N103B Supernova explosion: New suspect identified

This infrared image from NASA's Spitzer Space Telescope shows N103B, all that remains from a supernova that exploded a millennium ago in the Large Magellanic Cloud, a satellite galaxy 160,000 light-years away from our own Milky Way. 

Credit: NASA/JPL-Caltech/Goddard

Supernovas are often thought of as the tremendous explosions that mark the ends of massive stars' lives.

While this is true, not all supernovas occur in this fashion.

A common supernova class, called Type Ia, involves the detonation of white dwarfs, small, dense stars that are already dead.

New results from NASA's Spitzer Space Telescope have revealed a rare example of Type Ia explosion, in which a dead star "fed" off an aging star like a cosmic zombie, triggering a blast.

The results help researchers piece together how these powerful and diverse events occur.

"It's kind of like being a detective," said Brian Williams of NASA's Goddard Space Flight Center in Greenbelt, Maryland, lead author of a study submitted to the Astrophysical Journal.

"We look for clues in the remains to try to figure out what happened, even though we weren't there to see it."

Supernovas are essential factories in the cosmos, churning out heavy metals, including the iron contained in our blood.

Type Ia supernovas tend to blow up in consistent ways, and thus have been used for decades to help scientists study the size and expansion of our universe.

Researchers say that these events occur when white dwarfs, the burnt-out corpses of stars like our sun, explode.

Evidence has been mounting over the past 10 years that the explosions are triggered when two orbiting white dwarfs collide, with one notable exception.

Kepler's supernova, named after the astronomer Johannes Kepler, who was among those who witnessed it in 1604, is thought to have been preceded by just one white dwarf and an elderly, companion star called a red giant.

Scientists know this because the remnant sits in a pool of gas and dust shed by the aging star.

Spitzer's new observations now find a second case of a supernova remnant resembling Kepler's.

Called N103B, the roughly 1,000 year-old supernova remnant lies 160,000 light-years away in the Large Magellanic Cloud, a small galaxy near our Milky Way.

"It's like Kepler's older cousin," said Williams. He explained that N103B, though somewhat older than Kepler's supernova remnant, also lies in a cloud of gas and dust thought to have been blown off by an older companion star. "The region around the remnant is extraordinarily dense," he said.

Unlike Kepler's supernova remnant, no historical sightings of the explosion that created N103B are recorded.

Both the Kepler and N103B explosions are thought to have unfolded as follows: an aging star orbits its companion, a white dwarf.

As the aging star molts, which is typical for older stars, some of the shed material falls onto the white dwarf. This causes the white dwarf to build up in mass, become unstable and explode.

According to the researchers, this scenario may be rare. While the pairing of white dwarfs and red giants was thought to underlie virtually all Type Ia supernovas as recently as a decade ago, scientists now think that collisions between two white dwarfs are the most common cause.

The new Spitzer research highlights the complexity of these tremendous explosions and the variety of their triggers. The case of what makes a dead star rupture is still very much an unsolved mystery.

Hard-to-Kill Star Survives Nearby Supernova Explosion - Video

A lucky star somehow survived the explosive death of its stellar companion, new images reveal.

The explosion, known as a supernova, would have been visible from Earth several thousand years ago.

While the supernova remnant (called DEM L241) has been known since the 1970s, the companion star remained invisible until NASA's Chandra X-Ray Observatory recently examined the region.

Scientists explained the hard-to-kill star's supernova survival in a video.

The surviving star's days are numbered, however. Its massive size suggests it too is destined for a catastrophic explosion a few million years from now, researchers said.

Remnants of Ancient Supernova Explosion found in Magnetotactic Bacteria

Back in 2004, German scientists discovered traces of supernova ejecta that had been deposited in the deep-sea ferromanganese crust of the pacific ocean. 

They dated the supernova event to 2.8 million years ago (Mya), using estimates from the decay of iron-60 radioisotope.

They were also able to estimate the distance of the supernova event to 10 parsecs (pc) from our sun, based on the amount of iron-60 deposited.

Prof Shawn Bishop

At the April 14th meeting of the American Physical Society (APS), another German scientist, Shawn Bishop, reported finding traces of iron-60 of supernova origin in the fossilized remains of a common bacteria.

By accurately dating the sediment cores in which the samples were found, Bishop appears to have discovered the first biological signature of an ancient supernova event, and may even be able to link it to a specific exploding star.

Bishop analyzed sample cores from strata roughly 100,000 years apart within deposits from 1.7 to 3.3 Mya. Iron-60 is not a product of any processes occurring here on earth, so any supply of it can be assumed to from a non-terrestrial source.

Bishop was able to extract out all the iron-60 of biological origin, and quantify it with a mass spectrometer.

The amounts found were small, but they were enough to reliably date the sample to a period around 2.2 Mya.

Other researchers, peripheral to the project, were then able to suggest a possible candidate star that dates to this period may lie in the Scorpius-Centaurus stellar association, roughly 130 pcs (424 light-years) from the sun.

More information: Abstract: X8.00002 : Search for Supernova 60Fe in the Earth's Fossil Record, Bulletin of the American Physical Society, meetings.aps.org/Meeting/APR13/Event/192798

Supernova Explosion: Galaxy's Youngest Black Hole

W49B is much more barrel-shaped than most other remnants in X-rays and several other wavelengths, pointing to an unusual demise for this star.

The highly distorted supernova remnant shown in this image may contain the most recent black hole formed in the Milky Way galaxy. 

The image combines X-rays from NASA's Chandra X-ray Observatory in blue and green, radio data from the NSF's Very Large Array in pink, and infrared data from Caltech's Palomar Observatory in yellow.

The remnant, called W49B, is about a thousand years old, as seen from Earth, and is at a distance of about 26,000 light years away.

The supernova explosions that destroy massive stars are generally symmetrical, with the stellar material blasting away more or less evenly in all directions.

However, in the W49B supernova, material near the poles of the doomed rotating star was ejected at a much higher speed than material emanating from its equator. Jets shooting away from the star's poles mainly shaped the supernova explosion and its aftermath.

By tracing the distribution and amounts of different elements in the stellar debris field, researchers were able to compare the Chandra data to theoretical models of how a star explodes.

For example, they found iron in only half of the remnant while other elements such as sulfur and silicon were spread throughout. This matches predictions for an asymmetric explosion.

Also, W49B is much more barrel-shaped than most other remnants in X-rays and several other wavelengths, pointing to an unusual demise for this star.

The authors also examined what sort of compact object the supernova explosion left behind. Most of the time, massive stars that collapse into supernovas leave a dense spinning core called a neutron star.