NASA's Swift Mission Observes Mega Flares from Mini Star
By Francis Reddy NASA's Goddard Space Flight Center, Greenbelt, Maryland September 30, 2014
On April 23, NASA's Swift satellite detected the strongest, hottest, and longest-lasting sequence of stellar flares ever seen from a nearby red dwarf star. The initial blast from this record-setting series of explosions was as much as 10,000 times more powerful than the largest solar flare ever recorded.
"We used to think major flaring episodes from red dwarfs lasted no more than a day, but Swift detected at least seven powerful eruptions over a period of about two weeks," said Stephen Drake, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, who gave a presentation on the "superflare" at the August meeting of the American Astronomical Society’s High Energy Astrophysics Division. "This was a very complex event."
At its peak, the flare reached temperatures of 360 million degrees Fahrenheit (200 million Celsius), more than 12 times hotter than the center of the sun.
The "superflare" came from one of the stars in a close binary system known as DG Canum Venaticorum, or DG CVn for short, located about 60 light-years away. Both stars are dim red dwarfs with masses and sizes about one-third of our sun's. They orbit each other at about three times Earth's average distance from the sun, which is too close for Swift to determine which star erupted.
"This system is poorly studied because it wasn't on our watch list of stars capable of producing large flares," said Rachel Osten, an astronomer at the Space Telescope Science Institute in Baltimore and a deputy project scientist for NASA's James Webb Space Telescope, now under construction. "We had no idea DG CVn had this in it."
Most of the stars lying within about 100 light-years of the solar system are, like the sun, middle-aged. But a thousand or so young red dwarfs born elsewhere drift through this region, and these stars give astronomers their best opportunity for detailed study of the high-energy activity that typically accompanies stellar youth. Astronomers estimate DG CVn was born about 30 million years ago, which makes it less than 0.7 percent the age of the solar system.
Stars erupt with flares for the same reason the sun does. Around active regions of the star's atmosphere, magnetic fields become twisted and distorted. Much like winding up a rubber band, these allow the fields to accumulate energy. Eventually a process called magnetic reconnection destabilizes the fields, resulting in the explosive release of the stored energy we see as a flare. The outburst emits radiation across the electromagnetic spectrum [ http://hesperia.gsfc.nasa.gov/sftheory/glossary.htm#ELECTROMAGNETIC_SPECTRUM ], from radio waves to visible, ultraviolet and X-ray light.
At 5:07 p.m. EDT on April 23, the rising tide of X-rays from DG CVn's superflare triggered Swift's Burst Alert Telescope (BAT). Within several seconds of detecting a strong burst of radiation, the BAT calculates an initial position, decides whether the activity merits investigation by other instruments and, if so, sends the position to the spacecraft. In this case, Swift turned to observe the source in greater detail, and, at the same time, notified astronomers around the globe that a powerful outburst was in progress.
"For about three minutes after the BAT trigger, the superflare's X-ray brightness was greater than the combined luminosity of both stars at all wavelengths under normal conditions," noted Goddard's Adam Kowalski, who is leading a detailed study on the event. "Flares this large from red dwarfs are exceedingly rare."
The star's brightness in visible and ultraviolet light, measured both by ground-based observatories and Swift's Optical/Ultraviolet Telescope, rose by 10 and 100 times, respectively. The initial flare's X-ray output, as measured by Swift's X-Ray Telescope, puts even the most intense solar activity recorded to shame.
DG CVn, a binary consisting of two red dwarf stars shown here in an artist's rendering, unleashed a series of powerful flares seen by NASA's Swift. At its peak, the initial flare was brighter in X-rays than the combined light from both stars at all wavelengths under typical conditions. Image Credit: NASA's Goddard Space Flight Center/S. Wiessinger
The largest solar explosions are classified as extraordinary, or X class, solar flares based on their X-ray emission. "The biggest flare we've ever seen from the sun occurred in November 2003 and is rated as X 45," explained Drake. "The flare on DG CVn, if viewed from a planet the same distance as Earth is from the sun, would have been roughly 10,000 times greater than this, with a rating of about X 100,000."
But it wasn't over yet. Three hours after the initial outburst, with X-rays on the downswing, the system exploded with another flare nearly as intense as the first. These first two explosions may be an example of "sympathetic" flaring often seen on the sun, where an outburst in one active region triggers a blast in another.
