Posted on by Fraser Cain

New Form of Matter Created

A rotating superfluid gas of fermions pierced with vortices. Image credit: MIT. Click to enlarge.
MIT scientists have brought a supercool end to a heated race among physicists: They have become the first to create a new type of matter, a gas of atoms that shows high-temperature superfluidity.

Their work, to be reported in the June 23 issue of Nature, is closely related to the superconductivity of electrons in metals. Observations of superfluids may help solve lingering questions about high-temperature superconductivity, which has widespread applications for magnets, sensors and energy-efficient transport of electricity, said Wolfgang Ketterle, a Nobel laureate who heads the MIT group and who is the John D. MacArthur Professor of Physics.

Seeing the superfluid gas so clearly is such a dramatic step that Dan Kleppner, director of the MIT-Harvard Center for Ultracold Atoms, said, “This is not a smoking gun for superfluidity. This is a cannon.”

For several years, research groups around the world have been studying cold gases of so-called fermionic atoms with the ultimate goal of finding new forms of superfluidity. A superfluid gas can flow without resistance. It can be clearly distinguished from a normal gas when it is rotated. A normal gas rotates like an ordinary object, but a superfluid can only rotate when it forms vortices similar to mini-tornadoes. This gives a rotating superfluid the appearance of Swiss cheese, where the holes are the cores of the mini-tornadoes. “When we saw the first picture of the vortices appear on the computer screen, it was simply breathtaking,” said graduate student Martin Zwierlein in recalling the evening of April 13, when the team first saw the superfluid gas. For almost a year, the team had been working on making magnetic fields and laser beams very round so the gas could be set in rotation. “It was like sanding the bumps off of a wheel to make it perfectly round,” Zwierlein explained.

“In superfluids, as well as in superconductors, particles move in lockstep. They form one big quantum-mechanical wave,” explained Ketterle. Such a movement allows superconductors to carry electrical currents without resistance.

The MIT team was able to view these superfluid vortices at extremely cold temperatures, when the fermionic gas was cooled to about 50 billionths of a degree Kelvin, very close to absolute zero (-273 degrees C or -459 degrees F). “It may sound strange to call superfluidity at 50 nanokelvin high-temperature superfluidity, but what matters is the temperature normalized by the density of the particles,” Ketterle said. “We have now achieved by far the highest temperature ever.” Scaled up to the density of electrons in a metal, the superfluid transition temperature in atomic gases would be higher than room temperature.

Ketterle’s team members were MIT graduate students Zwierlein, Andre Schirotzek, and Christian Schunck, all of whom are members of the Center for Ultracold Atoms, as well as former graduate student Jamil Abo-Shaeer.

The team observed fermionic superfluidity in the lithium-6 isotope comprising three protons, three neutrons and three electrons. Since the total number of constituents is odd, lithium-6 is a fermion. Using laser and evaporative cooling techniques, they cooled the gas close to absolute zero. They then trapped the gas in the focus of an infrared laser beam; the electric and magnetic fields of the infrared light held the atoms in place. The last step was to spin a green laser beam around the gas to set it into rotation. A shadow picture of the cloud showed its superfluid behavior: The cloud was pierced by a regular array of vortices, each about the same size.

The work is based on the MIT group’s earlier creation of Bose-Einstein condensates, a form of matter in which particles condense and act as one big wave. Albert Einstein predicted this phenomenon in 1925. Scientists later realized that Bose-Einstein condensation and superfluidity are intimately related.

Bose-Einstein condensation of pairs of fermions that were bound together loosely as molecules was observed in November 2003 by independent teams at the University of Colorado at Boulder, the University of Innsbruck in Austria and at MIT. However, observing Bose-Einstein condensation is not the same as observing superfluidity. Further studies were done by these groups and at the Ecole Normale Superieure in Paris, Duke University and Rice University, but evidence for superfluidity was ambiguous or indirect.

The superfluid Fermi gas created at MIT can also serve as an easily controllable model system to study properties of much denser forms of fermionic matter such as solid superconductors, neutron stars or the quark-gluon plasma that existed in the early universe.

The MIT research was supported by the National Science Foundation, the Office of Naval Research, NASA and the Army Research Office.

Original Source: MIT News Release

Posted on by Fraser Cain

Extrasolar Planet Reshapes Ring Around a Star

Hubble image of the ring around Fomalhaut. Image credit: Hubble. Click to enlarge.
NASA Hubble Space Telescope’s most detailed visible-light image ever taken of a narrow, dusty ring around the nearby star Fomalhaut (HD 216956), offers the strongest evidence yet that an unruly and unseen planet may be gravitationally tugging on the ring.

