HD 15115, HD 32297, HD 61005, HD 181327, MP Mus
Hubble GO/12228 Program Debris Disk Sample
Astronomers using NASA's Hubble Space Telescope have completed the largest and most sensitive visible-light imaging survey of dusty debris disks around other stars. These dusty disks, likely created by collisions between leftover objects from planet formation, were imaged around stars as young as 10 million years old and as mature as more than 1 billion years old.
"It's like looking back in time to see the kinds of destructive
events that once routinely happened in our solar system after the
planets formed," said survey leader Glenn Schneider of the University
of Arizona's Steward Observatory. The survey's results appeared in the
Oct. 1, 2014, issue of The Astronomical Journal.
Once thought to be simply pancake-like structures, the unexpected
diversity and complexity of these dusty debris structures strongly
suggest they are being gravitationally affected by unseen planets
orbiting the star. Alternatively, these effects could result from the
stars' passing through interstellar space.
The researchers discovered that no two "disks" of material
surrounding stars look the same. "We find that the systems are not
simply flat with uniform surfaces," Schneider said. "These are actually
pretty complicated three-dimensional debris systems, often with
embedded smaller structures. Some of the substructures could be
signposts of unseen planets." The astronomers used Hubble's Space
Telescope Imaging Spectrograph to study 10 previously discovered
circumstellar debris systems, plus MP Mus, a mature protoplanetary disk
of age comparable to the youngest of the debris disks.
Irregularities observed in one ring-like system in particular, around
a star called HD 181327, resemble the ejection of a huge spray of
debris into the outer part of the system from the recent collision of
two bodies.
"This spray of material is fairly distant from its host star —
roughly twice the distance that Pluto is from the Sun," said
co-investigator Christopher Stark of NASA's Goddard Space Flight Center,
Greenbelt, Maryland. "Catastrophically destroying an object that
massive at such a large distance is difficult to explain, and it should
be very rare. If we are in fact seeing the recent aftermath of a
massive collision, the unseen planetary system may be quite chaotic."
Another interpretation for the irregularities is that the disk has
been mysteriously warped by the star's passage through interstellar
space, directly interacting with unseen interstellar material. "Either
way, the answer is exciting," Schneider said. "Our team is currently
analyzing follow-up observations that will help reveal the true cause of
the irregularity."
Over the past few years astronomers have found an incredible
diversity in the architecture of exoplanetary systems — planets are
arranged in orbits that are markedly different than found in our solar
system. "We are now seeing a similar diversity in the architecture of
accompanying debris systems," Schneider said. "How are the planets
affecting the disks, and how are the disks affecting the planets? There
is some sort of interdependence between a planet and the accompanying
debris that might affect the evolution of these exoplanetary debris
systems."
From this small sample, the most important message to take away is
one of diversity, Schneider said. He added that astronomers really need
to understand the internal and external influences on these systems,
such as stellar winds and interactions with clouds of interstellar
material, and how they are influenced by the mass and age of the parent
star, and the abundance of heavier elements needed to build planets.
Though astronomers have found nearly 4,000 exoplanet candidates since
1995, mostly by indirect detection methods, only about two dozen
light-scattering, circumstellar debris systems have been imaged over
that same time period. That's because the disks are typically 100,000
times fainter than, and often very close to, their bright parent stars.
The majority have been seen because of Hubble's ability to perform
high-contrast imaging, in which the overwhelming light from the star is
blocked to reveal the faint disk that surrounds the star.
The new imaging survey also yields insight into how our solar system
formed and evolved 4.6 billion years ago. In particular, the suspected
planet collision seen in the disk around HD 181327 may be similar to
how the Earth-Moon system formed, as well as the Pluto-Charon system
over 4 billion years ago. In those cases, collisions between
planet-sized bodies cast debris that then coalesced into a companion
moon.
CONTACT:
Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4514
villard@stsci.edu
Glenn Schneider
University of Arizona, Tucson, Ariz.
520-621-5865
gschneider@as.arizona.edu
Source: HubbleSite
