Nearby red dwarf star unleashes X100,000 superflare

The largest flare ever recorded on the sun, an X 45 event in November 2003, pales in comparison to the estimated X 100,000 flare seen on the red dwarf star DG CVn on April 23 by NASA’s Swift satellite. The sun image is an actual photo; the dwarf star flare an artist’s view. Credit: NASA

Sometimes big things come in small packages. Last April, DG CVn, a red dwarf star only one-third the size of the sun, cut loose with a flare 10,000 times more powerful than any solar flare ever recorded. The sun’s grandest was an X 45 on November 4, 2003 which happily was directed off its western limb away from Earth. Had it happened closer to the center of the solar disk, damage to satellite electronics and power grids on the ground might have been substantial.

NASA’s Swift mission detected a record-setting series of X-ray flares unleashed by DG CVn, a nearby binary consisting of two red dwarf stars, illustrated here. At its peak, the initial flare was brighter in X-rays than the combined light from both stars at all wavelengths under normal conditions. Credit: NASA’s Goddard Space Flight Center/S. Wiessinger

The superflare erupted from one or the other of two closely-orbiting red dwarfs in the constellation of Canes Venatici (abbreviated CVn) located beneath the handle of the Big Dipper. While only 60 light years from Earth, the two stars orbit each other only three times Earth’s distance from the sun which is too close for the Swift satellite to know which one did the deed.

At its peak the flare shot up to 360 million degrees F (200 million C) or 12 times hotter than the center of the sun. Despite its magnitude, the star is too far away to pose any harm to Earth. As to how a smaller, cooler dwarf could unleash such an energetic blast, we have two important leads.

The sun still has a lot pep left. This M7.3 (medium class) flare erupted along the sun’s western edge on October 2 as seen by the Solar Dynamics Observatory. It was not Earth-directed. Credit: NASA

Astronomers estimate DG CVn was born about 30 million years ago, which makes it less than 0.7% the age of the solar system. Like children, youthful stars are blessed with energy and show it through rapid rotation – DG completes one spin in just under a day or 30 times faster than the sun. The sun also rotated faster in its youth and may well have produced a few of its own superflares. Now it spins once every 27 days, fast enough to amplify magnetic fields to X-class strength but no match for the younger set.

Magnetic energy gets concentrated around sunspots or starspots in the case of DG CVn. In the turbulent environment, opposite polarities (north and south poles) can snap together and reconnect, releasing gobs of stored energy as a flare.

Flares are classified according to their energy output. The weakest – A,B and C-class – have almost no effect on Earth. M-class or medium flares accompanied by blasts of solar particles can cause radio blackouts and fire up northern and southern lights. The strongest are the X-class, which can lead to long-lasting radiation storms and nights-long auroral displays.

Aftermath of the X 45 flare in November 2003 clearly shows loops of solar gases outlining the powerful magnetic field rising above the sunspot group (not visible) below. Credit: NASA

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).

“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.”

Three hours later the system exploded with another weaker flare. More flares continued in a series for the next 11 days like aftershocks from an earthquake. Astronomers have observed the same phenomenon with the sun called “sympathetic flaring” where one explosion triggers another.

Stars delight the eye and make the Earth an abode for life, but don’t get too close. They’re scary.


Newfound alien planet Gliese 832c reminds us of home

Artistic representation of the potentially habitable Super-Earth Gliese 832c with an actual photo of its parent red dwarf star (center) taken on June 25, 2014. Credit: Efraín Morales Rivera, Astronomical Society of the Caribbean, PHL @ UPR Arecibo

An international team of astronomers, led by Robert A. Wittenmyer from Australia, report the discovery of a new potentially habitable ‘super-Earth’ around the red dwarf star Gliese 832 only 16 light years away in the constellation Grus the Crane. This is the second planet known to orbit the star. In 2009 astronomers discovered a cold, Jupiter-like world, Gliese 832b, circling the star at a distance comparable to our inner asteroid belt.

Potentially habitable exoplanet Gliese 832c as compared with Earth. Gliese 832 c is represented here as a temperate world covered in clouds. The relative size of the planet in the figure assumes a rocky composition but could be larger for a ice-gas composition. Credit: PHL @ UPR Arecibo

Gliese 832c revolves about its host star every 36 days at an average distance of 15 million miles and is at least 5.4 times as massive as the Earth. At less than half Mercury’s distance from the sun, you might think the new planet would be too hot for life. That might be true if the host star Gliese 832 were as hot as our sun, but red dwarfs are much less massive and cooler than most stars. Planets can orbit much more closely and not ‘get burned’.

In this case, the host star’s temperature is only 6,000 degrees F (3325 C) or 4,000 cooler than the sun, placing Gliese 832c along the inner edge of the ‘habitable zone’ where liquid water could exist on its surface. Given its elongated orbit, the planet may have more extreme seasons that we’re used to on Earth.

