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Herschel dusts off
hidden cosmic origin

Posted: 08 July 2011

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An exploding star which has expelled the equivalent of between 160,000 and 230,000 Earth masses of fresh dust has been revealed by ESA’s infrared Herschel Space Observatory, suggesting that supernovae like this one, also known as SN1987A, could be the answer to an age-old puzzle of what supplied our early Universe with dust.

This image compares two pictures of Supernova remnant called SN 1987A. The left images was taken by the Herschel Space Observatory, whereas the right is an enlarged view of the circled region at the left, taken with NASA’s Hubble Space Telescope. Image: ESA/NASA-JPL/STScI.

Cosmic dust, which is made of elements such as carbon, oxygen, iron and other atoms heavier than hydrogen and helium, is a key ingredient for making planets and even ourselves. It is also essential for star formation, and stars like our Sun spit out flecks of this material as they age, spawning new generations of stars and their orbiting planetary companions. “The Earth on which we stand is made almost entirely of material created inside a star,” explained the principal investigator of the survey project, Margaret Mexiner of the Space Telescope Science Institute, Baltimore, Maryland. “Now we have a direct measurement of how supernovae enrich space with the elements that condense into the dust that is needed for stars, planets and life.”

For decades, astronomers have wondered how dust was made in our early Universe, where back then, Sun-like stars had not been around long enough to produce the enormous amounts of dust observed in distant, early galaxies. In comparison, supernovae are the explosions of massive stars which do not live for very long, and it is the new Hershel observations that have revealed these temperamental stars to be the possible dust-making machines of the early cosmos. “This discovery illustrates the power of tackling a problem in astronomy with different wavelengths of light,” says Paul Goldsmith, the NASA Herschel project scientist of the Jet Propulsion Laboratory, Pasadena, California, who is not part of the current study. “Herschel’s eye for long-wavelength infrared light has given us new tools for addressing a profound cosmic mystery.”

The Herschel Space Telescope operates at longer wavelengths than Spitzer, making it possible for the instrument to probe cold regions of space. Image: ESA (Image by AOES Medialab.)

Astronomers focused on the remains of SN 1987A, the most recent stellar explosion to be witnessed with the naked eye from our home planet, for the study which is set to appear in the 8 July issue of the journal,Science. The stellar blast was believed to have occurred some 170,000 light-years away in 1987, where it was seen to brighten in the night sky before slowly fading over the months that followed. SN 1987A is one of the most extensively studied objects in the heavens due to astronomers being able to witness the star’s death throes over time. One such observation, which proved useful to the astronomers’ investigation, was a Herschel survey of the supernova’s host galaxy, the Large Magellanic Cloud, where SN 1987A was snapped.

After the scientists yielded the images from space, they were amazed to discover that SN 1987A was aglow with light and, with careful calculations, it was revealed that the radiancy was originating from enormous clouds of dust - consisting of 10,000 times more material than previously estimated. The dust, which is around -221 to -213 degrees Celsius, is colder than Pluto, whose distance from the Sun, leaves it with an icy -204 degrees Celsius. “Our Herschel discovery of dust in SN 1987A can make a significant understanding in the dust in the Large Magellanic Cloud,” says Mikako Matsuura of University College London, the lead author of the paper. “In addition to the puzzle of how dust is made in the early Universe, these results give us new clues to mysteries about how the Large Magellanic Cloud and even our own Milky Way became so dusty.”

It is not just this current study that has turned up evidence that supernovae are capable of producing dust. NASA’s Spitzer Space Telescope, which detects shorter infrared wavelengths than Herschel, uncovered 10,000 Earth-masses worth of fresh dust around the supernova remnant, Cassiopeia A. With Herschel, however, scientists can look into the coldest reservoirs of dust. “The discovery of up to 230,000 Earths worth of dust around SN 1987A is the best evidence yet that these monstrous blasts are indeed mighty dust makers,” says Eli Dwek, a co-author at NASA Goddard Space Flight Center in Greenbelt, Maryland.