A favorite theme of science fiction is “the portal”–an extraordinary opening in space or time that connects travelers to distant realms. A good portal is a shortcut, a guide, a door into the unknown. If only they actually existed….
It turns out that they do, sort of, and a NASA-funded researcher at the University of Iowa has figured out how to find them.
“We call them X-points or electron diffusion regions,” explains plasma physicist Jack Scudder of the University of Iowa. “They’re places where the magnetic field of Earth connects to the magnetic field of the Sun, creating an uninterrupted path leading from our own planet to the sun’s atmosphere 93 million miles away.”
Observations by NASA’s THEMIS spacecraft and Europe’s Cluster probes suggest that these magnetic portals open and close dozens of times each day. They’re typically located a few tens of thousands of kilometers from Earth where the geomagnetic field meets the onrushing solar wind. Most portals are small and short-lived; others are yawning, vast, and sustained. Tons of energetic particles can flow through the openings, heating Earth’s upper atmosphere, sparking geomagnetic storms, and igniting bright polar auroras.
NASA is planning a mission called “MMS,” short for Magnetospheric Multiscale Mission, due to launch in 2014, to study the phenomenon. Bristling with energetic particle detectors and magnetic sensors, the four spacecraft of MMS will spread out in Earth’s magnetosphere and surround the portals to observe how they work.
Just one problem: Finding them. Magnetic portals are invisible, unstable, and elusive. They open and close without warning “and there are no signposts to guide us in,” notes Scudder.
Actually, there are signposts, and Scudder has found them.
Portals form via the process of magnetic reconnection. Mingling lines of magnetic force from the sun and Earth criss-cross and join to create the openings. “X-points” are where the criss-cross takes place. The sudden joining of magnetic fields can propel jets of charged particles from the X-point, creating an “electron diffusion region.”
To learn how to pinpoint these events, Scudder looked at data from a space probe that orbited Earth more than 10 years ago.
“In the late 1990s, NASA’s Polar spacecraft spent years in Earth’s magnetosphere,” explains Scudder, “and it encountered many X-points during its mission.”
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Data from NASA’s Polar spacecraft, circa 1998, provided crucial clues to finding magnetic X-points. Credit: NASA Because Polar carried sensors similar to those of MMS, Scudder decided to see how an X-point looked to Polar. “Using Polar data, we have found five simple combinations of magnetic field and energetic particle measurements that tell us when we’ve come across an X-point or an electron diffusion region. A single spacecraft, properly instrumented, can make these measurements.”
This means that single member of the MMS constellation using the diagnostics can find a portal and alert other members of the constellation. Mission planners long thought that MMS might have to spend a year or so learning to find portals before it could study them. Scudder’s work short cuts the process, allowing MMS to get to work without delay.
It’s a shortcut worthy of the best portals of fiction, only this time the portals are real. And with the new “signposts” we know how to find them.
Astronomers working with the United Kingdom Infrared Telescope on Hawaii have discovered four pairs of stars that orbit each other in less than 4 hours.
Until now it was thought that such close-in binary stars could not exist.
About half of the stars in our Milky Way galaxy are, unlike our Sun, part of a binary system in which two stars orbit each other. Most likely, the stars in these systems were formed close together and have been in orbit around each other from birth onwards. It was always thought that if binary stars form too close to each other, they would quickly merge into one single, bigger star. This was in line with many observations taken over the last three decades showing the abundant population of stellar binaries, but none with orbital periods shorter than 5 hours.
For the first time, the team has investigated binaries of red dwarfs, stars up to ten times smaller and a thousand times less luminous than the Sun. Although they form the most common type of star in the Milky Way, red dwarfs do not show up in normal surveys because of their dimness in visible light.
“To our complete surprise, we found several red dwarf binaries with orbital periods significantly shorter than the 5 hour cut-off found for Sun-like stars, something previously thought to be impossible”, said Dr Bas Nefs of Leiden Observatory in the Netherlands, lead author of a paper accepted for publication in the journal Monthly Notices of the Royal Astronomical Society. “It means that we have to rethink how these close-in binaries form and evolve.”
Since stars shrink in size early in their lifetime, the fact that these very tight binaries exist means that their orbits must also have shrunk as well since their birth, otherwise the stars would have been in contact early on and have merged. However, it is not at all clear how these orbits could have shrunk by so much.
One possible answer to this riddle is that cool stars in binary systems are much more active and violent than previously thought.
It is possible that the magnetic field lines radiating out from the cool star companions get twisted and deformed as they spiral in towards each other, generating the extra activity through stellar wind, explosive flaring and star spots. Powerful magnetic activity could apply the brakes to these spinning stars, slowing them down so that they move closer together.
“Without UKIRT’s superb sensitivity, it wouldn’t have been possible to find these extraordinary pairs of red dwarfs,” said co-author Dr David Pinfield of the University of Hertfordshire. “The active nature of these stars and their apparently powerful magnetic fields has profound implications for the environments around red dwarfs throughout our Galaxy.”
Bibliographic information: Nefs SV et al. 2012. Four ultra-short period eclipsing M-dwarf binaries in the WFCAM Transit Survey. Accepted for publication in Mon. Not. R. Astron. Soc.; arXiv:1206.1200v1
A mysterious wave discovered in the Milky Way suggests our galaxy is still ringing like a bell from a galactic collision, a crash that possibly occurred within the last 100 million years, scientists say. Astronomers discovered that stars north and south of the midplane of the galaxy are distributed differently, suggesting that some recent event perturbed them. The most likely explanation is that a small satellite galaxy or clump of invisible dark matter plowed through the Milky Way, leaving behind the echoes that we see.
“Our part of the Milky Way is ringing like a bell,” Brian Yanny, of the Fermi National Accelerator Laboratory (Fermilab) in Batavia, Ill., said in a statement. “But we have not been able to identify the celestial object that passed through the Milky Way. It could have been one of the small satellite galaxies that move around the center of our galaxy, or an invisible structure such as a dark matter halo.”
The wave was discovered in data from the Sloan Digital Sky Survey, which has observed roughly 300,000 nearby Milky Way stars.
“We have found evidence that our Milky Way had an encounter with a small galaxy or massive dark matter structure perhaps as recently as 100 million years ago,” said Larry Widrow, a professor at Queen’s University in Canada. “We clearly observe unexpected differences in the Milky Way’s stellar distribution above and below the Galaxy’s midplane that have the appearance of a vertical wave – something that nobody has seen before.”
About 60 miniature “dwarf galaxies” have been discovered orbiting the Milky Way. Theory suggests that many invisible dark matter satellites also circle our galaxy, though these would only be detectable by their gravitational pull.
It’s likely that one of these may have slammed into the Milky Way, though even that is not certain.
“The perturbation need not have been a single isolated event in the past, and it may even be ongoing,” said Susan Gardner of the University of Kentucky. “Additional observations may well clarify its origin.”
The research is detailed in a recent edition of the Astrophysical Journal Letters.