It started over coffee in China.

Last month, a group of visiting astronomers at the Kavli Institute for Astronomy and Astrophysics at Peking University were talking about the latest “hot” topic: the curious case of two small but high temperature objects found orbiting around a pair of distant stars.

The discovery was made by Kepler — NASA’s planet-hunting satellite launched one year ago this week. Kepler’s approach is brute force; it continuously monitors a field of over 150,000 stars looking for those that periodically dim when orbiting planets block a tiny fraction of their light.

In January, when mission scientists unveiled their first discoveries with Kepler, a couple of strange stars turned up. Each has a light curve that is the reverse of what's expected from Kepler. The signal is dimmest when a planet-size companion passes behind the star rather that in front of it. This means the companions are brighter per unit surface area (and therefore hotter) than the stars they circle.

Jason Rowe, a NASA postdoctoral fellow based at the Ames Research Center in Moffett Field California, was puzzled when he first saw these light curves. “They stuck out like sore thumbs,” he says. The objects were dubbed KOI-81 and KOI-74 (mission-speak for “Kepler Object of Interest”).

It’s hard to imagine planets that are hotter than stars, so the Kepler team considered an alternative. Might they be white dwarfs? The degenerate cores of dead stars that have blown off their outer layers, white dwarfs are squeezed by their powerful self-gravity into small, dense, and very hot objects. The trouble was KOI-81 and KOI-74 didn’t seem small enough to be white dwarfs.

Clearly, the most relevant information would be the masses of the two hot companions. Were they heavy, like white dwarfs, or lightweights, like planets?

Kepler can’t measure an orbiting companion’s mass directly. But in a paper discussing the objects Rowe and his coauthors estimate the masses by measuring how much the hot companions seems to physically deform the stars they orbit. (The companion’s gravity squishes the star slightly, turning its spherical shape into something that is slightly more like a football). Such deformations produce slight variations in the light curves, which Kepler can measure.

These results point to objects that are less massive than a typical white dwarf star. KOI-74, in particular, seems to weigh in at no more than one tenth the Sun’s mass. Could it be a planet after all — a planet heated to more than 12,000 kelvins (21,600°F)?

The search for a resolution to this paradox is what brings us back to the Kavli Institute in China. The astronomers sipping coffee there and chewing over Kepler’s findings in mid-January included Marten Van Kerkwijk and Stephen Justham along with Rene Breton, a visiting postdoc from the University of Toronto. Their discussions were prompted by an email from MIT astronomer Saul Rappaport, and remotely included Philipp Podsiadlowski of Oxford University and Zhanwen Han of Yunnan Observatory.

The group realized there might be another way to measure the masses of the hot companions using the Kepler data. This is because Kepler is tailor-made not only to spot slight changes in the brightness of a star but also to do so at very well-defined wavelengths. This means it’s perfectly set up to detect “Doppler boosting”.

Doppler boosting means an approaching light source looks brighter because more of its photons are arriving at your detector per unit of time compared to when the object is stationary. The faster the approach the bigger the boost. Conversely, a receding source looks dimmer because you’re getting fewer photons per unit time. (The effect can be diminished depending on the colour of the source, but for the Kepler stars with the hot companions, it’s the photon count that dominates.)

Van Kerkwijk obtained the raw Kepler data for the two stars with the mysterious hot companions and found that, indeed, there was Doppler boosting in the signal. In each case, the strength of the boost is directly related to how much the orbiting companion is pulling on the primary star. The more massive the companion, the stronger the gravitational pull.

The method allowed the China group to recalculate the masses of the hot companions. Their results neatly resolve the paradox. The objects are light but still fall into the white-dwarf mass range, especially white dwarfs that form in binary systems where some transfer of mass onto the neighboring star is likely. After the recalculation, KOI-74 ends up being more like 20% of the Sun’s mass. This fits with the larger than standard radius detected by Kepler, since lower-mass white dwarfs have less self-gravity and so are less compact.

In another recent paper, Rosanne DiStefano of the Harvard-Smithsonian Center for Astrophysics has calculated that Kepler should detect about 1,000 transiting white dwarfs that are the products of mass-transfer binaries. If so, KOI-74 and KOI-81 are simply the first two entries in what could be quite a long list.

Finding a couple of white dwarfs is not exactly a home run for Kepler (it's supposed to be finding Earth-mass planets). On the other hand, showing that these objects are massive enough to be white dwarfs by using Doppler boosting is the equivalent of a nicely executed catch. It’s the kind of everyday science that doesn’t attract headlines, but that strengthens our understanding of the universe in a way that makes major discoveries possible down the road.

I see two encouraging signs from this little saga. The first is that Kepler is performing with exquisite precision. The effective use of Doppler boosting could not have been accomplished (at least not yet) from the ground. “The effect is very small,” says van Kerkwejk, “which means it can only be used with a space-based instrument.”

The second is that the excitement generated by this new piece of hardware is bringing out the best in the available software — namely, the collective brainpower of the astronomical community. Researchers are stimulated by the possibilities Kepler has opened up. They’re talking about it over coffee in China and in places around the globe where astronomers gather. And whenever there’s talk of this kind, innovations follow.

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Ivan Semeniuk is host of the podcast The Universe in Mind and a science journalist in residence at the Dunlap Institute for Astronomy and Astrophysics, University of Toronto.

Late one night a couple of years ago I found myself in the Green building, the signature high rise that towers over the MIT campus in Cambridge, Massachusetts — where I was watching asteroids with Rick Binzel.

Binzel is a consummate asteroid lover. He has studied them for decades with a passion that reminds us there are many more worlds in the solar system than the eight or nine planets whose names we learned in elementary school.

The asteroids he showed me that night were nothing more than dim blips on a video screen. Our view was a live connection to NASA’s Infrared Telescope Facility on Mauna Kea in Hawaii, which Binzel uses remotely to study near-Earth asteroids (NEAs), small bodies that pass near — sometimes uncomfortably near — to our planet.

There are thousands of NEAs out there, silently parading by in the shadows. Binzel is motivated to study these wayward drifters because he finds their many puzzles and quirks utterly fascinating. They also have the potential to dramatically disrupt the course of life on Earth.

Now it appears the reverse is also true: According to the data Binzel has patiently gathered, Earth can disrupt asteroids, subtly or dramatically, if they get too near. Furthermore, this intriguing result helps resolve a decades-long meteorite mystery.

The news follows from a study published this week in the journal Nature, in which Binzel and several collaborators investigate the motion of 95 asteroids known to cross the orbits of Mars and Earth. Their objective was to look at the relationships between two classes of asteroids, S and Q, and their orbital characteristics.

