March 1, 2013
According to a new proposal from astronomers and professors Avi Loeb and Dan Maoz, signs of life may be awaiting detection in the shadows of death. Looking to the abundance of dying stars known as white dwarfs, Loeb and Maoz devised a simple way to search for oxygen in the atmosphere of exoplanets which orbit around white dwarfs much the way Earth orbits the sun. Loeb says the theory could yield results within the decade with the launch of NASA’s James Webb Telescope in 2018.
The pair published a paper in February, ”Detecting bio-markers in habitable-zone earths transiting white dwarfs,” outlining their theoretical research. In it, Loeb, chair of Harvard University’s department of Astronomy and director of the Institute for Theory and Computation (ITC) within the Harvard-Smithsonian Center for Astrophysics, explains that though a white dwarf is simply the cooling core of a dead star, its radiant heat and light can host life on orbiting planets for billions of years.
“We know of a few thousand of those planets by now and there must be many more out there. And a key question is, if a planet is quite similar to Earth in terms of its rocky material; and if it’s the right distance from the furnace, the central star that keeps it warm so that adequate water can exist on its surface; would the chemistry of life naturally arise, and would life exist the same way it does on Earth?” Loeb says it’s a difficult question to address with theory alone. “The best way to approach it,” he says, “would be to try and observe other planets, and search for indications of life.” And that rather than visiting those places, Loeb recommends searching “for signatures of molecules that are naturally produced by life and the most generic one is oxygen.”
Recent research suggests not only that there are plenty of exoplanets out there like our own, but that they are often paired with and orbiting white dwarfs. According to Loeb, “Somewhere between 15 to 30 percent of [white dwarfs] show evidence of rocky material on their surface, and such material would not be there unless there was rocky stuff around them,” meaning that these are the exoplanets that could potentially sustain life.
With this in mind, Loeb and Maoz postulated that researchers could find oxygen by measuring the atmospheric transmission spectrum of these planets as it passes in front of a white dwarf. Unfortunately, the pair will have to wait until 2018, when the launch of the James Webb Telescope is scheduled. The measurements have to be taken outside the Earth’s atmosphere, where oxygen concentrations can alter the incoming light.
In the meantime, Loeb plans to use the results of an upcoming survey of stars to identify prime candidates for the space telescope to measure. “One can follow up on the sample of white dwarfs that is found by this survey and search for examples of where we see evidence of a planet transiting a white dwarf and, if it’s the right distance, that would be a very good candidate for JWST to look at.”
The researchers estimate that a sample size of some 500 white dwarfs will be needed, to account for a variety of alignments between planets and their stars, but he’s optimistic about the potential to find something.
“I think if we have the technology, we should do it,” he says. “There are several examples in the history of astronomy where people hesitated.” Most recently, he says, researchers were not given observation time to search for exoplanets. “Even though it was feasible technologically, they said no we won’t give the time for that because it’s speculative and the chance is very small that there would be a Jupiter close to a star.” Of course, “only a decade later these Jupiters were found by chance, and it opened completely this field of exoplanets.”
Loeb, who sprinkles his lectures with talk of religion and philosophy, says the lesson is to remain open-minded. “The way to make discoveries is not to have a prejudice and just to explore the universe because our imagination is quite limited.”
In the end, Loeb says his proposal is actually simple, a hallmark of his approach to physics that has earned him a Chambliss Astronomical Writing Award from the American Astronomical Society for his book, “How Did the First Stars and Galaxies Form?“
October 2, 2012
The point of no return has been discovered at last. Fifty million light-years from Earth, in the heart of the Messier 87 galaxy, a black hole that is six billion times more massive than the Sun has provided scientists with the first measurement of what is known as an “event horizon,” the point beyond which matter is forever lost to the black hole.
“Once objects fall through the event horizon, they’re lost forever,” says Shep Doeleman, a research associate at the Harvard-Smithsonian Center for Astrophysics and lead author on the paper published in Science Express.
Black holes are the densest objects in the universe. “There’s such intense gravity there that it’s not just matter that can cross the event horizon and get sucked into the black hole but even a photon of light,” says co-author Jonathan Weintroub, also at the Harvard-Smithsonian Center for Astrophysics. “There’s a bit of a paradox in claiming that we’ve measured a black hole, because black holes are black. We measure light, or in our case, radiowaves” from around the black hole, not the black hole itself.
The black hole in question is one of the two biggest in the sky, according to a September 2011 paper titled, “The size of the jet launching region in M87,” which outlined how measurements of the event horizon could be taken.
