Over a 30-hour period on September 26-27, 2009, an eruption occurred on the Sun. Carried by the Sun's changing magnetic field, a filament, also known as a prominence of hot gas rose from the star's surface. The event was observed <> by NASA's Solar Terrestrial Reflection Observatory (STEREO) <> mission. STEREO consists of twin spacecraft that orbit the Sun, one spacecraft ahead of the Earth and the other following behind. The spacecraft that trails behind Earth captured the image on the left, and the spacecraft that travels ahead of Earth captured the image on the right. The pictures show ultraviolet light; the hotter the temperature, the brighter the light. Although the gas in a prominence is unimaginably hot by human standards, it is actually cool compared to the Sun's surface. Compared to the mottled yellow of the surface, the filament looks dark. The prominence is more conspicuous in the right image, where much of the gas appears in profile. Viewed against the blackness of space, the prominence appears orange. The orange color is especially bright near the Sun's surface, but fainter wisps of orange also appear farther from the star. This prominence was one of the first that was large enough for both STEREO spacecraft to observe it for hours. Filaments are held in place by magnetic fields driven by electrical currents. The fields form loops near the Sun's surface, and cold, dense gas fills the loop. Most of this gas eventually falls back to the star's surface as the filament collapses, but powerful solar eruptions can send particles all the way to Earth. This prominence spans only part of the Sun's disk, but it easily dwarfs our own planet, whose size relative to the Sun is shown by the small white dot at the lower right of the STEREO Ahead image.
updated 11/20/2009 7:51:57 PM ET 2009-11-21T00:51:57

New images show the "last meal" of a giant cannibal galaxy as it gobbles down a smaller spiral galaxy, which has been twisted and warped from being devoured.

The giant galaxy, Centaurus A (NGC 5128) is the nearest giant, elliptical galaxy, at a distance of about 11 million light-years. The galaxy hosts a supermassive black hole that is 200 million times the mass of the sun, or 50 times the mass of the black hole at the center of the Milky Way.

At the galaxy's center is an opaque dust lane that is thought to be the remains of a cosmic merger between the galaxy and a smaller spiral galaxy full of dust.

Between 200 and 700 million years ago, this galaxy is believed to have consumed a smaller spiral, gas-rich galaxy — the contents of which appear to be churning inside Centaurus A's core, likely triggering new generations of stars.

First glimpses of the "leftovers" of this meal were obtained thanks to observations with the European Space Agency's Infrared Space Observatory, which revealed a 16,500 light-year-wide structure, very similar to that of a small barred galaxy.

More recently, NASA's Spitzer Space Telescope resolved this structure into a parallelogram, which can be explained as the remnant of a gas-rich spiral galaxy falling into an elliptical galaxy and becoming twisted and warped in the process. Galaxy merging is the most common mechanism to explain the formation of such giant elliptical galaxies.

The new images, taken by the European Southern Observatory's 3.58-metre New Technology Telescope (NTT) in La Silla, Chile, allow astronomers to get an even sharper view of the structure of this galaxy, completely free of obscuring dust.

What the astronomers found in the images was surprising: "There is a clear ring of stars and clusters hidden behind the dust lanes, and our images provide an unprecedentedly detailed view toward it," said Jouni Kainulainen, lead author of the paper reporting these results. "Further analysis of this structure will provide important clues on how the merging process occurred and what has been the role of star formation during it."

Video: Zoom in on a cosmic ‘cannibal’ (on this page) The technique used to observe Centaurus A could help scientists better understand star formation in galaxies.

"These are the first steps in the development of a new technique that has the potential to trace giant clouds of gas in other galaxies at high resolution and in a cost-effective way," said co-author João Alves. "Knowing how these giant clouds form and evolve is to understand how stars form in galaxies."

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Video: Zoom in on a cosmic ‘cannibal’


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