For decades, planetary astronomers have classified asteroids by the spectral characteristics of their surfaces. "S types" are found throughout the asteroid belt and also comprise most NEAs. They are very slightly reddish in hue, which is thought to be the result of “space weathering.” Over time, solar-wind particles and space radiation damages and discolors the minerals sitting on the asteroid’s surface, giving them a somewhat sunburned look.

Q-type asteroids seem to have none of this space weathering. Somehow they look “fresher” than S-type asteroids, like newly exposed slices of apple that haven’t yet turned brown. The question is, what is freshening up the Q-type asteroids? Initially, researchers thought impacts and collisions might do the job. The trouble is that Q-type asteroids aren’t found in the main asteroid belt, where collisions might be expected to be most frequent.

Binzel’s group used a numerical simulation to run the orbits of the 95 small asteroids backward in time. Some orbits point to close encounters with Earth in the past, while others do not. However, of the of 20 Q-type asteroids in the sample, all of them have orbits that made close encounters with Earth very likely. This supports a suggestion, made in 2005 by David Nesvorny of the Southwest Research Institute, that close encounters with a planet can turn an S-type into a Q-type asteroid — that is, change from red to gray — by gravitationally shaking it and bringing unexposed material to its surface.

The new research puts some hard numbers behind the suggestion. It also helps tie up what has come to be known as the “ordinary-chondrite problem”.

Ordinary chondrites are, by far, the most common kinds of meteorites found on Earth. Naively one would expect them to match the spectral properties of the dominant asteroid class, the S-types. Instead they match the Q-types. The favored explanation is that if you send a chunk of S-type asteroid plunging through Earth’s atmosphere, it’s stripped of its reddish tan and looks like a fresh asteroid once it plunks onto the ground. This idea received a big boost 10 years ago when the NEAR-Shoemaker asteroid mission found a mineralogical link between ordinary chondrites and the S-type asteroid 433 Eros.

Until now, the unresolved part of the meteorite-asteroid puzzle has been: so why are there Q-type asteroids?

The next step came in 2009 when Pierre Vernazza of the European Space Agency showed that asteroids can be reddened by the solar wind in less that one million years. Putting this all together, it’s possible to see why there are three kinds of asteroids in Binzel’s orbital analysis. Some asteroids that cross Earth’s orbit are in trajectories that will never bring them close to Earth itself. You would expect them to all be S-type, well-reddened by the solar wind, and so far that’s what Binzel’s group finds.

The remaining asteroids, 75 out of 95, are in orbits that could bring them very near Earth, closer than the Moon. Because of uncertainties in the simulation, it’s impossible to be sure if this has actually happened for any given object, but the inference is that the S-type asteroids in this group have not had a close encounter in the last million years. Meanwhile, the 20 Q-type asteroids in the sample are the ones that have had close encounters, so they’ve been sufficiently shaken up to lose their red color.

Exactly how the shaking up happens is still unknown, but the fact that it can happen at all supports the hypothesis that small NEA’s are not individual slabs of solid rock but piles of rubble that are easily jostled.

“It would seem to indicate that they’re loosely held together,” says Binzel. This opens up the tantalizing possibility that scientists could watch an asteroid switch from red to grey as it passes near Earth and experiences tidal stress from Earth’s gravity. Such an encounter is now projected for the S-type asteroid 99942 Apophis, which will pass within six times Earth’s radius in April 2029.

“My vision,” says Binzel, “is that we would have it all wired up and monitored so that we can listen to it creak and groan as it flies by.”

Perhaps the slow accordion-like stretch on Apophis will be enough to alter its surface, or perhaps the interaction will trigger landslides and other surface action that lead to it acquire a Q-type appearance. Either way, we have 19 years to prepare for this unprecedented opportunity.

In the meantime, Binzel will be watching up in the Green building at MIT, slowly accumulating data on the tiny and mysterious worlds that are, from time to time, our nearest neighbors in space.

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Ivan Semeniuk is host of the podcast The Universe in Mind and a science journalist in residence at the Dunlap Institute for Astronomy and Astrophysics, University of Toronto.

You may think you have a hard job, but imagine this item on your to-do list: saving Earth from nonexistence. It sounds like a task worthy of Superman, but it has fallen instead to computational astrophysicists like Mordecai-Mark Mac Low of the American Museum of Natural History to make sure our planet is spared oblivion — or at least virtual oblivion in numerical simulations.

Mac Low’s challenge stems from a key mystery in our current picture of how planets are formed. It’s long been thought that Earth coalesced from a gaseous disk swirling around the Sun. Strong support for the idea comes from the numerous examples of disks that have been spotted elsewhere in the Milky Way. Yet the mathematics that describes such systems reveals a disturbing paradox: the gravitational pull of a disk can steal orbital energy away from a planet as it's forming. Instead of maintaining a safe and steady orbit, the equations suggest the young Earth should have been locked in a death spiral that sent it plunging into the Sun.

There is, of course, some compelling evidence to the contrary. "We're still here!" says Mac Low.

Now, together with collaborators Wladimir Lyra and Simje-Jan Paardekooper, Mac Low has apparently found a loophole that allows planets like Earth to survive their origins.

The problem is decades old, but it became a front-burner issue once astronomers began discovering “hot Jupiters” in orbit around other stars. Such planets are massive gas giants like those in the outer solar system. Yet they are in extremely tight orbits that keep them much closer to their stars than Mercury is to our Sun. Since gas giants cannot form naturally in such orbits, they had to have shifted there after forming farther out.

"Classic theory shows that planets can migrate quickly inward," says Mac Low. The question then becomes, how did Earth avoid this fate?

Building on previous work, the team developed a new series of simulations of planet formation that include the subtle effects of temperature and entropy variations within the gas disk. Prior simulations assumed that temperatures fall smoothly with increasing radius from the Sun. But because the midplane of the disk is opaque, says Mac Low, heat cannot be easily radiated away and more abrupt temperature differences can arise. This, in turn, can have a profound effect on how the gas disk pulls on a planet in a particular orbit. It means, he says, "Both the strength and the direction of the planet’s migration can change."

The simplest version of planet migration is based on the fact that massive objects moving within a gas disk — the progenitor of Earth, for example — will generate spiral ripples in the disk that, in turn, pull on the planet. The outward ripple has the larger effect, which drags on the planet, causes it to lose energy, and drop to a lower orbit.

Temperature variations can complicate this picture, particularly when it comes to gas that’s in nearly the same orbital radius as the coalescing planet. Such gas is thought to move in "horseshoe orbits" with respect to the planet, alternately falling behind and moving ahead as it interacts with the planet's gravity. This back and forth motion leads to the compression of gas in some areas. Since gas compressibility depends on temperature, temperature differences play a key role in dictating how the gas influences the planet and, ultimately, where the planet migrates.