Hubble unequivocally shows that the center of the ring is a whopping 1.4 billion miles (15 astronomical units) away from the star. This is a distance equal to nearly halfway across our solar system. The most plausible explanation, astronomers said, is that an unseen planet moving in an elliptical orbit is reshaping the ring with its gravitational pull. The geometrically striking ring, tilted obliquely toward Earth, would not have such a great offset if it were simply being influenced by Fomalhaut’s gravity alone.

An offset of the ring center from the star has been inferred from previous and longer wavelength observations using submillimeter telescopes on Mauna Kea, Hawaii, the Spitzer Space Telescope, Caltech’s Submillimeter Observatory and applying theoretical modeling and physical assumptions. Now Hubble’s sharp images directly reveal the ring’s offset from Fomalhaut.

These new observations provide strong evidence that at least one unseen planetary mass object is orbiting the star. Hubble would have detected an object larger than a planet, such as a brown dwarf. “Our new Hubble images confirm those earlier hypotheses that proposed a planet was perturbing the ring,” said Paul Kalas of the University of California at Berkeley. The ring is similar to our solar system’s Kuiper Belt, a vast reservoir of icy material left over from the formation of our solar system planets.

The observations offer insights into our solar system’s formative years, when the planets played a game of demolition derby with the debris left over from the formation of our planets, gravitationally scattering many objects across space. Some icy material may have collided with the inner solar system planets, irrigating them with water formed in the colder outer solar system. Other debris may have traveled outward, forming the Kuiper Belt and the Oort Cloud, a spherical cloud of material surrounding the solar system.

Only Hubble has the exquisite optical resolution to resolve that the ring’s inner edge is sharper than its outer edge, a telltale sign that an object is gravitationally sweeping out material like a plow clearing away snow. Another classic signature of a planet’s influence is the ring’s relatively narrow width, about 2.3 billion miles (25 astronomical units). Without an object to gravitationally keep the ring material intact, astronomers said, the particles would spread out much wider.

“What we see in this ring is similar to what is seen in the Cassini spacecraft images of Saturn’s narrow rings. In those images, Saturn’s moons are ‘shepherding’ the ring material and keeping the ring from spreading out,” Kalas said.

The suspected planet may be orbiting far away from Fomalhaut, inside the dust ring’s inner edge, between 4.7 billion and 6.5 billion miles (50 to 70 astronomical units) from the star. The ring is 12 billion miles (133 astronomical units) from Fomalhaut, which is much farther away than our outermost planet Pluto is from the Sun. These Hubble observations do not detect the putative planet directly, so the astronomers cannot measure its mass. They will, instead, conduct computer simulations of the ring’s dynamics to estimate the planet’s mass.

Kalas and collaborators James R. Graham of the University of California at Berkeley and Mark Clampin of the NASA Goddard Space Flight Center in Greenbelt, Md., will publish their findings in the June 23, 2005 issue of the journal Nature.

Fomalhaut, a 200-million-year-old star, is a mere infant compared to our own 4.5-billion-year-old Sun. It resides 25 light-years away from the Sun. Located in the constellation Piscis Austrinus (the Southern Fish), the Fomalhaut ring is ten times as old as debris disks seen previously around the stars AU Microscopii and Beta Pictoris, where planets may still be forming. If our solar system is any example, planets should have formed around Fomalhaut within tens of millions of years after the birth of the star.

The Hubble images also provide a glimpse of the outer planetary region surrounding a star other than our Sun. Many of the more than 100 planets detected beyond our solar system are orbiting close to their stars. Most of the current planet-detecting techniques favor finding planets that are close to their stars.

“The size of Fomalhaut’s dust ring suggests that not all planetary systems form and evolve in the same way ? planetary architectures can be quite different from star to star,” Kalas explained. “While Fomalhaut’s ring is analogous to the Kuiper Belt, its diameter is four times greater than that of the Kuiper Belt.”

The astronomers used the Advanced Camera for Surveys’ (ACS) coronagraph aboard Hubble to block out the light from the bright star so they could see details in the faint ring.

“The ACS’s coronagraph offers high contrast, allowing us to see the ring’s structure against the extremely bright glare from Fomalhaut,” Clampin said. “This observation is currently impossible to do at visible wavelengths without the Hubble Space Telescope. The fact that we were able to detect it with Hubble was unexpected, but impressive.”

Kalas and his collaborators used Hubble over a five-month period in 2004 ? May 17, Aug. 2, and Oct. 27 ? to map the ring’s structure. One side of the ring has yet to be imaged because it extended beyond the ACS camera’s field of view. The astronomers will use Hubble again this summer to map the entire ring. They expect that the additional Hubble data will reveal whether or not the ring has any gaps, which could have been carved out by the gravitational influence of an unseen body. The longer, deeper exposures also may show whether the ring has an even wider diameter than currently seen. In addition, the astronomers will measure the ring’s colors to determine its physical properties, including its composition.

