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Giant new galaxy revealed on the edge of the universe

June 10, 2015 18:09 IST

ALMA image of the gravitationally lensed galaxy SDP.81. The bright orange central region of the ring (ALMA's highest resolution observation ever) reveals the glowing dust in this distant galaxy. The surrounding lower-resolution portions of the ring trace the millimeter wavelength light emitted by carbon monoxide. Photograph: ALMA (NRAO/ESO/NAOJ); B. Saxton NRAO/AUI/NSF

Astronomers have imaged in unprecedented detail a distant galaxy near the edge of the universe and found that it is forming stars hundreds to thousands of times faster than the Milky Way.

The astronomers used the Atacama Large Millimeter/submillimeter Array to image the monstrous galaxy SDP.81, located 11.7 billion light-years away from the earth in the constellation Hydra.

A gravitational lens created by a massive foreground galaxy 3.4 billion light-years from the earth acts as a natural telescope, magnifying the image of SDP.81.

ALMA/Hubble composite image of the gravitationally lensed galaxy SDP.81. Photographer: ALMA (NRAO/ESO/NAOJ); B. Saxton NRAO/AUI/NSF; NASA/ESA Hubble, T. Hunter (NRAO)

The image becomes brighter but smears into a ring shape, researchers said.

Yoichi Tamura and Masamune Oguri, assistant professors at the University of Tokyo, together with researchers at the National Astronomical Observatory of Japan, have constructed the best model to date for the gravitational lens.

Using this model, they corrected for lensing effects and found that SDP.81 is a monstrous galaxy forming stars at hundreds to thousands of times the rate seen in the Milky Way.

SDP.81 is an excellent example of an Einstein ring, researchers said. According to Einstein's theory of General Relativity, a massive object bends space and time.

The light travelling through this curved space-time bends to follow the curve, thus the massive object works as a cosmic lens.

ALMA's highest resolution image ever reveals the dust glowing inside the distant galaxy SDP.81. The ring structure was created by a gravitational lens that distorted the view of the distant galaxy into a ring-like structure. Photograph: ALMA (NRAO/ESO/NAOJ)

In the rare case that a distant galaxy, an intervening galaxy producing a gravitational lens, and the earth line up perfectly, the image forms a circle of light known as an Einstein ring.

Researchers using ALMA detected radio waves with a wavelength of one millimetre emitted by cold molecular gas and dust, the ingredients of stars and planets, with a resolution of 23 milliarcseconds, which surpasses the resolution of the Hubble Space Telescope.

The image is so sharp that researchers found bends, branches, and small grainy structures inside the ring.  To understand the causes of those fine structures, the research team produced a sophisticated model of the gravitational lens.

The model showed that the fine structures in the ring reflect the inner structure of SDP.81. Researchers found that several dust clouds with sizes of 200 to 500 light-years are distributed within an elliptic region 5,000 light-years across. The dust clouds are thought to be giant molecular clouds, the birthplaces of stars and planets.

The clouds in SDP.81 have sizes similar to those found in our Milky Way and nearby galaxies. This is the first time astronomers have been able to reveal the inner structure of such a distant galaxy.

The model also indicates the existence of a supermassive black hole, over 300 million times more massive than the Sun, at the centre of the foreground galaxy.

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