Astronomy.com blog : Francis Reddy

Moondust mirrors

Francis Reddy — Fri, 06 Jun 2008 16:22:00 GMT

Once upon a time, the buzzwords in telescope making were Teflon and Formica. In the future, though, they may be epoxy and lunar dust.

Peter Chen and his colleagues at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, presented a novel recipe for making telescope mirrors at the American Astronomical Society meeting in St. Louis June 4. For years, Chen has been exploring the use of composite materials in making lightweight, high-quality telescope mirrors with an eye to building big scopes on the Moon.

The key to building massive structures of any kind on the Moon is to use as many local resources as possible — “in situ resource utilization,” in NASA-speak. So, Chen’s team combined simulated moondust with carbon nanotubes. The result was a strong, thermally stable material with the consistency of concrete. Chen notes this stuff could be used as the building blocks of a lunar base.

The team poured layers of epoxy over a disk of this lunar concrete and spun the unit until the liquid cured. “I just used a pottery wheel,” Chen says, smiling. The result was a 12-inch-wide mirror blank with a parabolic surface. When they coated the blank with a small amount of aluminum, the researchers had a telescope mirror.

For building a lunar scope the size of Hubble, Chen’s process requires transporting 132 pounds (60 kilograms) of epoxy, 13 pounds (6 kg) of carbon nanotubes, and less than 1/3 ounce (1 gram) of aluminum. The remaining raw material required — 1,300 pounds (600 kg) of moondust — is already at the construction site.

But Chen is thinking much bigger than a lunar Hubble. "We could make huge telescopes on the Moon relatively easily," he says. "Since most of the materials are already there in the form of dust, you don't have to bring very much stuff with you, and that saves a ton of money."

He envisions monolithic mirrors as large as 50m across. That would take about 4,000 pounds (1,800 kg) of epoxy and a pound (about half a kilogram) of aluminum. How much lunar dust? “I don’t even want to think about that,” Chen says, laughing.

He suggests that future telescope makers might select a promising patch of lunar real estate and use robots to remove the rocks. Then solar concentrators — built using the same moondust-mirror material — could fuse the dust. Next, add layers of epoxy to create a smooth surface, then figure it to a parabola using ion beams, a process that would take advantage of the environment’s high vacuum.

Astronomers say a 50m lunar scope would let them record spectra from extrasolar planets and detect gases like ozone and methane, indicative of life. Add one or two more such scopes, and they could work together to directly image alien worlds.

That’s not a bad rationale for revisiting the Moon.

Are quirky supernovae “quark novae”?

Francis Reddy — Tue, 03 Jun 2008 18:35:00 GMT

Three of the most luminous supernovae on record — 2006gy, 2005gj, and 2005ap — pose problems for theorists. For example, 2006gy’s peak luminosity reached 50 billion Suns. That’s 10 times brighter than the average type Ia supernova and 100 times brighter than a representative type II. And 2005ap was 2 times brighter still.

What’s a theorist to do? In our January issue, I noted that astronomers suspected some of these events might be so-called “pair-production” supernovae. This mechanism was hypothesized 40 years ago, but no one’s ever seen a supernova that matches it. In essence, a star’s core gets so hot that colliding gamma rays spontaneously create pairs of particles — an electron and a positron. The particle creation removes pressure. The star begins to collapse, but then detonates in runaway thermonuclear reactions.

This scenario works better for some of the superbright supernovae than others. So what else do theorists have up their sleeves?

At the American Astronomical Society meeting in St. Louis today, Denis Leahy and Rachid Ouyed at the University of Calgary suggested something radical. They say the explosive conversion of a neutron star into a quark star has the right properties to account for all three of these quirky supernovae.

Neutron stars, the crushed, superdense cores of massive stars, form in some supernovae. They pack a mass of 1.5 Suns into a ball just 16 miles wide. Quark stars, if they exist, have similar masses, but are crunched down even smaller, to 12 miles across. Leahy and Ouyed suggest that, when a neutron star’s density gets too high, its neutrons dissolve into their component quarks — and release a burst of energy similar to the original supernova.

Here’s how they think it might have worked. Because the superbright supernovae all occurred far away, astronomers wouldn’t detect the initial neutron-star-forming explosion. The supernova remnant’s hot plasma expands to about 100 times the Earth-Sun distance.