The new simulations show that at certain locations within in the disk, the usual inward migration can be stalled or even reversed. In the end, says Mac Low, the planet shifts to an orbit where the forces of inward and outward migration are balanced. The planet is effectively “dropped off” into a stable orbit, where it remains long after the gas disk dissipates and the forces that shaped the planet’s orbit disappear.

The end point of the simulations is a result that looks comfortingly like our kind of solar system. Of course, even more comforting would be if the Kepler mission manages to find several more solar systems like our own in the next few years to verify that our survival is not just a crazy cosmic fluke.

As Andrew Youdin, of the Canadian Institute for Theoretical Astrophysics puts it: “While theory seem to offer unlimited possibilities for planet migration, the hope is that the detection of ever larger numbers of exoplanets — both near and far from their host sars over a range of mass — will impose tighter constraints on the imaginations of theorists.”

Amen. Meanwhile, if you’ve been lying awake lately wondering why we’re here you can probably rest easy.

On the other hand, if you’re wondering why some solar systems lead to hot Jupiters and some don’t, well . . . perhaps you’d better put the coffee on.

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Ivan Semeniuk is host of the podcast The Universe in Mind and a science journalist in residence at the Dunlap Institute for Astronomy and Astrophysics, University of Toronto.

Nothing kills a beautiful theory faster than an ugly fact, to paraphrase Thomas Huxley. But what happens when you have three competing theories and two new facts that point in opposite directions? Welcome to the increasingly confusing picture of what happened to the mammoths and mastodons of North America, along with the other dominant mammal species of the late Pleistocene.

For a number of years, scientists have been debating over two possible culprits that might explain the big die-off of megafauna. One is severe climate change, brought about by the onset of the Younger Dryas global-cooling event. Another is overhunting by a newly arrived human population in North America known as the Clovis culture. More recently, a third hypothesis claims that a comet impact or airburst over the Laurentide ice sheet triggered the changes that caused the animal population collapse (see my article in the September 2009 issue of Sky & Telescope.

All of these scenarios, or any combination of them, hinge on the fact that the big mammals died off rather abruptly starting around 12,900 years ago. This matches the onset of the climate change and comes right after Clovis appears on the scene. It also coincides with evidence that appears to support the comet hypothesis, including lots of tiny “nanodiamonds” that proponents say may have been generated in the impact and subsequent fires.

Until now, the debate has revolved around what happened. Now there are new questions about when it happened.

In a new paper in the journal Science, Jacuelyn Gill and others suggest that megafauna were in decline well before the 12,900 date. Gill, a doctoral candidate at University of Wisconsin, looked for spores of the fungus Sporormiella, known to grow in the dung of large herbivores. Those spores start to disappear from sites in New York state and Indiana between 14,800 and 13,700 years ago, suggesting an early disappearance for the mastodon.

But wait. Another recent paper by Neal Woodman and others in Quaternary Research finds that a mastodon skeleton discovered in Indiana in 1976 (and now on display at the Cincinnati Museum of Natural History) was dated incorrectly. A new analysis by the Smithsonian researcher finds that the mastodon was alive about 10,055 years ago.

Granted, one mastodon doesn’t make an entire population. But it can’t have been the only one. This means that some of the megafauna survived for thousands of years after they were supposed to have disappeared at the onset of the Younger Dryas, and long after the early decline suggested by Gill.

The commentary accompanying the Gill paper suggests that both the climate change and the impact hypothesis ideas are dead. Instead, the suggestion is that overhunting by paleo-Indians, already established in North America before the Clovis people arrived, is responsible for the early decline.

These conclusions seem premature. What can be said, based on the Gill paper, is that at least some local populations of megafauna were in trouble before the Younger Dryas, for reasons that remain unclear. From the Woodman paper we can infer that some other populations survived well after. And we know already, that an awful lot happened in between — which may or may not have included a comet impact.

It’s ironic that this picture is so confusing when the extinction of the dinosaurs by a large asteroid 65 million years ago now seems quite clear. But this is partly an effect of distance. If we could have visited Earth 12,900 thousand years after the dinosaurs went extinct it’s likely we would have found all kinds of interesting evidence, no longer available, that would have complicated the picture. The loss of the megafauna is both intriguing and hard to understand because it is so recent and there are so many more pieces of the puzzle to play with.

The only solution, as Woodman points out, is even more information. He suggests that mammoth and mastodon fossils in museums around the world should be looked again and redated if necessary to improve consistency in the data. There’s still more work to be done in sampling the environment too.

This debate is far from over. Like North America at the end of the ice age, it’s just getting warmed up.

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Ivan Semeniuk is host of the podcast The Universe in Mind and a science journalist in residence at the Dunlap Institute for Astronomy and Astrophysics, University of Toronto.

Call it the story of the young and the quarkless: Astronomers have a surprising new take on the youngest supernova remnant in our corner of the Milky Way, and it may solve a long standing mystery.

The object in questions is Cas A (rhymes with passé) a glowing wreath of energized gas that was discovered years ago in the constellation Cassiopeia. Cas A was created when a massive star reached the end of its nuclear rope about three centuries ago and blew itself to smithereens. What’s left at the center is a tiny nugget of superdense matter called a neutron star, the youngest example of one we know.

So far, so good. But there’s always been something weird about the neutron star in Cas A since it was first spotted by the Chandra X-ray Observatory in 1999. Now it looks like there’s an explanation.

First, the weirdness: Based on its brightness in the X-ray spectrum and its distance from Earth, astronomers initially calculated that the neutron star in Cas A is no more than about 10 km across. That’s too small to be a neutron star, according to what physics tells us a neutron star should be like.

One suggestion to account for this is that the X-ray emission is not coming from the entire neutron star but from a hot spot that is relatively small in size. The problem is the spot isn’t pulsing or blinking, which is what you’d expect from a neutron star that’s spinning around really fast (which neutron stars are wont to do).

An even stranger suggestion is that the object at the center of Cas A isn’t a neutron star at all but rather a hypothetical “quark star.” To become a quark star, the object’s gravity has to be so strong that it causes the neutrons in a regular neutron star to lose their individual identities and merge into one giant ball of quarks — including “strange quarks,” which are heavier than the “up” and “down” quarks that exist within individual neutrons. The resulting strange quark star would be more compact than a neutron star but not quite a black hole. Just a few months ago, the Astrophysical Journal published an interpretation of the X-ray data from Cas A as evidence for a strange quark star.

Now come Wynn Ho (Southhampton University) and Craig Heinke with a different way of approaching the problem.

