Mario Juric talks with
ScienceWatch.com and answers a few questions about
this month's Fast Breaking Paper in the field of Space
Science. The author has also sent along images of his
work.
Article Title: The milky way tomography with SDSS.
I. Stellar number density distribution
Authors: Juric,
M, et al.
Journal: ASTROPHYS J
Volume: 673
Issue: 2
Page: 864-914
Year: FEB 1 2008
* Princeton Univ, Dept Astrophys Sci, Princeton, NJ 08544
USA.
* Princeton Univ, Dept Astrophys Sci, Princeton, NJ 08544
USA.
* Inst Adv Study, Sch Nat Sci, Princeton, NJ 08540
USA.
(addresses have been truncated)
Why do you think your paper is highly
cited?
The relatively large number of citations is likely a combination of recent
resurgence of interest in studies of the Milky Way, and the number of
discoveries and measurements described in this paper.
Does it describe a new discovery, methodology, or
synthesis of knowledge?
This paper is the first in a series that describes our findings about the
structure of our galaxy, the Milky Way, as seen by the Sloan Digital Sky
Survey (SDSS).
It describes the measurements of Galactic structural parameters (in
essence, how the stars are distributed in our Galaxy) from a dataset 400
times larger than comparable prior ones, the discovery and characterization
of "Virgo Overdensity" (a large overdensity of stars caused by a merger of
a satellite galaxy with our own), and the general methods that may be used
to repeat this kind of research with future large-scale surveys.
Would you summarize the significance of your paper in
layman's terms?
In layman's terms, we measured the positions and distances to over 40
million stars, 400 times more than prior comparable surveys, and (within
the volume observed) produced the most accurate map of the Galaxy to date.
This enabled us to measure the size and height of the disk of our Galaxy to
unprecedented accuracy, as well as the shape of the tenuous envelope of
stars surrounding the Galactic disk (the "Galactic halo").
In the process, we discovered a huge overdensity of stars, extending over
an area of the sky equivalent to 5,000 full Moons, in the direction of the
constellation Virgo. This "Virgo overdensity" is likely a remnant of a
merger of a smaller galaxy with our own.
The big picture of our results is that by providing an accurate picture of
the Milky Way, we have created a test, a benchmark, against which the
theories and simulations of Milky Way formation will be compared in the
decades to come.
How did you become involved in this research, and were
there any problems along the way?
This research began as a joint project with Dr. Zeljko Ivezic, then at
Princeton University and now a professor in the Department of Astronomy at
the University of Washington in Seattle and project scientist of the Large
Synoptic Survey Telescope. However, it quickly evolved into a comprehensive
study of the Galaxy with SDSS data.
There were many problems along the way, ranging from technical (e.g., our
datasets included hundreds of millions of observations and were typically
on order of 50GB in size), to astrophysical (e.g., assessing whether
unidentified multiple stars—those are too close to each other to be
resolved in our telescopes—can influence our conclusions).
Where do you see your research leading in the
future?
My present focus is directed towards the understanding of the Milky Way by
using large sky surveys. I believe these surveys can lead us to a complete
picture of structure, formation, and evolution of the Milky Way before the
next decade is out.
The next such survey is PanSTARRS—Panoramic Survey Telescope &
Rapid Response System. It will be capable of extending the reach of our
SDSS study by factors of 10-100. This is what I plan to work on following
my move as a NASA Hubble Fellow to Harvard University later this year.
Do you foresee any social or political implications for
your research?
There will be little impact to the general public. However, I hope it will
influence the way in which the astrophysics community thinks about surveys,
as well as the way we teach and train our students today for the challenges
of the future.
An important aspect of this research is that it was enabled and done
entirely using an existing dataset produced by a large sky survey (the
SDSS) that was originally built for an entirely different purpose
(observations of far-away galaxies). While such reuse of archived data has
certainly happened in the past, because of the proliferation of information
technology and survey datasets I expect it will become common to the point
of dominance in the not-so-distant future.
The upcoming prevalence of such datasets will move the focus in astronomy
from data collection to data mining. This will, in turn, require a shift in
astronomers' thinking to a frame of mind quite opposite from the one we are
used to. Instead of "given the topic, what data would be best to understand
it?" one will instead need to ask "given the data, which topic can be
advanced the furthest?"
Successful data-driven astronomers will have to know the datasets at their
disposal, have broad interests and understanding of various areas of
astrophysics, and an intimate knowledge of computing and data mining
techniques. These skills and ways of thinking are something that we must
work to instill in our students in order to prepare them for the
survey-driven astronomy of tomorrow.
Dr. Mario Juric
Postdoctoral Member
School of Natural Sciences
Institute for Advanced Study
Princeton University
Princeton, NJ, USA