National Geographic Tales of the Weird
Page 24
Specifically, Hill and colleagues have been tracking buried “jet streams,” called torsional oscillations, encircling the sun. These bands of flowing material first appear near the sun’s poles and migrate toward the equator. The bands are thought to play a role in generating the sun’s magnetic field.
Sunspots tend to occur along the pathways of these subsurface bands, and the sun generally becomes more active as the bands near its equator, so they act as good indicators for the timing of solar cycles.
“The torsional oscillation … pattern for Solar Cycle 24 first appeared in 1997,” Hill said. “That means the flow for Cycle 25 should have appeared in 2008 or 2009, but it has not shown up yet.” According to Hill, their data suggest that the start of Solar Cycle 25 may be delayed until 2022—about two years late—or the cycle may simply not happen.
Crawl to the Poles
Adding to the evidence, Richard Altrock, manager of the U.S. Air Force’s coronal research program for the National Solar Observatory (NSO), has observed telltale changes in a magnetic phenomenon in the sun’s corona—its faint upper atmosphere.
Known as the “rush to the poles,” the rapid poleward movement of magnetic features in the corona has been linked to an increase in sunspot activity, with a solar cycle hitting its maximum around the time the features reach about 76 degrees latitude north and south of the sun’s equator.
The rush to the poles is also linked to the sun “sweeping away” the magnetic field associated with a given solar cycle, making way for a new magnetic field and a new round of sunspot activity.
This time, however, the rush to the poles is more of a crawl, which means we could be headed toward a very weak solar maximum in 2013—and it may delay or even prevent the start of the next solar cycle.
Quiet Sun Exciting for Science
Taken together, the three lines of evidence strongly hint that Solar Cycle 25 may be a bust, the scientists reported during a 2011 meeting of the American Astronomical Society in Las Cruces, New Mexico. But a solar lull is no cause for alarm, NSO’s Hill said: “It’s happened before, and life seems to go on. I’m not concerned but excited.”
In many ways a lack of magnetic activity is a boon for science. Strong solar storms can emit blasts of charged particles that interfere with radio communications, disrupt power grids, and can even put excess drag on orbiting satellites. “Drag is important for people like me at NASA,” SDO’s Pesnell said, “because we like to keep our satellites in space.”
What’s more, a decrease in sunspots doesn’t necessarily mean a drop in other solar features such as prominences, which can produce aurora-triggering coronal mass ejections. In fact, records show that auroras continued to appear on a regular basis even during the Maunder Minimum, Pesnell said.
Seeing Spots
Sunspots have been observed from Earth for centuries. Chinese astronomers first recorded seeing them with the naked eye more than 2,800 years ago. In the early 1600s, astronomers Thomas Harriot and Galileo Galilei were the first to observe them through a new invention, the telescope.
Instead, he said, the unusual changes to the sun’s activity cycles offer an unprecedented opportunity for scientists to test theories about how the sun makes and destroys its magnetic field. “Right now we have so many sun-watching satellites and advanced ground-based observatories ready to spring into action,” Pesnell said. “If the sun is going to do something different, this is a great time for it to happen.”
STAR-ON-STAR SNACKING
Star Caught Eating Another Star
X-Ray Flare Shows
Star light. Star bright. First star I eat tonight …
A tiny cannibal star has been caught munching on another star, thanks to a superbright flash of x-rays spied by cosmic hunters.
Stellar Munchies
The culprit is what’s known as a neutron star, the tiny but very dense corpse of a massive star that died in a supernova blast. Sitting 16,000 light-years away, this particular neutron star is normally among the faintest objects in the x-ray sky.
But during recent observations with the European Space Agency’s XMM-Newton space telescope, the star unexpectedly surged to 10,000 times its original brightness. “A companion blue supergiant star is believed to have thrown off a gigantic clump of super-heated gas from its surface, [which] got attracted by the intense gravitational field of the much smaller and denser neutron star orbiting nearby,” said study leader Enrico Bozzo, an astronomer with the ISDC Data Centre for Astrophysics in Geneva, Switzerland.
TRUTH:
THERE ARE MORE STARS IN THE UNIVERSE THAN GRAINS OF SAND ON EARTH.
A clump of matter from a blue supergiant star (left) heads toward a smaller companion neutron star. (Photo Credit 7.5)
The lump of wayward stellar matter measured an estimated 9.9 million miles (16 million kilometers) across and took up about a hundred billion times the volume of the moon. As it became part of the neutron star, the material was heated to millions of degrees, generating a brilliant x-ray flare that lasted for four hours.
“I really could not believe this was true that we were so lucky! I didn’t sleep for days. We are finally able to provide direct evidence for the existence of these clumps of matter.”
Enrico Bozzo
astronomer, describing his reaction upon discovering the cannibal star
Fast Flashes
Astronomers previously knew that the neutron star and the blue super-giant are part of a stellar odd couple known as a Supergiant Fast X-ray Transient, or SFXT. These usually faint binary stars are prone to occasional flare-ups that cause them to rival the brightest x-ray sources in the sky.
