Astronomers find solar storms behave like supernovae

 

Researchers have studied the behaviour of the Sun's coronal mass ejections, explaining for the first time the details of how these huge eruptions behave as they fall back onto the Sun's surface. In the process, they have discovered that coronal mass ejections have a surprising twin in the depths of space: the tendrils of gas in the Crab Nebula, which lie 6500 light-years away and are millions of times larger.

Researchers at UCL have studied the behaviour of the Sun's coronal mass ejections, explaining for the first time the details of how these huge eruptions behave as they fall back onto the Sun's surface. In the process, they have discovered that coronal mass ejections have a surprising twin in the depths of space: the tendrils of gas in the Crab Nebula, which lie 6500 light-years away and are millions of times larger.

On 7 June 2011, the biggest ejection of material ever observed erupted from the surface of the Sun. Over the days that followed, the plasma belched out by the Sun made its way out into space. But most of the material propelled up from the Sun's surface quickly fell back towards our star's surface.

For the solar physicists at UCL's Mullard Space Science Laboratory, watching these solar fireworks was a unique opportunity to study how solar plasma behaves.

"We've known for a long time that the Sun has a magnetic field, like the Earth does. But in places it's far too weak for us to measure, unless we have something falling through it. The blobs of plasma that rained down from this beautiful explosion were the gift we'd been waiting for," says David Williams, one of the study's authors.

Since 2010, the NASA Solar Dynamics Observatory (SDO) has been constantly photographing the surface of the Sun. To our eyes, our star seems almost unchanging, with occasional fleeting sunspots the only changes that can be seen without special apparatus. But the SDO's instruments can cut through the dazzling brightness, magnify the detail and see wavelengths of light which are blocked by the Earth's atmosphere. This combination of high-quality imaging and constant monitoring means that scientists can now see the detail of how the Sun's dynamic surface changes over time.

The 7 June 2011 eruption was by some margin the biggest recorded since this constant monitoring began, meaning the huge cascade of matter that fell back into the Sun following the eruption was a unique opportunity to study, on an unusually large scale, the fluid dynamics of these phenomena.

"We noticed that the shape of the plume of plasma was quite particular," says Jack Carlyle, lead author of the study. "As it fell into the Sun, it repeatedly split apart like drops of ink falling through water, with fingers of material branching out. It didn't stick together. It's a great example of an effect where light and heavy fluids mix."

Less dense materials typically float on top of denser ones without mixing together, for example oil sitting on water, or layers of different liqueurs in a cocktail. Change the order by putting the denser fluid on top, however, and the denser one will quickly fall through the less-dense one until their positions are reversed.

 The complex pattern formed by the denser fluid as it repeatedly splits and branches into ever-finer 'fingers' of matter, is caused by a phenomenon known as the Rayleigh-Taylor instability.

The team noticed in SDO's high-resolution images that the falling plasma clearly underwent the Rayleigh-Taylor instability as it returned to the Sun's surface. This is as would be expected -- the solar plasma is denser than the solar atmosphere it is falling through. In space, a similar effect has been observed before, albeit on a much larger scale, in the Crab Nebula.

 The Crab Nebula is the remnant of a supernova which exploded in the 10th century. In the millennium that has followed the explosion, denser matter has started to fall back into the centre of the nebula, exhibiting the same finger-like structures as the team observed in the Sun.

A major study of the Crab Nebula in 1996 found that the Rayleigh-Taylor instability in the Crab Nebula was actually slightly modified. The highly magnetised environment in the nebula changes the proportions of the fingers, making them fatter than they would be otherwise.

The UCL team found that the same effect was going on in the 7 June 2011 coronal mass ejection: even in an area where the Sun's magnetic field was weak, it was modifying the Rayleigh-Taylor effect, changing the shape of the plume of plasma as it fell back into the Sun.This is the most spectacular example of the effect ever observed on the Sun.

Kepler finds a very wobbly planet: Rapid and erratic changes in seasons

Kepler finds a very wobbly planet: Rapid and erratic changes in seasons

Imagine living on a planet with seasons so erratic you would hardly know whether to wear Bermuda shorts or a heavy overcoat. That is the situation on a weird, wobbly world found by NASA's planet-hunting Kepler space telescope.

Imagine living on a planet with seasons so erratic you would hardly know whether to wear Bermuda shorts or a heavy overcoat. That is the situation on a weird, wobbly world found by NASA's planet-hunting Kepler space telescope.