In the November 5th edition of Nature, Ho and Heinke report that if you assume the object at the heart of Cas A is shining through an atmosphere of carbon atoms, its brightness corresponds to a neutron star about 24 to 30 km across — basically normal size, if you can call a neutron star “normal.”

So why a carbon atmosphere? First of all, it’s not unusual to think of a neutron star with a hydrogen atmosphere, since that’s the material that surrounds it after the massive star blows up. Most of the glowing gas in Cas A is hydrogen.

Heinke points out that neutron stars are hot when they’re young — so hot that a surrounding envelope of hydrogen might fuse into helium and then into carbon. The carbon layer is only ankle high, but it’s enough to radically change the way the neutron star looks. Over time, that carbon would settle into the body of the neutron star and be replaced by fresh hydrogen from above. By then the neutron star has cooled enough that it can no longer fuse hydrogen above its surface, so the hydrogen remains as a residual atmosphere.

It’s a nice story that seems to explain why Cas A is different — not because it’s full of quark matter, but because of its relative youth.

“It’s immensely satisfying,” to have come up with such a tidy solution, says Heinke, “and it fits the data beautifully.”

Heinke admits that it would have been fun to verify something as strange as the existence of strange quark stars. On the other hand the universe is plenty weird enough without them.

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Ivan Semeniuk is host of the podcast The Universe in Mind and a science journalist in residence at the Dunlap Institute for Astronomy and Astrophysics, University of Toronto.

A team of Harvard researchers has upped the ante in the race to discover the true nature of dark matter.

In a new paper posted online this week, the team says NASA’s Fermi satellite has confirmed the existence of a vast cloud of energetic electrons surrounding the center of our galaxy — electrons, they suggest, which could be subatomic shrapnel from dark matter particles colliding with one another.

If correct, their interpretation of the Fermi data would tie together a number of hints and puzzling observations that suggest dark matter is making itself visible through a process of annihilation. It also implies the existence of a new force to which only dark matter particles are attuned.

“It’s very easy to produce this kind of a signal with dark matter,” says Doug Finkbeiner of the Harvard-Smithsonian Center for Astrophysics, who led the analysis with Greg Dobler and others. “It’s not so easy to do it with other things.”

In contrast, scientists involved in gathering and analyzing the Fermi data have expressed caution over the claim. “While this work is certainly interesting, it’s premature to draw any conclusions, especially if it requires exotic physics models.” says Simona Murgia, a Stanford University physicist and Fermi science team member.

The new result is the latest twist in a story that began in 2004, when Finkbeiner reported the existence of an unexplained “haze” of microwave emission around the center of the galaxy as seen by the Wilkinson Microwave Anisotropy Probe (WMAP). He suggested then that the haze could be the mark of electrons produced when dark matter particles, thought to be concentrated near the galactic center, interact and mutually destruct.

Since then, ongoing debate over whether the haze really exists — let alone whether it’s a byproduct of dark matter — has kept the question open.

Last year, the European PAMELA satellite and a balloon-borne detector called ATIC fueled excitement by detecting, respectively, energetic positrons and electrons in greater than expected numbers in Earth’s vicinity. One possible source could be dark matter annihilations in or near the solar system, although a more conventional source, such as a nearby pulsar, could explain the excess

Fermi’s Large Area Telescope (LAT) is sensitive to both electrons and positrons, and early results discussed by team members in the spring seem to be consistent with the existence of a local excess.

Now Finkbeiner says that Fermi is also seeing a counterpart to the WMAP haze. The new result comes in the form of a diffuse glow of gamma rays around the galactic center. The properties of the gamma rays suggest they are emitted by the kind of energetic electrons expected from dark matter annihilations. Most importantly, he says, the location and distribution of the “Fermi haze” closely fits that of the WMAP haze.

Since the summer Finkbeiner has been sharing his analysis with colleagues, including the Fermi science team. The reservations they have expressed over the dark matter story stems from the basic challenge in understanding all the possible sources that could be contributing to Fermi’s overall picture of the galactic center.

“The gamma ray sky is very complex,” says Murgia. “If a signal of dark matter annihilation is there it will be mixed with other conventional components, such as gamma rays produced in cosmic ray interactions.”

For his part, says Finkbeiner, “I’m confident we’re seeing the electrons we predicted” based on WMAP.

If Finkbeiner and his colleagues are right about what Fermi is seeing, it will be harder for others to come up with convincing explanations for the haze that don’t involve dark matter.

For example the energy and smoothness of the gamma ray distribution suggests it is not the product of a single cataclysmic event, or even several discreet events, such as supernovae. Instead, the observations favor a process that generates high energy electrons throughout the galactic center on a more continuous basis.

Dark matter annihilation could account for this, because theories in which dark matter is explained by supersymmetry suggest that the lowest mass dark matter particle — also called the neutralino — is its own antiparticle. That means two neutralinos would annihilate in a flash of energy when they encounter each other, producing photons and ordinary matter particles, including electrons.

The catch is that the expected rate of annihilations should be far lower than what is needed to create the observed haze. To account for this, theorists have proposed a new force among dark matter particles that enhances the likelihood of particles meeting and boosts the expected dark matter signal.

“This has led to a nice picture where the ‘dark force’ simultaneously explains why there are so many electrons and why the annihilation rate is so high.” says co-author Neal Weiner of New York University.

The new results add to a growing sense that the identity of dark matter, a decades-old conundrum in astronomy and physics, is close to being cracked.

In addition to Fermi and related observations, researchers say efforts to detect dark matter directly in underground experiments such as XENON100 and LUX, along with the possibility that dark matter could be produced in the Large Hadron Collider, will soon narrow the range of possible explanations for the mysterious substance that accounts for 85% of the matter in the universe.

"I'm very excited about these developments," says Katherine Freese, a theoretical physicist at the University of Michigan. “It could be that a problem I’ve been working on for twenty years is on the verge of being solved.”

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Ivan Semeniuk is host of the podcast The Universe in Mind and a science journalist in residence at the Dunlap Institute for Astronomy and Astrophysics, University of Toronto.

A black hole is like a scary monster from children’s literature. It’s vividly imagined but never actually seen in real life.

This is true even for the largest black holes we know — the ones that reside at the centers of galaxies. The nearest of these lies some 30,000 light-years away, in the core of the Milky Way. If you placed it in our solar system it would probably span the orbit of Mercury. Yet, because of its great distance, it’s a mere speck against the sky, about 36 million times smaller than the full Moon. How could anyone see any detail when looking at something with an apparent size that small?

Amazingly, there is a way. And now it’s promising not only to reveal the giant black hole in our own galaxy, but also a much larger and more active one in the galaxy known as M87 in Virgo.

