Runaway Glacier melt in West Antarctica Ice

The leading edge of the floating ice tongue of the Pine Island Glacier, Antarctica. 

Credit: M. Wolovick

Reports that a portion of the West Antarctic Ice Sheet (WAIS) has begun to irretrievably collapse, threatening a 4-foot rise in sea levels over the next couple of centuries, surged through the news media last week.

But many are asking if even this dramatic news will alter the policy conversation over what to do about climate change.

West Antarctic Ice Sheet (WAIS)

Glaciers like the ones that were the focus of two new studies move at, well, a glacial pace. Researchers are used to contemplating changes that happen over many thousands of years.

This time, however, we're talking hundreds of years, perhaps—something that can be understood in comparison to recent history, a timescale of several human generations.

In that time, the papers' authors suggest, melting ice could raise sea levels enough to inundate or at least threaten the shorelines where tens of millions of people live.

"The high-resolution records that we're getting and the high-resolution models we're able to make now are sort of moving the questions a little bit closer into human, understandable time frames," said Kirsty Tinto, a researcher from Lamont-Doherty Earth Observatory who has spent a decade studying the Antarctic.

"We're still not saying things are going to happen this year or next year. But it's easier to grasp [a couple of hundred years] than the time scales we're used to looking at."

The authors of two papers published last week looked at a set of glaciers that slide down into the Amundsen Sea from a huge ice sheet in West Antarctica, which researchers for years have suspected may be nearing an "unstable" state that would lead to its collapse.

The West Antarctic Ice Sheet (WAIS) is mostly grounded on land that is below sea level (the much larger ice sheet covering East Antarctica sits mostly on land above sea level).

Advances in radar and other scanning technologies have allowed researchers to build a detailed picture of the topography underlying these glaciers, and to better understand the dynamics of how the ice behaves.

Where the forward, bottom edge of the ice meets the land is called the grounding line. Friction between the ice and the land holds back the glacier, slowing its progress to the ocean.

Beyond that line, however, the ice floats on the sea surface, where it is exposed to warmer ocean water that melts and thins these shelves of ice.

As the ice shelves thin and lose mass, they have less ability to hold back the glacier.

What researchers are finding now is that some of these enormous glaciers have become unhinged from the land – ice has melted back from earlier grounding lines and into deeper basins, losing its anchor on the bottom, exposing more ice to the warmer ocean water and accelerating the melting.

The glaciers studied by Eric Rignot’s research team. 

Red indicates areas where flow speeds have increased over the past 40 years. 

The darker the colour, the greater the increase. 

The increases in flow speeds extend hundreds of miles inland. 

Credit: Eric Rignot.

In their paper published in Geophysical Research Letters, Eric Rignot and colleagues from the University of California, Irvine, and NASA's Jet Propulsion Laboratory in Pasadena, Calif., described the "rapid retreat" of several major glaciers over the past two decades, including the Pine Island, Thwaites, Haynes, Smith and Kohler glaciers.

"We find no major bed obstacle upstream of the 2011 grounding lines that would prevent further retreat of the grounding lines farther south," they write.

"We conclude that this sector of West Antarctica is undergoing a marine ice sheet instability that will significantly contribute to sea level rise in decades to come."

More information: Widespread, rapid grounding line retreat of Pine Island, Thwaites, Smith and Kohler glaciers, West Antarctica from 1992 to 2011, E. Rignot, J. Mouginot, M. Morlighem, H. Seroussi, B. Scheuchl, Geophysical Research Letters (2014)

Marine Ice Sheet Collapse Potentially Underway for the Thwaites Glacier Basin, West Antarctica, Ian Joughin, Benjamin E. Smith, Brooke Medley, Science (2014)

NASA Chandra observes runaway pulsar firing an extraordinary jet

Credit X-ray: NASA /CXC /ISDC /L.Pavan et al, Radio: CSIRO /ATNF /ATCA Optical: 2MASS /UMass /IPAC-Caltech /NASA /NSF

NASA's Chandra X-ray Observatory has seen a fast-moving pulsar escaping from a supernova remnant while spewing out a record-breaking jet, the longest of any object in the Milky Way galaxy, of high-energy particles.