Previous thermal emission maps of Fomalhaut showed that one side of the ring is warmer than the other side, implying that the ring is off center by about half the distance measured by Hubble. This difference might be explained by the fact that Hubble’s ACS images of the ring’s structure are 100 times sharper than the longer wavelength observations, and hence, yield a much more accurate result. Or the discrepancy might imply that the ring’s size looks different at other wavelengths.

Fomalhaut’s dust ring was discovered in 1983 in observations made by NASA’s Infrared Astronomical Satellite (IRAS). The system is a compelling target for future telescopes such as the James Webb Space Telescope and the Terrestrial Planet Finder, Kalas said.

Original Source: Hubble News Release

Posted on by Fraser Cain

Natural Particle Accelerator Discovered

HESS image of binary pair PSR B-1259-63 / SS 2883. Image credit: HESS. Click to enlarge.
Binary pair PSR B-1259-63 / SS 2883 is located some 5,000 light-years distant in the general direction of the southern hemisphere constellation Crux (the Southern Cross). The duo consists of a pulsar (PSR B-1259) and massive blue giant (SS 2883) locked into a widely-swinging dance that repeats steps every 3.4 years. The pulsar?s orbit of the more massive primary is so eccentric that the pair passes within 100 million kilometers at closest approach and they separate roughly ten times that distance at their furthest point. During closest approach, signals from the pulsar drop off significantly as it is eclipsed by the massive blue giant.

Observers using the 12.5 metre High Energy Stereoscopic System (HESS) recorded the pair’s dance during moonless nights from February through April 2004, and timed them as the pulsar approached and receded from the duo’s closest point. The astronomers found that radio waves from the pulsar matched up with ultra-high gamma radiation coming from the region.

According to Felix Aharonian of the Max Plank Institute for Nuclear Physics, Heidelberg Germany, this binary system “allows ‘on-line watch’ of the extremely complex MHD (magnetohydrodynamic) processes of creation and termination of the ultrarelativistic pulsar wind, as well as particle acceleration by relativistic shock waves, through the study of spectral and temporal characteristics of the high energy gamma-radiation of the system. In this regard the binary system PSR B1259-63 is a unique laboratory to explore the physics of the pulsar winds.”

The pulsar was first detected by a team of astronomers in 1992 using the Parkes radio telescope in Australia. Its magnetic jet orients toward the Earth 20 times a second. In addition to radio emission, the pulsar broadcasts X-rays – at various energy levels – throughout its orbit. These X-rays are thought to be the result of radiation that occurs when the pulsar’s magnetic field interacts with gases released by the companion blue giant.

The blue giant SS 2883 was first discovered to be a companion with the pulsar in 1992. It’s ten times the mass of the Sun, but has high temperatures and a rapidly burning fusion engine. It rotates very quickly and ejects material from its equator on a sporadic basis. According to the paper ‘Discovery of the Binary Pulsar PSR B-1259-63 … with H.E.S.S.’, “Be stars are known to have non-isotropic stellar winds forming an equatorial disk with enhanced mass outflow.”

The paper goes on to say that “timing measurements suggest that the disk is inclined with respect to the orbital plane…” such an orbital inclination causes the “pulsar to cross the disk two times near periastron.” And it is at these crossings that things really get souped up as the pulsar’s magnetic field begins to interact with charged particles in the reverse shock region of the stellar ejecta.

As a result, this system is said to be a ‘binary plerion’ where “The intense photon field provided by the companion star not only plays an important role in the cooling of relativistic electrons but also serves as the perfect target for the production of high-energy gamma rays through inverse Compton (IC) scattering.” Felix expands on this notion by saying that “the pulsar is not isolated, but located in a binary system close to a powerful optical star. In this case, because of interaction with the stellar wind under high gas pressure, the pulsar wind terminates within the binary system where the magnetic field is quite high (approximately 1 G, i.e. 10,000 to 100,000 times larger than in standard plerions). Furthermore, because of the optical star’s presence, the electrons suffer severe losses during interactions (Compton scattering) with starlight. This makes the lifetime of electrons very short, 1 hour or less. High energy gamma-rays can be produced also by interactions of electrons (and perhaps also protons) with the dense gas of the stellar disk (also on quite short timescales!).”

As a binary plerion, the star system displays a wide-ranging energy signature based on the pulsar’s eccentric orbit and broad variations in the density of circumstellar matter around SS 2883 with which it interacts. Near periastron, The “cold” pulsar wind interacting with the ambient plasma, terminates with the creation of a relativistic shock wave which in turn accelerate particles to extremely high energies, 1 TeV or more. Heat in these particles is then ‘cooled’ as photons strike fast-moving electrons and positrons. This inverse Compton scattering effect carries off energy by amplifying photon frequencies wildly. Simply said, photons of low-energy “visible light” are boosted to much higher energy levels – some achieving the terra-electron volt region of the upper gamma ray / lower cosmic ray domain.

