What’s the News: While the Kepler spacecraft is busy finding solar system-loads of new planets, other astronomers are expanding our idea where planets could potentially be found. One astronomer wants to look for habitable planets around white dwarfs, arguing that any water-bearing exoplanets orbiting these tiny, dim stars would be much easier to find than those around main-sequence stars like our Sun. Another team dispenses with stars altogether and speculates that dark matter explosions inside a planet could hypothetically make it warm enough to be habitable, even without a star. “This is a fascinating, and highly original idea,” MIT exoplanet expert Sara Seager told Wired, referring to the dark matter hypothesis. “Original ideas are becoming more and more rare in exoplanet theory.”

How the Heck:

• Because white dwarfs are much smaller than our Sun, an Earth-sized planet that crossed in front of it would block more of its light, which should make these planets easier to spot. So astronomer Eric Agol suggests survey the 20,000 white dwarfs closest to Earth with relatively meager 1-meter ground telescopes.
• And because white dwarfs are so cool, a planet in a white dwarfs habitable zone would be very close, meaning its transit would happen very fast. Agol says we’d only need to watch a star for 32 hours to pick up on any transiting, habitable planets.
• One leading theory about dark matter is that it’s made of theoretical particles called WIMPS (weakly interacting massive particles). It’s thought that when WIMPs collide (if, of course, they exist), they would explode. Astronomers think that these WIMP explosions could possibly heat a planet enough to make it habitable.
• There are no immediate plans to test the dark matter hypothesis, which is quite theoretical, and any plan to find dark matter-fueled planets would need to look far from here: our part of the universe doesn’t have nearly enough dark matter to bring a planet to habitability.

What’s the Context:

• In other white dwarf news, astronomers have discovered a red dwarf in an extremely tight orbit with a white dwarf.
• And others are still wrangling over what dark matter really is.
• As for exoplanets, astronomers have actually seen one—as in, with visible light—orbiting its star.

Not So Fast:

• It’s not at all clear if white dwarfs have any planets, and if so, whether any of them could possibly support water or life as we know it. For one thing, planets in the habitable zone would be tidally locked with the star—permanent scalding daylight on one side; permanent frozen nighttime on the other.
• Taking 32 hours to find a planet orbiting a white dwarf may seem like a short time, but when you’re looking at tens of thousands of stars, it adds up. Agol told UW Today, “This could take a huge amount of time, even with [a network of telescopes].”
• And just like star-orbiting planets have their Goldilocks zones (not to hot or too cold), dark matter-containing planets would need the right amount of dark matter to be habitable. “It’s not something that’s likely to produce a lot of habitable planets,” Fermilab researcher Dan Hooper told Wired. “But in very special places and in very special models, it could do the trick.” 

References: Eric Agol. “TRANSIT SURVEYS FOR EARTHS IN THE HABITABLE ZONES OF WHITE DWARFS.” doi: 10.1088/2041-8205/731/2/L31

Dan Hooper and Jason H. Steffen. “Dark Matter And The Habitability of Planets.” arXiv:1103.5086v1

Image: NASA/European Space Agency

A study by Yale astronomer Pieter van Dokkum just took the estimated number of stars in the universe—100,000,000,000,000,000,000,000, or 100 sextillion—and tripled it. And you thought nothing good ever happens on Wednesdays.

Van Dokkum’s study in the journal Nature focuses on red dwarfs, a class of small, cool stars. They’re so small and cool, in fact, that up to now astronomers haven’t been able to spot them in galaxies outside our own. That’s a serious holdup when you’re trying to account for all the stars there are.

As a consequence, when estimating how much of a galaxy’s mass stars account for – important to understanding a galaxy’s life history – astronomers basically had to assume that the relative abundance of red-dwarf stars found in the Milky Way held true throughout the universe for every galaxy type and at every epoch of the universe’s evolution, Dr. van Dokkum says. “We always knew that was sort of a stretch, but it was the only thing we had. Until you see evidence to the contrary you kind of go with that assumption,” he says. [Christian Science Monitor]

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A new study of binary galaxies in deep space is inching us closer to understanding the nature of dark energy, the mysterious force pulling our universe apart at an ever-increasing rate.