Unfortunately for astronomers, these flares take place randomly only a few times a year, and they last just a couple hours, making them practically impossible to catch from beginning to end. What makes this event even harder to see is that most space-based observatories with sensitive x-ray detectors can observe only a tiny fraction of the sky at a time, and they can’t be swung into action fast enough when these flares go off.
“What usually ends up happening is that these events are detected by instruments that can move very fast or have much larger fields of view, but which suffer from reduced sensitivity, so that they just can’t provide a clear understanding of what caused such an event,” Bozzo said.
First Proof of Star’s Cannibalism
One theory was that the flares are caused by the neutron star devouring matter cast off by its hefty companion. Most massive stars generate a constant “wind” of charged particles, which pushes large quantities of stellar material in all directions into space.
Instead of a steady outflow of gas, the blue supergiant in an SFXT system may be emitting winds studded with large “bullets” of material, according to the theory. Flares happen when the neutron star gets shot by one of these clumps.
However, existing observations couldn’t offer clear proof for this theory—until now. By chance, XMM-Newton caught such a flare in 2010 during a scheduled 12.5-hour observation of the SFXT system known as IGR J18410–0535.
TRUTH:
THE BRIGHTER THE STAR, THE SHORTER ITS LIFE SPAN.
“I really could not believe this was true that we were so lucky! I didn’t sleep for days,” Bozzo said. “We are finally able to provide direct evidence for the existence of these clumps of matter.”
Bozzo and his team now hope to make observations of other SFXTs with XMM-Newton, to better understand the unusual flares. “We think it’s the right time,” he said, “to ask for an unprecedented large observational time with the space observatory and provide a final clear answer to the nature of these sources.”
LET IT SNOW! LET IT SNOW!
Saturn Moon
Coated in Fresh Powder
It’s a winter wonderland on Saturn’s moon Enceladus, where scientists have found 330 feet (100 meters) of snow on the surface.
Skiers, get your poles ready: Saturn’s moon Enceladus appears to be cloaked in drifts of powdery snow, sc
ientists announced.
Fluffy White Stuff
The researchers think superfine snowflakes are blasted out of geyser-like jets, which emanate from long fissures called tiger stripes on the moon’s southern hemisphere. Some of the snow from these plumes falls back to the moon’s surface, coating older fractures and craters in a slow process of accumulation.
“The particles are only a fraction of a millimeter in size … even finer than talcum powder,” study leader Paul Schenk, a planetary scientist at the Lunar and Planetary Institute in Houston, Texas, said in a statement. “This would make for the finest powder a skier could hope for.”
The finding is based on new high-resolution pictures of Enceladus from NASA’s Cassini orbiter, as well as global maps of color patterns that help reveal the ages of surface features.
“The particles are only a fraction of a millimeter in size … even finer than talcum powder. This would make for the finest powder a skier could hope for.”
Paul Schenk
planetary scientist, Lunar and Planetary Institute, Houston
From Geyser to Blizzard
In 2005, Enceladus’s icy geysers were first seen spewing from the moon’s south polar region in pictures from the Cassini spacecraft. Further Cassini data have since shown that the active tiger-stripe fissures are warmer than the surrounding icy terrain, hinting that the jets are being driven by a subsurface liquid ocean. Cassini’s close flybys of the moon also revealed that Enceladus’s geysers may contain the chemical ingredients for life. Enceladus is so far from the sun, however, that its surface temperature is about -330 degrees Fahrenheit (-200 degrees Celsius), causing water vapor spewed from its geysers to condense into ice crystals.
TRUTH:
SATURN HAS MORE THAN 60 MOONS.
According to the new study, as Enceladus’s powdery snow falls back to the surface, it softens the contours of the underlying landscape. The rims of older craters and fissures appear to have been smoothed by the blanket of snow, while the edges of newer fractures are more distinct. Based on such images, Schenk estimates that snow has accumulated to depths of 250 to 400 feet (75 to 125 meters) in places.
Enceladus’s Old Faithfuls
Scientists estimate that Enceladus’s low gravity—about 1 percent that of Earth—allows some of the ice emitted by the polar geysers to jet into space rather than falling back to the moon’s surface. Enough material escapes to form an entire ring of Saturn, called the E ring. The wispy E ring is so tenuous that astronomers didn’t see it until 1967.
Scientists previously estimated that if Enceladus’s geysers were to shut off, Saturn’s E ring would dissipate within a few hundred to a few thousand years. This would mean that the entire E ring—and the geysers that feed it—could be quite recent features that we just happen to be seeing at the right time.
But the large accumulations of snow on Enceladus’s surface prove otherwise, Schenk argued at a joint meeting of European and American planetary scientists. That’s because the snowfall on Enceladus is incredibly light, with accumulations of less than a thousandth of a millimeter a year. For snow to build up to depths of hundreds of feet would require tens of millions of years, he said—indicating that the geysers have been active for a very long time.
STELLAR EXPECTORATION
Star Found Shooting Water “Bullets”
How rude. Young sunlike stars have been seen spitting water out into space. Is it just a phase that all protostars go through?
Seven hundred and fifty light-years from Earth, a young, sunlike star has been found with jets that blast epic quantities of water into interstellar space, shooting out droplets that move faster than a speeding bullet.