The planet, designated Kepler-413b, precesses, or wobbles, wildly on its spin axis, much like a child's top. The tilt of the planet's spin axis can vary by as much as 30 degrees over 11 years, leading to rapid and erratic changes in seasons. In contrast, Earth's rotational precession is 23.5 degrees over 26,000 years. Researchers are amazed that this far-off planet is precessing on a human timescale.

Kepler 413-b is located 2,300 light-years away in the constellation Cygnus. It circles a close pair of orange and red dwarf stars every 66 days. The planet's orbit around the binary stars appears to wobble, too, because the plane of its orbit is tilted 2.5 degrees with respect to the plane of the star pair's orbit. As seen from Earth, the wobbling orbit moves up and down continuously.

Kepler finds planets by noticing the dimming of a star or stars when a planet transits, or travels in front of them. Normally, planets transit like clockwork. Astronomers using Kepler discovered the wobbling when they found an unusual pattern of transiting for Kepler-413b.

"Looking at the Kepler data over the course of 1,500 days, we saw three transits in the first 180 days -- one transit every 66 days -- then we had 800 days with no transits at all. After that, we saw five more transits in a row," said Veselin Kostov, the principal investigator on the observation. Kostov is affiliated with the Space Telescope Science Institute and Johns Hopkins University in Baltimore, Md. The next transit visible from Earth's point of view is not predicted to occur until 2020. This is because the orbit moves up and down, a result of the wobbling, in such a great degree that it sometimes does not transit the stars as viewed from Earth.

Astronomers are still trying to explain why this planet is out of alignment with its stars. There could be other planetary bodies in the system that tilted the orbit. Or, it could be that a third star nearby that is a visual companion may actually be gravitationally bound to the system and exerting an influence.

"Presumably there are planets out there like this one that we're not seeing because we're in the unfavorable period," said Peter McCullough, a team member with the Space Telescope Science Institute and Johns Hopkins University. "And that's one of the things that Veselin is researching: Is there a silent majority of things that we're not seeing?"

Even with its changing seasons, Kepler-413b is too warm for life as we know it. Because it orbits so close to the stars, its temperatures are too high for liquid water to exist, making it inhabitable. It also is a super Neptune -- a giant gas planet with a mass about 65 times that of Earth -- so there is no surface on which to stand.

Ames is responsible for the Kepler mission concept, ground system development, mission operations and science data analysis. NASA's Jet Propulsion Laboratory in Pasadena, Calif., managed Kepler mission development. Ball Aerospace & Technologies Corp. in Boulder, Colo., developed the Kepler flight system and supports mission operations with the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder. The Space Telescope Science Institute in Baltimore archives, hosts and distributes Kepler science data. Kepler is NASA's 10th Discovery mission and was funded by the agency's Science Mission Directorate.

Your memory is no video camera: It edits the past with present experiences

Your memory is a wily time traveller, plucking fragments of the present and inserting them into the past, reports a new study. In terms of accuracy, it's no video camera. Rather, memory rewrites the past with current information, updating your recollections with new experiences to aid survival. Love at first sight, for example, is more likely a trick of your memory than a Hollywood-worthy moment.

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Your memory is a wily time traveller, plucking fragments of the present and inserting them into the past, reports a new North western Medicine® study. In terms of accuracy, it's no video camera.

Rather, the memory rewrites the past with current information, updating your recollections with new experiences.

Love at first sight, for example, is more likely a trick of your memory than a Hollywood-worthy moment."When you think back to when you met your current partner, you may recall this feeling of love and euphoria," said lead author Donna Jo Bridge, a post doctoral fellow in medical social sciences at North western University Feinberg School of Medicine. "But you may be projecting your current feelings back to the original encounter with this person."

This the first study to show specifically how memory is faulty, and how it can insert things from the present into memories of the past when those memories are retrieved. The study shows the exact point in time when that incorrectly recalled information gets implanted into an existing memory.

To help us survive, Bridge said, our memories adapt to an ever-changing environment and help us deal with what's important now.

"Our memory is not like a video camera," Bridge said. "Your memory re frames and edits events to create a story to fit your current world. It's built to be current."

All that editing happens in the hippo campus, the new study found. The hippo campus, in this function, is the memory's equivalent of a film editor and special effects team.