“We have an amazingly simple picture of the universe,” says Princeton University astrophysicist Michael Strauss. “Of course, we don’t understand that picture—we don’t know what dark energy is, and we don’t know what dark matter is.” [Scientific American]

To get a better handle on these “dark” forces, which we can’t detect with our puny human equipment, researchers Christian Marinoni and graduate student Adeline Buzzi from the University of Provence used an approach that’s actually been around longer than the idea of dark energy–a 1979 theory from Charles Alcock.

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For the first time, physicists say they have witnessed a subatomic particle change its “flavor.” Physicists at OPERA, run by Italy’s national nuclear physics institute, announced yesterday that they have observed one neutrino change its type, or flavor, spontaneously. The experiment solves a 50-year-old physics mystery, and may uncover some of the universe’s hidden mass.

The Mystery

Neutrinos, which come in three different flavors, can have fairly violent births: they can come into the world via nuclear reactions in the sun, particle decay, or collisions in particle accelerators. But, once formed, they seem to ignore almost everything around them, including magnetic fields, electric fields, and matter. In fact, there are trillions of them zipping through each of us every second; they go right through our bodies and keep on moving through the planet itself.

The mystery of “neutrino oscillations” began with the number of neutrinos that should be coming from the sun. Theory predicted a certain number of various flavors to arrive, but observation showed much less:

The neutrino puzzle began with a pioneering and ultimately Nobel Prize winning experiment conducted by US scientist Ray Davis beginning in the 1960s. He observed far fewer neutrinos arriving at the Earth from the Sun than solar models predicted: either solar models were wrong, or something was happening to the neutrinos on their way. [CERN]

In 1969, Bruno Pontecorvo and Vladimir Gribov theorized that the neutrinos weren’t disappearing, they were changing their flavors mid-journey. Though physicists were looking for one type, they weren’t finding what they ordered.

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The theory of general relativity: It works. OK, it’s not exactly Earth-shattering news that Albert Einstein’s century-old idea works in real life. That’s been shown over and over. But what had been difficult for researchers to do until now was verify the theory on truly massive scales beyond the solar system, that of whole galaxies and clusters of galaxies. This week in Nature, Reinabelle Reyes and colleagues report that they did it, and that Einstein was proven correct once more.

While the find is a nice coup for Reyes’ team, its importance goes beyond just reaffirming the great scientists of yesteryear with yet another “Einstein was right” story. The existence of dark matter and dark energy is based on the assumption that Einstein’s gravity is affecting galaxies billions of light-years from Earth in the same way that it affects objects in our solar system [National Geographic]. However, if the study had shown that general relativity needed a slight adjustment at vast distances (like the nudge Einstein himself provided to Newton’s physics), that could have altered prevailing ideas about dark matter and energy. This research indicates those pesky ideas may be here to stay [Space.com].

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There’s nothing like the round number at the start of a new decade to get everyone prognosticating (yes, we know some of you are in the crowd that says the new decade doesn’t begin until 2011; OK, fine). To predict what the scientific scene will be like in 2020, the journal Nature brought in experts from 18 fields. Though the collection doesn’t encapsulate the “world of tomorrow” feel of, say, the old Omni magazine, it’s still packed with sunny (and scary) forecasts. Some show lingering uncertainty, some unbridled optimism, and some give warnings to the world to make a much-needed course correction. Here are five we thought were particularly telling.

1. In 2020, Google defines your reality (even more than it does already).

Peter Norvig, Google’s director of research, tackles the question of where search will be a decade hence. Advanced, he says, but also troublesome: Most searches will be spoken rather than typed, and designers will be experimenting with search systems that read your brain waves. “Users will decide how much of their lives they want to share with search engines, and in what ways”—such is Norvig’s polite description of a world with even less digital privacy than today’s.

