Mark J. Reid: Mapping the Spiral Structure of the Milky Way
New Hot Paper Commentary, September 2010
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ArticlE: TRIGONOMETRIC PARALLAXES OF MASSIVE STAR-FORMING REGIONS. VI. GALACTIC STRUCTURE, FUNDAMENTAL PARAMETERS, AND NONCIRCULAR MOTIONS
Authors: Reid, MJ;Menten, KM;Zheng,
XW;Brunthaler, A;Moscadelli, L;Xu, Y;Zhang, B;Sato,
M;Honma, M;Hirota, T;Hachisuka, K;Choi, YK;Moellenbrock,
GA;Bartkiewicz, A |
Mark J. Reid talks with ScienceWatch.com and answers a few questions about this month's New Hot Papers paper in the field of Space Science.
Why do you think your paper is highly
cited?
This paper collected new results of extremely accurate distance measurements to regions of star formation across the Milky Way. The measurements came from the (USA) Very Long Baseline Array and (Japanese) VERA radio telescopes. We used the "gold standard" of astronomical distance techniques called trigonometric parallax (essentially triangulation using the Earth's orbit as one leg of a triangle).
For the first time, we were able to locate a substantial number of sources with reliable distances and begin to map the spiral structure of the Milky Way.
Modeling the locations and full three-dimensional motions of the star-forming regions revealed evidence that the Milky Way was rotating about 15% faster than previously estimated. This has significant implications for the mass of its dark matter halo (increasing estimates by ~50%). Increasing the rotation speed of the Milky Way significantly affects the dynamics of our Local Group of galaxies (e.g., are the Magellanic Clouds bound to the Milky Way?) and the expected signatures for the direct detection of dark matter annihilations.
Figure 1:
A diagram of the locations of the 10 antennas of the
NRAO/NSF VLBA.
Image credit:
NRAO/NSF.
Figure 2:
An artists impression of what the Milky Way might look
like, viewed from afar.
Image credit:
NASA / JPL-Caltech / R. HUrt (SSC-Caltech).
View larger images & complete descriptions in tabs
below.
Additionally, we found that star-forming regions appeared to orbit the Milky Way slower than they would were they in circular orbits. These results are controversial and prompted several groups to reanalyze the data and to question longstanding results. For example, James Binney and collaborators changed their widely accepted estimate of the peculiar (non-circular Galactic orbit) motion of the Sun, a fundamental parameter for the study of Galactic structure.
Does it describe a new discovery, methodology, or synthesis of knowledge?
The distance measurements were made possible by recent advances in astrometric techniques that allowed the (USA) Very Long Baseline Array and (Japanese) VERA radio telescopes to achieve unprecedented positional accuracy of ~10 micro-arcseconds. This is approximately 100 times better than achieved by the HIPPARCOS astrometric satellite and comparable to future space telescopes like the European GAIA and USA SIM missions.
Would you summarize the significance of your paper
in layman's terms?
Astronomers are on the verge of charting our Galaxy, the Milky Way, for the first time with extraordinarily accurate measurements. Using telescopes that span the Earth, they achieve angular resolution comparable to being able reading these words from Moon.
The results reported in Reid et al. (2009) accurately locate some of the spiral arms of the Milky Way and indicate that it rotates faster than previously thought. This implies that the Milky Way is substantially more massive than previously thought.
How did you become involved in this research, and
how would you describe the particular challenges, setbacks, and
successes that you've encountered along the way?
I have been doing Very Long Baseline Interferometry since graduate school in the 1970s. This technique originally promised extraordinary angular resolution and positional accuracy. While imaging with milli-arcsecond resolution was soon achieved, astrometric accuracy stalled out at roughly the milli-arcsecond level.
Once the Very Long Baseline Array (a dedicated VLBI array with excellent high frequency capabilities) was completed in the 1990s, I worked to continually improve the calibrations necessary to achieve routinely a positional accuracy approaching 0.01 milli-arcseconds, promised decades earlier but seldom achieved.
Where do you see your research leading in the
future?
We have started a very large project to measure the three-dimensional locations and motions of several hundred star forming regions across the Milky Way. This NRAO Key Science Project is called the BeSSeL (Bar and Spiral Structure Legacy) survey, named in honor of Friedrich Bessel who measured the first stellar parallax in 1838.
We hope to determine the spiral structure of the Milky Way, a problem that has resisted solution for nearly a century, in part because optical light is absorbed by dust and cannot reach us from most of the Milky Way. View our website.
Do you foresee any social or political
implications for your research?
The appearance of the Milky Way to the eye as a broad bright band across the sky has in the past been well known to much of the general public. The opportunity to see and appreciate the Milky Way hopefully will continue to be available to those who live well outside cities.
However, with increasing light pollution near urban environments, seeing the Milky Way is becoming less common. Only a small fraction of children growing up in industrialized countries can see the Milky Way, and only a very small fraction of those will understand what they are seeing.
We hope to be able to provide a scientifically accurate model of the Milky
Way that could only otherwise be obtained by a space traveler viewing it
from a great distance or from another nearby galaxy. Hopefully, this will
inspire people to minimize "light pollution" and retain our view of one of
the more spectacular and meaningful astronomical images: the Milky
Way.
Mark J. Reid
Harvard-Smithsonian Center for
Astrophysics
Cambridge, MA, USA
KEYWORDS: ASTROMETRY, GALAXY, FUNDAMENTAL PARAMETERS, HALO, KINEMATICS, DYNAMICS, STRUCTURE, STARS, FORMATION, HIPPARCOS PROPER MOTIONS, MILKY WAY GALAXY, ROTATION CURVE, SPIRAL STRUCTURE, BLACK HOLE, STELLAR ORBITS, OB STARS, DISTANCE, DISK.
Figure 1:
Figure 1: A diagram of the locations of the 10 antennas of the NRAO/NSF VLBA. Image credit: NRAO/NSF.
Figure 2:
Figure 2: An artists impression of what the Milky Way might look like, viewed from afar. Image credit: NASA / JPL-Caltech / R. HUrt (SSC-Caltech).