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28/6/06 - DJ:

Hubble revela dos discos de polvo alrededor de estrella

Imágenes detalladas de la estrella Beta Pictoris, tomadas por el Hubble, confirman la existencia de, no uno, sino dos discos de polvo alrededor de la estrella. Las imágenes ofrecen evidencias de por lo menos un planeta del tamaño de Júpiter orbitando Beta Pictoris.

Fast Facts — Technical information
About the Object
Object Name: Beta Pictoris
Object Description: Star with Disk
Position (J2000): R.A. 05h 47 m 17s.09
Dec. -51° 03' 59".5
Constellation: Pictor
Distance: 63 light-years (19 parsecs)

About the Data
Data Description: The Hubble images were created from HST data from proposal 9987: H. Ford (Johns Hopkins University) and J. Krist (STScI). The science team for this release is led by D. Golimowski (Johns Hopkins University).
Instrument: ACS/HRC
Exposure Date(s): October 1, 2003
Exposure Time: 4 hours
Filters: F435W (B), F606W (Broad V), F814W (I)

About the Image

Image Credit: NASA, ESA, and D. Golimowski (Johns Hopkins University)
Release Date: June 27, 2006


El newsletter completo enviado por NASA dice:
June 27, 2006

Erica Hupp/Dwayne Brown
Headquarters, Washington
202-358-1237/1726

Donna Weaver
Space Telescope Science Institute, Baltimore, Md.
410-338-4493

RELEASE: 06-250

NASA'S HUBBLE REVEALS TWO DUST DISKS AROUND NEARBY STAR

NASA's Hubble Space Telescope has revealed two dust disks circling the
nearby star Beta Pictoris. The images confirm a decade of scientific
speculation that a warp in the young star's dust disk may actually be
a second inclined disk, which is evidence for the possibility of at
least one Jupiter-size planet orbiting the star.

The disk is fainter than the star because, at the visible wavelengths
measured, its dust only reflects light. To see the faint disk,
astronomers used Hubble's Advanced Camera for Surveys' coronagraph,
which blocked the light from Beta Pictoris. The images clearly show a
distinct secondary disk that is tilted by about four degrees from the
main disk. The secondary disk is visible out to roughly 24 billion
miles from the star, and probably extends even farther. The finding
appears in the June 2006 issue of the Astronomical Journal.

The best explanation for the observations is that a suspected unseen
planet, up to 20 times the mass of Jupiter and in an orbit within the
secondary disk, is using gravity to sweep up material from the
primary disk.

"The Hubble observation shows that it is not simply a warp in the dust
disk but two concentrations of dust in two separate disks," said lead
astronomer David Golimowski of Johns Hopkins University in Baltimore.
"The finding suggests that planets could be forming in two different
planes. We know this can happen because the planets in our solar
system are typically inclined to Earth's orbit by several degrees.
Perhaps stars forming more than one dust disk may be the norm in the
formative years of a star system."

Computer models by David Mouillet and Jean-Charles Augereau of
Grenoble Observatory in France suggest how a secondary dust disk can
form. A massive planet in an inclined orbit gravitationally attracts
small bodies of rock and/or ice, called planetesimals, from the main
disk, and moves them into an orbit aligned with that of the planet.

These perturbed planetesimals then collide with each other, producing
the tilted dust disk seen in the new Hubble images.

"The actual lifetime of a dust grain is relatively short, maybe a few
hundred thousand years," Golimowski said. "So the fact that we can
still see these disks around a 10- to 20-million-year-old star means
that the dust is being replenished by collisions between
planetesimals."

Astronomers do not know how the massive planet, if it exists, settled
into an inclined orbit. However, computer simulations by multiple
research teams show planet embryos, which start out in a very thin
plane, can, through gravitational interactions, scatter into orbits
that become inclined to the primary disk.

Beta Pictoris is located 63 light-years away in the southern
constellation Pictor. Although the star is much younger than the sun,
it is twice as massive and nine times more luminous. Beta Pictoris
entered the limelight more than 20 years ago when the multinational
Infrared Astronomical Satellite detected excess infrared radiation
from the star. Astronomers attributed this excess to the presence of
warm dust in a disk around the star. The dust disk was first imaged
by ground-based telescopes in 1984. The images showed the disk is
seen nearly edge-on from Earth. Hubble observations in 1995 revealed
an apparent warp in the disk. Subsequent images obtained in 2000 by
Hubble's Imaging Spectrograph confirmed the warp.

The latter study was led by Sara Heap of NASA's Goddard Space Flight
Center in Greenbelt, Md. Heap and her colleagues suggested the
apparent warp may be an unresolved secondary disk tilted about four
degrees from the main disk. Several teams of astronomers attributed
the warp to a planet in a tilted orbit out of the plane of the main
disk.

Astronomers using ground-based telescopes also found various
asymmetries in the star's disk. Infrared images taken in 2002 by the
Keck II Observatory in Hawaii showed that another smaller inner disk
may exist around the star in a region the size of our solar system.
Golimowski's team did not spot the inner disk because it is small and
blocked by the Advanced Camera's coronagraph. This possible inner
disk is tilted in the opposite direction from the disk seen in the
new Hubble images. This misalignment implies the tilted disks are not
directly related. Nevertheless, they both may bolster evidence for
the existence of one or more planets orbiting the star.

Images and more information about Beta Pictoris are available at:

http://hubblesite.org/news/2006/25

The Hubble Space Telescope is an international cooperative project
between NASA and the European Space Agency. The Space Telescope
Science Institute is operated for NASA by the Association of
Universities for Research in Astronomy, Inc., Washington.


-end-

Más info: HubbleSite

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