National Geographic Tales of the Weird

by David Braun

  The Oddly Tilted Planet

  Uranus is a bit of an oddball planet, and scientists are intrigued by its curiosities:

  1. Uranus spins on its side. It’s the only planet with a rotational axis that’s tilted almost into its orbital plane.

  2. Unlike the other gas giants, Uranus doesn’t emit much heat.

  3. Uranus has the most powerful known winds in the solar system, blowing at more than 500 miles an hour (805 kilometers an hour).

  During an equinox on Uranus, the planet is “completely sideways to the sun,” Hammel said. Uranus’s exposure to light and dark is therefore more similar to that experienced by the other planets, and the resulting temperature differences allow the icy giant’s atmosphere to “turn on” and see more circulation.

  Hubble Hopes

  Hammel and other astronomers have been studying the planet’s cloud activity since the last equinox to track how seasonal changes affect the weather. Until this new spot was observed, researchers had thought Uranus’s spring period was over. Now astronomers aren’t sure just how long the planet will continue to form such clouds.

  Hammel is hoping more astronomers will study Uranus’s new spot, and that enough independent confirmation of the feature will prompt Hubble managers to once again look at Uranus. After all, the last time this planet experienced a change in seasons was 1965. “This is the first opportunity in modern astronomy to look at Uranus with this detail,” she said.

  COSMIC DUST-UP

  Planets Being Pulverized

  Near Giant Black Holes?

  A planetary “roller derby” may be playing out around the supermassive black hole at the heart of the Milky Way, according to a new theory that could help solve a dusty mystery.

  For planets and asteroids, life near a black hole can be nasty, brutish, and short. But astronomers believe that in their demise may be found the origin of giant cosmic dust clouds.

  Planet Smashing

  Almost all of the large galaxies observed so far have central black holes, each billions of times the mass of our sun. But about half of these cosmic monsters are obscured by dense rings of dust, and astronomers have been uncertain where all this dust comes from and how it’s remained intact over time.

  According to the new theory, it’s possible that newly formed planets and asteroids whirling close to these giant black holes are continually being smashed to smithereens, creating the thick, donut-shaped clouds of debris.

  TRUTH:

  NOTHING CAN ESCAPE FROM A BLACK HOLE.

  “Near a supermassive black hole, velocities are hundreds to a few thousand kilometers per second,” said study leader Sergei Nayakshin of the University of Leicester in the United Kingdom. At such speeds, “hitting an Earth-size planet with a solid object a few kilometers across could fragment [the planet] into lots of smaller fragments that, over time, become nothing more than dust.”

  Supermassive Attack

  Supermassive black holes are the largest black holes in a galaxy, and recently, one was caught eating a star. Astronomers observed a burst of high-energy gamma rays emanating from the center of a dwarf galaxy 3.8 billion light-years away. The flash, one of the brightest and longest gamma ray bursts ever seen, was believed to be caused by a supermassive black hole destroying a star that got too close to its gravitational pull. While supermassive black holes are thought to exist in most large galaxies, such an event may happen only once every hundred million years in any given galaxy.

  When Worlds Collide

  In 2006, astronomers discovered a population of stars in two rotating disks around the Milky Way’s central black hole. Nayakshin’s team believes these stars may have also formed their own planets and asteroids, similar to the objects in our solar system. Such planets would have to be orbiting their host stars extremely closely to be able to form under the intense gravitational forces that exist near a black hole.

  At the same time, stellar densities are very high near the giant black hole, so its possible that the gravitational pull of closely passing stars frequently causes planets to unbind from their host stars and smash into each other, according to the new theory.

  The dust created by these pulverized worlds might be similar to the zodiacal dust in our solar system—the result of ancient collisions between newborn planets, asteroids, and comets. A similar mechanism could be at work across the universe, filling other galaxies with dust near their central black holes.

  For the study, Nayakshin and his colleagues looked at existing observations of dust clouds around supermassive black holes and compared them with computer models of dust-cloud creation in planetary systems. “If you know this process to actually work on a smaller scale in a somewhat similar setting, then chances are that it may work in the bigger system you’re studying,” Nayakshin said.

  The team found that the type of microscopic dust generated as planets and asteroids collided would in fact block light even from actively feeding black holes, which spew intense radiation as matter falls toward the black hole, compresses, and heats up.

  Galactic Protection

  Of course, the future for any newly formed planet orbiting a galactic black hole may seem bleak. But the violent demise of star systems could have a protective effect for other parts of some galaxies. If the resulting clouds of dust are massive enough, Nayakshin believes, they can obscure much of the lethal x-rays and gamma rays that are constantly bellowing out from the edges of an actively feeding supermassive black hole.

  While much of the area surrounding such a black hole would be sterile, Nayakshin said, “parts of the galaxy that are shielded by the ring of dust—about 50 percent of it—will have a safer and quieter environment for star and planet formation.” Overall, he added, the theory raises some interesting new possibilities for the exotic environments close to supermassive black holes.

  TRUTH:

  THERE IS NO TIME AT THE CENTER OF A BLACK HOLE.