For the experiment, 17 men and women studied 168 object locations on a computer screen with varied backgrounds such as an underwater ocean scene or an aerial view of Midwest farmland. Next, researchers asked participants to try to place the object in the original location but on a new background screen. Participants would always place the objects in an incorrect location.

For the final part of the study, participants were shown the object in three locations on the original screen and asked to choose the correct location. Their choices were: the location they originally saw the object, the location they placed it in part 2 or a brand new location.

"People always chose the location they picked in part 2," Bridge said. "This shows their original memory of the location has changed to reflect the location they recalled on the new background screen. Their memory has updated the information by inserting the new information into the old memory."

Participants took the test in an MRI scanner so scientists could observe their brain activity. Scientists also tracked participants' eye movements, which sometimes were more revealing about the content of their memories -- and if there was conflict in their choices -- than the actual location they ended up choosing.

The notion of a perfect memory is a myth, said Joel Voss, senior author of the paper and an assistant professor of medical social sciences and of neurology at Feinberg.

"Everyone likes to think of memory as this thing that lets us vividly remember our childhoods or what we did last week," Voss said. "But memory is designed to help us make good decisions in the moment and, therefore, memory has to stay up-to-date. The information that is relevant right now can overwrite what was there to begin with."

Bridge noted the study's implications for eyewitness court testimony. "Our memory is built to change, not regurgitate facts, so we are not very reliable witnesses," she said.

A caveat of the research is that it was done in a controlled experimental setting and shows how memories changed within the experiment. "Although this occurred in a laboratory setting, it's reasonable to think the memory behaves like this in the real world," Bridge said.

Nature can, selectively, buffer human-caused global warming, say scientists

Nature can, selectively, buffer human-caused global warming, say scientists

Can naturally occurring processes selectively buffer the full brunt of global warming caused by greenhouse gas emissions resulting from human activities? Yes, says a group of researchers in a new study.

Can naturally occurring processes selectively buffer the full brunt of global warming caused by greenhouse gas emissions resulting from human activities?

Yes, find researchers from the Hebrew University of Jerusalem, Johns Hopkins University in the US and NASA's Goddard Space Flight Centre.

As the globe warms, ocean temperatures rise, leading to increased water vapour escaping into the atmosphere. Water vapour is the most important greenhouse gas, and its impact on climate is amplified in the stratosphere.

In a detailed study, the researchers from the three institutions examined the causes of changes in the temperatures and water vapour in the tropical troposphere layer (TTL). The TTL is a critical region of our atmosphere with characteristics of both the troposphere below and the stratosphere above.

The TTL can have significant influences on both atmospheric chemistry and climate, as its temperature determines how much water vapour can enter the stratosphere. Therefore, understanding any changes in the temperature of the TTL and what might be causing them is an important scientific question of significant societal relevance, say the researchers.

The Israeli and US scientists used measurements from satellite observations and output from chemistry-climate models to understand recent temperature trends in the TTL. Temperature measurements show where significant changes have taken place since 1979.

The satellite observations have shown that warming of the tropical Indian Ocean and tropical Western Pacific Ocean -- with resulting increased precipitation and water vapour there -- causes the opposite effect of cooling in the TTL region above the warming sea surface. Once the TTL cools, less water vapor is present in the TTL and also above in the stratosphere.

Since water vapor is a very strong greenhouse gas, this effect leads to a negative feedback on climate change. That is, the increase in water vapour due to enhanced evaporation from the warming oceans is confined to the near- surface area, while the stratosphere becomes drier. Hence, this effect may actually slightly weaken the more dire forecaster aspects of an increasing warming of our climate, the scientists say.

The researchers are Dr. Chaim Garfinkel of the Fredy and Nadine Herrmann Institute of Earth Sciences at the Hebrew University and formerly of Johns Hopkins University, Dr. D. W. Waugh and Dr. L. Wang of Johns Hopkins, and Dr. L. D. Oman and Dr. M. M. Hurwitz of the Goddard Space Flight Centre. Their findings have been published in the Journal of Geophysical Research: Atmosphere, and the research was also highlighted in Nature Climate Change.

Making color: When two red photons make a blue photon

Making color: When two red photons make a blue photon

Can scientists generate any color of light? The answer is not really, but the invention of the laser in 1960 opened new doors for this endeavor. Scientists have now demonstrated a new semiconductor microstructure that performs frequency conversion. This design is a factor of 1000 smaller than previous devices.