Beyond being fantastically, mind-bogglingly bizarre, black holes are also useful targets for study, explains Weintroub, particularly the ten percent that exhibit what are known as jets, or light-emitting bursts of matter being converted into energy as masses approach the event horizon. Supported by Einstein’s general theory of relativity, these jets provided the radiation Weintroub’s team needed to take its measurements.
Using the combined data from radio telescopes in Hawaii, Arizona and California, researchers created a “virtual” telescope capable of capturing 2,000 times more detail than the Hubble Space Telescope. At this level of detail, researchers were able to measure what is known as the “innermost stable circular orbit” of matter outside the black hole as well as M87′s event horizon. If the event horizon is the door into a black hole, then the innermost stable circular orbit is like the porch; past that point, bodies will begin to spiral toward the event horizon.
“We hope to add more telescopes,” says Weintroub. “That’s really what we need to do to start to make new images and understand what the hell is going on at the base of the jet.”
As a point of clarification on what the team has actually done, Weintroub says, “I’ve seen headlines saying we made an image of the black hole–we didn’t in fact make an image of anything, and if we made an image, it would be the pattern of radiation in the immediate neighborhood of the black hole, because the black hole is black.”
While the appearance of black holes may be simple to describe (they’re black), their behavior quickly gets weird and that’s precisely the scintillating promise waiting at the event horizon.
“Black holes are interesting,” says Weintroub, “because one of the things that Einstein predicts with his theory of general relativity is that radiation bends light.” In truth, Weintroub continues, Einstein posited that the gravity of massive objects (black holes included) actually bends the space through which light travels.
As Weintroub puts it, “Gravity bends the very fabric of space, and intense gravity bends the fabric of space intensely.”
As the virtual telescope expands to other sites in Chile, Europe, Mexico, Greenland and the South Pole, Weintroub says they’ll be able to create ever more detailed images within roughly five years. “When we start making images,” he says, “we’ll be able to see whether or not the radiation that a black hole admits is ‘lensed,’” or bent, as Einstein predicted.
Meanwhile, here in the Milky Way, things are equally exciting for different reasons. Though the black hole at the center of our galaxy is what Weintroub calls “quiet” and lacks a jet, this September researchers at the Harvard-Smithsonian Center for Astrophysics discovered a gas cloud with planet-forming capabilities headed toward the Milky Way’s black hole.
August 30, 2012
Late at night, when Alex Parker is in the middle of an eight to ten-hour long calibration at the Harvard-Smithsonian Center for Astrophysics, he likes to listen to early Nine Inch Nails or Led Zeppelin to stay alert. To finish the evening, he says he switches to instrumental music. Parker was a musician long before he was an astronomer. He says music has a place in the study of the sky, particularly when creating visualizations.
“When getting into data visualization, it seemed that audio is an under-utilized resource which could enhance or, in some circumstances, replace visualization,” says Parker. To that end, he has created a series of musically rich animations that show everything from the orbits of the many potential planets captured by the Kepler mission to a patch of sky erupting with supernova each assigned a different note.
Turns out, the silent environment of outer-space lends itself quite well to a variety of musical selections. “Some astrophysical processes seem very serene and elegant, while others are sudden and phenomenally violent, and the music I would associate with each might have radically different character,” Parker explains. For his most recent project, Worlds: The Kepler Planet Candidates (at the top of the post), which shows potential planets picked up by the team’s measurements dancing around a single star, he went with the instrumental Nine Inch Nails song, “2 Ghosts 1.” Though the visualization is based on real data, Parker says, “The illustrated planet candidates orbit around 1770 unique stars, and packing that many planets into a single system would rapidly lead to extreme chaos.”
When creating the video for his Supernova Sonata (above), Parker began experimenting with percussive sounds, but found that coordinating the stars’ activity to generated notes provided a nice contrast to the violent detonations.
In Kepler Sonata (above), Parker coordinated the motion of the six-planet system, Kepler 11, as detected by the Kepler observatory, to create not only a visual experience of a system’s dynamic movement but also an auditory representation.
Parker, whose father is a professional musician, says that, though he doesn’t instantly hear music in his mind when he contemplates the night sky, he is one of many observational astronomers who rely on an “Observing Playlist,” to provide a soundtrack to their work.
March 30, 2012
In 2005, Warren Brown of the Smithsonian Astrophysical Observatory noticed something rather unusual in the sky: a star traveling out of the Milky Way galaxy at roughly 1.5 million miles per hour. The strange discovery could only be explained by an even stranger prediction, made nearly two decades earlier by an astronomer named J.G. Hills.
