THE EARLY UNIVERSE IS DUSTY, AND ASTRONOMERS FINALLY KNOW WHY
June 8, 2006
McMaster University and Gemini Observatory News Release
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Gemini Multi-object Spectrograph (GMOS) image of galaxy NGC 628 (M74) taken in August 2001 which contains the star which became SN 2003gd. See Gemini story on the detection of the progenitor star for SN 2003gd with the data from this image published in January 2004. Image obtained with the Gemini North telescope on Mauna Kea Hawai‘i. Image is rotated ~ 135 degrees counter-clockwise from north up.
HAMILTON, ON. June 8, 2006 - Massive star supernovae have been major "dust factories" ever since the first generations of stars formed several hundred million years after the Big Bang, according to an international study to be published in Science magazine on July 14, 2006.
The scientific team trained their telescopes on Supernova 2003gd, which exploded in the spiral galaxy NGC 628 located about 30 million light-years from Earth. The light from the 2003gd first reached Earth on March 17, 2003. At its brightest, it could be seen in an amateur astronomer's telescope. While many supernovae are discovered each year, this particular one stood out because it was relatively nearby and could be followed for a long-than-usual time by the specialized infrared detectors of the Spitzer Space Telescope, and by an optical spectrograph on the Gemini North telescope.
"2003gd is, quite literally, the smoking gun," says Doug Welch, professor, physics & astronomy at McMaster University, and one of 17 astronomers involved in the study. "These carbon and silicon dust particles which form from the supernovae blast make possible the many generations of high-mass stars and all the heavy elements they produce. These are elements which make up the bulk of everything around us on Earth, including you and me."
In August 2004, Welch and co-author Geoff Clayton of Louisiana State University, visited the Gemini North telescope in Hawaii to take optical spectra, with the Gemini Multi-object Spectrograph (GMOS), of ancient massive star supernovae in their hunt for the formation of dust.
Making space dust requires elements heavier than hydrogen and helium - the only elements in existence after the Big Bang. Once dust is available stars form much more quickly and efficiently. Up until now, the efficiency and rapidity of the creation of dust by massive star supernovae has been unknown.
"We have finally shown that supernovae could have been major contributors to the dust present in the early Universe," said Ben Sugerman, of the Space Telescope Science Institute in Baltimore, MD. "Until now, the available evidence has pointed to the contrary."
Supernovae expand and dissipate into space quickly, so scientists require extremely sensitive telescopes to study them even a few months after the initial explosion. Dust does not begin to form until two years after an explosion, so while astronomers have suspected that most supernovae do produce dust, their ability to confirm this stellar dust production in the past was limited by the available technology.
The study utilized Hubble Space Telescope data as well as new observations from the Spitzer Space Telescope (currently trailing the Earth along its orbit) and the Gemini North telescope of the Gemini Observatory on Mauna Kea, Hawai'i.
"This work demonstrates the enormous value of working in different parts of the spectrum and the critical need for both ground-based and space-based facilities," says Welch.
Funding for the research was provided in part by the Natural Sciences and Engineering Research Council. Canada's participation in the Gemini Observatory is funded by the National Research Council of Canada's Herzberg Institute for Astrophysics. The Gemini Observatory consists of twin 8-meter telescopes in Hawai'i and Chile funded by an international partnership that includes: US, UK, Canada, Australia, Brazil, Argentina and Chile.
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Animated GIF showing field around SN 2003gd revealing the change in the supernova relative to the surrounding galaxy (flashing star at center).
A mosaic of images from the Spitzer Space Telescope covering the entire galaxy NGC 628 on July 28, 2004. Normal stars appear blue, hot dust (about 200 deg Celsius) appears green, and cooler dust appears red. NGC 628 is 30 million light years away from Earth. The white box shows the area enlarged in the other images. The green object at the centre of the white box is the supernova 2003gd.
A pair of false colour images of the spiral galaxy NGC 628 was obtained with the Spitzer Space Telescope (these images were used to make the animated GIF sequence at right). Each was produced by combining images at three different infrared wavelengths. Stars of any sort appear blue, hot dust appears green and cool dust appears red. Supernova 2003gd is near the centre of each frame. The left image was taken on Jul 28, 2004 when its dust had a temperature of about 200 deg Celsius. In the right image, taken on Jan 15, 2005, the dust has cooled below detection limits. The centre of NGC 628 is at the right. A spiral arm containing cool dust can be seen sweeping from upper right through the central part of the image.