Over the next 11 days, Swift detected a series of successively weaker blasts. Osten compares the dwindling series of flares to the cascade of aftershocks following a major earthquake. All told, the star took a total of 20 days to settle back to its normal level of X-ray emission.
How can a star just a third the size of the sun produce such a giant eruption? The key factor is its rapid spin, a crucial ingredient for amplifying magnetic fields. The flaring star in DG CVn rotates in under a day, about 30 or more times faster than our sun. The sun also rotated much faster in its youth and may well have produced superflares of its own, but, fortunately for us, it no longer appears capable of doing so.
Astronomers are now analyzing data from the DG CVn flares to better understand the event in particular and young stars in general. They suspect the system likely unleashes numerous smaller but more frequent flares and plan to keep tabs on its future eruptions with the help of NASA's Swift.
On July 23, 2012, a massive cloud of solar material erupted off the sun's right side, zooming out into space. It soon passed one of NASA's Solar Terrestrial Relations Observatory, or STEREO, spacecraft, which clocked the CME as traveling between 1,800 and 2,200 miles per second as it left the sun. This was the fastest CME ever observed by STEREO.
Two other observatories – NASA's Solar Dynamics Observatory and the joint European Space Agency/NASA Solar and Heliospheric Observatory -- witnessed the eruption as well. The July 2012 CME didn't move toward Earth, but watching an unusually strong CME like this gives scientists an opportunity to observe how these events originate and travel through space.
STEREO's unique viewpoint from the sides of the sun combined with the other two observatories watching from closer to Earth helped scientists create models of the entire July 2012 event. They learned that an earlier, smaller CME helped clear the path for the larger event, thus contributing to its unusual speed.
Such data helps advance our understanding of what causes CMEs and improves modeling of similar CMEs that could be Earth-directed.
This video features two model runs. One looks at a moderate coronal mass ejection (CME) from 2006. The second run examines the consequences of a large coronal mass ejection, such as The Carrington-Class CME of 1859. These model runs allow us to estimate consequences of a large event hitting Earth, so we can better protect power grids and satellites.
In an effort to understand and predict the impact of space weather events on Earth, the Community-Coordinated Modeling Center (CCMC) at NASA Goddard Space Flight Center, routinely runs computer models of the many historical events. These model runs are then compared to actual data to determine ways to improve the model, and therefore forecasts of future space weather events.
Sometimes we need an actual event to have data for comparison. Extreme space weather events are one example where researchers must test models with a rather limited set of data.
The vertical lines on the left represent magnetic field lines from the sun.
The sun emitted a mid-level solar flare, peaking at 3:01 p.m. EDT on Oct. 2, 2014. NASA's Solar Dynamics Observatory, which watches the sun 24-hours a day, captured images of the flare. Solar flares are powerful bursts of radiation. Harmful radiation from a flare cannot pass through Earth's atmosphere to physically affect humans on the ground, however -- when intense enough -- they can disturb the atmosphere in the layer where GPS and communications signals travel.
This flare is classified as an M7.3 flare. M-class flares are one-tenth as powerful as the most powerful flares, which are designated X-class flares.
Music: “No Comment Before Sunset" by Lars Leonhard, courtesy of the artist and BineMusic.
By Steele Hill NASA's Goddard Space Flight Center, Greenbelt, Md.
A snaking, extended filament of solar material currently lies on the front of the sun-- some 1 million miles across from end to end. Filaments are clouds of solar material suspended above the sun by powerful magnetic forces. Though notoriously unstable, filaments can last for days or even weeks.
SDO Watches Giant Filament - 193+335 Wavelength A dark snaking line in the upper right of this image on Sept. 30, 2014, show a filament of solar material hovering above the sun's surface.If straightened out, the filament would reach almost across the whole sun, about 1 million miles or 100 times the size of Earth. NASA's Solar Dynamics Observatory, or SDO, captured the image in extreme UV light of 193 Angstrom and 335 Angstrom – different colors represent different wavelengths of light and different temperatures of solar material. Credit: NASA/SDO
SDO Watches Giant Filament - 304+193 Wavelength A dark snaking line in the upper right of this image on Sept. 30, 2014, show a filament of solar material hovering above the sun's surface.If straightened out, the filament would reach almost across the whole sun, about 1 million miles or 100 times the size of Earth. NASA's Solar Dynamics Observatory, or SDO, captured the image in extreme UV light of 304 Angstrom – different colors represent different wavelengths of light and different temperatures of solar material. Credit: NASA/SDO
NASA's Solar Dynamics Observatory, or SDO, which watches the sun 24 hours a day, has observed this gigantic filament for several days as it rotated around with the sun. If straightened out, the filament would reach almost across the whole sun, about 1 million miles or 100 times the size of Earth.
