Strong Pull of Black Holes

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Every second, intense beams of maser emission (like laser emission but at radio frequencies) arrive on Earth from clouds of water vapor orbiting supermassive black holes (SMBHs), millions to billions of times the mass of the Sun, at centers of galaxies hundreds of millions of light years away. Ingyin Zaw, assistant professor of Physics at NYU Abu Dhabi, is using the largest and best radio telescopes in both the Northern and Southern hemispheres to tease out information from these maser systems in the attempt to unravel the nature and behavior of their host SMBHs.

Although SMBHs are only a small fraction of the total mass of the galaxies they inhabit, their growth and evolution are intimately linked with that of their host galaxies across cosmic time. A key in regulating this relationship is the process of accretion — how gas and dust from the galaxy falls into the SMBH — and outflows — material that is driven from the vicinity of the SMBH. Both accretion and outflows influence physical processes, like star formation, in the host galaxy.

Water masers occupy a unique location within a few light months to a few light years of the SMBH. They are in a region where the gravity of the SMBH dominates over that of the galaxy. From their location and motion, many properties of the SMBH and surrounding material can be deduced, including the mass of the SMBH, the geometry and temperature of the material around the SMBH, the shape of outflows, and the distance to the host galaxy.

"I'm amazed at how well we can study objects so far away," said the Burmese-born, Harvard-educated Zaw. The maser emission, up to hundreds of millions times weaker than the average TV signal, is discovered by large single-dish telescopes, approximately 100-meter versions of rooftop satellite dishes. Then, using very long baseline interferometry — a group of telescopes that spread out over the Earth but act as one — astronomers are able to image the individual maser clumps. The resolution produced by this method is the equivalent on Earth of being able to see the face of a person standing on the moon.

In addition, Zaw wants to combine this information with data of light emitted at other frequencies, since different physical processes at different locations near the SMBH emit at different frequencies. This way, she will be able to disentangle the complex physical conditions near the SMBH, then build models and compare them to theoretical predictions.

I'm amazed at how well we can study objects so far away.

Ingyin Zaw, NYUAD assistant professor of Physics.

Zaw was in Australia in April 2014 to work with the Southern Hemisphere's largest radio telescope, the 70-meter Tidbinbilla antenna, a part of NASA's Deep Space Network, near Canberra. She and Lincoln Greenhill, a senior researcher at the Harvard-Smithsonian Center for Astrophysics, are co-principal investigators on the Tidbinbilla AGN Maser Survey, known as TAMS. The seven-person team, which spans three continents, comprises Zaw's postdoctoral researcher Aquib Moin and collaborators at Australian National University's Jet Propulsion Laboratory and the Canberra Deep Space Communication Complex. The arrangement is ideal for splitting up observing sessions that can be scheduled for any time, day or night, said Zaw. She is also excited to supervise research projects of NYUAD students using the data from the TAMS project.

Zaw and two other NYUAD Physics faculty, Visiting Professor of Practice of Physics Mallory Roberts and Assistant Professor of Physics Joseph Gelfand, are also working on a partnership with the National Radio Astronomy Observatory's 100-meter Green Bank Telescope in Green Bank, West Virginia, to conduct maser and pulsar observations.

The Australian project has been allotted 1,200 hours of telescope time to be spread out over the next few years. During her April 2014 trip, Zaw calibrated the instrument and prepared to begin the first year of study, designated as a pilot phase. "We need cold dry nights," she said, and the Australian winter fits that requirement.

"When it's all set up," she added, her tone revealing her enthusiasm for the project, "I'll be able to sit in my office at NYU Abu Dhabi and control the telescope remotely. It is truly a privilege."

Zaw cites a quote from the poem "Planetarium" by Adrienne Rich that inspires her:

I am bombarded yet I stand
I have been standing all my life in the
direct path of a battery of signals
the most accurately transmitted most
untranslatable language in the universe
I am an instrument in the shape
of a woman trying to translate pulsations
into images for the relief of the body
and the reconstruction of the mind.

This article originally appeared in NYUAD's 2013-14 Research Report (13MB PDF).