Solar Photosphere: Hot explosions on the cool sun

Sizzling star: Hot explosions in an active region of the Sun. 

In this image of the photosphere that was obtained at the end of September 2013 with the help of IRIS, the explosions are the bright spots. 

The image shows a sector with a size of 50,000 kilometers by 25 000 kilometers. 

Credit: NASA

The Sun is more spirited than previously thought. Apart from the solar eruptions, huge bursts of particles and radiation from the outer atmosphere of our star, also the cooler layer right below can be the site of explosions: in some areas magnetic energy builds up and discharges within only a few minutes in temperature eruptions of up to 100000 degrees.

Researchers under the lead of the Max Planck Institute for Solar System Research have now for the first time found evidence of such short-lived heat pockets in data from NASA's space telescope IRIS (Interface Region Imaging Spectrograph).

The Sun is an incredibly hot place, but even though in all its layers the temperatures are daunting, some are hotter than others.

With a temperature of approximately 5000 degrees, the Sun's visible surface, the photosphere, for example, is comparatively cool.

Going outward from there, the temperatures within the Sun's atmosphere rise, first moderately and then sharply, until they reach one million degrees.

"Our analysis shows, that this temperature distribution is not the same everywhere, and is constantly in motion", says Prof. Dr. Hardi Peter from the MPS, the paper's first author.

Together with an international team of scientists, Peter analyzed data from the space telescope IRIS taken from active regions on the Sun.

These regions within the photosphere are characterized by high magnetic field strengths and are the "birth places" of the dark sunspots, which cover the Sun's surface, at some times more, at others less abundantly.

"In these regions we found heat pockets as big as half of Germany. They are up to 20 times as hot as their surroundings", the astrophysicist describes. The heat pockets flash up for only minutes and then return to their normal state.

The amount of energy released during these explosions would be sufficient to provide all of Germany with electrical power for 8000 years.

The massive photospheric explosions cannot be spotted in visible light, but leave traces in the ultraviolet radiation the Sun emits into space.

IRIS can split this ultraviolet radiation into its constituting wavelengths more precisely than any other solar observatory before. In addition, it offers an unprecedented spatial resolution.

When IRIS opened its eyes to the Sun for the first time in July of last year, it could discern structures with a size of only 250 kilometers and examine radiation from such small regions separately.

"To our great surprise, we found well-defined areas within the active regions emitting radiation quite unlike the radiation from their vicinity", says Peter.

The researchers discovered characteristic wavelengths that special highly ionized atoms within the solar plasma such as triply ionized silicon ions emit into space.

"The presence of these wavelengths within the spectra points to very high temperatures", says Peter.

Only under such conditions can silicon loose three of its electrons, but in which of the Sun's layers did this temperature arise? Truly within the cool photosphere? Or maybe, and this would be much less spectacular, farther outside in the much hotter atmosphere?

The spectral data from IRIS proved to be so detailed that the researchers could extract further decisive clues.

For example, they were able to infer the density of the solar plasma where the radiation originated. In addition, they showed that the radiation had encountered singly-ionized iron ions on its way outward. These ions occur only in cooler regions.

"All in all, we found a coherent picture: the unusual radiation must originate in the cool outer photosphere" says Peter.

The researchers believe that the strong magnetic fields in the photosphere provide the necessary energy for the explosions.

In the area of the sun spots, the magnetic field lines protrude in a loop-like fashion from the Sun's surface; hot plasma flows there. When these flows are short-circuited, the explosions occur.

"The new results have fundamentally changed our understanding of the Sun's outer buildup", says Peter. "Instead of a stable temperature distribution, there are apparently dynamical processes within the cool photosphere that can turn everything topsy turvy."

Already in 1917, the American physicist Ferdinand Ellermann discovered areas with higher temperatures within the photosphere.

However, they differed from their surroundings only by a few thousand degrees and can therefore be considered rather minor temperature deviations. Whether the newly discovered explosions are linked to this phenomenon, is still unclear.

One of the other publications in Science magazine, to which scientists from the MPS have contributed, also paints a new picture of the processes on the Sun.

Researchers under the lead of the Harvard-Smithsonian Center for Astrophysics found that the solar wind, the continuous stream of particles from the Sun, does not leave the Sun's surface uniformly, but locally in highly energetic jets. These observations, too, are based on data from IRIS.

More information: 
H. Peter et al. "Hot Explosions in the Cool Atmosphere of the Sun." Science, 17 October 2014 - DOI: 10.1126/science.1255726

H. Tian et al. "Prevalence of Small-scale Jets from the Networks of the Solar Transition Region and Chromosphere." Science, 17 October 2014 - DOI: 10.1126/science.1255732

Betelgeuse: Mysterious hot spots observed in a cool red supergiant

Comparison between the red supergiant Antares and the Sun, shown as the tiny dot toward the upper right. 

