Our Sun May Experience a Surprisingly Explosive Death

Our sun will not explode as a powerful supernova when it eventually runs out of fuel, but that doesn't mean there won't be fireworks.

Our sun will not explode as a powerful supernova when it eventually runs out of fuel, but that doesn't mean there won't be fireworks.

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When our sun runs out of hydrogen fuel in its core, the star will puff up into a huge red giant and torment itself with powerful stellar winds, eventually stripping its self bare, creating a vast planetary nebula with a small yet dense white dwarf in its core.

Until now, this progression from dying star to nebula has been assumed to be a slow and fairly ‘gentle' process - when compared with the sheer violence of a massive star's supernova at least. A new study published in The Astrophysical Journal, however, suggests that the death of low to intermediate mass stars (like the sun) is anything but subdued.

"In a few thousand million years, the sun will exhaust its nuclear fuel, expand into a red giant and eject a major part of its mass," said lead researcher José Francisco Gómez, of the Institute of Astrophysics of Andalusia (IAA-CSIC) in Granada, Spain. "The final result will be a white dwarf surrounded by a glowing planetary nebula. Even though every star with a mass below ten solar masses goes through this short but important final transition, many details of the process still evade us."

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Gómez's team's research focused on IRAS 15103-5754, an object that is currently transitioning from a red giant into a planetary nebula. Nicknamed "water fountains," objects like IRAS 15103-5754 generate powerful emissions produced by water vapor molecules (known as water maser emission). Jets of ejected material can therefore be detected and their outflow speeds measured.

As a part of a wider survey of 16 dying stars, IRAS 15103-5754 stands out as the velocity of its jets increases with distance from the central star. And this provides an interesting clue as to the dynamics of planetary nebulae and how stars like our sun die.

"Water molecules are generally destroyed soon after the planetary nebula is formed, and in the rare cases where a maser emission has been detected, the velocity has always been very low," said collaborator Luis F. Miranda, of the IAA-CSIC and University of Vigo, Spain. "In IRAS 15103-5754 we are seeing for the first time a water maser emission at velocities of hundreds of kilometers (miles) per second. We are witnessing the transition of a star into a planetary nebula in real time."

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"The high velocity can only be explained by the occurrence of an explosion," said Gómez. "Our results show that, contrary to the most widespread theories, when a star turns into a planetary nebula an enormous explosion is produced - short-lived but highly energetic - which will determine the evolution of the star in its last phases of life."

As we look deep into our galaxy, an array of planetary nebulae of a variety of morphologies have been observed, a fact that isn't easily explained by current theories. Now that astronomers are revealing the formation of these nebulae may be more violent than previously thought, perhaps we'll have a better grasp on what dynamics drive the death of stars like our sun and why planetary nebulae are so varied.

Source: Institute of Astrophysics of Andalusia

This observation shows radio and infrared images of IRAS 15103-5754 showing the velocity of the material in the jet.

The sun may be an average star when compared to the menagerie of stars that exist in our galaxy, but to Earth and all life on our planet, the sun is the most important object in the Universe. However, regardless of its importance and close proximity, our nearest star holds many mysteries that continue to fox solar physicists after decades of modern studies with cutting-edge observatories. One of the biggest mysteries surrounding the sun is the underlying mechanisms that drive solar flares and coronal mass ejections (CMEs). Monday evening (EST), the sun reminded us that it hasn't quite finished with the current solar maximum (of solar cycle 24), unleashing a powerful X4.9 solar flare -- the biggest of 2014. An armada of space telescopes witnessed the event, including NASA's Solar Dynamics Observatory that can spy the sun's temper tantrums in astounding high definition. Shown here, 5 of the 10 filters from the SDO's Atmospheric Imaging Assembly (AIA) instrument are featured, showing the sun's lower corona (the solar multimillion degree atmosphere) through 5 wavelengths; each wavelength of extreme ultraviolet light representing a different plasma temperature and key coronal features -- such as coronal loops (highlighted here in the 'yellow' 171A filter) and ejected plasma that formed a CME.

At 7:13 p.m. EST (00:13 UT, Feb. 25) -- pictured here on the far left -- the active region (AR) 1990 was crackling with activity. Then, as magnetic field lines from the sun's interior forced together and through the solar photosphere, large-scale reconnection events occurred. Reconnection is a magnetic phenomena where field lines "snap" and reconnect, releasing huge quantities of energy in the process. At 7:44 p.m. EST (00:44 UT) -- second frame from the right -- a kinked coronal loop can be seen rising into the corona. At 7:59 p.m. EST (00:59 UT) -- far right -- solar plasma contained within the magnetic flux is accelerated to high energy, generating powerful x-rays and extreme ultraviolet radiation, creating the X-class flare.

The X4.9 flare was caught through the range of SDO fliters, including this dramatic view as seen through the 131A filter. The flare was so bright that photons from the flare overloaded the SDO's CCD inside the AIA instrument, causing the signal to "bleed" across the pixels. This bleeding effect is common for any optical instrument observing powerful solar flares.

Intense coronal activity is often associated with active regions -- the active lower corona is pictured here, left. In this case, the flare erupted from AR1990, at the limb of the sun. Also associated with active regions are sunspots, dark patches observed in the sun's photosphere (colloquially known as the sun's "surface") -- pictured right. The sun's cooler photosphere has been imaged by a different SDO instrument called Helioseismic and Magnetic Imager (HMI), which detects the intensity of magnetic fields threading though the sun's lower corona and photosphere.

In the case of AR1990, a large sunspot can be seen at the base of the coronal loops that erupted to generate the powerful flare. This is a prime example of how sunspots can be used to gauge solar activity and how they are often found at the base of intense coronal activity and flares.

The HMI monitors magnetic activity across the disk of the sun and can also generate a picture on the direction of the magnetic field polarity. In this observation of the sun's magnetic field around the time of the recent X-class flare, other active regions can be easily seen -- intense white and black regions highlighting where magnetic field lines emerge and sink back into the sun's interior in active regions.

The joint NASA/ESA Solar and Heliospheric Observatory (SOHO), which has been watching the sun since 1996, also spotted the flare, tracking a CME that was generated shortly after. Seen here by SOHO's LASCO C2 instrument, that monitors the interplanetary environment surrounding the sun for CMEs and comets, a growing bubble of solar plasma races away from the sun.

Approximately an hour after the flare, the CME grew and continued to barrel into interplanetary space. Space weather forecasters don't expect that this CME will interact with the Earth's atmosphere as it is not Earth-directed. This observation was captured by SOHO's LASCO C3 instrument -- an occulting disk covers the sun to block out any glaring effect. By combining observations by the SDO, SOHO and other solar observatories, the connection between the sun's internal magnetic "dynamo", the solar cycle, flares and CMEs, solar physicists are slowly piecing together what makes our nearest star tick, hopefully solving some of the most persistent mysteries along the way.