Meanwhile as the pulsar moves away from the stellar primary, it encounters fewer and fewer charged particles, meanwhile the density of visible light photons from the central star also falls off. As this occurs, scattering of photons is reduced and synchrotron radiation begins to dominate. Because of this, lower power-level X-rays begin to dominate the energy signature of the system as the pulsar slows and moves away from the star.

Finally, there are two periods in the pulsars orbit where it crosses the equatorial plane of the blue giant’s circumstellar disk. These transition points can result in the creation of numerous super-energized photons, electrons, positrons and even some protons. As relativistically accelerated particles are created, they in turn interact with a region able to spawn a multitude of other particles capable of breaking down into high-energy photons and other particles.

From the paper published June 13, 2005, “Up to now the theoretical understanding of this complex system, involving pulsar and stellar winds interacting with each other is quite limited because of the lack of constraining observations.” But now because of IACTS (Imaging Atmospheric Cherenkov Telescopes) such as H.E.S.S., astronomers are now able to resolve many new near-point sources of high energy gamma rays from other systems such as PSR B-1259-63 / SS 2883.

In the PSR B-1259-63 / SS 2883 system, nature seems to have provided astronomers – and physicists – with her very own version of a super-high energy particle accelerator – one that is thankfully well contained and a safe distance from Earth.

Written by Jeff Barbour

Posted on by Fraser Cain

Solar Sail Goes Missing

The Planetary Society’s solar sail prototype Cosmos 1 was launched from a Russian submarine yesterday, but it seems have gone missing. There are conflicting reports coming from Russian news sources that say that the Volna rocket booster failed 83 seconds after launch because of problems with the first stage of its three-stage rocket. This is different from a US team also working to track the solar sail who said they’ve detected it a few times in orbit (link to BBC article).

Posted on by Fraser Cain

Mars Express Booms All Deployed

Artist illustration of Mars Express with all three booms deployed. Image credit: ESA. Click to enlarge.
MARSIS, the Mars Advanced Radar for Subsurface and Ionosphere Sounding on board ESA?s Mars Express orbiter, is now fully deployed, has undergone its first check-out and is ready to start operations around the Red Planet.

With this radar, the Mars Express orbiter at last has its full complement of instruments available to probe the planet?s atmosphere, surface and subsurface structure.

MARSIS consists of three antennas: two ?dipole? booms 20 metres long, and one 7-metre ?monopole? boom oriented perpendicular to the first two. Its importance is that it is the first- ever means of looking at what may lie below the surface of Mars.

The delicate three-stage phase of radar boom deployment, and all the following tests to verify spacecraft integrity, took place between 2 May and 19 June. Deployment of the first boom was completed on 10 May. That boom, initially stuck in unlocked mode, was later released by exploiting solar heating of its hinges.

Taking advantage of the lessons learnt from that first boom-deployment, the second 20-metre boom was successfully deployed on 14 June. Subsequently, ESA?s ground team at the European Space Operations Centre (ESOC) in Darmstadt, Germany, commanded the non-critical deployment of the third boom on 17 June, which proceeded smoothly as planned.

MARSIS?s ability to transmit radio waves in space was tried out for the first time on 19 June, when the instrument was switched on and performed a successful transmission test.

The instrument works by sending a coded stream of radio waves towards Mars at night, and analysing their distinctive echoes. From this, scientists can then make deductions about the surface and subsurface structure. The key search is for water. But MARSIS’s capabilities do not stop there. The same methods can also be used by day to probe the structure of the upper atmosphere.

Before starting its scientific observations, MARSIS has to undergo its commissioning phase. This is a routine procedure for any spacecraft instrument, necessary to test its performance in orbit using real targets in situ. In this case, the commissioning will last about ten days, or 38 spacecraft orbital passes, starting on 23 June and ending on 4 July.

During the commissioning phase, MARSIS will be pointed straight down (nadir pointing mode) to look at Mars from those parts of the elliptical orbit where the spacecraft is closest to the surface (around the pericentre). During this phase, it will cover the areas of Mars between 15? S and 70? N latitude. This includes interesting features such as the northern plains and the Tharsis region, so there is a small chance of exciting discoveries being made early on.

On 4 July, when the commissioning operations end, MARSIS will start its nominal science observations. In the initial phase, it will operate in survey mode. It will make observations of the Martian globe?s night-side. This is favourable to deep subsurface sounding, because during the night the ionosphere of Mars does not interfere with the lower-frequency signals needed by the instrument to penetrate the planet’s surface, down to a depth of 5 kilometres.