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Color is strange, mainly due to perception. Setting aside complex brain processes, what we see is the result of light absorption, emission, and reflection. Trees appear green because atoms inside the leaves are emitting and/or reflecting green photons. Semiconductor LED brake lights emit single color light when electrical current passes through the devices.

Here's a question: Can scientists generate any color of light? The answer is not really, but the invention of the laser in 1960 opened new doors for this endeavor. An early experiment injected high-power laser light through quartz and out popped a different color. This sparked the field of nonlinear optics and with it, a new method of color generation became possible: frequency conversion.

Not all crystals can perform this trick and only through careful fabrication of certain materials is frequency conversion possible. In a result published in Nature Communications, scientists demonstrate a new microstructure that does what's called second harmonic generation (SHG), where the output light has twice the frequency as the input. This new device is a factor of 1000 smaller than previous frequency converters.

You can't really get something from nothing here. Physics demands that both energy and momentum are conserved in the frequency-doubling process. The energy of light is directly related to its frequency through a fundamental constant, thus this conservation law is automatically satisfied. Two photons of fixed energy pass into the conversion crystal and the output photon has a frequency, thus energy, equal to their sum.

The challenging part is momentum conservation and achieving it takes careful engineering. This difficulty arises because light has an associated direction of travel. Materials bend and delay light, and how it occurs is very material dependent. Even more, different frequencies (colors) are bent and delayed differently by a given material. This is called dispersion and is perhaps most familiar as a rainbow, where the constituent colors of sunlight are separated.

Even with dispersion, some materials have naturally occurring refractive properties that allow momentum-matching, and thus frequency conversion. Until about 20 years ago, these materials were the only option for frequency conversion. In the 1990s, scientists began to tackle the momentum conservation issue using a technique called quasi-phase matching (QPM).

When a light wave enters and moves through a crystal its properties such as velocity are altered depending on its color. In the case of second-harmonic generation, the injection light strongly interacts with the medium and a second color, having twice the frequency, is generated. Due to dispersion, the second light wave will be delayed. In QPM, scientists vary the spacing and orientation between the internal crystal layers to compensate for the delay, such that momentum conservation between the injection and output light is conserved. This method of QPM is successful but can be difficult from a fabrication point-of-view. Moreover, miniaturizing their overall size for integration onto chips is limited. This is because the frequency conversion process depends on the physical length of the interaction medium, thus scaling down these types of crystals will lead to an inherent reduction in efficiency.

Now this team has demonstrated a new, arguably simpler way, to achieve QPM and thus frequency conversion. In the new design, gallium arsenide (GaAs) is fabricated into a micrometer-sized disk 'whispering gallery' cavity. Notably, GaAs has one of the largest second-harmonic frequency conversion constants measured. Previously, scientists have harnessed its extremely nonlinear properties through the layer-varying QPM method, leading to device sizes in the centimeter range. This new device is 1000 times smaller.

In the experiment, light from a tapered optical fiber is injected into the cavity. When light travels in a loop with the proper orientation, as opposed to a linear geometry, QPM, and therefore color conversion is achieved. This team skirts around the miniaturization problem because the light can interact many times with the medium by circulating around the disk, yet the overall size can remain small. Using a cavity also means that since the power builds up in the microdisk, less injection power can be used. Think of the architectural example of a whispering gallery -- wherein sound waves add together such that small input signals (whispers) can be heard. This resonant enhancement also happens for light trapped inside microdisk cavities.

NIST scientist and author Glenn Solomon continues, "Through a combination of microcavity engineering and nonlinear optics, we can create a very small frequency conversion device that could be more easily integrated onto optical chips."

Lead author Paulina Kuo, who is currently doing research at NIST in the Information Technology Laboratory,adds, "I am excited because this method for phase-matching is brand new. It is amazing that the crystal itself can provide the phase-matching to ensure momentum conservation, and it's promising to see efficient optical frequency conversion in a really tiny volume."

In terms of future quantum information applications, the simple harmonic generation process can be considered as parametric down conversion (PDC) in reverse. PDC is a method for generating entangled photon pairs and so this device could provide a new technique for accomplishing this.

Gallium arsenide (GaAs) is a common semiconductor and has added benefits such as transmitting and emitting in the infrared (IR) and near IR light, respectively. IR-colored light has applications that include telecommunications and chemical sensing. Kuo adds, "The presence of an absorbing species affects the cavity resonance conditions and, in turn, the amount of frequency conversion in the microdisk. Thus, this device could be used in novel sensing applications."