The black circle is the size of the orbit of Mars. 

Arcturus is also included in the picture for size comparison. 

Credit: Wikipedia.

Astronomers have released a new image of the outer atmosphere of Betelgeuse – one of the nearest red supergiants to Earth – revealing the detailed structure of the matter being thrown off the star.

The new image, taken by the e-MERLIN radio telescope array operated from the Jodrell Bank Observatory in Cheshire, also shows regions of surprisingly hot gas in the star's outer atmosphere and a cooler arc of gas weighing almost as much as the Earth.

Betelgeuse is easily visible to the unaided eye as the bright, red star on the shoulder of Orion the Hunter.

The star itself is huge – 1,000 times larger than our Sun – but at a distance of about 650 light years it still appears as a tiny dot in the sky, so special techniques combining telescopes in arrays are required to see details of the star and the region around it.

The new e-MERLIN image of Betelgeuse – published in the journal Monthly Notices of the Royal Astronomical Society, shows its atmosphere extends out to five times the size of the visual surface of the star.

It reveals two hot spots within the outer atmosphere and a faint arc of cool gas even farther out beyond the radio surface of the star.

The hot spots are separated by roughly half the visual diameter of the star and have a temperature of about 4,000-5,000 Kelvin, much higher than the average temperature of the radio surface of the star (about 1,200 Kelvin) and even higher than the visual surface (3,600 Kelvin).

The arc of cool gas lies almost 7.4 billion kilometres away from the star – about the same distance as the farthest Pluto gets from the Sun. It is estimated to have a mass almost two thirds that of the Earth and a temperature of about 150 Kelvin.

Dr Anita Richards

Lead author Dr Anita Richards, from The University of Manchester, said that it was not yet clear why the hot spots are so hot.

She said: "One possibility is that shock waves, caused either by the star pulsating or by convection in its outer layers, are compressing and heating the gas. Another is that the outer atmosphere is patchy and we are seeing through to hotter regions within. The arc of cool gas is thought to be the result of a period of increased mass loss from the star at some point in the last century but its relationship to structures like the hot spots, which lie much closer in, within the star's outer atmosphere, is unknown."

The mechanism by which supergiant stars like Betelgeuse lose matter into space is not well understood despite its key role in the lifecycle of matter, enriching the interstellar material from which future stars and planets will form.

Detailed high-resolution studies of the regions around massive stars like the ones presented here are essential to improving our understanding.

Dr Richards, who is based in Manchester's School of Physics and Astronomy, added: "Betelgeuse produces a wind equivalent to losing the mass of the Earth every three years, enriched with the chemicals that will go into the next generation of star and planet formation. The full detail of how these cool, evolved stars launch their winds is one of the remaining big questions in stellar astronomy."

"This is the first direct image showing hot spots so far from the centre of the star. We are continuing radio and microwave observations to help decide which mechanisms are most important in driving the stellar wind and producing these hot spots. This won't just tell us how the elements that form the building blocks of life are being returned to space, it will also help determine how long it is before Betelgeuse explodes as a supernova."

Future observations planned with e-MERLIN and other arrays, including ALMA and VLA, will test whether the hotspots vary in concert due to pulsation, or show more complex variability due to convection. If it is possible to measure a rotation speed this will identify in which layer of the star they originate.

More information: 'e-MERLIN resolves Betelgeuse at wavelength 5 cm: hotspots at 5R*,' Monthly Notices of the Royal Astronomical Society, 2013.

Voyager Instrument Cooling Rapidly: Heater Turned off

To decisively reduce power consumption, mission managers have turned off a heater on part of NASA's Voyager 1 spacecraft, dropping the temperature of its ultraviolet spectrometer instrument more than 23 degrees Celsius (41 degrees Fahrenheit).

It is now operating at a temperature below minus 79 degrees Celsius (minus 110 degrees Fahrenheit), the coldest temperature that the instrument has ever endured.

This heater shut-off is a step in the careful management of the diminishing electrical power so that the Voyager spacecraft can continue to collect and transmit data through 2025.

At the moment, the spectrometer continues to collect and return data.

It was originally designed to operate at temperatures as low as minus 35 degrees Celsius (minus 31 degrees Fahrenheit), but it has continued to operate in ever chillier temperatures as heaters around it have been turned off over the last 17 years.