Through to mid-July, the radar will look at all Martian longitudes between 30? S and 60? N latitude, in nadir pointing mode. This area, which includes the smooth northern plains, may have once contained large amounts of water.

The MARSIS operation altitudes are up to 800 kilometres for subsurface sounding and up to 1200 kilometres for studying the ionosphere. From mid-July, the orbit’s closest approach point will enter the day-side of Mars and stay there until December. In this phase, using higher frequency radio waves, the instrument will continue shallow probing of the subsurface and start atmospheric sounding.

?Overcoming all the technical challenges to operate an instrument like MARSIS, which had never flown in space before this mission, has been made possible thanks to magnificent cooperation between experts on both sides of the Atlantic,? said Professor David Southwood, ESA’s Science Programme Director. ?The effort is indeed worthwhile as, with MARSIS now at work, whatever we find, we are moving into new territory; ESA?s Mars Express is now well and truly one of the most important scientific missions to Mars to date,? he concluded.

Original Source: ESA News Release

Posted on by Fraser Cain

Podcast: Into the Submillimeter

When you look into the night sky with your eyes, or through a telescope, you’re seeing the Universe in the spectrum of visible light. Unfortunately, this is a fraction of the entire electromagnetic spectrum, ranging from radio waves to gamma radiation. And that’s too bad because different wavelengths are better than others for revealing the mysteries of space. Technology can let us “see” what our eyes can’t, and instruments here on Earth and in space can detect these different kinds of radiation. The submillimeter wavelength is part of the radio spectrum, and gives us a very good view of objects which are very cold – that’s most of the Universe. Paul Ho is with the Harvard-Smithsonian Center for Astrophysics, and an astronomer working in world of the submillimeter. He speaks to me from Cambridge, Massachusetts.
Continue reading “Podcast: Into the Submillimeter”

Posted on by Fraser Cain

First View of Tempel 1’s Nucleus

Deep Impact’s measurements of Comet Tempel 1’s nucleus. Image credit: NASA/JPL/UM. Click to enlarge.
For the first time, scientists have processed images from NASA’s Deep Impact spacecraft and clearly seen the solid body, or nucleus, of the comet through the vast cloud of dust and gas that surrounds it. The new images provide important information about the mission’s target: the “heart” of comet Tempel 1.

The images were taken at the end of May with the spacecraft’s medium resolution camera, at a distance of some 20 million miles from the comet. Unprocessed, the images are dominated by the comet’s huge cloud of dust and gas, which scientists call the coma. However, scientists used a neat photometric trick to isolate the relatively small (3-mile by 9-mile) nucleus from the comet’s coma, or atmosphere. The much larger, but less dense atmosphere was mathematically identified and then subtracted from the original images leaving images of the nucleus, the bright point in the center of the coma.

“Its exciting to see the nucleus pop out from the coma,” said University of Maryland astronomer Michael A’Hearn, who leads the Deep Impact mission. “And being able to distinguish the nucleus in these images helps us to better understand the rotational axis of the comet’s nucleus, which is helpful for targeting this elongated body.”

“This is an important milestone for the Deep Impact team,” explained Carey Lisse, a member of the Deep Impact team and leader of the effort to extract views of the nucleus from the spacecraft images. “From here on in we just watch the nucleus grow and grow and become brighter and bigger as the spacecraft closes in on the comet. We detected the nucleus a lot sooner than expected, but now we’ll be watching the nucleus all the way to impact!”

As illustrated in the attached figure, Deep Impact images taken on May 29-31 contain a well-formed coma with a detectable point source at the position of the brightest pixel. The brightness of the nucleus as determined from these images was close to that predicted from earlier observations with the Hubble and Spitzer space-telescopes and observations from large telescopes on the ground. At present, the nucleus contributes about 20 percent of the total brightness near the center of the comet.

“The early detection of the nucleus in these images helps us to set the final exposure times for our encounter observations,” said Michael Belton, deputy principal investigator for the Deep Impact Mission. “Next we need to determine, using additional nucleus detections, how the comet is rotating in space, so we can figure out what part we will hit on July 4th.”

5 – 4 – 3 – 2 – 1 – IMPACT
Deep Impact — which consists of a sub-compact-car-sized flyby spacecraft and a five-sided impactor spacecraft about the size of a washing machine — carries four instruments. The flyby spacecraft carries two imaging instruments, the medium resolution imager and the high resolution imager, plus an infrared spectrometer that uses the same telescope as the high-resolution imager. The impactor carries a single imager. Built to science team specifications by Ball Aerospace & Technologies Corp., the three imaging instruments are essentially digital cameras connected to telescopes. They record images and data before, during, and after impact.