SDO captured images of the filament in numerous wavelengths, each of which helps highlight material of different temperatures on the sun. By looking at any solar feature in different wavelengths and temperatures, scientists can learn more about what causes such structures, as well as what catalyzes their occasional giant eruptions out into space.
Look at the images to see how the filament appears in different wavelengths. The brownish combination image was produced by blending two wavelengths of extreme UV light with a wavelength of 193 and 335 Angstroms. The red image shows the 304 Angstrom wavelength of extreme UV light.
By Karen C. Fox NASA's Goddard Space Flight Center, Greenbelt, Md.
A magnetic filament of solar material erupted on the sun in late September, breaking the quiet conditions in a spectacular fashion. The 200,000 mile long filament ripped through the sun's atmosphere, the corona, leaving behind what looks like a canyon of fire. The glowing canyon traces the channel where magnetic fields held the filament aloft before the explosion. Visualizers at NASA's Goddard Space Flight Center in Greenbelt, Md. combined two days of satellite data to create a short movie of this gigantic event on the sun.
In reality, the sun is not made of fire, but of something called plasma: particles so hot that their electrons have boiled off, creating a charged gas that is interwoven with magnetic fields.
These images were captured on Sept. 29-30, 2013, by NASA's Solar Dynamics Observatory, or SDO, which constantly observes the sun in a variety of wavelengths.
Different wavelengths help capture different aspect of events in the corona. The red images shown in the movie help highlight plasma at temperatures of 90,000° F and are good for observing filaments as they form and erupt. The yellow images, showing temperatures at 1,000,000° F, are useful for observing material coursing along the sun's magnetic field lines, seen in the movie as an arcade of loops across the area of the eruption. The browner images at the beginning of the movie show material at temperatures of 1,800,000° F, and it is here where the canyon of fire imagery is most obvious. By comparing this with the other colors, one sees that the two swirling ribbons moving farther away from each other are, in fact, the footprints of the giant magnetic field loops, which are growing and expanding as the filament pulls them upward.
Four images of a filament on the sun from August 31, 2012 are shown here in various wavelengths of light as captured by NASA’s Solar Dynamics Observatory (SDO). Starting from the upper left and going clockwise they represent light in the: 335, 171, 131 and 304 Angstrom wavelengths. Since each wavelength of light generally corresponds to solar material at a particular temperature, scientists can compare images like this to observe how the material moves during an eruption. Credit: NASA/SDO/AIA/GSFC
Close-up still of filament eruption. Credit: NASA/SDO/AIA/GSFC
[ http://www.youtube.com/watch?v=sfNZ_Qw5AHs (with comments; as embedded)] A long filament erupted on the sun on August 31, 2012, shown here in a movie captured by NASA's Solar Dynamics Observatory (SDO) from noon EDT to 1:45 a.m. the next morning. The filament lies in the lower left corner of the sun. The movie shows light at 304 Angstroms and 171 Angstroms, both of which help scientists observe the sun's atmosphere, or corona. Following SDO's view are two taken by the Solar and Heliospheric Observatory (SOHO) and the Solar Terrestrial Relations Observatory (STEREO) showing the associated coronal mass ejection (CME). Credit: NASA/SDO/AIA, NASA/STEREO, SOHO (ESA & NASA) Download video [ http://www.nasa.gov/multimedia/videogallery/index.html?collection_id=15504&media_id=151653121 ]
By Karen C. Fox NASA Goddard Space Flight Center, Greenbelt, MD
On August 31, 2012 a long filament of solar material that had been hovering in the sun's atmosphere, the corona, erupted out into space at 4:36 p.m. EDT. The coronal mass ejection, or CME, traveled at over 900 miles per second. The CME did not travel directly toward Earth, but did connect with Earth's magnetic environment, or magnetosphere, with a glancing blow. causing aurora to appear on the night of Monday, September 3.
Swirls of green and red appear in an aurora over Whitehorse, Yukon on the night of September 3, 2012. The aurora was due to the interaction of a coronal mass ejection (CME) from the sun with Earth's magnetosphere. The CME left the sun on August 31 and arrived on September 3. Image Courtesy of David Cartier, Sr.
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