New images of starburst galaxy M82 reveal multiple sources of its superwind
The wind originates from multiple ejection sites spread over hundreds of light-years rather than emanating from any single cluster of new stars.
March 7, 2011
The Subaru Telescope, fitted with the Cooled Mid-Infrared Camera and Spectrometer (COMICS), has produced a new image of the interior of the starburst galaxy M82 that reveals young star clusters as well as the sources of its superwind in spectacular detail. The ultra-sharp image contributes to our understanding of this complex, young galaxy by showing that M82's galactic windstorms emanate from many sites rather than from any single cluster of stars.
Images of M82. top: Subaru high-resolution image of the interior of M82. middle: Mid-infrared image of M82 from the Spitzer Space Telescope showing an overview of the galaxy. bottom: Optical image of M82 from Subaru Telescope showing the superwind crossing the disk structure. Subaru Telescope facility
Antoine de Saint-Exupery wrote, "What is essential is invisible to the eye," and this has certainly been true for examining the details of early galaxies undergoing bursts of star formation. The study of starburst galaxies enables astronomers to effectively peer back into our own galaxy's past. Like human beings, galaxies and the stars within them have a life cycle — they are born, grow, mature, and eventually die. Starburst galaxies are real "baby boomers," creating new stars at a rate faster than the combined speed of many Milky Way-like galaxies that are in a later phase of development. The dusty "ash" left over from successive generations of star formation in more mature galaxies blocks out much of the starlight, rendering it invisible to the human eye. The bulk of the energy from starbursts emerges at longer wavelengths; therefore, astronomers must turn to infrared rather than visible-light observations in order to understand the nature of these cosmic stellar factories.
An international team of scientists, led by Poshak Gandi of the Japan Aerospace Exploration Agency (JAXA) in Kanagawa, Japan, used the Subaru Telescope to produce a new view of M82 at infrared wavelengths that are 20 times longer than those visible to the human eye. M82 is located close to the ladle of the Big Dipper in the constellation Ursa Major and is the nearest starburst galaxy at a distance of about 11 million light-years from Earth.
The combination of the Subaru Telescope's large 8.2-meter primary mirror and its mid-infrared instrument COMICS allowed the team to obtain a sharp, magnified view of the inner area of the galaxy. "Together they give us the capability to capture fine details equivalent to the ability to see a small coin from a distance of 6 miles (10 km), or being able to recognize a truck 6,200 miles (10,000 km) away — as far as London is from Tokyo," said Aya Bamba from the Dublin Institute for Advanced Studies and JAXA. The final result of the observations is a spectacular image showing the base of a dusty superwind and young star clusters with extraordinary detail, better than could be expected from space telescopes, which have smaller apertures that limit the extent to which they can resolve fine details.
Previous observations of M82 with infrared telescopes have found a strong wind emanating from it — a superwind that is composed of dusty gas and extends over many hundreds of thousands of light-years. This high-powered windstorm ejects material from the galaxy at a speed of about a half million miles per hour, sweeping it up from the central regions and depositing it far and wide over the galaxy and beyond. The contents of this material are seeds for solar systems like our own, and perhaps for life itself. The dusty superwind glows brightly in the infrared because billions of bright, newly formed stars heat it up.
The Subaru image gives scientists insight about the sources of the superwind. "The wind is found to originate from multiple ejection sites spread over hundreds of light-years rather than emanating from any single cluster of new stars,” said Gandhi. “We can now distinguish pillars of fast gas, and even a structure resembling the surface of a bubble about 450 light-years wide." COMICS has detectors particularly adept at indicating the presence of warm dust, which found it was more than 100° hotter than the bulk of material filling the rest of the galaxy. The widespread, continuous flow of energy from young stars into the galactic expanse keeps the dust hot.
Further insights from the Subaru mid-infrared image emerge by combining it with the Hubble Space Telescope's near-infrared image and the Chandra X-ray Observatory's X-ray data of M82. Their integration produces a beautiful mosaic that provides the first opportunity to isolate M82's infrared properties. Supported by these data, scientists can study the broad spectrum of radiation of different kinds of objects spread over the galaxy's plane, including supernovae, star clusters, and black holes.