Date: July 15, 2010
Title: Black Holes & More Megamasers!
Podcaster: Richard Drumm
Description: Dr. Jim Braatz of the NRAO continues to talk about the radio astronomical study of megamasers and the by-product of that research that sheds light on the mass of black holes. He also describes how planets can generate masers.
Bio: Dr. Jim Braatz, who received his Ph.D. from the University of Maryland in 1996, was a Jansky Fellow at NRAO in 1998 and has been a member of the Scientific staff of NRAO since 2000. His research interests include cosmic masers, cosmology and AGNs (Active Galactic Nuclei).
Richard Drumm is the President of the Charlottesville Astronomical Society and President of 3D – Drumm Digital Design LLC, a video & audio production company in Charlottesville, Virginia.
Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by the American Association of Variable Star Observers, the world’s leader in variable star data and information, bringing professional and amateur astronomers together to observe and analyze variable stars, and promoting research and education using variable star data. Visit the AAVSO on the web at www.aavso.org
Transcript:
Thanks go out once again to George Hrab for that wonderful introductory music! You can buy his book at lulu.com and his music can be purchased at both CD Baby if you want the CD disk (complete it’s fabulous packaging designed by Donna Mugavero of Sheer Brick) and iTunes if you want just the digital file by itself. While you’re over at the iTunes Store, you should definitely subscribe to the Geologic Podcast, which, though it has really very little to do with geology, it has a lot to do with Geo and logic.
Hello, I’m Richard Drumm The Astronomy Bum in Charlottesville, Virginia, home of the University of Virginia, which has a really great astronomy department, and also the NRAO, the National Radio Astronomy Observatory. It was at the NRAO a couple months ago where I met…
JB:
Jim Braatz. And I’m an astronomer at the National Radio Astronomy Observatory in Charlottesville, Virginia.
RBD:
And here we continue talking about his radio astronomy research into black holes and a little more about the Megamaser Cosmology Project and megamasers in general.
01:08
RBD:
OK, black holes, everybody loves black holes, uh, I think maybe we can figure out why, I mean they’re the strangest of the strange. Tell me about your black hole work.
JB:
OK. Well, using this same project that we’re talking about, the Megamaser Cosmology Project, one of the scientific by-products that we get is a measurement of the mass of the black hole in the center of the galaxy. So that’s because when we make an image of these masers as they’re circling around, we’re actually measuring the velocity as these maser clouds are orbiting the black hole.
01:42
And we can measure the velocity very precisely, which is a good thing, and just for reference the typical velocities of the rotation are, let’s say, 600 km/second which is over a million miles per hour. So this is measured at a distance of only, say, a tenth or a couple of tenths of a parsec from the black hole. So there’s an advantage here. The advantage is we’re able to measure rotation of gas directly in the sphere of influence of the black hole.
So that means, at these distances, nothing else matters dynamically except the black hole itself. It doesn’t matter if you have some star clusters that are outside the range, and it doesn’t matter if there’s a population of gas or something nearby, because dynamically these are all miniscule compared to the 10^7 solar mass black hole sitting in the center.
And in fact this is the best technique for measuring black hole masses in significant numbers, uh, for this reason: Because we’re able to measure the dynamics directly in the sphere of influence.
Now, when you use a telescope like HST to measure black hole masses, HST has done 30 or 40 such things, they have to rely on motions of gas or stars that can be somewhat more distant from the black hole. So they’re not directly looking at the sphere of influence. Now their technique does work for a larger number of galaxies than the maser technique does, but on each individual basis we can get a more precise measurement.
And it’s also valuable, I should point out, that the type of galaxies that we’re looking at are a little bit different than the type that usually are measured with Hubble or with other large optical telescopes. Hubble is good at measuring black hole masses for very large elliptical galaxies with very massive central black holes, maybe 10^8 and 10^9 solar masses, and the technique that I’m talking about, these masers tend to be found in relatively lower mass black holes, so they’re 10^7ish solar masses.
And this is interesting, because there’s a relationship that associates the mass of a black hole with properties of the bulge of the galaxy. So sometimes you can hear about the M-sigma relationship…
(see http://en.wikipedia.org/wiki/M-sigma_relation)
…or the M-L bulge relationship, so what it’s saying is that for some reason that’s not entirely understood, the mass of a black hole in the center of a galaxy seems to be related to the larger scale galaxy properties associated with the bulge. Now these are on entirely different size scales. The black hole is right in the nucleus…
RBD:
Right.
