At a very early age, children learn how to classify objects according to their shape. Now, new research suggests studying the shape of the aftermath of supernovas may allow astronomers to do the same.

A new study of images from NASA's Chandra X-ray Observatory on supernova remnants -- the debris from exploded stars - shows that the symmetry of the remnants, or lack thereof, reveals how the star exploded. This is an important discovery because it shows that the remnants retain information about how the star exploded even though hundreds or thousands of years have passed.

"It's almost like the supernova remnants have a 'memory' of the original explosion," said Laura Lopez of the University of California at Santa Cruz, who led the study. "This is the first time anyone has systematically compared the shape of these remnants in X-rays in this way."

Astronomers sort supernovas into several categories, or "types," based on properties observed days after the explosion and which reflect very different physical mechanisms that cause stars to explode. But, since observed remnants of supernovas are leftover from explosions that occurred long ago, other methods are needed to accurately classify the original supernovas.

Lopez and colleagues focused on the relatively young supernova remnants that exhibited strong X-ray emission from silicon ejected by the explosion so as to rule out the effects of interstellar matter surrounding the explosion. Their analysis showed that the X-ray images of the ejecta can be used to identify the way the star exploded. The team studied 17 supernova remnants both in the Milky Way galaxy and a neighboring galaxy, the Large Magellanic Cloud.

For each of these remnants there is independent information about the type of supernova involved, based not on the shape of the remnant but, for example, on the elements observed in it. The researchers found that one type of supernova explosion -- the so-called Type Ia -- left behind relatively symmetric, circular remnants. This type of supernova is thought to be caused by a thermonuclear explosion of a white dwarf, and is often used by astronomers as "standard candles" for measuring cosmic distances.

On the other hand, the remnants tied to the "core-collapse" supernova explosions were distinctly more asymmetric. This type of supernova occurs when a very massive, young star collapses onto itself and then explodes.

"If we can link supernova remnants with the type of explosion," said co-author Enrico Ramirez-Ruiz, also of University of California, Santa Cruz, "then we can use that information in theoretical models to really help us nail down the details of how the supernovas went off."

Models of core-collapse supernovas must include a way to reproduce the asymmetries measured in this work and models of Type Ia supernovas must produce the symmetric, circular remnants that have been observed.

Out of the 17 supernova remnants sampled, ten were classified as the core-collapse variety, while the remaining seven of them were classified as Type Ia. One of these, a remnant known as SNR 0548-70.4, was a bit of an "oddball." This one was considered a Type Ia based on its chemical abundances, but Lopez finds it has the asymmetry of a core-collapse remnant.

"We do have one mysterious object, but we think that is probably a Type Ia with an unusual orientation to our line of sight," said Lopez. "But we'll definitely be looking at that one again."

While the supernova remnants in the Lopez sample were taken from the Milky Way and its close neighbor, it is possible this technique could be extended to remnants at even greater distances. For example, large, bright supernova remnants in the galaxy M33 could be included in future studies to determine the types of supernova that generated them.

The paper describing these results appeared in the November 20 issue of The Astrophysical Journal Letters. NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge, Mass.

More information, including images and other multimedia, can be found at:

http://chandra.harvard.edu

It was taken on 24 October using two of Herschel’s instruments: the Photodetector Array Camera and Spectrometer (PACS) and the Spectral and Photometric Imaging Receiver (SPIRE). The two bright regions are areas where large newborn stars are causing hydrogen gas to shine.

The new OSHI website that goes live today will become the library of Herschel’s best images. Stunning views of the infrared sky will be made available as the mission progresses. Each will be captioned in a way to make them accessible to media representatives, educators and the public.

Embedded within the dusty filaments in the Aquila image are 700 condensations of dust and gas that will eventually become stars. Astronomers estimate that about 100 are protostars, celestial objects in the final stages of formation. Each one just needs to ignite nuclear fusion in its core to become a true star. The other 600 objects are insufficiently developed to be considered protostars, but these too will eventually become another generation of stars.

This cloud is part of Gould’s Belt, a giant ring of stars that circles the night sky – the Solar System just happens to lie near the centre of the belt. The first to notice this unexpected alignment, in the mid-19th century, was England’s John Herschel, the son of William, after whom ESA’s Herschel telescope is named. But it was Boston-born Benjamin Gould who brought the ring to wider attention in 1874.

Gould’s Belt supplies bright stars to many constellations such as Orion, Scorpius and Crux, and conveniently provides nearby star-forming locations for astronomers to study. Observing these stellar nurseries is a key programme for Herschel, which aims to uncover the demographics of star formation and its origin, or in other words, the quantities of stars that can form and the range of masses that such newborn stars can possess. Apart from this region of Aquila, Herschel will target 14 other star-forming regions as part of the Gould’s Belt Key Programme.

Notes for editors:

The scientific rights of these Herschel observations are owned by the consortium of the Gould Belt Key Programme, led by P. André (CEA Saclay). A total of 15 nearby star-forming regions such as Aquila will be studied as part of this Programme.