The nifty trick that puts this ambitious goal within reach is called very long baseline interferometry. VLBI involves two or more radio dishes that are spaced as far apart as possible — for example, in Arizona and Hawaii. The dishes observe the same radio sources in the sky, and when their signals are combined they form an image that’s as sharp as what you would get from a single receiver as big as the separation between the dishes. The idea is to show the way radio emission is spatial distributed across a small region of sky. It’s just what you need to “see” a black hole.

But what does that mean? Aren’t black holes supposed to be, well, black?

Yes and no. If completely isolated in space, a black hole would indeed be well camouflaged. But in the densely populated center of the Milky Way, there is plenty of hot gas swirling around the giant black hole there.

The energized ions in the gas give off radio waves. Seen up close, there should also be a dark sphere at the center of that swirl of gas, where matter funnels in and never comes out. The dark sphere is the infamous event horizon. It’s the point of no return, from which not even light can escape. In this case, “seeing” the black hole means seeing the event horizon silhouetted against the glowing gas.

Shep Doeleman of the Massachusetts Instistute of Technology has been leading the charge to image the Milky Way’s central black hole, and he and his collaborators have made astounding progress. They’ve looked deep into the heart of the radio source known as Sagittarius A*, where the black hole is believed to be lurking. What they’ve got is not exactly an image but a sense that there is some structure on the scale of a supermassive black hole deep in the heart of the radio source.

The complication in mapping out an image of this object is that Sgr A* is changing on a regular basis, presumably as clumps of gaseous matter go a-whirling around the black hole.

This is not going to be a problem when it comes to looking at even bigger black holes, like the giant monster at the center of the galaxy M87 in Virgo. It devours vast quantities of gas and spits out a spectacular jet that extends far into extragalactic space.

Recently, Karl Gebhardt of the University of Texas at Austin and Jens Thomas of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, set about measuring the size of M87 by running existing data through a new model that mimics the galaxy star by star. Unlike earlier efforts, their model also takes into account the unseen halo of dark matter that surround the visible portion of the galaxy. This turned out to have an unexpected affect on the way the model calculates the mass in the stars that illuminate the galaxy’s core. In the final analysis, it allocates far more mass — a whopping 6.4 billion suns — to the galaxy’s monstrous central black hole.

The surprising corollary to this is that M87’s black hole, if viewed from Earth, should be the same apparent size as the black hole in Sgr A* — just as the Sun and the Moon appear roughly the same size, though the Sun is larger and much farther way. That puts M87’s black hole within reach of Doeleman’s radio telescopes. It may even be easier to image than Sgr A* because it’s larger size means it doesn’t change nearly as rapidly.

What’s particularly exciting to theorists like Avery Broderick, of the Canadian Institute for Theoretical Astrophysics in Toronto, is that M87’s black hole is also violently active, with a vast disk of gas around it and a big jet of shooting out in one direction. A radio image of this black hole might not only reveal the event horizon but show us the region where the jet is launched.

“It’s kind of exciting as an alternate object because it is so different from the supermassive black hole in our backyard,” says Avery. “Between them, they span the range of what we expect from these objects.”

Stay tuned. Modern astronomy is increasingly become the science in which the unseen becomes seeable. Before long we’ll be adding black holes to that list.

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Ivan Semeniuk is host of the podcast The Universe in Mind and a science journalist in residence at the Dunlap Institute for Astronomy and Astrophysics, University of Toronto.

What do you do when a raging wildfire threatens to engulf your observatory? You light backfires, spray fire retardant and water bomb the slopes… but mostly you just hope for good luck.

Last month, the Mt. Wilson Observatory got a welcome dose of good luck when it escaped destruction by the notorious Station Fire, which burned out of control for weeks in the mountainous woodlands north of Los Angeles.
Mt. Wilson is home to the 100-inch Hooker telescope, one of the most storied instruments in the history of astronomy. It’s here that Edwin Hubble gathered the crucial evidence that allowed him to demonstrate, in 1925, that the universe is much, much bigger than previously thought.

In this episode of The Universe in Mind podcast, Harold McAllister, director of the Mt. Wilson Institute, talks about the observatory’s brush with oblivion. Marcia Bartusiak, author of The Day We Found the Universe explains how Hubble’s work on Mt. Wilson was the culmination of an amazing epoch of discovery that saw the cutting edge of observational astronomy migrate from Europe to the New World.

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Ivan Semeniuk is host of the podcast The Universe in Mind and a science journalist in residence at the Dunlap Institute for Astronomy and Astrophysics, University of Toronto.

Do planets around other stars have magnetic fields? It may seem an esoteric question, but life as we know it — at least terrestrial life — could not survive on Earth without the magnetic umbrella that protects us from an onslaught of hard solar radiation.

Now it appears a planet that is light years from our own may be depending on a magnetic field for its continued existence.

The planet in question is HD 209458b. Admittedly, it's more of a serial number than a name, but to astronomers it's one of the most infamous handles in the galaxy.

HD209458b caused a sensation back in 2003 when astronomers using the Hubble Space Telescope discovered a vast envelope of hydrogen gas and other atoms surrounding the planet. This was a shock because HD 209458b is also a "hot Jupiter". Although it is a gas giant planet, it is less that 1/20th the distance from its star that Earth is from the sun. At such close quarters, any gas lying beyond the planet's immediate atmosphere should quickly be torn away. Thus, the existence of a large gaseous envelope suggests a situation that is both temporary and terminal: a planet evaporating before our eyes.

Type HD 209458b into Google, and you'll find plenty of references to its apparent doom, including the nickname Osiris, the Egyptian god of the afterlife. One group came up with the term "chthonian planet" to describe what you get when a gas giant planet is whittled down to its rocky core — the assumption being that HD209458b is on its way to becoming just such a place.

Now Phil Arras and colleagues at the University of Virginia have another idea. They've been working on the question of what a magnetic field might do in such a circumstance. Given that our own Jupiter has a very strong magnetic field, it's not a stretch to imagine HD 209458b has one too. Arras reasons that a strong-enough field would be very effective at trapping any ions that surround the planet. Instead of escaping forever, they would be directed toward the planet's magnetic poles — quite possibly creating spectacular aurorae in the process. To top it off, because the planet is so close to its star, that big envelope of gas must be thoroughly ionized — and therefore thoroughly magnetized — by the heat.

The picture this leaves us with is a planet that travels around embedded in a cloud of hot, ionized fog. The ions fill up the planet's magnetosphere like smoke in a bottle, but they're not stripped away. There's no need to explain why the planet is evaporating, because it isn't. "If you heat up a planet's atmosphere, then its gas can begin to flow out to infinity," says Arras. "But when you add a magnetic field, the gas is trapped."