JB:
…and the bulge is a substantial fraction of the entire galaxy. And the fact that people have noticed this correlation, that the black hole mass relates to the bulge, tells us that somehow these two components must’ve formed simultaneously or at least there must be some sort of feedback between the two that allows the formation of the galaxy and the formation of the black hole somehow to be associated.
The correlation is getting tighter. The, the main discovery came a few years ago, but it’s getting tighter and actually one of the things that we’re starting to, to understand a little bit better now is that, what was once thought to be a universal relationship might not necessarily be as universal as we thought.
Some of the black holes in particular that we’re measuring seem to differ a little bit from the M-Sigma relationship. And what that’s suggesting is that there could be a different mechanism that produces black holes up until they get to let’s say 10^6 or 10^7 solar masses as the mechanism that produces say the, the biggest 10^9 solar mass black holes.
RBD:
Big honking black holes! Yes.
How will ALMA help out with the MCP, the Megamaser Cosmology Project?
JB:
So ALMA won’t be a direct contributor to the project, but it will have a number of contributing, kind of side science projects. The main result that we are working with is based on observations of molecules in galaxies, so we’re looking at the water molecule, emission from the water molecule. And ALMA will be the best instrument in the world for understanding molecular emission, not only in external galaxies but of course in our own galaxy as well.
This particular water line that I’ve been talking about, the emission line, the frequency is 22 gigahertz, so this about 1 centimeter in wavelength. So this is a wavelength that’s very good for telescopes like the Green Bank Telescope, the VLA, the VLBA, but ALMA will work at much higher frequencies.
RBD:
Right.
JB:
The water molecule itself, and it’s photons at a large range of frequencies, all the way up through those that ALMA will observe. So ALMA will observe water in galaxies, but it won’t be used for quite the same purpose as what we’re doing with the megamaser project.
RBD:
Ummm, well, what other, uh, projects are you, are you working on? What other areas of interest are in your research?
JB:
My main interest is in applying, uh, masers to whatever sort of environment we can apply them and, uh, masers in general are interesting, as we talked about with the megamaser project, that you can use them as kind of test particles to understand dynamics and understand something about the environment that they reside in.
There’s one project, just kind of a side project, that my student Cheng Yu Quo is working on with me, and we’ll probably observe this sometime in the spring of 2010, and that is to try and find masers in the, uh, atmosphere or the environment of Saturn. So it’s believed that some planets may even produce masers. Now these are intrinsically much less luminous type masers than what I’ve been talking about in external galaxies. But because Saturn is so close by there’s some hope that we might actually be able to detect a maser there.
And it would have some interest because, of course, water, although we haven’t used it in the context we’ve been talking so far, we haven’t used it in the context of life in the universe, but of course people that are interested in understanding how life develops and forms in the universe are very interested in the water molecule. It’s, it’s essential to our own life here on Earth. And so if we can understand whether water can be detected and associated with planets then we might be someday able to, for example, look at exoplanets and see if we can make a direct detection of water in an exoplanet, which would be a very exciting discovery.
RBD:
So Saturn’s rings would be a, sort of a, uh, an accretion disk in miniature.
JB:
In miniature, that’s right.
RBD:
What about accretion disks in star forming regions, and, and planetary accretion disks? Would they mase in any way?
JB:
They do, in fact, so star forming regions turn out to be the brightest, uh, masers that we see on the sky. So in the Orion molecular cloud, in the Orion Nebula that we’re all familiar with, there is a water maser there and it’s in fact one of the brightest water masers on the sky. It’s very bright also because it’s close by. Now, again, intrinsically the, the power associated with that maser isn’t the same as the power associated with megamasers but it’s much closer and so it’s actually, uh, very much brighter. It’s, it’s very easy to detect the maser in Orion. And so this happens because essentially to make these masers all you need is a population of water molecules and an energy source. And then, of course, you have to have the densities be about right and the temperatures be about right. But it’s not uncommon to see these masers throughout the universe.
I should point out also that water is not the only molecule that produces masers. Other molecules that produce masers are the hydroxyl molecule, OH, uh, methanol, and there are a number of other masing molecules.
RBD:
Well, thank you Dr. Braatz, it’s been very interesting!
JB:
Thank you for having me, my pleasure!
End of podcast:
365 Days of Astronomy
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