Mar 21 2016

From The Space Library

Caught For The First Time: The Early Flash Of An Exploding Star

The brilliant flash of an exploding star’s shockwave—what astronomers call the “shock breakout”—has been captured for the first time in the optical wavelength or visible light by NASA's planet-hunter, the Kepler space telescope.

An international science team led by Peter Garnavich, an astrophysics professor at the University of Notre Dame in Indiana, analyzed light captured by Kepler every 30 minutes over a three-year period from 500 distant galaxies, searching some 50 trillion stars. They were hunting for signs of massive stellar death explosions known as supernovae.

In 2011, two of these massive stars, called red supergiants, exploded while in Kepler’s view. The first behemoth, KSN 2011a, is nearly 300 times the size of our sun and a mere 700 million light years from Earth. The second, KSN 2011d, is roughly 500 times the size of our sun and around 1.2 billion light years away.

“To put their size into perspective, Earth's orbit about our sun would fit comfortably within these colossal stars,” said Garnavich.

Whether it’s a plane crash, car wreck or supernova, capturing images of sudden, catastrophic events is extremely difficult but tremendously helpful in understanding root cause. Just as widespread deployment of mobile cameras has made forensic videos more common, the steady gaze of Kepler allowed astronomers to see, at last, a supernova shockwave as it reached the surface of a star. The shock breakout itself lasts only about 20 minutes, so catching the flash of energy is an investigative milestone for astronomers.

“In order to see something that happens on timescales of minutes, like a shock breakout, you want to have a camera continuously monitoring the sky,” said Garnavich. “You don’t know when a supernova is going to go off, and Kepler's vigilance allowed us to be a witness as the explosion began.”

Supernovae like these — known as Type II — begin when the internal furnace of a star runs out of nuclear fuel causing its core to collapse as gravity takes over.

The two supernovae matched up well with mathematical models of Type II explosions reinforcing existing theories. But they also revealed what could turn out to be an unexpected variety in the individual details of these cataclysmic stellar events.

While both explosions delivered a similar energetic punch, no shock breakout was seen in the smaller of the supergiants. Scientists think that is likely due to the smaller star being surrounded by gas, perhaps enough to mask the shockwave when it reached the star's surface.

“That is the puzzle of these results,” said Garnavich. “You look at two supernovae and see two different things. That’s maximum diversity.”

Understanding the physics of these violent events allows scientists to better understand how the seeds of chemical complexity and life itself have been scattered in space and time in our Milky Way galaxy

"All heavy elements in the universe come from supernova explosions. For example, all the silver, nickel, and copper in the earth and even in our bodies came from the explosive death throes of stars," said Steve Howell, project scientist for NASA's Kepler and K2 missions at NASA’s Ames Research Center in California's Silicon Valley. "Life exists because of supernovae."

Garnavich is part of a research team known as the Kepler Extragalactic Survey or KEGS. The team is nearly finished mining data from Kepler’s primary mission, which ended in 2013 with the failure of reaction wheels that helped keep the spacecraft steady. However, with the reboot of the Kepler spacecraft as NASA's K2 mission, the team is now combing through more data hunting for supernova events in even more galaxies far, far away.

"While Kepler cracked the door open on observing the development of these spectacular events, K2 will push it wide open observing dozens more supernovae," said Tom Barclay, senior research scientist and director of the Kepler and K2 guest observer office at Ames. "These results are a tantalizing preamble to what's to come from K2!"

In addition to Notre Dame, the KEGS team also includes researchers from the University of Maryland in College Park; the Australian National University in Canberra, Australia; the Space Telescope Science Institute in Baltimore, Maryland; and the University of California, Berkeley.

The research paper reporting this discovery has been accepted for publication in the Astrophysical Journal.

Ames manages the Kepler and K2 missions for NASA’s Science Mission Directorate. NASA's Jet Propulsion Laboratory in Pasadena, California, managed Kepler mission development. Ball Aerospace & Technologies Corporation operates the flight system with support from the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder.

Authored by H. Pat Brennan/JPL and Michele Johnson/Ames

RELEASE 16-11 NASA Study Finds Climate Change Shifting Wine Grape Harvests in France and Switzerland

A new study from NASA and Harvard University finds that climate change is diminishing an important link between droughts and the timing of wine grape harvests in France and Switzerland.

During a study of wine grape harvest dates from 1600 to 2007, researchers discovered harvests began shifting dramatically earlier during the latter half of the 20th century. These shifts were caused by changes in the connection between climate and harvest timing. While earlier harvests from 1600 to 1980 occurred in years with warmer and drier conditions during spring and summer, from 1981 to 2007 warming attributed to climate change resulted in earlier harvests even in years without drought.

The finding is important because higher-quality wines are typically associated with earlier harvest dates in cooler wine-growing regions, such as France and Switzerland.

“Wine grapes are one of the world’s most valuable horticultural crops and there is increasing evidence that climate change has caused earlier harvest days in this region in recent decades,” said Ben Cook, lead author and climate scientist at NASA's Goddard Institute for Space Studies and the Lamont Doherty Earth Observatory at Columbia University in New York. “Our research suggests that the climate drivers of these early harvests have changed.”

Indicators of wine quality, such as wine ratings, show the best years for grape harvest typically include warm summers with above-average rainfall early in the growing season and late-season drought.

“This gives vines plenty of heat and moisture to grow early in the season, while drier conditions later in the season shift them away from vegetative growth and toward greater fruit production,” said the study’s co-author, ecologist Elizabeth Wolkovich of Arnold Arboretum and the Department of Organismic and Evolutionary Biology at Harvard University, Cambridge, Mass.

Researchers conducted an analysis using 400 years of harvest data from Western Europe. The study considered variability and trends in harvest dates, climate data from instruments during the 20th century, and reconstructions from historical documents and tree rings of temperature, precipitation and soil moisture dating back to 1600.

That analysis was compared with shifts in wine quality in the Bordeaux and Burgundy regions of France based on the ratings of vintages during the past 100 years. Detailed quality information was available for those two regions in addition to the broader harvest data available throughout France and Switzerland.

The results indicate a fundamental shift in the role of drought and moisture as large-scale drivers of harvest time and wine quality. While warm temperatures have consistently led to earlier harvests and higher-quality wines, in recent decades the impact of drought has largely disappeared as a result of large-scale shifts in climate.

“Wine quality also depends on a number of factors beyond climate, including grape varieties, soils, vineyard management and winemaker practices,” Cook said. “However, our research suggests the large-scale climate drivers these local factors operate under has shifted. And that information may prove critical to wine producers as climate change intensifies during the coming decades in France, Switzerland and other wine-growing regions."

The paper was published March 21 in the journal Nature Climate Change.