At the beginning of July, after a voyage of some 268 million miles, the joined spacecraft will reach comet Tempel 1. The spacecraft will approach the comet and collect images and spectra of it. Then, some 24 hours before the 2 a.m. (EDT) July 4th impact, the flyby spacecraft will launch the impactor into the path of the onrushing comet. Like a copper penny pitched up into the air just in front of a speeding tractor-trailer truck, the 820-pound impactor will be run down by the comet, colliding with the nucleus at an impact speed of some 23,000 miles per hour. A’Hearn and his fellow mission scientists expect the impact to create a crater several hundred feet in size; ejecting ice, dust and gas from the crater and revealing pristine material beneath. The impact will have no significant affect on the orbit of Tempel 1, which poses no threat to earth.

Nearby, Deep Impact’s ‘flyby’ spacecraft will use its medium and high resolution imagers and infrared spectrometer to collect and send back to Earth pictures and data of the event. In addition, the Hubble and Spitzer space telescopes, the Chandra X-ray Observatory, and large and small telescopes on Earth also will observe the impact and its aftermath.

The University of Maryland, College Park, conducts the overall mission management for Deep Impact, which is a Discovery class NASA program. NASA’s Jet Propulsion Laboratory(JPL) handles project management for the Deep Impact mission. The spacecraft was built for NASA by Ball Aerospace & Technologies Corporation, Boulder, Colo.

Original Source: University of Maryland News Release

Posted on by Mark Mortimer

Book Review: Story – The Way of Water


For those unfamiliar with Story Musgrave, a quick list is in order. Story worked at NASA for 30 years. As mission specialist or payload commander for six shuttle flights, he contributed to many scientific endeavours, including the mission to fix the Hubble telescope. While on ground, he kept busy by helping design the EVA suit, being the CapCom for many missions, giving soaring and flight lessons as well as using his medical doctorate at hospitals to perform surgery on patients. With many degrees, he has kept his mind sharp, while with many contributions he has endeavoured to use the knowledge to great benefit.
Continue reading “Book Review: Story – The Way of Water”

Posted on by Fraser Cain

Audio: Into the Submillimeter

Artist illustration of the Atacama Large Millimeter Array currently under construction. Image credit: ESO. Click to enlarge.
Listen to the interview: Get Ready for Deep Impact (4.8 MB)

Or subscribe to the Podcast: universetoday.com/audio.xml

Fraser Cain: Can you give me some background on the submillimeter spectrum? Where does that fit?

Paul Ho: The submillimeter, formally, is at a wavelength of 1 millimeter and shorter. So 1 millimeter wavelength in frequency corresponds to about 300 gigahertz or 3×10^14 hertz. So, it is a very short wavelength. From that down to a wavelength of about 300 microns, or a third of a millimeter, is what we call the submillimeter range. It is sort of what we call the end of the atmospheric window as far as the radio is concerned, because shorter, about a third of a millimeter they sky becomes essentially opaque due to the atmosphere.

Fraser: So, these are radio waves, like what you’d listen to on the radio, but much shorter – nothing I could ever pick up on my FM radio. Why are they good for viewing the Universe where it’s cold?

Ho: Any object that we know of, or see, typically is radiating a spread of energy characterizing the materials that we’re talking about, so we call this a spectrum. And this energy spectrum typically has a peak wavelength – or the wavelength at which the bulk of the energy is radiated. That characteristic wavelength depends on the temperature of the object. So, the hotter the object, the shorter the wavelength comes out at, and the cooler the object, the longer the wavelength comes out at. For the Sun, which has a temperature of 7,000 degrees, you’d have a peak wavelength which comes out in the optical, which is of course why our eyes are tuned to the optical, because we live near the Sun. But as the material cools, the wavelength of that radiation gets longer and longer, and when you get down to a characteristic temperature of say 100 degrees above Absolute Zero, that peak wavelength comes out somewhare in the far infrared or submillimeter. So, a wavelength on the order of 100 microns, or a little bit longer than that, which puts it into the submillimeter range.

Fraser: And if I were able to swap out my eyes, and replace them with a set of submillimeter eyes, what would I be able to see if I looked up into the sky?

Ho: Of course, the sky would continue to be quite cool, but you’d begin to pick up a lot of things that are rather cold that you would not see in the optical world. Things like materials that are swirling around a star which are cool, on the order of 100 Kelvin; pockets of molecular gas where stars are forming – they would be colder than 100 K. Or in the very distant, early Universe when galaxies are first assembled, this material is also very cold, which you would not be able to see in the optical world, that you might be able to see in the submillimeter.

Fraser: What instruments are you using, either here or in space?