This is not the first or even the best evidence that exoplanets can be magnetized. For Evgenya Shkolnik, the magic number that brings back the thrill of discovery is HD 179949. In 2003 she and Gordon Walker of the University of British Columbia published evidence that this star has a bright spot that moves around its surface ever three days, keeping perfect time with a hot Jupiter-sized planet that's orbiting with the same period. Their conclusion is that as the planet barrels through the star's atmosphere, or corona, its magnetic field is continually triggering the release of energy within the star's much stronger magnetic field. This energy is transferred down to a region near the star's surface, forming a hot spot that follows the planet, like a mobile, never-ending solar flare.

This kind of magnetic communication between planet and star had been predicted by others but it was Shkolnik and Walker who first saw it in action. "It was tremendously exciting," Shkolnik recently told me when she recounted the story.

But the effort has not stopped at simply looking for evidence of planetary magnetic fields. "If a planet has a magnetic field then we can start inferring things about its internal structure," says Shkolnik, who is now based at the Carnegie Institution of Washington.

More than a half century ago, two of Shkolnik's predecessors at Carnegie, Bernard Burke and Kenneth Franklin, accidentally discovered the first known magnetic field around another planet. In 1955, using an early radio array made up of wire strewn across a farmer's field on the north shore of the Potomac River, the pair set about scanning the skies for signs of radio waves from distant stars and galaxies. What they got instead — to their surprise and everyone else's — were regular bursts of static from Jupiter, which happened to be high above the horizon at the time. These proved to be telltale emissions from electrons trapped in Jupiter's magnetic field.

A generation later, the magnetic personalities of other, more distant Jupiters are beginning to reveal themselves. The prospect of finding another Earth, complete with its own life-protecting magnetic field, could be just over the horizon.

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Ivan Semeniuk is host of The Universe in Mind podcast and a science journalist in residence at the Dunlap Institute for Astronomy and Astrophysics, University of Toronto.

At the end of the last ice age, North America was in the midst of an epic thaw. The giant glaciers that had covered nearly all of Canada and the northern United States for millennia were receding fast. Spring was in the air.

This was, presumably, good news for all the exotic creatures that populated North America at the time, including the mammoths, mastodons, giant sloths, sabre-tooth cats, dire wolves, and several other large species, collectively known as the Pleistocene megafauna. It was also good news for the Clovis people, a population of Paleolithic hunters who found their way into North America from Siberia, via an ice-free corridor that ran just east of the Rockies. They had plenty of big game to live on, as their kill sites demonstrate.

So what happened?

Just under 13,000 years ago, with everything looking rosy, the climate suddenly took a precipitous swing back toward the deep freeze. Temperature plummeted. At the same time, the big animals disappeared — and so did the Clovis people. Today what we consider to be the native wildlife of North America is just a pale shadow of what once was. A moose is impressive, to be sure, but there should also be mastodon running around in the forests of Appalachia, and curvy-tusked mammoth right alongside those buffalo on the Great Plains.

Theories abound to explain what exactly eliminated these giant species. It’s possible that a sudden release of meltwater into the North Atlantic temporarily shut down the ocean’s circulatory system. Without the Gulf Stream to bring warm water up from lower latitudes the climate would have cooled, forests would have dried out and burned, and large species would have been severely compromised. Add humans to the mix and perhaps excessive hunting was the straw that broke the prehistoric pachyderm’s back.

Or maybe a comet did it.

That’s what one team of researchers is now saying, and they base their conclusion on microscopic diamonds that have turned up all over the Northern Hemisphere in sediments that date back to the extinction of the megafauna. However, critics counter that this scenario is, at best, highly unlikely. Now everyone is looking for new clues to resolve the controversy.

You can read about the current state of this topic in the September issue of Sky & Telescope magazine. And in the latest episode of The Universe in Mind podcast you can hear from researchers on both sides of the debate. It’s a great story — one we certainly haven’t heard the last of yet.

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Ivan Semeniuk is host of the podcast The Universe in Mind and a science journalist in residence at the Dunlap Institute for Astronomy and Astrophysics, University of Toronto.

Astronomy is the ultimate “seeing” science. Unlike our experience of everyday reality, there’s no sound out in the cosmos, so the processes and events that we observe in the universe unfold before us like a silent movie.

Now some researchers are trying to add a soundtrack to that movie. They are the ones searching for gravitational waves — ripples in space-time caused by the rapid motion of massive objects. If detected, these waves will offer an entirely new way to perceive the universe — one that has more in common with hearing than seeing.

In Episode #11 of The Universe in Mind podcast, we hear from Neil Cornish (Montana State University, Bozeman) about recent progress in the hunt for gravitational waves, and we get a bold prediction for how soon these elusive but revealing signals will be detected.

Jacqueline Radigan of the University of Toronto also drops by to explain how brown dwarfs — objects that are midway between stars and planets — can have their own weather patterns

Enjoy the program!

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Ivan Semeniuk is host of the podcast The Universe in Mind and a science journalist in residence at the Dunlap Institute for Astronomy and Astrophysics, University of Toronto.

There are only so many mountains where you can put a telescope on this Earth and when you’re trying to build the biggest telescope ever you want to choose a good one. That much is obvious, but the selection of a site for a major observatory is no simple matter. Rather, it is the result of a complex interplay of astronomy, geography and economics. If you want to see where the pristine but unfeeling grandeur of the cosmos comes cheek to jowl with the messy subjectivity of human affairs then eavesdrop on a telescope site-selection meeting.

Last week, the Thirty Meter Telescope (TMT) consortium announced the result of a long deliberation over where to park their 1,430-ton spyglass, to be built over the next 10 years. This may not seem like a big surprise — after all, Mauna Kea is already home to the largest concentration of major telescopes in the world. But there is a strong contender in Chile named Cerro Armazones that could have come out ahead.

I’m interested in understanding why Hawaii prevailed. Sure enough, there’s a politics-behind-the-science story here. But there’s an even more fascinating science-behind-the-politics story too.

My guide in teasing out the finer points of the TMT decision is Rene Racine, a TMT board member and professor emeritus at the Université de Montréal. Racine has first hand experience with both Hawaiian and Chilean skies, having helped to build one observatory (Univeristy of Toronto Southern Observatory) on Las Campanas and directed another (Canada-France-Hawaii Telescope) on Mauna Kea.

To get an idea of why this decision matters so much let’s consider a few facts. First, TMT is one of a new generation of telescopes that is expected to vault ground-based astronomy to previously unimagined heights. As its name suggests, its primary mirror is 30 meters across. It’s composed of 492 hexagonal segments which collectively will have a light gathering area 144 times that of the Hubble Space Telescope and nearly 10 times the resolution at infrared wavelengths. That’s according to TMT’s own PR, but clearly there’s nothing like it around today.

