A Rare Glimpse Of An Einstein Ring’s Blackhole

The highest-ever resolution images of the SDP.81 galaxy have shed light on a supermassive black hole 300 million times the mass of the Sun.

AsianScientist (Oct. 19, 2015) – Astronomers at the Institute of Astronomy and Astrophysics (ASIAA) have calculated that the supermassive black hole located near the center of the lensing galaxy SDP.81 may contain over 300 million times the mass of the sun. Their research, published in The Astrophysical Journal, used the highest-ever resolution images of SDP.81 taken by the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile.

Objects with extremely large masses, such as galaxies, can deform the fabric of spacetime, causing light to bend around them in a phenomenon known as gravitational lensing. SDP.81 is special type of lensing galaxy called an Einstein ring, which bends the light from a more distant galaxy into a complete circle. This rare and beautiful phenomenon occurs through a chance alignment of three objects: the Earth and two other galaxies, all located in a straight line separated by a great distance of 12 billion light years.

The ASIAA team further explained that there are in fact two galaxies in this Einstein ring system: the foreground galaxy, which is four billion light-years away, and the background galaxy, whose light has taken 12 billion years to reach us. The gravity of the massive foreground galaxy deflects the light from the background galaxy and creates the ring structure. The background galaxy contains a large amount of dust that has been heated by vigorous star formation, causing it to shine brightly in submillimeter light. ALMA is a submillimeter telescope which is best for observing dusty objects.

By analyzing the high-resolution data and modeling the gravitational lensing effect, the team determined that the massive lensing galaxy contains over 350 billion times the mass of the sun within the ring. Dr. Kenneth Wong, together with Dr. Sherry Suyu and Dr. Satoki Matsushita of ASIAA, analyzed the central regions of SDP.81 and found the predicted central image of the background galaxy to be extremely faint.

Lensing theory predicts that the central image of a lensing system is very sensitive to the mass of a supermassive black hole in the lens galaxy: the more massive the black hole, the fainter the central image. From this, they calculated that the supermassive black hole, located very close to the center of the SDP.81, may contain over 300 million times the mass of the Sun.

The first author of the article, Wong, explained the information behind this image. He says almost all massive galaxies seem to have supermassive black holes at their centers.

“They can be millions, or even billions of times more massive than the sun. However, we can only directly calculate the mass for very nearby galaxies. With ALMA, we now have the sensitivity to look for the central image of the lens, which can allow us to determine the mass of much more distant black holes,” Wong said.

Measuring the masses of more distant black holes is the key to understanding their relationship with their host galaxies and how they grow over time, Wong added.

“This is the highest-resolution image of a gravitational lens that has ever been taken,” said Wong, “The amount of detail in this image is much greater than even space telescope observations,”

“ALMA opens a new frontier to weigh supermassive black holes at centers of lensing galaxies, which cannot be done previously with optical telescopes,” said co-author Suyu of ASIAA.

“With the high-resolution capabilities of ALMA, which we helped to realize in the last five years, it is now possible to perform new science that cannot be done with any other instrument,” said co-author Matsushita of ASIAA.

Wong, Suyu and Matsushita, along with collaborators in Japan, have been awarded time on ALMA within the next year to observe a more distant gravitational lens similar to SDP.81, one which they anticipate will have a brighter central image that could directly constrain the mass of the supermassive black hole. With the capabilities of ALMA, they hope to continue investigating the formation and evolution of these massive galaxies and their supermassive black holes.

The article can be found at: Wong et al. (2015) The Innermost Mass Distribution of the Gravitational Lens SDP.81 from ALMA Observations.

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Source: Institute of Astronomy and Astrophysics, Academia Sinica.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

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