By then, the unstable neutron star shudders into its new, more compressed configuration: a quark star. The shock wave from this second explosion drives into and heats the existing remnant. The large size of the remnant at the time of the second explosion is the key to making superluminous supernovae, the scientists say.

Heh. Quark stars. I love astrophysics.

John Archibald Wheeler (1911–2008)

Francis Reddy — Mon, 14 Apr 2008 21:27:00 GMT

Best known to astronomical trivia buffs as the man who coined the term “black hole,” University of Texas physicist John A. Wheeler died this morning at the age of 96.

Wheeler “was legendary for his way with words, coining such terms as wormholes, quantum foam, black holes, and the wave function of the universe,” writes Wheeler’s former student and current University of Chicago physicist Daniel Holz over at Cosmic Variance. Wheeler’s scientific resume extended from quantum mechanics — he collaborated with Niels Bohr on early nuclear fission research — to cosmology, but he’s best known for his contributions to general relativity.

“For the first half-century of its life, general relativity was a theorist’s paradise, but an experimentalist’s hell. No theory was thought more beautiful, and none was more difficult to test.” That summary comes from the 1973 edition of Gravitation, the bible of relativity, written by Charles W. Misner and Kip S. Thorne — two former students of Wheeler’s — and, of course, the man himself.

The chapter concludes that relativity “has emerged from each of its tests unscathed — a remarkable 1973 tribute to the 1915 genius of Albert Einstein.” It’s a remarkable 2008 tribute as well, for relativity still reigns supreme.

Following the implications of relativity’s equations led physicists to ponder black holes. In 1939, J. Robert Oppenheimer and Hartland Snyder at the University of California, Berkeley, used them to show that when a big enough star runs out of fuel, it must collapse to densities so great even light cannot escape it. Moreover, the collapse continues forever.

At first, Wheeler fought the notion that a collapsing mass could cut itself off from communication with the rest of the universe. But, by the mid-1960s, intense theoretical work showed there was no way of avoiding these so-called “frozen stars.” In 1967, Wheeler hit on a more dramatic — yet scientifically justified — term: black hole.

By then, astronomers had already identified a candidate — now considered a confirmed — black hole. The object, named Cygnus X-1, is one of the brightest X-ray sources in the sky. The radiation arises as gas stolen from a blue supergiant streams onto a disk of matter gathered around a stellar-mass black hole. A few dozen such systems are known.

These are small-fry compared to their supermassive brethren at the cores of galaxies. The black hole at the Milky Way’s center weighs in at 3 to 4 million Suns.

But back to Wheeler. Those interested in hearing these developments in the physicist's own voice should consult his science autobigraphy, Geons, Black Holes, and Quantum Foam: A Life in Physics, written with Kenneth W. Ford (W. W. Norton & Co., 2000).

Encounters with Arthur C. Clarke

Francis Reddy — Tue, 25 Mar 2008 14:52:00 GMT

On Saturday, March 22, friends and family bid farewell to science-fiction writer Arthur C. Clarke, who died March 19 at his home in Sri Lanka. Best known for the novel and screenplay 2001: A Space Odyssey (1968), Clarke wrote fiction that often juxtaposed themes as audacious as humanity’s destiny with prophetic visions of coming technology. Little wonder that his work influenced generations of scientists and engineers.

“All of us who have been entertained and inspired by Sir Arthur Clarke's writings mourn his passing,” writes David Morrison at NASA’s Ames Research Center in California. Morrison chaired a 1992 NASA workshop that recommended funding for ground-based observatories designed to discover more than 90 percent of all Near-Earth Objects (asteroids and comets) larger than 1 kilometer within 25 years. The project was named the Spaceguard Survey after a similar system described in Clarke’s novel, Rendezvous with Rama (1972). “Clarke graciously endorsed our use of the term,” Morrison says. “He himself supported our efforts to initiate this survey and was pleased to have his name associated with such a worthy endeavor.” This BBC report sums up several of the author’s other predictions.

Edward Rothstein’s appraisal of Clarke’s fiction in the March 20 New York Times gets it right, I think: “Mr. Clarke’s writings were the most biblical, the most prepared to amplify reason with mystical conviction, the most religious in the largest sense of religion: speculating about beginnings and endings, and how we get from one to the other.” Eulogies from filmmaker George Lucas, writer Harlan Ellison, and others give a sense of how far and wide Clarke’s influence runs.