TMT will also cost between 1 and 2 billion dollars when all is said and done. This is not quite at the scale of the world’s biggest science projects, like the Large Hadron Collider or the James Webb Space Telescope, but it’s getting there. In fact, TMT and other proposed observatories of this generation may end up being the biggest telescopes on Earth for all time because the funding required to go even larger would more logically be directed towards putting telescopes in orbit.

TMT has its roots at Caltech, which operates the mighty Keck telescopes on Mauna Kea. Given the infrastructure at hand on the Hawaiian peak it would seem inevitable that TMT would end up there. Furthermore, for reasons of politics and access, US partners in the project are naturally interested in seeing TMT built on US soil. Canada, another partner, is also well ensconced at Mauna Kea. Ditto for the Japanese, who are looking to buy into TMT. Japan already has its big Subaru telescope on Mauna Kea, so the Japanese like the idea of keeping their eggs in the Hawaiian basket.

But back in 2002, the Office of Hawaiian Affairs filed suit to prevent Keck from adding two small outrigger telescopes citing lack of an adequate environmental assessment. It was a shocking wake-up call for astronomers, who suddenly realized that not everyone with a stake in Mauna Kea was thrilled with the prospect of yet more construction on a site that is sacred to native Hawaiians.

For TMT that means being open to possibilities beyond Mauna Kea, and most of those possibilities are in Chile. Cerro Armazones is a particularly appealing choice. It is within sight of Paranal, which is home to Europe’s most advanced observatory (the VLT) and it may be slightly better for observing. The Chilean government rolled out the red carpet for TMT, giving it the first crack at Armazones.

On top of that, TMT has two competing megascopes that are also on the drawing board. One of those, the 27-meter Giant Magellan Telescope (GMT) has already settled on a location in Chile. The other, the European Extremely Large Telescope (EELT) is giving Chile strong consideration.

(Click here for S&T.com's list of the world's largest optical telescopes.)

That’s the politics. But here’s where the science comes in. From a big telescope’s perspective, the atmosphere has two layers. The lower atmosphere is basically the first few hundred meters or so. It’s the boundary layer where proximity to the surface affects the movement of air. The upper atmosphere is everything else.

Turbulence in the atmosphere is what limits how well optical telescopes can see the sky. It’s like looking at pebbles at the bottom of a stream. The more waves there are on the surface of the water the more distorted the image of the pebbles becomes.

If you’re talking about natural seeing conditions — literally, how sharp the stars appear — then Armazones is close if not better than Mauna Kea despite being a full kilometer lower in altitude. On top of that, Armazones is located in the Atacama Desert, the driest place on Earth. That means it has many more clear nights than Mauna Kea. Hour for hour, any telescope on Armazones is bound to be more productive.

But now let’s bring adaptive optics into the picture. This is the technology that allows a big telescope to monitor air movement and deform its own optics to compensate for atmospheric turbulence. It’s only effective at infrared wavelengths but what it does is amazing. Adaptive optics essentially gives the telescope a view that is similar to what the pebbles in the stream would look like if the water were perfectly still.

Adaptive optics is a big part of TMT’s design. It will work both on Mauna Kea and Armazones, but astronomers expect it will work better on Mauna Kea. This is because the upper atmosphere — the part above the boundary layer — is somewhat less turbulent above Mauna Kea than it is above Armazones. Why? According to Racine it’s partly a function of latitude. Because Mauna Kea is nearer the equator it’s relatively unaffected by the jet streams that flow at higher latitudes both north and south. Armazones’ upper atmosphere is a bit more turbulent in comparison and so somewhat harder for adaptive optics to deal with.

Racine estimates that more than half of TMT’s observing projects will be in the infrared. The likely targets at these wavelengths include the earliest galaxies, the birthplaces of stars and newborn exoplanets — all hot topics. The chance to maximize the impact of adaptive optics on these objects is a big factor in the TMT decision to go with Mauna Kea.

So what about the Office of Hawaiian Affairs? Racine says the dispute over the Keck outriggers is still cause for concern, but the TMT group has made Hawaiian community input a high priority. There’s still the possibility that there will be future problems but in this case the benefits outweigh the risk.

That makes Cerro Armazones the most eligible mountain without an observatory—a fact that will not have escaped the attention of the European Extremely Large Telescope. The Europeans have political factors of their own to deal with, including some strong incentives to locate on La Palma, one of the Spanish Canary Islands. They’ll make their site decision by the end of this year, which means we’ll soon have another chance to see the geopolitics of astronomy in action.

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Ivan Semeniuk is host of the podcast The Universe in Mind and a science journalist in residence at the Dunlap Institute for Astronomy and Astrophysics, University of Toronto.

Sometimes, seeing is not just believing, seeing is celebrating.

Astronomers working with the Herschel mission are in good spirits this week after capturing a stunning new image of M51, the Whirlpool galaxy. The galaxy’s elegant spiral arms can easily be discerned in the infrared image, which is far sharper at long wavelengths than images by Herschel's predecessor, NASA’s Spitzer Space Telescope.

“It’s very exciting to see the first images from Herschel,” says Christine Wilson of McMaster University in Hamilton, Ontario. Wilson leads the Herschel Key Project, which will characterize interstellar dust in nearby galaxies.

“M51 is one of our targets,” says Wilson. “The picture is really spectacular and I have been thinking today about what it means.”

The sharpness of the image comes as a relief to project scientists, since Herschel's optical components cannot be adjusted after launch. Because of the way the spacecraft was designed and constructed it was not possible to test all the telescope's optical components together at the same time.

Among the interesting details in the new image is the slight color difference between M51 and a smaller elliptical galaxy, which appears as a bright bluish dot in the upper left part of the image. This galaxy is passing by the Whirlpool and has been gravitationally interacting with it for millions of years. According to Wilson, the contrasting colors hint at “some difference in the emission processes in the two galaxies.”

The Herschel Key Project will focus on 13 relatively close galaxies including some that are merging or have been disrupted by past collisions. Among the questions the project seeks to answer is whether different kinds of galaxies, such ellipticals and spirals have different kinds of dust mixed in among their stars.

Herschel is ideal for measuring the size, composition and temperature of dust grains within the Milky Way and in distant galaxies. Dust naturally absorbs light from stars and re-emits that energy at infrared wavelengths. The study of dust is particularly important in astronomy because dust is crucial to the formation of solar systems with rocky planets like Earth.