Ho: There are ground and space instruments. 20 years ago, people began to work in the submillimeter, and there were a few telescopes that were beginning to operate in this wavelength. In Hawaii, on Mauna Kea, there are two: one called the James Clerk Maxwell Telescope, which has a diameter of about 15 metres, and also the Caltech Submillimeter Observatory, which has a diameter of about 10 metres. We have built an interferometer, which is a series of telescopes which are coordinated to operate as a single instrument on top of Mauna Kea. So 8 6-metre class telescopes which are linked together and can be moved apart or moved closer together to a maximum baseline of, or separation, of half a kilometre. So this instrument is simulating a very large telescope, on the size of half a kilometre at its maximum, and therefore achieving a very high angle of resolution compared to existing single element telescopes.

Fraser: It’s much easier to combine the light from radio telescopes, so I guess that’s why you’re able to do that?

Ho: Well, the interferometer technique has been used in radio for quite some time now, so we have perfected this technique fairly well. Of course, in the infrared and optical, people are also beginning to work in this way, working on interferometers. Basically, combining the radiation, you have to keep track of the phase front of the radiation coming in. Normally I explain this as if you had a very large mirror and broke it so you just reserve a few pieces of the mirror, and then you want to reconstruct the information from those few pieces of mirror, there are a few things you need to do. First, you have to be able to keep the mirror pieces aligned, relative to each other, just like it was when it was one whole mirror. And second, to be able to correct for the defect, from the fact that there’s a lot of missing information with so many pieces of mirror that are not there, and you’re only sampling a few pieces. But this particular technique called aperture synthesis, which is to make a very large aperture telescope by using small pieces, of course, is the produce of Nobel prize winning work by Ryle and Hewish some years ago.

Fraser: What instruments are going to be developed in the future to take advantage of this wavelength?

Ho: After our telescopes are built and we’re working, there will be an even larger instrument that’s being constructed now in Chile called the Atacama Large Millimeter Array (ALMA), which will consist of many more telescopes and larger apertures, which will be much more sensitive than our pioneering instrument. But our instrument will hopefully begin to discovery the signs and the nature of the world in the submillimeter wavelength before the larger instruments come along to be able to follow along and do more sensitive work.

Fraser: How far will those new instruments be able to look? What could they be able to see?

Ho: One of the targets for our discipline of submillimeter astronomy is to look back in time at the earliest part of the Universe. As I mentioned earlier, in the early stage of the Universe, when it was forming galaxies, they tend to be much colder in the early phases when galaxies were being assembled, and it will radiate, we think, principly in the submillimeter. And you can see them, for example, using the JCM telescope on Mauna Kea. You can see some of the early Universe, which are very highly redshifted galaxies; these are not visible in the optical, but they are visible in the submillimeter, and this array will be able to image them, and locate them very actively as to where they are located in the sky so that we can study them further. These very early galaxies, these early formations, we think are at very high redshifts – we give this number Z, which is a redshift of 6, 7, 8 – very early in the formation of the Universe, so looking back to perhaps 10% of the time when the Universe was being assembled.

Fraser: My last question for you… Deep Impact is coming up in a few weeks. Will your observatories be watching this as well?

Ho: Oh yes, of course. The Deep Impact indeed is something we’re interested in. For our instrument, we have been studying Solar System type bodies, and this includes not only the planets, but also the comets as they come close or impact, we expect to see material to spew off, which we should be able to track in the submillimeter because we’ll be looking not only at the dust emissions, but we will be able to watch the spectral lines of the gasses which come out. So, we’re expecting to be able to turn our attention to this event, and to also be imaging it.

Paul Ho is an astronomer with the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.

Posted on by Fraser Cain

What’s Up This Week – June 20 – June 26, 2005

View of Mars. Image credit: NASA/JPL. Click to enlarge.
Monday, June 20 – Have you checked out Mars lately? Today Mars crosses the celestial equator positioning it higher amoungst the constellations. Since we are focusing on planetary motions this week, see in your mind’s eye that we are on a type of racetrack. Since Earth is closer to the Sun than Mars, we move around that inside track much quicker, and right now we are coming up behind Mars at a speed of 23,500 mph, which means Mars getting bigger and brighter every day – and will be spectacular by October. Now rather “football” shaped, be sure to look in a telescope to see if you can catch a glimpse of the polar caps. Be sure to check next week when the crescent Moon and Mars make a pleasing conjunction in the morning sky!

Tonight on the lunar surface, use binoculars to spot the dark oval of Grimaldi just south of central on the terminator. If you chose to scope, look for the great form of Pythagorus to the north and its sharp central peak.

Although the peak time for the June Ophiuchids happened in the early morning hours, you still might catch some of the stream tonight. Its radiant is near Sagittarius and the fall rate varies from 8 to 20, with possibility of many more.

Tuesday, June 21 – Today the Sun achieves its highest point for the year at midday for the northern hemisphere. Known as the Summer Solstice the exact moment occurs at 06:46 UT, and also marks the Winter Solstice for our friends in the Southern Hemisphere.