Astronomy Contributing Editor Martin Ratcliffe had the good fortune of meeting Clarke twice. “He was a longtime member of the British Astronomical Association (BAA), and I was a council member of the BAA in the 1980s,” Ratcliffe writes. “Through the BAA's office, I was approached by his brother, Fred, to assist with Arthur's scientific autobiography, Ascent to Orbit (1984). This volume represented all his early scientific papers, which were numerous…. Following completion, I was invited to the press premier of the movie 2010: The Year We Make Contact and met Arthur and his brother. Some months later a signed copy of Ascent to Orbit came to me — one of my most treasured possessions.”

The next time they met, in 1998, was just before a BAA meeting after Clarke had been knighted. “I sat and talked for a few minutes, and then he proudly and quietly showed me the medal he had received an hour earlier from the Queen,” Ratcliffe says.

My odyssey with Clarke’s fiction and non-fiction began at age 13, when I picked up a copy of Childhood’s End (1953). From that moment, I was hooked. Looking back from a distance of nearly 4 decades, Clarke’s prose may have been my strongest influence in deciding to pursue a career that blended both science and writing.

Years later, as I was about to enter my junior year in college, a visit to the National Air and Space Museum in Washington, D. C., inspired me to write the closest thing to a fan letter I’ve ever drafted. In the museum’s gift shop, I noticed half a dozen autographed copies of The Coming of the Space Age (1967), an anthology Clarke had edited. This modest stack was surrounded and outnumbered by Carl Sagan’s latest work and Isaac Asimov’s 200th book. I figured I might get a reply from a busy Clarke if I could make him laugh, and wrote to him how shocked — shocked! — I was at this “heinous crime” of book placement.

To my disbelief, I received an air-mail letter from Sri Lanka several weeks later. It contained a printed sheet of Clarke’s answers to frequently asked questions on which he had written: “Many thanks for the information! Heads will roll….”

For those of you who’d like to see what Clarke was saying about himself in July 1979, I’ve scanned the document. Here’s page 1, and here’s page 2.

Visit an astro-software goldmine

Francis Reddy — Mon, 17 Mar 2008 15:56:00 GMT

There’s no better place to find astronomy related software than the web archive created by Astro Events Group of Ostend, Belgium. “Our compilation will actually never be complete,” says Patrick Jaecques, a member of the group. “We have updates about every week. It’s also the only part of our Dutch web site that is translated into French, German and English.”

There you’ll find hundreds of programs for a wide variety of computing environments, including Java, Pocket PC, Palm, and — the usual suspects — various Windows and Mac flavors. They even have one entry for my old Psion Series 5 palmtop. (Hey, it was hot stuff in the last millennium.)

Folks at Astro Events Group assembled the archive to support and promote their favorite hobby. “This project started out about five years ago, when we saw how amazed people were at our big-screen projections of planetarium software,” Jaecques says. Teachers at schools where the nonprofit group gave presentations asked where they could find such programs. So, Astro Events members began burning “Heavenly Moments” CDs that included the best freeware and shareware programs.

Demand for these CDs quickly outstripped the group’s means of producing them, so they turned to the web. “Our archive consists of just over 400 programs, all placed on our own server for optimal connection speeds while downloading.” Jaecques says. “Every program is placed alphabetically by type, and comes with a handy screenshot and a link to the maker’s homepage.”

If you visit through their home page, www.astro-event-group.be, go to the Educatief (Educational) menu and select Software. Better yet, use this direct link to the catalog.

Light, mirrors, gravity!

Francis Reddy — Mon, 10 Mar 2008 21:40:00 GMT

Yesterday’s Milwaukee Journal Sentinel ran a nice summary of efforts by the University of Wisconsin - Milwaukee to detect gravitational waves. The article focuses on NEMO, the $1.8 million, 1,560 CPU, Beowulf-class computing cluster built and operated by the school’s gravitational-wave group. (Ah, I love that kind of talk.)

NEMO was commissioned in 2006. Since then, it’s been chugging through data produced by the Laser Interferometer Gravitational Wave Observatories (LIGO) in Hanford, Washington, and Livingston, Louisiana. Here’s an informative cartoon of the setup.