The discovery suggests that protostars may be seeding the universe with water. These stellar embryos shoot jets of material from their north and south poles as their growth is fed by infalling dust that circles the bodies in vast disks.
“If we picture these jets as giant hoses and the water droplets as bullets, the amount shooting out equals a hundred million times the water flowing through the Amazon River every second,” said Lars Kristensen, a postdoctoral astronomer at Leiden University in the Netherlands.
TRUTH:
COLD STARS ARE RED, WHILE HOT STARS ARE BLUE.
“We are talking about velocities reaching 200,000 kilometers [124,000 miles] per hour, which is about 80 times faster than bullets flying out of a machine gun,” said Kristensen, lead author of the new study detailing the discovery, which has been accepted for publication in the journal Astronomy & Astrophysics.
Protostar in Perseus
Located in the northern constellation Perseus, the protostar is no more than a hundred thousand years old and remains swaddled in a large cloud—gas and dust from which the star was born.
Using an infrared instrument on the European Space Agency’s Herschel Space Observatory researchers were able to peer through the cloud and detect telltale light signatures of hydrogen and oxygen atoms—the building blocks of water—moving on and around the star.
After tracing the paths of these atoms, the team concluded that water forms on the star, where temperatures are a few thousand degrees Celsius. But once the droplets enter the outward-spewing jets of gas, 180,000-degree-Fahrenheit (100,000-degree-Celsius) temperatures blast the water back into gaseous form.
A star is born in this illustration: Gas and dust swirl inward, while polar jets spurt outward. (Photo Credit 7.6)
Once the hot gases hit the much cooler surrounding material—at about 5,000 times the distance from the sun to Earth—they decelerate, creating a shock front where the gases cool down rapidly, condense, and reform as water, Kristensen said.
“If we picture these jets as giant hoses and the water droplets as bullets, the amount shooting out equals a hundred million times the water flowing through the Amazon River every second. We are talking about velocities reaching 200,000 kilometers (124,000 miles) per hour, which is about 80 times faster than bullets flying out of a machine gun.”
Lars Kristensen
postdoctoral astronomer, Leiden University, Netherlands
Stellar Sprinkler Nourishes Galactic “Garden”
What’s really exciting about the discovery is that it appears to be a stellar rite of passage, the researchers say, which may shed new light on the earliest stages of our own sun’s life—and how water fits into that picture.
“We are only now beginning to understand that sunlike stars probably all undergo a very energetic phase when they are young,” Kristensen said. “It’s at this point in their lives when they spew out a lot of high-velocity material—part of which we now know is water.”
Like a celestial sprinkler system, the star may be enriching the interstellar medium—thin gases that float in the voids between stars. And because the hydrogen and oxygen in water are key components of the dusty disks in which stars form, such protostar sprinklers may be encouraging the growth of further stars, the study says.
The water-jet phenomenon seen in Perseus is “probably a short-lived phase all protostars go through,” Kristensen said. “But if we have enough of these sprinklers going off throughout the galaxy—this starts to become interesting on many levels.”
SPOT ON!
Uranus Has a Bright New Spot
Picture Shows
Uranus’s cool turquoise exterior appears tranquil and serene, but astronomers have spotted a new stormy spot.
In a surprise to astronomers, Uranus recently presented onlookers with a new spot on its northern hemisphere.
Stormy Weather
Near-infrared pictures from the 8.1-meter Gemini North telescope in Hawaii have revealed a region on the giant planet that’s much brighter than its surroundings. The spot is likely a tall methane cloud that reaches high enough for us to see sunlight scattered by its icy particles, said Uranus expert Heidi Hammel, executive vice president of the Association of Universities for Research in Astronomy (AURA).
The Uranian cloud is probably similar to an anvil
cloud, the type of towering cumulonimbus cloud that’s associated with severe thunderstorms on Earth. The cloud is also at a lower latitude on Uranus than any that have been observed before. That could mean the spot is a storm that has migrated south.
TRUTH:
THE NORTH POLE OF URANUS GETS NO SUNLIGHT FOR ABOUT 42 YEARS AT A TIME.
A Hubble picture of Uranus in 2005, shortly before the planet’s equinox (Photo Credit 7.7)
Seeing Spots
Hammel first saw bright spots on Uranus a few years before the planet’s spring equinox in 2007. She was turned on to the spots’ presence thanks to a photo of Uranus in another researcher’s presentation on the ice giant’s moons. “I said, ‘Wow, what’s this?’ And he said, ‘I don’t know, it’s just the way Uranus looks.’ I said, ‘No it’s not!’ ”
Subsequent observations made with the Hubble Space Telescope and ground-based telescopes revealed that the spots were most likely storms, similar to Jupiter’s Great Red Spot. Storms are unusual on Uranus because the planet has very little large-scale atmospheric circulation—movements that are driven mostly by temperature differences.
That’s because, unlike the other seven planets in our solar system, Uranus’s axis of rotation is tilted on its side. In addition, at an average of 1.7 billion miles (2.8 billion kilometers) from the sun, the planet completes an orbit every 84 years.