It was not known if the spectrometer would continue working, but since 2005, it has been operating at minus 56 degrees Celsius (69 degrees Fahrenheit.) So engineers are encouraged that the instrument has continued to operate, even after the nearby heater was turned off in December.

(The spectrometer is likely operating at a temperature somewhat lower than minus 79 degrees Celsius, or minus 110 degrees Fahrenheit, but the temperature detector does not go any lower.)

Scientists and mission managers will continue to monitor the spectrometer's performance.

It was very active during Voyager 1's encounters with Jupiter and Saturn, and since then an international team led by scientists in France has been analyzing the spectrometer's data.

This latest heater shut-off was actually part of the nearby infrared spectrometer, which itself has not been operational on Voyager 1 since 1998.

NASA Spitzer Image: Coolest of Companions

These two infrared images were taken by NASA's Spitzer Space Telescope in 2004 and 2009. 

They show a faint object moving through space together with a dead star called a white dwarf. 

The object, thought to be a "failed" star, or brown dwarf, is the coldest stellar companion to be directly imaged outside our solar system. Credit: NASA/JPL-Caltech/Penn State

NASA's Spitzer Space Telescope has captured a picture of a nearby star and its orbiting companion -- whose temperature is like a hot summer day in Arizona.

"We have discovered a new record-holder for the coldest companion imaged outside of the solar system, which is nearly as cold as Earth," said Kevin Luhman, an astronomer at The Pennsylvania State University, University Park, and lead author of a pair of papers on the findings in The Astrophysical Journal. "We believe the object is a brown dwarf, but it could be a gas-giant planet as well."

Based on the infrared light that it emits, the cool object, named WD 0806-661 B, appears to have a temperature in the range of 80 and 160 degrees Fahrenheit (about 27 to 70 degrees Celsius).

On the lower end, WD 0806-661 B offers a rather pleasant terrestrial temperature and is not even as warm as the human body.

Researchers ballpark WD 0806-661 B's mass between six and nine Jupiters, which means it could still qualify as a planet, albeit a particularly hefty one made mostly of gas. Instead, they suspect it's a type of failed star, called a brown dwarf.

WD 0806-661 B probably belongs to a recently discovered new class of objects called Y dwarfs, the coldest category of brown dwarfs.

Astronomers using NASA's Wide-field Infrared Survey Explorer (WISE) announced the unveiling of the first six Y dwarfs in August.

Those objects do not orbit stars and instead are floating by themselves in space, unlike WD 0806-661 B.

Together, WISE and Spitzer are proving complementary in tracking down ever-cooler brown dwarfs, all the way down to the Y class.

ESA Proba-2: Ffuel tank refilled from ‘solid gas’

Proba-2 is flight-testing a total of 17 technology demonstrators for future ESA missions. 

It also serves as a scientific platform for solar and space weather observations.

Credits: ESA/Pierre Carril

Sometimes all it takes is fresh air to get a new lease of life. ESA’s Proba-2 microsatellite is a good example: an influx of nitrogen has replenished its fuel tank, in the process demonstrating a whole new space technology.

On 16 August a telecommand was sent from ESA’s Redu ground station in Belgium to boost the gases in Proba-2’s unusual ‘resistojet’ engine.

Used to maintain the microsatellite’s orbit at 600 km altitude, this experimental engine runs on xenon gas heated before ejection to provide added thrust.

The command added nitrogen gas to the fuel tank, bringing its pressure close to its launch level.

	cool-gas generators

“What makes this repressurisation unique is that the added gas was not stored in a pressurised state but produced from a solid material at room temperature, the first of four ‘cool-gas generators’ on Proba-2,” explained Laurens van Vliet of Dutch research organisation TNO, which developed the technology.

“Nitrogen, like xenon, is an inert, non-reactive gas, so the resistojet can work just as well with a xenon–nitrogen mixture.”

The bottle-shaped cool-gas generators are filled with a rigid solid material that, once triggered, produces more than 250 times its own volume in pure nitrogen gas.

Integrating TNO's four cool-gas generators aboard Proba-2

Credits: TNO

To read more on this subject visit the ESA Proba-2 portal

NASA: Thermal control and Electronic Cooling pump

The more advanced the electronics, the more power they use. The more power they use, the hotter they get.

The hotter they get, the more likely they’ll overheat. It doesn’t take a rocket scientist to understand what typically happens next: The electronics fry.

In the world of electronics, thermal control is always one of the limiting factors -- particularly in space where there is no air to help cool down electronic components.