These facilities bounce lasers back and forth to track length changes smaller than the diameter of a hydrogen atom. Such changes would occur when gravitational waves pass by and ripple through our local space-time. Relativity predicts such things, but so far, no one has detected them.

Scientists continually are improving the reach and sensitivity of these observatories. Sooner or later, they’ll detect signals from things like inspiraling pairs of neutron stars or black holes, core-collapse supernovae, and possibly even gravitational waves from the Big Bang.

You can participate, too. Since early 2005, LIGO data has been distributed to personal computers and processed using the Einstein@Home project’s nifty screensaver. This gives users eye candy in return for background use of their computers (more about it here).

Einstein@Home lets users “compete” as teams. I formed Team Astronomy as soon as the project went public. We now boast 69 members with computing credits, which are points awarded based on the amount and speed of data processing by each computer.

Team Astronomy now ranks in the top 45 in terms of recent average credits, but I think we can do better. Feel free to join us in search of gravitational waves. It may be the closest you’ll get to a Nobel prize.

The Internet as a telescope

Francis Reddy — Thu, 28 Feb 2008 14:30:00 GMT

Until now, I couldn’t tell you about one exhibit I saw at January’s American Astronomical Society (AAS) meeting. The embargo lifted yesterday, when Microsoft announced its WorldWide Telescope project at the TED2008 conference in Monterey, California.

Imagine terabytes of astronomical imagery, ranging across the spectrum from radio waves to X-rays, seamlessly integrated and available in an easy-to-use interface. Pan left, right, up, down. Zoom in, merge different wavelengths, zoom some more — zoom down to the limit of the data.

“When the entire world's astronomy data is on the Internet and is accessible as a single distributed database, the Internet will be the world's best telescope,” observed Microsoft researcher Jim Gray in 2002. Now, 13 months after Gray disappeared on a solo boating trip, WorldWide Telescope is dedicated to him as it races toward its spring release date.

The presentation is simply gorgeous. But what makes WorldWide Telescope sing is the interface’s fluidity, which allows you to merge multiwavelength imagery from 10 different observatories — including the Hubble Space Telescope. That’s in part what brought a tear to the eye of tech blogger Robert Scoble: “It’s been a long while since Microsoft did something that had an emotional impact on me like that.” One key to this deft tool is its use of Microsoft’s Photosynth technology.

While I ogled the giant image of M31 and scanned poster papers at the AAS meeting, Microsoft’s Curtis Wong saw my ID badge and scooped me up. “You need to see this,” he said.

Wong’s partner, software engineer Jonathan Fay, was panning and zooming around the X-ray sky. As he passed over faint wisps from old supernova remnants, one object so compact and brilliant that I almost squinted came into view. A quick transition to optical wavelengths — ah, the Crab Nebula! — and then Fay zoomed into the data’s full resolution.

What’s important to remember is that this project grew from roots that run deep into the astrophysical community. Wong and Fay know it will interest amateur astronomers, educators, and techno-geeks. But it’s also designed as a research tool for professionals.

Here’s what we know at the moment: WorldWide Telescope will be available for free, but there’s no official release date yet, and it runs only on Windows. Wong and Fay have built it with an eye toward creating an active online community. It will run narrations and tours — some of which will be contributed by users, some by content partners.

I’ve been invited to participate in the software’s current “private alpha” testing, and frankly, I can’t wait. Expect I’ll have much more to say about this when the project launches.

A black hole named Edd

Francis Reddy — Fri, 11 Jan 2008 14:52:00 GMT

One of the pleasures of attending American Astronomical Society meetings is strolling through a sea of poster papers. A poster paper is exactly what it sounds like — it’s an oversized page that summarizes the results of a single study.

Now and then, you spot displays where the science comes mixed with whimsy. Such is the case with “Discovery and Interpretation of an X-ray Period in the Galactic Center Source CXOGC J174536–2856,” a study led by Valerie Mikles at the University of Florida. The poster features art of a massive star blowing a dense stellar wind toward a putative black hole represented by … Godzilla. (PDF here; be warned, it’s large.)

Mikles and her colleagues nicknamed the object Edd-1, which is hardly your typical astronomical moniker. “It actually has no scientific significance whatsoever,” she says.

The story: She first presented this source in an earlier poster that included a picture of Edvard Munch's "The Scream." “I used ‘The Scream’ because the iron line and the hydrogen lines are screamingly bright — the iron line is one of the largest ever seen,” Mikles explains. The line comes from iron atoms that have lost 24 electrons (FeXXV). “It’s stripped pretty bare,” she says.