With a primary mirror 3.5 meters across, Herschel became the largest space telescope ever when it was launched by the European Space Agency on May 14th. It is currently on its way to L₂, a point some 1.5 million km away where the combined gravitational pull of the Sun and Earth allow spacecraft to travel in sync with our planet.

Herschel’s relatively larger mirror accounts for why its view is so much sharper at some wavelengths than Spitzer’s. You can find a comparison of the two here.

M51 is located about 25 million light-years from the Milky Way. Its grand design spiral shape and face-on orientation have made it a perennial favorite with backyard astronomers.

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Ivan Semeniuk is host of the podcast The Universe in Mind and a science journalist in residence at the Dunlap Institute for Astronomy and Astrophysics, University of Toronto.

As molecules go, formic acid isn’t much to look at. You’ve got a carbon atom, two oxygens, and two hydrogens. Stick them together to make a little Tinkertoy arrangement, and there it is.

Nevertheless, formic acid has a way of commanding one’s attention. You’ll know this if an ant has ever bitten you, since formic acid is the active ingredient in ant venom. (It’s in bee venom too, but bee stings are more complicated.)

It also commands the attention of scientists interested in the origins of life. This is because formic acid is merely the simplest and shortest version of a fatty acid. In true Tinkertoy fashion you can replace one of it hydrogen atoms with a chain of carbons and end up with all manner of compounds that are biologically important — if nutritionally suspect. Or you can also attach an amino group to formic acid and make an amino acid instead.

All this plays into the question of how life on Earth came to be. Astronomers can detect formic acid in the cold dark recesses of interstellar space. Did the formic acid up there somehow play a role in the emergence of the first biologically active molecules down here?

Now we may have part of the answer thanks to the Tagish Lake meteorite. It’s been nearly 10 years since its blazing fireball ripped across the early morning skies of Yukon and northern British Columbia. What witnesses thought was an incoming missile proved to have a happier explanation. It was a massive meteorite — more than 50 tons — that disintegrated as it plowed through Earth’s atmosphere at high speed.

In what is surely the biggest break in meteorite history, a fragment of the meteorite was picked up and retrieved by a passerby, who used a plastic baggie to handle it and promptly tossed it in his freezer. Sitting there among the steaks, the meteorite remained uncontaminated by human hands and its temperature never rose above freezing.

This turned out to be very important, since the Tagish Lake meteorite has the highest carbon content of any meteorite ever recovered. It offers a fascinating profile of what kind of material might have made its way to Earth’s surface billions of years ago.

A decade after its recovery, techniques are still being developed to tease interesting details out of the Tagish lake meteorite. The latest is the report of abundant quantities of formic acid, four times higher than seen in any other meteorite.

The work was done by Chris Herd and colleagues at the University of Alberta in Edmonton. To find out more I spoke with Chris Herd. You can find the full interview in the latest episode of the Universe in Mind podcast.

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Ivan Semeniuk is host of the podcast The Universe in Mind and a science journalist in residence at the Dunlap Institute for Astronomy and Astrophysics, University of Toronto.

One of the true pleasures in science comes when a new and surprising fact is uncovered about something thought to be utterly familiar. Such is the case this week with the revelation that Spica, one of the best-known stars in the night sky, is an eclipsing binary. Every 4.0145 days one of the two separate stars that makes up this system crosses in front of the other, blocking a portion of its light.

How could astronomers have missed this fact? It’s no scandal. Spica’s eclipses are the merest grazes. Each time it happens the total light output of the system dips by less than one hundredth of a visual magnitude. Nevertheless, these events are of interest to science because they offer a greatly improved understanding of the two star's sizes and shapes and the complex physics at work in a nearby and rather special star system. Astronomers have known since 1890 that Spica was a spectroscopic binary, but now we have a better handle on it.

What's most amazing is that the eclipses were seen at all. For that we have MOST to thank — the hardest working microsatellite in astronomy.

MOST stands for Microvariability and Oscillation of Stars. It’s a suitcase-sized satellite that specializes in staring at stars for weeks on end — something that is not practical with ground-based telescopes that have to deal with day and night. And because it's above our twinkle-inducing atmosphere, MOST can measure star brightnesses with much higher precision that is ever possible from the ground.

Maarten Desmet, a Ph.D. student at the Institute for Astronomy, Katholieke Universiteit in Leuven, Belgium, and his supervisor Conny Aerts, led the Spica campaign in collaboration with the MOST team. The observations involved more than three weeks of steady staring at Spica to get a crisp, complete, light curve of several complete orbits.

What makes detecting the eclipses a challenge is that Spica already varies in brightness once per orbit. Spica's two components are both intensely hot and pale blue. The larger and brighter of the pair is a slightly pulsating variable of the Beta Cephei variety. Moreover, they orbit one another so closely that their shapes are distorted by their mutual gravity into egg shapes, (prolate spheroids), with their long axes directed toward one another.

Historically, this configuration led to confusion about whether Spica is an eclipsing binary. Because prolate spheroids look bigger when viewed sideways (click here to manipulate a prolate spheroid and see for yourself!), Spica gets marginally brighter when its two stars are oriented side-on to us rather than end-on.

This so-called “ellipsoidal” variation was originally mistaken for a slight periodic eclipse. You can find it misidentified this way in the venerable Burnham’s Celestial Handbook. By the 1970’s, however, that view was changing, and in more recent literature Spica is referred to as non-eclipsing.

The books will have to be corrected once more now that Spica’s grazing-eclipsing nature has been established by MOST. The variations are much smaller than those previously attributed to eclipses, so this effect is not what was measured in earlier decades.

A Pre-Supernova to Study

So what do astronomers get out of this? Plenty, says Jason Aufdenberg of Embry-Riddle Aeronautical University in Florida, who was not a member of the discovery team. For starters, we get the diameter of the eclipsed star, putting an upper limit on its mass. We also get a more accurate value for the inclination of the system’s orbit (how it’s oriented with respect to our line of sight). These can help nail down the more complex aspects of the system, including how the mass distribution in the two stars is affected by their tidal interactions.

“This a fascinating system,” says Aufdenberg.

At 260 light years away, Spica offers one of the nearest examples of stars that are likely go supernova one day. The better they can be characterized the more confident astronomers can be about using them as a reference to understand more distant stars of the same type.

“The eclipses mean it’s one-shop-stopping for this type of star,” says Jaymie Matthews of the University of British Columbia, who is lead scientist for MOST.

The results will be unveiled tomorrow at the Stellar Pulsationmeeting in Santa Fe, New Mexico.

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Ivan Semeniuk is host of the podcast The Universe in Mind and a science journalist in residence at the Dunlap Institute for Astronomy and Astrophysics, University of Toronto.