What search engines give you back will change, too. Particularly, he says, they will come up with a way to judge relevance and quality that doesn’t rely on popularity: “Thus, a site that claims that the Moon landings were a hoax and seems to have a coherent argument structure will be judged to be lower quality than a legitimate astronomy site, because the premises of the hoax argument are at odds with reality.”

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If you were following Cosmic Variance yesterday, you saw its live blogging of one of the most anticipated recent announcements in physics: the team from Cryogenic Dark Matter Search (CDMS) telling the world whether a Minnesota detector spotted evidence of dark matter. The answer? Maybe (pdf).

CDMS scientists use super-cooled detectors made of germanium and silicon to search for weakly interacting massive particles (WIMPs), one of the leading suspects for what could make up dark matter. The detector is deep underground in the Soudan mine in Minnesota, which scientists also use to hunt for neutrinos. WIMPs streaming in from space would very rarely jostle the germanium nuclei, some 800 meters underground in the Soudan mine, generating a tiny amount of heat and slightly altering the charge on the detectors in a characteristic pattern [Science News].

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Researchers have recalculated the mass of a gigantic black hole at the core of the M87 galaxy, and found that it’s about two times as massive as previously estimated: The new study says that M87′s black hole weighs the same as 6.4 billion suns. Researchers say the findings may indicate that many black holes have been underestimated, and also say that the results from this “local” galaxy only 50 million light-years away may solve a mystery regarding the extremely distant black holes known as quasars.

Astronomers had previously estimated M87′s total mass, calculating how much of that mass came from both the galaxy’s stars and its central black hole. But previous models didn’t have the supercomputing power to estimate the mass contributed by the galaxy’s “dark halo.” The dark halo is a spherical region surrounding the galaxy that extends beyond its main visible structure. It contains “dark matter”, an as yet unidentified material that cannot be directly detected by telescopes but which astronomers know is there from its gravitational interaction with everything else that can be seen [BBC News].

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Three recent studies raised hopes that physicists had caught the first glimpses of dark matter, but the somewhat contradictory results guarantee that researchers will be puzzling over the issue  for some time to come. The latest results come from NASA’s orbiting Fermi Gamma-ray Space Telescope, which was launched last June. The evidence is a reported excess of high-energy electrons and their antimatter counterparts, positrons, which could be created as dark matter particles annihilate or decay [Nature News].

Peter Michelson, principal investigator for the instrument on Fermi that made the detection, cautions that his group is not yet claiming to have found a smoking gun for dark matter. The signal could also come from more mundane sources nearby, such as pulsars, the spinning remnants of supernovae. “But if it isn’t pulsars, it is some new physics,” says Michelson [Nature News]. The new findings are published in Physical Review Letters. Meanwhile, a satellite named PAMELA recently detected higher than expected numbers of positrons, which seems to corroborate the Fermi findings. But results from a balloon experiment conducted high over Antarctica last year add a dash of confusion to the mix.

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The mysterious stuff known as dark matter may have left a calling card at the edge of the Earth’s atmosphere where a space-faring satellite named PAMELA could pick it up. Researchers are reporting that PAMELA detected a high number of the subatomic particles called positrons, the positively-charged counterpoints to electrons, which could have been created by collisions between dark matter particles. “PAMELA found a number of positrons much higher than expected,” the mission’s principal investigator Piergiorgio Picozza [said]. “Many think this could be a signal from dark matter” [SPACE.com]. But of course, others think there’s a more mundane explanation.

Dark matter is one of the greatest enigmas in astrophysics: It cannot be observed directly, so researchers have to study its effects on normal matter to try to deduce what it’s made of. The top candidates for dark matter, the heavy but invisible stuff that makes up 23 percent of the universe, are weakly-interacting massive particles. Contrary to their WIMPy name, when two of these particles collide, they annihilate each other in a burst of energy and propel a cloud of matter and antimatter particles into space. The theory has been a favorite of physicists for years, but until now, no one had detected evidence of these collisions [Wired].

