Hubble Views of Beta Pictoris (1997 and 2012)
Astronomers have used NASA's Hubble Space Telescope to take the most
detailed picture to date of a large, edge-on, gas-and-dust disk
encircling the 20-million-year-old star Beta Pictoris.
Beta Pictoris remains the only directly imaged debris disk that has a
giant planet (discovered in 2009). Because the orbital period is
comparatively short (estimated to be between 18 and 22 years),
astronomers can see large motion in just a few years. This allows
scientists to study how the Beta Pictoris disk is distorted by the
presence of a massive planet embedded within the disk.
The new visible-light Hubble image traces the disk in closer to the
star to within about 650 million miles of the star (which is inside the
radius of Saturn's orbit about the Sun).
"Some computer simulations predicted a complicated structure for the
inner disk due to the gravitational pull by the short-period giant
planet. The new images reveal the inner disk and confirm the predicted
structures. This finding validates models, which will help us to deduce
the presence of other exoplanets in other disks," said Daniel Apai of
the University of Arizona. The gas-giant planet in the Beta Pictoris
system was directly imaged in infrared light by the European Southern
Observatory's Very Large Telescope six years ago.
When comparing the latest Hubble images to Hubble images taken in
1997, astronomers find that the disk's dust distribution has barely
changed over 15 years despite the fact that the entire structure is
orbiting the star like a carousel. This means the disk's structure is
smoothly continuous in the direction of its rotation on the timescale,
roughly, of the accompanying planet's orbital period.
In 1984 Beta Pictoris was the very first star discovered to host a
bright disk of light-scattering circumstellar dust and debris. Ever
since then Beta Pictoris has been an object of intensive scrutiny with
Hubble and with ground-based telescopes. Hubble spectroscopic
observations in 1991 found evidence for extrasolar comets frequently
falling into the star.
The disk is easily seen because it is tilted edge-on and is
especially bright due to a very large amount of starlight-scattering
dust. What's more, Beta Pictoris is closer to Earth (63 light-years)
than most of the other known disk systems.
Though nearly all of the approximately two-dozen known
light-scattering circumstellar disks have been viewed by Hubble to
date, Beta Pictoris is the first and best example of what a young
planetary system looks like, say researchers.
One thing astronomers have recently learned about circumstellar
debris disks is that their structure, and amount of dust, is incredibly
diverse and may be related to the locations and masses of planets in
those systems. "The Beta Pictoris disk is the prototype for
circumstellar debris systems, but it may not be a good archetype," said
co-author Glenn Schneider of the University of Arizona.
For one thing the Beta Pictoris disk is exceptionally dusty. This may
be due to recent major collisions among unseen planetary-sized and
asteroid-sized bodies embedded within it. In particular, a bright lobe
of dust and gas on the southwestern side of the disk may be the result
of the pulverization of a Mars-sized body in a giant collision.
Both the 1997 and 2012 images were taken in visible light with
Hubble's Space Telescope Imaging Spectrograph in its coronagraphic
imaging mode. A coronagraph blocks out the glare of the central star so
that the disk can be seen.
Contact
Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4514
villard@stsci.edu
Daniel Apai / Glenn Schneider
University of Arizona, Tucson, Ariz.
520-621-6534 / 520-621-5865
apai@arizona.edu / gschneider@as.arizona.edu
Source: HubbleSite