So, the “Ed” in Edd-1 comes from Edvard. The second “d” is a pop-culture reference to “Ed, Edd n Eddy” on Cartoon Network. “That's why Edd-1 is a nickname and not an alternative name, like Cyg X-1,” Mikles notes.

It’s also lots easier to type than CXOGC J174536–2856.

After dealing with the nickname, the science is pretty straightforward. Observations using NASA’s Chandra X-ray Observatory and ESA’s XMM-Newton reveal that Edd-1’s X-ray flux waxes and wanes over 189 days. That’s possibly an orbital period, and, if it is, the changes in brightness could occur because the X-ray source regularly becomes eclipsed. Alternatively, the changes might be due to variations in the fuel supply fed to an accreting object, like a neutron star or a black hole.

Combined with infrared observations taken with NASA’s Infrared Telescope in Hawaii, the emerging picture of Edd-1 is consistent with a binary where at least one object is a massive star throwing off a thick stellar wind. If the other object is also a massive star, the X rays could arise where these winds collide.

But Edd-1’s infrared spectra don’t seem very similar to those of known massive-star binaries, with O-type or Wolf-Rayet stars. So, Mikles thinks the companion is a neutron star or a black hole. It’s difficult to distinguish between them, she explains, but, if she were betting on it: “I’d say it’s a black hole.”

Google’s new Sky

Francis Reddy — Thu, 10 Jan 2008 17:05:00 GMT

On Wednesday, at the American Astronomical Society meeting in Austin, Texas, Google engineering director Andrew Moore introduced a new version of the company’s Sky application in Google Earth.

Of particular interest to me is the inclusion of historical star maps from the ginormous collection of David Rumsey at Cartographic Associates. He’s amassed some 150,000 maps of Earth and sky. Google Earth added the first terrestrial maps November 2006.

Now, Google Sky adds historical sky maps dating back to 1792. By turning on different layers, you can immediately compare views of the same sky region in different maps. There’s even an “Art layer” built from Johannes Hevelius’ beautiful 1690 constellation engravings.

Some historical cartographers drew their maps as if the constellations were viewed from the outside of the celestial sphere. In Google Sky, the labels on those original maps appear backward because the application is viewing them from the inside — that is, the way we actually see them.

More significantly, Google has also released the Sky Application Programming Interface (API). This is a set of tools for passing data to Google Sky so developers can make their own “mashups” using its data. Here’s one example, and here’s another for the iPhone.

Have you found other astronomy-related mashups? Tell us about them!

A wall-sized M31

Francis Reddy — Wed, 09 Jan 2008 20:19:00 GMT

I was checking out the exhibitors at this week’s American Astronomical Society meeting in Austin, Texas, and trying hard to avoid information overload. The booth for the Pan-STARRS project stopped me in mid-stride. In fact, I may have actually done a double-take.

There, a giant poster of the Andromeda Galaxy (M31) formed the booth’s backdrop. Only this wasn’t a poster. It was an image taken with the 1.4-billion-pixel charge-coupled-device camera on the Pan-STARRS prototype telescope.

And the print was less than half its actual size.

“We keep apologizing for having to make it so small,” the University of Hawaii’s Paul Price said with a grin. “The wall isn’t high enough to show it full size.”

Pan-STARRS — the Panoramic Survey Telescope and Rapid Response System — is a wide-field survey project designed to detect asteroids and comets that could pose a threat to Earth. The PS1 prototype, located on Haleakala, Maui, is essentially one-quarter of Pan-STARRS, which will combine four such units.

The PS1 and its 1.4 Gigapixel Camera will scan the sky for the next 3 years to test the technology and pave the way for Pan-STARRS. In fact, astronomers expect PS1 will be able to scan the entire visible sky to between magnitude 22 and 23 in less than a week, depending on the filter used and how much moonlight interferes.

“The Gigapixel Camera is working great,” said James Heasley, also from the University of Hawaii. A series of exposures taken during the PS1’s December 2007 commissioning run were combined to make the full-color image.

The Andromeda Galaxy will be getting a lot more attention, too. “Our intent is to observe M31 at every opportunity,” explained Price. “We’ll create the deepest, most detailed record of this galaxy yet.”