AsianScientist (Jun. 26, 2015) – For centuries, cartographers were fond of depicting monsters along the edges of their maps. Now, researchers have depicted a monstrous galaxy near the edge of the charted Universe with unprecedented detail using the Atacama Large Millimeter/submillimeter Array (ALMA) with the assistance of a ‘natural telescope’ known as a gravitational lens.
A team of Japanese researchers modeled the lensing effects and corrected for them to reveal the distribution of huge stellar cradles in the monstrous galaxy. The model indicates, for the first time, the existence of a supermassive black hole at the center of the foreground galaxy. Their findings have been published in Publications of the Astronomical Society of Japan.
During its high resolution test observation campaign in October 2014, ALMA imaged 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 us acts as a natural telescope, magnifying the image of SDP.81. The image becomes larger and brighter but smears into a ring shape. This ultra-sharp image of the ring astounded astronomers around the globe, but it has been difficult to understand the details of its complicated structure.
Assistant Professors Yoichi Tamura and Masamune Oguri at the University of Tokyo, together with researchers at the National Astronomical Observatory of Japan (NAOJ), constructed the best model to date for the gravitational lens. Using this model, they corrected for lensing effects and revealed that SDP.81 is a monstrous galaxy forming stars at hundreds to thousands of times the rate we see in the Milky Way. This is an important step to understand the evolutionary process of starburst galaxies and supermassive black holes in galaxies.
Einstein’s theory of General Relativity tells us that a massive object bends space and time. The light traveling through this curved space-time bends to follow the curve, thus the massive object works as a cosmic lens. In rare cases that a distant galaxy, an intervening galaxy producing a gravitational lens and the Earth lines up perfectly, the image forms a circle of light known as an ‘Einstein ring’.
SDP.81 is an excellent example of an Einstein ring. ALMA detected radio waves with a wavelength of one millimeter 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.
The high-resolution ALMA image also enables researchers to seek “the central image” of the background galaxy, which is predicted to appear at the center of the Einstein ring. If the foreground galaxy has a supermassive black hole at the center, the central image becomes much fainter. Thus the brightness of the central image reflects the mass of the black hole in the foreground galaxy. The central image of SDP.81 is very faint, leading the team to conclude that the foreground galaxy holds a giant black hole over 300 million times more massive than the Sun.
Using powerful telescopes, the team continues to unravel the mysteries surrounding the formation and evolution of monstrous starburst galaxies and supermassive black holes.
The article can be found at: Tamura et al. (2015) High-Resolution ALMA Observations Of SDP.81. I. The Innermost Mass Profile Of The Lensing Elliptical Galaxy Probed By 30 milli-arcsecond images.
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Source: The National Astronomical Observatory of Japan.
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