MONSTER GALAXY spotted hiding behind IMMENSE BLACK HOLE

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Credit: Y. Tamura (The University of Tokyo)/ALMA (ESO/NAOJ/NRAO) National Astronomical Observatory of Japan

Astro-boffins have detailed a "monstrous" galaxy near the edge of the charted universe, and have done so to an unprecedented degree of detail using the Atacama Large Millimetre/submillimetre Array (ALMA), with the assistance of a natural telescopic phenomenon known as a gravitational lens.

According to the National Institutes of Natural Sciences, the team from the University of Tokyo modeled the lensing effects – as popularly featured in the film Insterstellar – and corrected for them to reveal the distribution of huge stellar cradles in the monstrous galaxy.

The paper is titled High-resolution ALMA observations of SDP.81. I. The innermost mass profile of the lensing elliptical galaxy probed by 30 milli-arcsecond images and published in the Publications of the Astronomical Society of Japan (PASJ).

As a bonus, the research also indicated the existence of a super-massive black hole at the centre of the foreground galaxy, which lies at the edge of the charted universe.

The observation campaign launched in October 2014. ALMA used its high-resolution instrument to image what is being described as a "monstrous" galaxy, known as SDP.81, which is located 11.7 billion light-years away from the Earth in the constellation of Hydra.

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

However, while the image becomes brighter, it is also distorted into a ring shape, as can be seen in the index image. 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.

Yoichi Tamura and Masamune Oguri – assistant professors at the University of Tokyo – together with researchers at the National Astronomical Observatory of Japan (NAOJ), constructed the best model to account for the gravitational lens' effects.

Using this model, they corrected for lensing effects and revealed that SDP.81 is an enormous galaxy, forming stars at hundreds to thousands of times the rate we see in the Milky Way.

This is an important step towards understanding the evolutionary process of starburst galaxies and super-massive black holes in galaxies.

Einstein's theory of General Relativity suggests that a massive object bends space and time, so that light travelling through the curved space-time will follow this curvature, thus allowing massive objects situated directly between an observer and the object to be observed to work as an enormous cosmic lens.

In the rare cases that this phenomenon has situated Earth as the observer, the image forms a circle of light known as an Einstein ring. These gravitational lenses make the distant objects look much larger and brighter, helping astronomers to study galaxies, black holes, and dark matter in the distant universe.

SDP.81 is an excellent example of an Einstein ring. 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. This model is unique in its ability to precisely adjust for distortions in the lens, like correcting astigmatism.

The high-resolution ALMA image also enabled the boffins to seek "the central image" of the background galaxy, which is predicted to appear at the centre of the Einstein ring.

It is known that if the foreground galaxy has a supermassive black hole at the center, the central image will become much fainter. Thus the brightness of the central image above reflects the mass of the black hole in the foreground galaxy.

The central image of SDP.81 is indeed 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. ®


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