diffracted, or absorbed. Light enters the eye as parallel beams from the distance. Because it is limited in aperture, the eye is only able to collect a very small proportion of the rays coming from any one thing. That collecting area – roughly 38 square millimeters (fully dilated and dark-adapted), allows the eye to normally see stars down to about magnitude 6. Ancient astronomers – free of the effects of modern sources of atmospheric illumination (light pollution) – were able to catalogue about 6000 individual stars (with a sprinkling of other objects). The faintest of these were classed of the “sixth magnitude”, and brightest of the “first”.

But the eye is also limited by the principle of diffraction. This principle prevents us from seeing exceedingly fine details. Because the eye is limited in aperture, parallel beams of light begin to “spread out” or propagate after entering the iris. Such diffusion means that – despite the use of refraction to focus – photons can only come so close together. For this reason, there is an ultimate limit to how much detail may be seen by any aperture – and that includes the eye itself.

The eye, of course, exploits the principle of refraction to organize beams of light. Photons enter the cornea, bend, and pass to the lens behind it. (The cornea does the bulk of the focusing and leaves about a third up to the lens.) The lens itself adjusts ray angles to bring things – near or far – to focus. It does this by changing radius of curvature. In this way, parallel rays from a distance or diverging rays from nearby may project an image on the retina where tiny neurons convert light-energy into signals for interpretation by the brain. And it is the brain – primarily the occipital lobes at the back of the head – that does the “image processing” needed to give coherence to that steady stream of neural signals arriving from the eye.

To detect light, the retina employs the principle of absorption. Photons cause sensory neurons to depolarize. Depolarization projects chemo-electrical signals from axons to dendrites deeper in the brain. Retinal neurons may be rod-shaped or conical. Rods detect light of any color and are more sensitive to light than cones. Cones detect specific colors only and are found in greater concentration along the main axis of the eye. Meanwhile rods dominate off-axis. The averted eye can see stars roughly two and half-times fainter than those held direct.

Beyond aversion, neural signals passing from the retina (via the optical chiasm) are first processed by the superior collicus. The collicus gives us our visual “flinch” response – but more importantly – it does less filtering of the visual field than the occipital lobes. Because of this, the collicus can detect even fainter sources of light – but only when in apparent motion. Thus the discerning observer can detect faint stars – and faintly glowing objects – some 4 times fainter than those seen through ordinary “straight-on” viewing. (This is done by sweeping the eye across the night sky – or across the field of view of the telescope.)

In addition to aversion and eye movement, the eyes increase sensitivity by adapting to low light conditions. This is done in two ways: First, fine muscles retract the iris (located between cornea and lens) to admit as much light as possible. Second, within roughly 30 minutes of exposure to darkness, “visual purple” (rhodopsin) on retinal rods takes on a transmissive rosey-red color. This change increases the sensitivity of rods to the point where even a single photon of visible light may be detected.

Aside from limitations imposed by diffraction, there is a second natural limit to how much detail can be seen by the eye. For neurons can be made only so small and placed only so close together. Meanwhile at about 25mm’s in focal length, the eye can only see “1x”. Add this to the fact that the greatest opening achieved by the eye (the entrance pupil) is 7mms and human eyes become the effective equivalent of a pair of “1x7mm” binoculars.

All these factors limit the eye – even under the best observing conditions (like the vacuum of space) – to seeing stars (using direct vision) of the eighth magnitude (1500 times fainter than the brightest stars) and resolving close pairs to about 2 arc-minutes of angular separation (1/15th the apparent size of the Moon).

Observational astronomy begins with the eyes. But new instrumentation evolved because some eyes have difficulty focusing light. Because of human near- and far- sightedness, the first spectacle lenses were ground. And it was only a matter of experimentation before someone combined one of each type lens together to form the first telescope or “instrument of long seeing”.

Today’s astronomers are able to augment the human eye’s capacity to the point where we can almost peer back to the beginning of time itself. This is done through the use of chemical and solid-state principles embodied in photography and charge-coupled devices (CCDs). Such tools are able to accumulate photons in a way the eye can not. As a result of these “visual aids”, we have discovered things once unimagined about the universe. Many of these discoveries were unknown to us – even as recently as the beginning of the era of the Great Observatories (the early twentieth century). Today’s astronomy has expanded the range of cosmic vision across numerous bands of the electromagnetic spectrum – from radio to X-rays. But we do far more than simply find stuff and measure positions. We seek to grasp more than light – but comprehension as well…

Today’s amateur astronomers – such as the author – use hand- and mass-produced telescopes from all parts of the world to peer billions of light-years into the depths of the Universe.^-2 This type long-seeing is possible because the eye and telescope can work together to collect “more and finer light” from on high.

How far can you see?

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^-1According to NASA the Milky Way galaxy would appear very much like 15.3 MLY distant barred spiral M83 found in the constellation Hydra (as seen at right). A human being in space would just be able to hold the bright central portion of this 8.3 magnitude galaxy as a “fuzzy star” using averted vision. M83 can easily be found using low power binoculars from Earth.

^-2 Bearing a variable visual magnitude of 12.8, 2 billion-light year distant quasar 3C273 can just be held direct by the human eye when augmented by a six-inch / 150mm aperture telescope at 150x through night time skies of 5.5 unaided limiting magnitude and 7/10p seeing stability. A pair of 10x50mm binoculars would reveal 3C273 as a faint star from Earth orbit.

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