  People used to think all that existed around such black holes was gas and dust, Nayakshin said. “But if we are right, then there are also planets, asteroids, and comets that exist there too—so it is a much more diverse environment than people ever thought.”

  BIG BABY

  Youngest Planet Picture

  Gas Giant Seen in Throes of Creation

  Everyone loves to show off baby pictures, and astronomers are no exception. When they got a snapshot of the youngest planet, they were proud to share it with the world.

  A new picture of a Jupiter-like world swaddled in gas and dust is a direct image of what may be the youngest planet yet seen, astronomers report. The newborn gas giant, dubbed LkCa 15b, orbits a sunlike star 450 light-years away in the northern constellation Taurus. The planet orbits inside a disk of material around the star that’s no more than two million years old.

  The big baby planet may be up to six times the mass of Jupiter, according to theory-based calculations, and it appears to orbit 11 times farther from its parent star than Earth does from our sun. The new picture was made in near-infrared light, but “the planet would probably appear a deep red to our eye, since it’s still glowing from the heat of being formed,” said Adam Kraus, lead study author and an astronomer at the University of Hawaii.

  TRUTH:

  MORE THAN 500 CONFIRMED PLANETS HAVE BEEN DISCOVERED ORBITING OTHER STARS.

  Mind the Gap

  Kraus and colleagues zeroed in on the young star based on previous observations that showed a conspicuous gap in the star’s surrounding debris disk. Such gaps are thought to be telltale signs that massive, newly formed planets are circling inside the disks—a protoplanet’s gravity would clear away a wide swath of gas and dust as it accumulates matter.

  “This [gap] is a huge benefit for astronomers who want to find planets—we know a planet is probably there, and we even know approximately where to look,” Kraus said. “We just needed to find a way to distinguish the very faint planet from its very bright parent star.”

  For this, the team turned to the Keck II 10-
meter telescope on the summit of Hawaii’s Mauna Kea. First off, the telescope’s deformable mirror was able to correct for distortions in the collected starlight caused by Earth’s atmosphere. The team then used a small mask with several holes placed over the light-collecting mirrors, a method called aperture mask interferometry. This technique allowed the team to block out the light from the host star while capturing the fainter glow of the disk and its embedded planet.

  Theories of Planet Formation Debunked!

  Just when scientists thought they had planets all figured out, new discoveries pop up that change their thinking about just how planets behave. Here are some theories that are being overturned:

  THEORY 1: All planetary orbits are roughly circular. In fact, only about one in three of the known exoplanets has a circular or near-circular orbit.

  THEORY 2: With minor exceptions, everything in a star system orbits in the same plane and in the same direction. One in three exoplanets’ orbits are “misaligned.” Some orbit in the opposite directions of their stars’ rotations, and others are tilted well out of the ecliptic.

  THEORY 3: Giants the size of Neptune are rare. The size range where theory suggested there should be the fewest planets—3 to 15 times the size of Earth—has been the most commonly found.

  “Baby” Pictures

  Kraus and his team plan to continue observing LkCa 15b so they can pin down its temperature and orbital characteristics, such as the shape and orientation of its path around the star. The team also hopes to expand the search to other stars that have surrounding disks with gaps—and perhaps begin to answer some basic questions about early planet formation.

  “We’d been looking for this kind of planet for several years, specifically because we know that observing planet formation in action would tell us a lot about how it actually works,” Kraus said. “My first reaction was that this is finally going to tell us how planets really form!”

  DIAMONDS IN THE SKY

  “Diamond” Planet Found

  May Be Stripped Star

  An exotic planet as dense as diamond has been found in the Milky Way. Astronomers think the world is a former star that got transformed by its orbital partner.

  “In terms of what it would look like, I don’t know I could even speculate. I don’t imagine that a picture of a very shiny object is what we’re looking at here.”

  Ben Stappers

  University of Manchester, on the “diamond” planet

  An odd planet was discovered orbiting what’s known as a millisecond pulsar—a tiny, fast-spinning corpse of a massive star that died in a supernova. Astronomers estimate that the newfound planet is 34,175 miles (55,000 kilometers) across, or about five times Earth’s diameter.

  In addition, “We are very confident it has a density about 18 times that of water,” said study leader Matthew Bailes, an astronomer at the Swinburne Centre for Astrophysics & Supercomputing in Melbourne, Australia. “This means it can’t be made of gases like hydrogen and helium like most stars but [must be made of] heavier elements like carbon and oxygen, making it most likely crystalline in nature, like a diamond.”

  In this depiction, the newfound “diamond” planet orbits the pulsar so closely that the entire system would fit inside the sun. (Photo Credit 7.8)

  Millisecond Pulsars

  The new millisecond pulsar, dubbed PSR J1719–1438, lies about 4,000 light-years away in the southern constellation Serpens. Bailes and his team found the star during a pulsar survey using the radio telescope at Australia’s Parkes Observatory. A pulsar is a type of stellar corpse that emits powerful beams of radio waves from its poles. If these beams sweep across Earth’s field of view as the star rotates, radio telescopes on Earth can detect the star’s regular pulses.

