Sun, Oct 04, 2015 - Page 3 News List

Researchers calculate mass of black hole

By Chen Wei-han  /  Staff reporter

Academia Sinica researchers said they have calculated that a supermassive black hole in a galaxy 4 billion light-years away might contain more than 300 million times the Sun’s mass by analyzing images taken by radio telescopes, adding that the findings are key to understanding the formation and evolution of black holes and their host galaxies.

A team led by research fellows Kenneth Wong (黃活生), Sherry Suyu (蘇游瑄) and Satoki Matsushita on Monday said that it analyzed the high-resolution images of SDP.81, a galaxy located 4 billion light-years from Earth, taken by the Atacama Large Millimeter Array (ALMA) in Chile — the biggest radio telescope array in the world for observing radiation from the early universe, molecular gas and interstellar dust.

The images were taken during a chance alignment of the Earth, SDP.81 and another galaxy — all located in a straight line spanning 12 billion light-years, Wong said.

The images display what is known as the Einstein ring: the deformation of light from a source — in this case, the background galaxy 12 billion light-years away — into a ring due to gravitational lensing by an object with an extremely large mass — SDP.81, Wong said.

The gravity of the massive foreground galaxy deflects the light from the background galaxy and creates the ring structure, allowing the team to calculate the mass of a supermassive black hole, located near the center of SDP.81, by analyzing the brightness of the ring and of the central image within the ring, Wong said, adding that the Hubble Space Telescope is unable to capture such images as it only detects visible and infrared light.

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

Almost all massive galaxies seem to have supermassive black holes at their centers. Previously, scientists could only directly calculate the mass for galaxies immediately adjacent, Wong said.

“ALMA now gives us the sensitivity to look at 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 critical to understanding their relationship with their host galaxies and how they grow over time, he added.

The research was published last month in the peer-reviewed Astrophysical Journal periodical.

Next year the team plans to observe a gravitational lens located 6 billion light-years away.

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