“He predicted that if you have two stars orbiting each other—a so-called binary system—and they get too close to the central black hole in the Milky Way, they will get ripped apart,” says SAO astrophysicist Avi Loeb. “One of the stars will go into a tighter orbit around the black hole, and the second one will be flung out of the galaxy.”
Since Brown’s 2005 discovery, at least 21 hypervelocity stars (as they’ve come to be called) have been observed speeding out of our galaxy. But only recently did anyone look to see if there might be hypervelocity planets, as well. “My collaborator Idan Ginsburg and I did some work on hypervelocity stars, and at some point, I was talking with him about perhaps looking into planets,” Loeb says. “One day, at lunch, it clicked: we could actually write a paper on them, because there is a method of finding them.”
Loeb had realized that a planet orbiting one of these hypervelocity stars could be observed by what’s called the transit method: when a distant planet crosses between its star and our telescope, the light of the star dims slightly, indicating the presence of the planet. First, though, he and Ginsburg had to determine whether these planets could theoretically exist in the first place. Their calculations, published last week in the Monthly Notices of the Royal Astronomical Society, went beyond even what he had suspected.
Hypervelocity planets can indeed exist—and according to the research team’s simulations, they may approach speeds as high as 30 million miles per hour, making them some of the fastest-moving objects in the known universe.
“We asked what would happen if there were planets around hypervelocity stars,” Loeb says. “So we started with a simulation of a binary system, and then sprinkled planets around each of the stars.” Their calculations showed that, if the binary star system was ripped apart by gravitational forces near the galaxy’s central black hole, a small percentage of the planets would stay bound to one of the stars, either following them on their journey out of the galaxy, or diving more closely into the depths of the black hole. The majority of planets, however, would be flung away from their parent stars, traveling even faster to the edges of the Milky Way.
“Their speed can reach up to ten thousands kilometers per second—a few percent of the speed of light,” says Loeb. “If you imagine a civilization living on such a planet, they would have a tremendous journey.” The voyage from the center of the galaxy to the edge of the observable universe, he says, would take 10 billion years.
The potential existence of hypervelocity planets is far more than a mere curiosity, since it would provide us information about conditions near the center of the galaxy, and if planets can even form there. “It’s a very unusual environment, because the density of stars there is more than a million times than the density near the sun,” Loeb says. “There is a very high temperature, and every now and then the black hole at the center gets fed with gas, so it shines very brightly, which could in principle disrupt a system that tries to make planets.” His team’s calculations showed that, if planets can indeed form in this area, they should be observable when bound to hypervelocity stars.
None of these planets has been spotted, but Loeb hopes that some will be found in coming years. Just as astronomers have recently discovered hundreds of extrasolar planets using the transit method as part of NASA’s Kepler Mission, they can scrutinize hypervelocity stars in much the same way to spot these runaway planets. And if things progress along the same time frame as J.G. Hills’ 1988 prediction of hypervelocity stars, Loeb can expect to have his predictions confirmed within his lifetime—sometime around the year 2029.
March 15, 2012
Readers questions continue this month with some really intriguing queries. Can you identify a bird just by its feather? The aptly named Carla Dove, a Smithsonian ornithologist weighs in on that one in the video above. And speaking of our fine feathered friends, another reader wonders why it is that birds all seem to want to hang out near electrical transformers? From dinosaurs to telescopes to gemstones, you asked and we found the answers.
Are there any paleontological discoveries, such as dinosaur bones, left to be made in the United States?
Susanne Ott, Bern, Switzerland
There sure are. This is such a large country, and there are so many areas yet to be searched, that we may not run out of finds for several lifetimes. Just think: We have found only about 2,000 species of dinosaurs for the 160 million years they were alive on Earth. Given that a species lasts only a few million years, we must be missing many thousands of dinosaur species. The most promising places are out West, where it’s drier and paleontologists can get access to fossil-bearing rocks.
Matthew Carrano, Paleontologist
Museum of Natural History
How much artistic license do scientists use when they portray astronomical features detected by radio telescopes?
Jeanne Long, Atlanta, Georgia
A lot, actually. Radio-telescope images differ from the images captured by the Hubble Space Telescope—while Hubble images are recorded in the visible wavelengths of light we see in rainbows, radio telescopes record electromagnetic radio waves sent out by distant galactic objects. They detect what our ears might pick up if we could hear the universe. (Luckily, we can’t, or the world would be a jumbled mess of rumbling sounds.) Based on the intensity of the radio waves, astronomers plot signal strengths and assign different colors to them.
