CONTACT: Ray Villard

Space Telescope Science Institute, Baltimore, MD

(Phone: 410-338-4514, E-mail:

Paul Kalas

Space Telescope Science Institute, Baltimore, MD

(Phone: 410-338-4379, E-mail:



The planetary dust disk around the star Beta Pictoris is dynamically “ringing like a bell,”
according to astronomers investigating NASA Hubble Space Telescope images. The “clapper” is
the gravitational wallop of a star that passed near Beta Pictoris some 100,000 years ago.

The surprising findings, presented at the 195th Meeting of the
American Astronomical Society, show that a close encounter with a neighboring star can
severely disrupt the evolution and appearance of thin disks, which are the nurseries of
planetary systems. Similar fly-bys of our solar system long ago may have reshuffled the
comets that now populate our Oort cloud and Kuiper belt.

Discovered in 1983, the dust disk around the nearby star Beta
Pictoris — long suspected to harbor a planetary system — has
puzzled astronomers because it contains more dust grains than
any other comparable system. Also, the dust spreads over a huge 65-billion-mile-diameter
area. Yet, one side of the disk is
20 percent longer and thinner than the other side.

In these latest findings, Hubble astronomers carefully studied the appearance of the disk using
10 years of archival data from the
Hubble Space Telescope and from ground-based telescopes in Hawaii and Chile. Hidden within
the densest part of the disk are clumps of dust that are present only on the long, thin side of
the disk. Because the disk is tilted edge-on to our line-of-sight, the
astronomers inferred that the clumps might represent rings if the disk was viewed face-on.
They hypothesized that these rings must be highly elliptical if they appear only on one side of
the disk, and this could arise if another massive object, like a passing star, recently disturbed
the entire system.

To test their ideas the researchers asked theorist John Larwood of Queen Mary and Westfield
College (London, United Kingdom) to create a computer simulation of a quiescent disk made of
one million test particles orbiting a virtual star. The simulation explored what would happen if
another star zipped by it in a near-collision
trajectory. In the simulation, the gravity of the passing star
rearranged the orbit of each particle, setting up an elliptical ring system 100,000 years after
the almost catastrophic event. The model also reproduced the 20 percent asymmetry in the
disk, which has
mystified astronomers since the Beta Pictoris disk was first seen 16 years ago.

The astronomers are continuing their detective work, searching for the intruder star among
186 suspects near Beta Pictoris. Their
simulations predict it might be only a fraction of the mass of our Sun (a class called an
M-dwarf star). The present results will be published in a future issue of Astrophysical Journal

The Hubble research team, led by Paul Kalas (Space Telescope Science Institute, Baltimore,
Md.), consists of John Larwood (Queen Mary and Westfield College, London, United Kingdom),
Bradford Smith
(University of Hawaii, Institute for Astronomy, Honolulu, Hawaii), and Alfred Schultz (Space
Telescope Science Institute).

The Space Telescope Science Institute is operated by the Association of Universities for
Research in Astronomy, Inc. for NASA, under
contract with NASA’s Goddard Space Flight Center, Greenbelt, Md. The Hubble Space Telescope
is a project of international cooperation between NASA and the European Space Agency.


NOTE TO EDITORS: Images are available on the Internet at: and via links in and

Higher resolution digital versions (300 dpi JPEG and TIFF) are
available at:



EMBARGOED UNTIL: 9:20 a.m. (EST) January 15, 2000




A NASA Hubble Space Telescope false-color, visible-light picture of one side of the edge-on dust
disk around the star Beta Pictoris. Knots in the disk (marked A,B,C,D) are interpreted as rings
of dust, seen edge-on.

Image credit: NASA and Paul Kalas (Space Telescope Science Institute)


A still frame from a computer simulation, which shows a circumstellar dust disk highly
perturbed by the gravitational pull of a bypassing star. The gray solid area represents the
initial shape and size of the undisturbed disk. In the simulation, the gravity of the passing star
rearranges the orbit of each particle, setting up an elliptical ring system that may have
survived for the last 100,000 years since the impact occurred.

Simulation courtesy: John Larwood (Queen Mary and Westfield College, London, United