Dr. Anca Constantin and junior physics major Emil Christensen (top photo) review megamaser data captured by radio telescopes. They compare data from galaxies where water megamasers have been found to galaxies where they hope to find more of them.
Scientists are on the verge of unlocking answers to two of
astronomy's biggest questions and a JMU researcher is right in the middle of
it.
Dr. Anca Constantin, an assistant professor of physics and
astronomy, recently received a $10,000 grant from the Jeffress Memorial Trust
to continue working on her part of the project—finding water megamasers suitable
for measuring distances from earth to the galaxies they reside in and for
measuring the mass of their galaxy's supermassive black hole.
"For the whole history of astronomy, we wanted to get
estimates of these," said Constantin, who has received several other
grants for the research and who is part of the National Radio Astronomy
Observatory's Megamaser Cosmology Project.
"We do have some other methods for weighing
supermassive black holes, but this method gives us the most accurate estimate
on how massive they are," Constantin said. As for measuring distances to
galaxies in the outer reaches of the universe, certain megamasers—those located
near the supermassive black hole in the center of their galaxies and whose
water molecules produce the emissions—provide the most accurate distances ever.
"We know many things about how the universe looks geometrically, but it's
not going to be as accurate as the distance given by this information,"
she said. "It's a direct method."
An astrophysical maser is similar to a laser, which stands
for light amplification by stimulated emission of radiation. The difference is
that maser emissions are typically in the microwave portion of the
electromagnetic spectrum while laser emissions are in the visible light portion
of the spectrum. Dr. James Braatz, who leads the Megamaser Cosmology Project,
described masers as the radio-frequency equivalent of lasers.
Because megamaser emissions are not visible to optical
telescopes, they are observed through radio telescopes such as the Green Bank Telescope,
the world's largest fully steerable radio telescope, located just two hours southwest
of Harrisonburg in Green Bank, W.Va. Finding the right kind of megamaser to
make the measurements is a challenge, especially since there are hundreds of
billions of galaxies in the universe. That's where Constantin comes in, with
her research identifying properties of galaxies that host megamasers.
"There seems to be a Goldilocks region for a bunch of
properties, like the rate of accretion of matter onto that supermassive black
hole has to be in a certain narrow range, the density of the material in the
nuclear region needs to be in a certain narrow range, the galaxy can't be too
big or too small, the star population can't be too old or too young," she
said.
Added Emil Christensen, a junior physics major who is
assisting Constantin with the research and with a paper they are writing about
the research, "We try to find out what makes them tick, why they are
there."
Water megamasers that are formed in disk-like configurations
are like "holy grails of astronomy," Constantin said. "If it's
in a disk, we can actually map the rotation of the disk. It's actually a very
simple mathematical model that any planet would follow in its orbit around its
sun," she explained. "So you fix mathematically those positions and
velocities of those masers and you can obtain the most accurate measurements of
how massive the thing in the middle is, and that is the mass of the
supermassive black hole."
And if the disk is face-on, simple geometry can be used to
measure the distance to the galaxy, she said.
Megamasers are relatively new to astronomers, having been
discovered about 50 years ago, and water megamaser disks have been rare finds. So
far, only about eight megamaser disks with the right properties for making the
measurements have been discovered. More are needed to improve the accuracy of
the results so knowing where to look is vitally important. "We just don't
have the time, the money to point these radio dishes toward all of these
galaxies," Constantin said. "We're just never going to find them. We
need to be more efficient in our search."
The way to do that, she said, is by comparing the properties
of the galaxies where they have been found to the properties of galaxies known
to contain maser emissions. So far, there are about 150 galaxies with detected
maser emissions and about 40 of those seem to show promise for having the right
properties.
"It's not easy," Constantin said, explaining that
researchers have to mine the data captured by the telescopes to find what
they're looking for. "It's a lot of work, but it's amazing when you find
something."
"It's very incremental," Christensen said of his
search through various databases and literature. "We learn a little bit of
the puzzle, a very little bit. But it is important. And if somehow we get
something that really can narrow it down, we find a lot of them, then
statistically, a certain fraction of them are going to be useful."
And that information could be very useful to
answer another burning question in astronomy—how do galaxies form? "What's
the relationship between the galaxy and the black hole in the center? It's like
a chicken or the egg question, what came first, the black hole or the
galaxy?" Constantin said. "There are some hints that they
co-evolved."
By Eric Gorton ('86,'09), JMU Public Affairs
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Posted March 4, 2013