Although it would be handy and logical, there is no set convention to those color assignments. Scientists choose different colors to bring out specific details or molecules found in the image. (If you do a quick Google image search for the Trifid Nebula, you’ll see images with different color representations of the same object.) Is it fair to randomly assign different colors to objects in space? To astronomers, that’s not an issue. They are simply trying to isolate data. And the truth is, the human eye is not sensitive enough to pick up the true colors of these objects anyway. So, the next time you see a breathtaking picture from space, thank a scientist for putting it all together.
David Aguilar, Astronomer and illustrator
Smithsonian Astrophysical Observatory
Is it true that the Smithsonian is still cataloguing items from Charles Wilkes’ United States Exploring Expedition?
Kevin Ramsey, Washington, D.C.
That expedition returned from its four-year exploration of the Pacific in 1842 with an immense trove—hundreds of fish and mammal specimens, more than 2,000 bird specimens, 50,000 plant specimens, a thousand live plants, some 4,000 ethnographic objects, such as Fijian war clubs, Samoan fish hooks and New Zealand baskets. But no, the Smithsonian is not still cataloguing them. That job largely fell to the scientists who accompanied Wilkes, and they completed it, well, expeditiously. The collection was exhibited in the Patent Office Building in Washington, D.C. for several years, before it came to the Smithsonian.
Pamela M. Henson, Historian
Smithsonian Institution Archives
Did Mathew Brady really take all the Civil War photographs that are credited to him?
Patrick Ian, Bethesda, Maryland
No. By 1861, Mathew Brady was one of the best-known photographers in America, with portrait studios in New York City and Washington, D.C. While his staff handled day-to-day operations, Brady provided the creative vision and marketing expertise that made his studios famous. When the Civil War began, he assembled and outfitted teams of photographers and sent them into the field to ensure that his cameras would be present to produce a visual record of the conflict. Although Brady traveled periodically to battlefields and encampments, the Civil War photographs that carry his credit line were typically made by his cameramen. The look of the portraits produced in Brady’s studios—such as those featured in the National Portrait Gallery’s new exhibition, Mathew Brady’s Photographs of Union Generals (March 30, 2012-May 31, 2015)—reflected his aesthetic even when he was not present for the portrait session.
Ann M. Shumard, Curator of Photographs
National Portrait Gallery
Why do birds like to congregate around electric transformers?
Luis Tewes, Palm Beach Gardens, Florida
While the ever-growing electrical grid spells trouble for most species of birds, some have incorporated human structures into their lives. Power lines are a flight hazard to many species, but they also provide elevated perches, particularly in open country where there are few natural alternatives, for sit-and-wait predators, such as bluebirds, shrikes and small raptors. Many species use electric lines to rest or monitor their territories; and flocks of blackbirds and starlings and other birds gather on wires before they join large communal roosts. Power-line poles and towers and their attendant transformers provide additional support and protection for flocks and larger species, such as raptors. A few species even commandeer power poles and transformers as nesting sites. Transformers may produce some heat, which may explain why some birds like them. The monk parrakeet, introduced from Argentina, nests and roosts around transformers and has expanded into some pretty cold urban areas.
Birds’ use of power equipment illustrates their impressive adaptability, but awareness of high-voltage electric currents is not in their DNA. While a bird can perch on a high-voltage line in complete safety, as soon as it makes secondary contact with a conductor that leads to a ground, it will be fried. Large birds taking flight or producing “streamers” of fecal material often complete the circuit to their demise. Fecal build-up, gnawing (by parrots) and nesting material can short out lines or transformers, leading to massive power outages. Bird mortality might be reduced, and electrical service might be more reliable, if we had a better-designed grid.
Russell Greenberg, Wildlife Biologist,
Migratory Bird Center, National Zoo
In aserated (or “starred”) gemstones, such as the ruby and sapphire varieties of corundum, what is the average amount of rutile per square millimeter? And how many asterated gemstones does the Smithsonian Institution have?
Davis M. Upchurch, Fletcher, North Carolina
In synthetic asterated corundum, about 0.1 to 0.3 percent titanium oxide is typically mixed with the aluminum oxide. That gives you a ballpark idea as to the fraction of rutile (which is usually given as an amount per cubic millimeter). The Museum of Natural History has about 50 asterated gems in its collection, including, 21 specimens of corundum. We add new ones sporadically, and we’re always on the lookout for different or better examples.
Jeffrey Post, Curator of Gems and Minerals,
Museum of Natural History
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