For most observers, the Moon will appear to be full, but will not actually reach that point until 04:14 UT tomorrow morning. Just take some time to watch it rise! Known as the Rose Moon, Strawberry Moon and Honey Moon, if atmospheric conditions are right, you might see an orangish tint to its form, but the real fun is “moon illusion”! Everyone knows the Moon looks larger on the horizon, but did you know this is a psychological phenomena and not a physical one? Prove it to yourself by looking at the rising Moon upright… It looks larger, doesn’t it? Now stand on your head, or find a way comfortable to view it upside down… Now how big is it?

Wednesday, June 22 – Today celebrates the founding of the Royal Greenwich Observatory in 1675. That’s 330 years of astronomy! Also on this date in history, in 1978 James Christy of the US Naval Observatory in Flagstaff, AZ discovered Pluto’s satellite Charon.

Tonight let’s race ahead of the rising Moon and capture comet 9/P Tempel 1. (Remember there are very accurate night-by-night locator charts on Heavens Above.) If you can find Jupiter, then you’re definitely in the neighborhood to locate this comet. Just to Jupiter’s east is Omicron Virginis. Consider this to be “one step”. Now take two more “steps” east and you are in the general vicinity. While the comet is still rather faint for smaller instruments, magnitude 10 should still be within the reach of most backyard scopes.

Thursday, June 23 – The time has come at last! In case the weather should turn cloudy, be sure to go out tonight and enjoy the western horizon just after sunset. The grouping of Venus, Saturn, and Mercury low in the west-northwest should not to be missed. Venus, by far the brightest of the three, sits central. Mercury will appear just slightly more than one degree to Venus’ lower right and Saturn about two and half degrees to Venus’ upper left. Timing is critical, so start your observations about 30 to 45 minutes after sunset.

Once you’ve viewed the planets, let’s set a telescope toward 6 Comae, just east of Denebola. Less than a degree (50′) to its southeast, you will find the spectacular M99. Discovered by Mechain in 1781 and then confirmed by Messier, this magnitude 10.5 spiral beauty has wonderful structure and a highly apparent arm to smaller scopes on the west side. Return to 6 Comae and travel a half degree to the west and you will find M98. Again discovered by Mechain in 1781, this nearly edge-on spiral has a bright nucleus and is very extended for the larger scope.

Friday, June 24 – On this day in 1881, Sir William Huggins makes the first photographic spectrum of a comet (1881 III) and discovers the cyanogen (CN) emission at violet wavelengths. This discovery caused near mass hysteria some 29 years later when Earth passed through the tail of Halley’s Comet.

Our trio of planets, Saturn, Venus and Mercury have now come together within two and a half degrees of each other, making the area small enough to fit easily within most all binocular’s field of view. The orbital motions of Venus and Mercury are carrying them past Saturn, so watch as the “Ring King” drops away over the next few days. Please take the time to look at the extraordinary display of planetary motion!

Since Huggins viewed a comet 124 years ago on this night, why don’t we? The “Magnificent Machholz” is still around and sailing through Canes Venetici. Locate bright Cor Caroli and head south about two degrees to identify star 14. You will find C/2004 Q2 just about a degree to its southeast.

Saturday, June 25 – The planetary show just keeps getting better as our trio reaches its tightest configuration after sunset tonight. Saturn, Venus and Mercury are now within a degree and half of each other, and easily covered by your thumb held at arm’s length. Their relative positions planets are changing rapidly, with Saturn dropping to the lower left of Venus and Mercury to the lower right. This will be an awesome photographic opportunity and I wish all of you success and clear skies!

Sunday, June 26 – Today is the birthday of none other than Charles Messier, the famed French comet hunter. Born in 1730, Messier is best known for cataloging the 100 or so bright nebulae and star clusters the we now refer to as the Messier objects. The catalog was to keep both Messier and others from confusing these stationary objects with possible new comets. In 1949, asteroid Icarus was discovered on a 48-inch Schmidt plate made nine months after the telescope went into operation, and just prior to the beginning of the multi-year National Geographic – Palomar Sky Survey. The asteroid was found to have a highly eccentric orbit and a perihelion distance of just 17 million miles, closer to the Sun than Mercury, giving it its unusual name. It was just four million miles from Earth at the time of discovery, and variations in its orbital parameters have been used to determine Mercury’s mass and test Einstein’s theory of general relativity.

And what of Mercury? Tonight both Mercury and Venus have moved above Saturn by about a degree and a half, almost doubling that separation. Get out your scopes, because Venus and Mercury now are only 0.2 degrees apart. But wait… The show gets even better tomorrow night! Be sure to look for next week’s “What’s Up”!

For now, the Moon rises later and later each night allowing us more opportunity to study the deep sky! May all your journeys be at Light Speed… ~Tammy Plotner