"Our jaws dropped when we saw the movies for the first time," said space scientist Larry Lyons of the University of California-Los Angeles (UCLA), a member of the team that made the discovery. "These outbursts are telling us something very fundamental about the nature of auroras."

The collisions occur on such a vast scale that isolated observers on Earth -- with limited fields of view -- had never noticed them before. It took a network of sensitive cameras spread across thousands of miles to get the big picture.

NASA and the Canadian Space Agency created such a network for THEMIS, short for "Time History of Events and Macroscale Interactions during Substorms." THEMIS consists of five identical probes launched in 2006 to solve a long-standing mystery: Why do auroras occasionally erupt in an explosion of light called a substorm?

Twenty all-sky imagers (ASIs) were deployed across the Alaskan and Canadian Arctic to photograph auroras from below while the spacecraft sampled charged particles and electromagnetic fields from above. Together, the on-ground cameras and spacecraft would see the action from both sides and be able to piece together cause and effect-or so researchers hoped. It seems to have worked.

The breakthrough came earlier this year when UCLA researcher Toshi Nishimura assembled continent-wide movies from the individual ASI cameras. "It can be a little tricky," Nishimura said. "Each camera has its own local weather and lighting conditions, and the auroras are different distances from each camera. I've got to account for these factors for six or more cameras simultaneously to make a coherent, large-scale movie."

The first movie he showed Lyons was a pair of auroras crashing together in Dec. 2007. "It was like nothing I had seen before," Lyons recalled. "Over the next several days, we surveyed more events. Our excitement mounted as we became convinced that the collisions were happening over and over."

The explosions of light, they believe, are a sign of something dramatic happening in the space around Earth-specifically, in Earth's "plasma tail." Millions of kilometers long and pointed away from the sun, the plasma tail is made of charged particles captured mainly from the solar wind. Sometimes called the "plasma sheet," the tail is held together by Earth's magnetic field.

The same magnetic field that holds the tail together also connects it to Earth's polar regions. Because of this connection, watching the dance of Northern Lights can reveal much about what's happening in the plasma tail.

THEMIS project scientist Dave Sibeck of NASA's Goddard Space Flight Center, Greenbelt, Md. said, "By putting together data from ground-based cameras, ground-based radar, and the THEMIS spacecraft, we now have a nearly complete picture of what causes explosive auroral substorms."

Lyons and Nishimura have identified a common sequence of events. It begins with a broad curtain of slow-moving auroras and a smaller knot of fast-moving auroras, initially far apart. The slow curtain quietly hangs in place, almost immobile, when the speedy knot rushes in from the north. The auroras collide and an eruption of light ensues.

How does this sequence connect to events in the plasma tail? Lyons believes the fast-moving knot is associated with a stream of relatively lightweight plasma jetting through the tail. The stream gets started in the outer regions of the plasma tail and moves rapidly inward toward Earth. The fast knot of auroras moves in synch with this stream.

Meanwhile, the broad curtain of auroras is connected to the stationary inner boundary of the plasma tail and fueled by plasma instabilities there. When the lightweight stream reaches the inner boundary of the plasma tail, there is an eruption of plasma waves and instabilities. This collision of plasma is mirrored by a collision of auroras over the poles.

National Science Foundation-funded radars located in Poker Flat, Alaska, and Sondrestrom, Greenland, confirm this basic picture. They have detected echoes of material rushing through Earth's upper atmosphere just before the auroras collide and erupt. The five THEMIS spacecraft also agree. Last winter, they were able to fly through the plasma tail and confirm the existence of lightweight flows rushing toward Earth.

Scientists from NASA's Langley Research Center and Hampton University in Hampton, Va., and the National Center for Atmospheric Research in Boulder, Colo., presented these results at the fall meeting of the American Geophysical Union in San Francisco from Dec. 14 to 18.

Earth's thermosphere and mesosphere have been the least explored regions of the atmosphere. The NASA Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) mission was developed to explore the Earth’s atmosphere above 60 km altitude and was launched in December 2001. One of four instruments on the TIMED mission, the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument, was specifically designed to measure the energy budget of the mesosphere and lower thermosphere. The SABER dataset now covers eight years of data and has already provided some basic insight into the heat budget of the thermosphere on a variety of timescales.

The extent of current solar minimum conditions has created a unique situation for recent SABER datasets, explains Stan Solomon, acting director of the High Altitude Observatory, National Center for Atmospheric Research in Boulder, Colo. The end of solar cycle 23 has offered an opportunity to study the radiative cooling in the thermosphere under exceptionally quiescent conditions.

"The Sun is in a very unusual period," said Marty Mlynczak, SABER associate principal investigator and senior research scientist at NASA Langley. "The Earth’s thermosphere is responding remarkably — up to an order of magnitude decrease in infrared emission/radiative cooling by some molecules."

