Sabtu, 11 Oktober 2014

The terrible anger of a young turbulent star

The terrible anger of a young turbulent star

On April 23, a series of eruptions produced a dazzling line 60 light years red dwarf surprised astronomers. The Swift satellite that issued the alert and scrutinized the phenomenon several days, noted that the most intense event was 10,000 times more powerful than the most violent eruptions recorded on the surface of our sun. How such small stars can they be the scene of such a strong and sudden activity?

Illustration torque red dwarf DG or DG Canum Venaticorum CVn, located about 60 light years from the Solar System.  One of them had several eruptions, the most important was 10,000 times more powerful than the most intense solar flare known, recorded in November 2003 Its brightness in X-rays exceeded that of two stars in all lengths wave.
Mood swings, the sun knows a lot. More or less intense. It depends on the period of its activity cycle which lasts 11 years on average. The dark spots, active regions, the source of flares are more numerous when peaking effect caused by the inversion of the magnetic field . The current cycle 24 is however below the previous (Cycle 23 peaked between 2001 and 2003), so that solar physicists believe that our star is going through a "mini max." Admittedly, the term suggests a mini activity down, but do not exclude that solar supertempĂȘtes can manifest as was the case July 23, 2012 (without hitting our magnetosphere ).

The solar flares are created by the twists of an intense magnetic field that, in the active regions, store energy and release it suddenly after a magnetic reconnection . They are classified into three categories (or classes) according to the intensity of X-rays: A, B and C for the lowest, M for Moderate and X for the most powerful. They emit in all wavelengths. The most powerful of Cycle 24 occurred August 9, 2011 and was classified X6.9. But the one that beats them all deployed energy since we are able to observe the surface of our star dated November 4, 2003 . She was then classified X28 and X45 to review.

Series of super eruptions stellar 60 light years

Although these tantrums are impressive, they seem pretty ridiculous compared to what astronomers have caught April 23, 2014 from a pair of red dwarf named DG Canum Venaticorum (abbreviated as DG CVn). Although a less massive than a third yellow dwarf like the Sun, one of the two star located about 60 light years from the solar system was the site of a 10,000 times more powerful than the eruption in November 2003 (in the case of the Sun). The two stars are separated only three astronomical units (three times the Earth-Sun distance), it is difficult since the orbit Earth to determine which of the two is at the origin. It is the instrument BAT ( Burst Alert Telescope ) satellite Swift dedicated to the detection of the most violent radiation in the Universe (X and gamma) that gave the alert. Moments later, several observatories were informed and the telescope spatial began a more extensive observational campaign.
"Three minutes after the BAT, the X-rays of this super eruption was above the brightness of the two stars combined in all wavelengths under normal conditions, " recalls Adam Kowalski GSFC ( Goddard Space Flight Center ), which studied the phenomenon, adding that "eruptions of this magnitude are extremely rare for red dwarfs" . Moreover, "the system (...) was not on our watch list of stars that could produce large eruptions, confesses Rachel Osten ( Space Telescope Science Institute in Baltimore). We had no idea that DG CVn was in it " . Indeed, the radiation was multiplied by 10 in the visible and 100 in the ultraviolet as pointed instruments. Measurements indicate that at the height of the event, the temperature was about 200 million degrees Celsius , or more than 12 times that which prevails in the center of the Sun!

Previously, many thought, as Stephen Drake, an astrophysicist at GSFC who introduced last August, the results of this study to the meetings of the High Energy Division of the American Astronomical Society ( American Astronomical Society ), that "the major eruptions on the surface red dwarfs can not exceed one day " . But Swift showed it occurred in at least seven in the space of two weeks! "It was a very complex event. " About three hours after the first eruption, a second was evident with almost as much intensity. The following eleven days, the satellite has observed many more, but increasingly weak. Researchers found that everything was back to normal after 20 days. Rachel Osten compares the phenomenon to replicas after an earthquake of a magnitude significant.

Turbulent youth

For researchers, these sudden exhalations power from such a small star are due to his youth. Or rather his childhood as DG CVn has only 30 million years, only 0.7% of the age of our Sun. These stars toddlers are about a thousand within 100 light years. In just out of the cradle, the two red dwarfs still turn on themselves very quickly, in just one day (on average 30 times faster than the Sun). Also the effect dynamo created by the differential rotation, which generates the magnetic field, is it amplified. The situation refers to the one could have known at an early stage our star. It is important to keep an eye on these stars because they show the stellar youth and interactions with their surroundings.

Very common throughout the Milky Way and probably surrounded, for the most part, gas planets and rocky, the red dwarfs , however, are often disqualified by astronomers and exobiologistes looking for potentially habitable planets . Involved, in addition to the violence of some eruptions in their youth, the erosion of magnetic fields and atmospheres of these worlds by stellar winds.

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