The pulsar, a type of neutron star, is known as IGR J11014-6103.

IGR J11014-6103's peculiar behaviour can likely be traced back to its birth in the collapse and subsequent explosion of a massive star.

Originally discovered with the European Space Agency satellite INTEGRAL, the pulsar is located about 60 light-years away from the center of the supernova remnant SNR MSH 11-61A in the constellation of Carina.

Its implied speed is between 2.5 million and 5 million mph, making it one of the fastest pulsars ever observed.

Lucia Pavan

"We've never seen an object that moves this fast and also produces a jet," said Lucia Pavan of the University of Geneva in Switzerland and lead author of a paper published Tuesday in the journal Astronomy and Astrophysics.

"By comparison, this jet is almost 10 times longer than the distance between the sun and our nearest star."

The X-ray jet in IGR J11014-6103 is the longest known in the Milky Way galaxy.

In addition to its impressive span, it has a distinct corkscrew pattern that suggests the pulsar is wobbling like a spinning top.

IGR J11014-6103 also is producing a cocoon of high-energy particles that enshrouds and trails behind it in a comet-like tail.

This structure, called a pulsar wind nebula, has been observed before, but the Chandra data show that the long jet and the pulsar wind nebula are almost perpendicular to one another.

Pol Bordas

"We can see that this pulsar is moving directly away from the center of the supernova remnant based on the shape and direction of the pulsar wind nebula," said co-author Pol Bordas, from the University of Tuebingen in Germany. "The question is, why is the jet pointing off in this other direction?"

Usually, the spin axis and jets of a pulsar point in the same direction as they are moving, but IGR J11014-6103's spin axis and direction of motion are almost at right angles.

Gerd Puehlhofer

"With the pulsar moving one way and the jet going another, this gives us clues that exotic physics can occur when some stars collapse," said co-author Gerd Puehlhofer also of the University of Tuebingen.

One possibility requires an extremely fast rotation speed for the iron core of the star that exploded.

A problem with this scenario is that such fast speeds are not commonly expected to be achievable.

The supernova remnant that gave birth to IGR J11014-6013 is elongated from top-right to bottom-left in the image roughly in line with the jet's direction.

These features and the high speed of the pulsar are hints that jets could have been an important feature of the supernova explosion that formed it.

More information: arxiv.org/abs/1309.6792

Runaway binary stars

A Hubble image of the binary stars Sirius A and B. Sirius B, the very faint companion, is a white dwarf, an evolved star that has burned its nuclear fuel.

There is one known binary star pair consisting of two white dwarfs that is also a "runaway" star, moving very rapidly through the galaxy. 

A new study concludes that this runaway star was probably ejected from a dense stellar cluster. 

Credit: NASA/Hubble

CfA astronomers made a remarkable and fortuitous discovery in 2005: an extremely fast moving star, clocked going over three million kilometers an hour.

It appears to have been ejected from the vicinity of the galactic center's supermassive black hole around 80 million years ago by powerful gravitational effects as it swung past the black hole.

Racing outward from the galaxy, the star lends added credibility to the picture of a massive black hole at the galactic center, and to calculations of how black holes might interact with their stellar environments.

Other hypervelocity stars and less fast-moving runaway stars have also been found. Most of them have been accelerated by one of the two other gravitational mechanisms: ejection from a dense cluster of stars as random motions bring it into a slingshot-like orbit, or ejection from a supernova binary system after the supernovae explodes and frees it from its orbit.

A binary star is a pair of stars that orbit each other, and many (perhaps most) stars are members of binary systems.

So far, there have been no hypervelocity binary stars discovered. They have been predicted, however, with at least one theory proposing that the discovery of a hypervelocity binary pair might indicate that the nuclear black hole is itself a binary pair.

More information: Kilic, M. et al. The Runaway Binary LP 400/22 is Leaving the Galaxy, MNRAS, 434, 3582, 2013.