However, Jeffrey Didion, a thermal engineer at the NASA Goddard Space Flight Center in Greenbelt, Md., and Dr. Jamal Seyed-Yagoobi, a professor at the Illinois Institute of Technology in Chicago, Ill., have collaborated to develop a technology that may overcome current limitations. They have formed technical partnerships with the U.S. Air Force and National Renewable Energy Laboratory to address the thermal-control concerns.

Called electrohydrodynamic (EHD)-based thermal control, the technology promises to make it easier and more efficient to remove heat from small spaces -- a particular challenge for engineers building advanced space instruments and microprocessors that could fail if the heat they generate is not removed.

"Today, higher-power computer chips are available, but they generate too much heat," said Didion, who is leading the technology-development effort also involving Matthew Showalter, associate branch chief of Goddard’s Advanced Manufacturing Branch, and Mario Martins of Edge Space Systems, an engineering company specializing in thermal systems in Glenelg, Md. "If I can carry away more heat, engineers will be able to use higher-power components. In other words, they will be able to do more things."

The project, a joint activity between NASA Goddard and its partners, received support from the Goddard Internal Research and Development (IRAD) program, which funds the development of promising new technologies that could advance NASA’s scientific and exploration goals. It is being demonstrated in June on a Terrier-Improved Orion sounding rocket mission, which also is flying the Small Rocket/Spacecraft Technology (SMART) platform, a microsatellite also developed at Goddard. This new microsatellite measures about 16 inches in diameter and was specifically designed to give scientific users less expensive access to space. (Read the related press release.)

Boiling Bubbles AIds Cooling In Space

It may seem illogical, but boiling is a very efficient way to cool engineering components and systems used in the extreme environments of space.

An experiment to gain a basic understanding of this phenomena launched to the International Space Station on space shuttle Discovery Feb. 24.

The Nucleate Pool Boiling Experiment, or NPBX, is one of two experiments in the new Boiling eXperiment Facility, or BXF.

Nucleate boiling is bubble growth from a heated surface and the subsequent detachment of the bubble to a cooler surrounding liquid. As a result, these bubbles can efficiently transfer energy from the boiling surface into the surrounding fluid.

This investigation provides an understanding of heat transfer and vapor removal processes that happen during nucleate boiling in microgravity. Researchers will glean information to better design and operate space systems that use boiling for efficient heat removal.

Bubbles in microgravity grow to different sizes than on Earth. This experiment will focus on the dynamics of single and multiple bubbles and the associated heat transfer.

NPBX uses a polished aluminum wafer, powered by heaters bonded to its backside, and five fabricated cavities that can be controlled individually. The experiment will study single and/or multiple bubbles generated at these cavities.

It will measure the power supplied to each heater group, and cameras will record the bubble dynamics. Analysis of the heater power data and recorded images will allow investigators to determine how bubble dynamics and heat transfer differ in microgravity.

"With boiling, the size and weight of heat exchange equipment used in space systems can be significantly reduced," said Vijay Dhir, the experiment's principal investigator at the University of California, Los Angeles.

"Boiling and multiphase heat transfer is an enabling technology for space exploration missions including storage and handling of cryogenic, or extremely low temperature liquids, life support systems, power generation and thermal management."

"The cost of transporting equipment to space depends on the size and weight of the equipment," added David Chao, the project scientist from NASA's Glenn Research Center in Cleveland. "The knowledge base that will be developed through the experiment will give us the capability to achieve cooling of various components and systems used in space in an efficient manner and could lead to smaller and lighter spacecraft."

NASA, ESA Cassini Fly-by: Titan's Cool and Sluggish Interior

This artist's illustration shows the likely interior structure of Saturn's moon Titan deduced from gravity field data collected by NASA's Cassini spacecraft.

The investigation by Cassini's radio science team suggests that Titan's interior is a cool mix of ice studded with rock, though the outermost 500 kilometers (300 miles) appear to be ice essentially devoid of any rock.

Many planets and moons, including the Earth, evolve into a body with a clearly distinct rocky core. This radio science investigation suggests Titan's interior, cool and sluggish, failed to allow the interior to separate into completely differentiated layers of ice and rock.

In addition to the hazy surface of Titan (yellow), the layers in the cutaway show an ice layer starting near the surface (light gray), an internal ocean hypothesized from other Cassini data (blue), another layer of ice (light gray) and the mix of rock and ice in the interior (dark gray). In the background are the Cassini spacecraft and Saturn, not to scale.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of Caltech, manages the project for NASA's Science Mission Directorate in Washington.

The Cassini orbiter was designed, developed and assembled at JPL. Cassini's radio science subsystem has been jointly developed by NASA and the Italian Space Agency.

For more information about the Cassini-Huygens mission visit http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov/.

Image credit: NASA/JPL