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An enormous helium balloon floating about 24 miles above Antarctica has detected a mix of high-energy electrons so exotic that researchers say the particles must have been created by some fascinating process: They may have been formed when dark matter particles collided and annihilated each other, or else a surprisingly close astronomical object like a pulsar could be spitting the electrons at Earth.

Researchers can’t yet determine which answer is correct, but say the dark matter explanation is more exciting. Dark matter is one of astrophysics’ greatest enigmas. It is thought to be five times more common than visible matter, but there is no proof of what it is made of. The existence of dark matter has largely been inferred from its gravitational effects, such as the fact that most galaxies have enough mass to remain as well-defined objects despite having too little visible matter to account for the necessary gravity [National Geographic News]. If the research balloon did detect the signature of dark matter through the particles left over from collisions, it would be the closest researchers have ever gotten to seeing the mysterious stuff.

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The Fermi Gamma-ray Space Telescope may have just gotten a hint in its hunt for the mysterious dark matter that is thought to make up the bulk of the universe’s mass. A group of astrophysicists has run a simulation of the distribution of dark matter in a galaxy like our Milky Way, and say that if the telescope scans the right region of space it may be able to detect gamma rays given off by collisions between the particles that are thought to make up dark matter (which have never been directly detected, and are still speculative).

Previously, some cosmologists have proposed that the best chance of a detection lies in nearby dwarf galaxies, since they should contain dense nuggets of dark matter that could be relatively easy to pinpoint. But a new study argues that a diffuse dark matter ‘halo’ surrounding the Milky Way offers an even better shot at glimpsing the mysterious stuff. “I would bet on it,” says lead author Volker Springel…. “And I’d be willing to risk a bit of money as well” [New Scientist].

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Strange things are afoot at the Tevatron particle collider at Fermilab, and the aging U.S. particle smasher is getting an unexpected moment in the spotlight while physicists wait for the repairs of the Large Hadron Collider in Switzerland. Researchers say experiments at the Tevatron have produced particles that they are unable to explain using the standard model of physics, and say it’s possible that they’ve detected a previously unknown particle. If the result does turn out to be due to some unexpected new process, it would be the most significant discovery in particle physics for decades [Physics World].

Bloggers and theorists are already lining up explanations that involve unseen particles, hypothetical strings, or modifications of conventional physics. The finding is so controversial that about one-third of the 600-person experiment that detected it are refusing to put their names on the 69-page paper purporting its discovery [Nature News], which was posted in advance of publication on the server arXiv.

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Just beyond the Milky Way, astronomers have found an extremely dim dwarf galaxy that appears to have just a few hundred stars, but is surprisingly massive. Researchers say the galaxy, called Segue 1, must be packed with mysterious dark matter in order to give it such bulk.

Dark matter has never been directly detected, and its presence can only be deduced: Although dark matter doesn’t emit or absorb light, scientists can measure its gravitational effect on ordinary matter and believe it makes up about 85 percent of the total mass in the universe. Dark matter is thought to play a crucial role in galaxy formation, perhaps by contributing to the clumps that stimulate star formation in a budding galaxy and by contributing to the overall matter of a galaxy that allows it to lure other matter and galaxies inward in a growth-by-merger process [SPACE.com].

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The cosmic collision of two galaxy clusters has given astronomers a clearer look at the mysterious substance known as dark matter. Researchers say when the two clusters crashed into each other, the dark matter from each cluster [appeared] to pass through the cosmic mess unscathed, leaving ordinary matter behind in the galactic pileup [SPACE.com]. Using data from NASA‘s Hubble and Chandra space telescopes, astronomers were able to produce an image showing clouds of dark matter, colored blue, on either side of the impact site.

Dark matter, mysterious stuff that exerts a gravitational force on other matter, was originally proposed to explain what holds spinning galaxies, like the Milky Way, together. Observations suggest it outweighs ordinary matter by a factor of about 6 to 1. But no one knows what it is made of, and normally dark matter and ordinary matter are too well mixed to observe the dark matter independently [New Scientist].

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