  A millisecond pulsar is thought to form when the pulsar is siphoning material from a companion star. The action of eating matter speeds up the pulsar’s spin to hundreds of rotations a second. So far it seems millisecond pulsars are rare, with only about a hundred found in the last 30 years. The study team found PSR J1719–1438 by using supercomputers to comb through almost 200,000 gigabytes of data—enough to fill more than 23,500 standard DVDs.

  The data show that the pulsar spins more than 10,000 times a minute. The astronomers also noticed that the star’s radio pulses have an unusual modulation, which the team concluded must be due to the gravitational pull of a small orbiting object.

  A Stripped Star?

  About 70 percent of the known millisecond pulsars have orbital companions, but PSR J1719–1438 is only the second thought to have a planetary partner. That’s probably because planets don’t form around millisecond pulsars in the usual way, Bailes said.

  Diamonds Are Forever

  The diamond planet, dubbed J1719–1438, has a stable system, with no evidence that it will change for billions of years. “Of course,” notes Michael Keith of the Australia Telescope National Facility, “this also means that it could well have been around for a long time, just waiting for us to find it. Since it’s likely to last for longer than the Earth or the sun, I would say that in this case, a diamond really is forever.”

  Astronomers think planets are created from dusty disks of material swirling around newborn stars. As this material orbits the star, gravitational interactions cause clumps to form, and the clumps build mass as they sweep through the disk. By contrast, the new study hints that pulsars can strip material away from their companions until all that’s left of the consumed star is enough mass for a planetlike object.

  The newfound “diamond” planet probably formed from a white dwarf star—the core of a dead sunlike star—that was being stripped of matter by the pulsar. The leftover object likely represents just 0.1 percent of the white dwarf’s original mass, Bailes said. Based on their data, the team calculates that the planet orbits the pulsar in just two hours and ten minutes at a distance of about 372,822 miles (600,000 kilometers).

  More Pulsar Planets Out There

  Bailes and his team would now like to know exactly how rare their discovery really is. In all likelihood, this weird method of planet production requires special circumstances that rely on the white dwarf companion having a particular mass and chemical composition.

  But even if the diamond planet is a result of a perfect storm of special circumstances, there should be more such worlds out there, Bailes said.

  “The most exciting aspect to me is that we’ve only processed a small fraction of space so far,” he said. “With the new supercomputers coming online, we should be in a strong position to possibly make many more discoveries like this one.”

  SEVEN LITTLE SUPERNOVAE

  Seven Supernovae

  Found in Single Galaxy—A First

  In a galaxy 250 million light-years from Earth, astronomers have spotted a record-breaking seven supernovae, and they were all found at the same time.

  Astronomers have spotted a record-breaking seven supernovae in a prodigious galaxy known as Arp 220. This galaxy is thought to have formed from the merger of two smaller galaxies and is well known to host a very intense burst of star formation, easily seen in visible wavelengths.

  The galaxy Arp 220, where the seven supernovae were found (Photo Credit 7.9)

  A New Record

  “As far as we know, only three supernovae in a single galaxy were found at once so far, which is already an impressive number,” said study leader Fabien Batejat, a Ph.D. student at Chalmers University of Technology in Onsala, Sweden. “But we can confirm seven supernovae [in a single galaxy], thanks to a 17-year monitoring of the radio sources in Arp 220.”

  The unprecedented find may offer a unique cosmic laboratory for studying galaxy evolution. The new data also confirm that Arp 220 is a very efficient factory for explosive star deaths, giving scientists a glimpse of how the earliest galaxies in the universe may have behaved.

  Rogue Planets

  A new theory suggests that when a star dies in a violent supernova, some of its planets may survive the blast but be ejected
from orbit and sent wandering the galaxy. This would offer an explanation for some of the free-roaming planets that have been found and it could mean that more exist across the Milky Way. In rare cases, some survivor planets may remain bound to supernova remnants, finding new orbits around the neutron stars or black holes left behind by the explosions.

  Telescope Como Revealed Supernovae

  Each of the supernovae found in Arp 220 spans less than a light-year, and at such a great distance, each radio signal covers an angle in the sky less than 0.5 milliarcseconds across, Batejat said. “To give you an idea of how small this is, this size corresponds to what you would see if you would look into a straw of about 1,500 kilometers [932 miles] long,” Batejat said.

  “In order to see such small objects, we would need a telescope of 10,000 kilometers [6,214 miles] across, which is a bit less than the diameter of the Earth itself. But since we can’t build such gigantic telescopes, we use interferometry to simulate them.” In astronomy, interferometry uses the combined power of an array of telescopes—rather than a single, huge telescope—to create high-resolution images that can probe deep into the universe.

  Batejat’s team used 57 of the largest radio telescopes on Earth, which are spread across two continents and five countries. The project included data from the European VLBI Network, the Very Long Baseline Array, the Green Bank Telescope, and the Arecibo Observatory.