The TIMED measurements show a decrease in the amount of ultraviolet radiation emitted by the Sun. In addition, the amount of infrared radiation emitted from the upper atmosphere by nitric oxide molecules has decreased by nearly a factor of 10 since early 2002. These observations imply that the upper atmosphere has cooled substantially since then. The research team expects the atmosphere to heat up again as solar activity starts to pick up in the next year.

While this warming has no implications for climate change in the troposphere, a fundamental prediction of climate change theory is that the upper atmosphere will cool in response to increasing carbon dioxide. As the atmosphere cools the density will increase, which ultimately may impact satellite operations through increased drag over time.

The SABER dataset is the first global, long-term, and continuous record of the Nitric oxide (NO) and Carbon dioxide (CO2) emissions from the thermosphere.

"We suggest that the dataset of radiative cooling of the thermosphere by NO and CO2 constitutes a first climate data record for the thermosphere," says Mlynczak.

The TIMED data provide a climate record for validation of upper atmosphere climate models, which is an essential step in making accurate predictions of climate change in the high atmosphere. SABER provides the first long-term measurements of natural variability in key terms of the upper atmosphere climate.

"A fundamental prediction of climate change theory is that upper atmosphere will cool in response to greenhouse gases in the troposphere," says Mlynczak. "Scientists need to validate that theory. This climate record of the upper atmosphere is our first chance to have the other side of the equation."

James Russell III, SABER principal investigator and co-director of the Center for Atmospheric Sciences at Hampton University in Hampton, Va., agrees adding, "The atmosphere is a coupled system. If you pick up one end of the stick, you automatically pick up the other – they're intrinsically linked. To be as accurate as possible, scientists have to understand global change throughout the atmosphere."

As the TIMED mission continues, these data derived from SABER will become important in assessing long term atmospheric changes due to the increase of carbon dioxide in the atmosphere.

TIMED is the first mission in the Solar Terrestrial Probes Program within the Heliophysics Division in NASA's Science Mission Directorate in Washington.

Related Links:
› TIMED Mission
› SABER Instrument

Researchers report that in 2004, the state’s natural ecosystems absorbed as much carbon dioxide from the atmosphere as fossil fuel carbons emitted into the atmosphere. They also discovered that during periods of above normal rainfall, ecosystems trapped significant amounts of carbon dioxide from the atmosphere in forests and soils. For these reasons, researchers suggest the ecosystems should be more extensively protected and conserved, and their emissions be monitored as closely as fossil fuel sources of GHG emissions. The results, based largely on a computer model called the NASA-Carnegie Ames Stanford Approach (CASA), will be presented this morning at the 2009 American Geophysical Union Fall meeting in San Francisco.

"One way to facilitate emissions reductions is by using regional and national carbon budgets," explained Christopher Potter, senior research scientist at NASA Ames Research Center, Moffett Field, Calif., and author of this study. "California’s growing population and demand for all forms of energy make it essential to maintain an accurate and complete accounting of the state’s greenhouse emissions inventory," Potter added.

California’s population is more than 10 percent of the total population in the United States, and produces 13 percent of the U.S. gross domestic product, according to 2000 U.S. Census Bureau data. Because of its large population, the state also contributes significantly to global GHG emissions. If California was a country, it would rank among the top 20 national GHG emitters worldwide.

The carbon budget of a region is determined by the amounts of carbon dioxide and methane gases absorbed or released by “green” vegetative ground cover, as observed by NASA satellites. These fluctuations are important to quantify, because they originate from both natural and anthropogenic processes.

In California, the main sources of carbon dioxide emissions are energy consumption in commercial, residential, industrial, and transportation sectors, production of cement and lime, and waste treatment. The main sources of methane emission are derived from landfills and agricultural (principally livestock-based) systems.

Scientists believe that California’s carbon budget is of special interest because the state may represent a U.S. national carbon budget; both have diversified lands, similar consumption of natural resources, and urban lifestyles. Other similarities include a mix of fossil fuel emissions, alternative energy sources, and ecosystem sinks.

Each year, California is required by law to compile a new carbon emission inventory, which is conducted by the California Energy Commission and California’s Air Resources Board. To refine the state’s emission inventory, NASA was asked to provide NASA satellite imaging data and carbon models. To locate the largest ecosystem sources and carbon sinks in California, scientists used the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the NASA Terra satellite. The vegetation “greenness” data from the MODIS sensor was directly downloaded into the CASA ecosystem simulation model. Scientists used the data to estimate monthly variations in the accumulated biomass of wood and other plant materials, such as the accumulated dead leaf biomass transferred into soil carbon pools. Inventory data from the California Energy Commission also was used to model the carbon dioxide emissions from fossil fuel combustion and greenhouse gas emissions from agricultural lands throughout the state.

This project was funded by NASA as part of a long-term research program dedicated to understanding how human-induced and natural changes affect our global environment.