Artists views of 23 known planets around other stars (exoplanets) with any potential to support surface life as we know it. Most of them are larger than Earth and we are less certain about their composition and habitability. They’re ranked here from closest to farthest from Earth. Earth, Mars, Jupiter, and Neptune are shown for scale on the right. Click to learn more about the Habitable Exoplanets Catalog. Credit: PHL@UPR Arecibo

Astronomers rate new exoplanets using the Earth Similarity Index or ESI which compares how physically similar a planet is to Earth on a scale from ‘0’ to ‘1’(Earth=1). ESI takes into account the planet’s size, density and surface temperature among other factors. Gliese 832c ranks a 0.81, high enough to make place it as one of the top three most Earth-like planets known to date along with Gliese 667c and Kepler-62e.

Of course we need to keep in mind that other factors like the composition of the atmosphere play an important role in whether the world is capable of sustaining life. A denser atmosphere and Gliese 832c might resemble Venus more than Earth.

Let’s just say we’ve got a hot possibility here. Gliese 832c is now the 23rd potentially habitable planet discovered. Amazing considering we only started finding planets beyond the sun beginning in 1995.

Dwarf star Wolf 359 endures after fictional Borg battle

Wolf 359 photographed several years apart so you can see its movement across the sky. The star travels 0.4 arc seconds per year – the moon’s diameter in 4,500 years – against the distant starry background. Credit: ESO, Digitized Sky Survey, U.K. Schmidt Telescope, PPARC and the Association of Universities for Research in Astronomy, Inc. (AURA).

The Borg were probably the most frightening and evil of all the alien races in Star Trek: The Next Generation. Outside of their collective group, nothing mattered. It was just kill, kill, kill and assimilate. If you were captured, the Borg hooked you into the network, sucked every thought from your brain and used the knowledge to destroy the next heroic attempt to snuff them out.

A famous fictional battle took place between the good guys and the Borg happened in the year 2367 near the star Wolf 359. Why Wolf 359 was chosen I don’t know, but it is a real star and a special one at that. Perhaps the writers wanted a star near Earth to bring home the impending threat to our own solar system.

Wolf 359 is a very faint star located in the southern half of Leo the Lion. This map shows the sky facing east in late Jan. – early Feb. around 9 p.m. local time. Created with Stellarium

Wolf 359 was the 359th star of more than a thousand found discovered by German astrophysicist Max Wolf to have a large motion across the sky, what astronomers refer to as proper motion. All stars are moving around the center of the Milky Way galaxy. Nearby stars generally appear to move more quickly across the sky than distant ones because they’re closer to us. Kind of like driving along the freeway where a service station quickly recedes into the distance while the distant mountain ahead appears nearly still for many miles.

Astronomers are able to measure distances to stars with large proper motions, and once you know distance, you know how big and bright a star really is. What we learn from them can then be applied to more distant stars, the movements of which are nearly impossible to detect. That’s why Wolf cataloged as many of these stellar midges as he could.

The size of our sun and Wolf 359 compared. Illustration: Bob King

Outside of the sun, Wolf 359 is the third closest star to Earth after the Alpha Centauri system and Barnard’s Star. Just 7.7 light years away, it’s one light year closer than the sky’s brightest star, Sirius. You’d think something so close would outshine Sirius or at least be visible with the naked eye. I wish. Wolf 359 shines at a paltry 13.5 magnitude, requiring at least an 8-inch telescope to see.

Unlike Sirius, which is both hotter and nearly twice as large as the sun, Wolf 359 is a red dwarf only about 16% the size of the sun or approximately 140,000 miles across. That’s hardly twice the size of Jupiter. If Wolf 359 were at the center of our solar system, you’d need binoculars to see it as a disk. Not only that, but with an energy output of 1/10th of 1% of the sun, it would only be as bright as ten full moons squished into a tiny dot.

Astronomer Max Wolf

Red dwarfs are red because their surfaces are cool, and like an ember, emit more red light than green or blue. They’re also small. Wolf 359 is about as small as star can be and still fuse hydrogen atoms together in its core to create energy the way the sun does. Its surface cooks at at a tepid 4,000-4,700 degrees F, cool enough to allow molecules like water and carbon monoxide to form. You won’t find that happening on old Sol.

Despite its diminutive persona, Wolf 359 will outlast the sun and nearly every star we see in the night sky. Being cool, red dwarfs burn their hydrogen fuel frugally compared to larger stars that devour theirs at prodigious rates. Not only that, but hydrogen is continually recycled throughout the interior of red dwarfs and available for burning. In sun-sized and larger stars, hydrogen is converted into helium ash, which settles in the core. The sun will continue to burn hydrogen in its old age, but only in a thin shell around the core.

When the sun runs out of fuel in another 5 billion years and evolves into a white dwarf star, Wolf 359 will keep the home fires burning for up to 10 trillion years. No matter what happens in science fiction, Wolf 359 will endure.