NASA astronomers using the Space Telescope Imaging Spectrograph (STIS) instrument on board Hubble discovered that the disk of gas and dust surrounding a young star has a gap, possibly caused by gravitational influence of a nascent planet.

The gap appears about 30 billion miles from the star, more than seven times the distance from the Sun to Pluto, the most remote planet in our solar system. The STIS instrument also revealed that the star is ejecting jets of gas at hundreds of miles per second from its poles, a feature usually seen in much younger stars.

"If the clearing in the disk is due to planet formation, it suggests we have a lot more to learn about how planets form, but we may be on the right track, which is very exciting," said Dr. Carol Grady of NASA's Goddard Space Flight Center, Greenbelt, Md.

"The potential planet is much further away from its star than any known bodies in the plane of our solar system, and it is forming much faster than most models predict," added Dr Grady.

"This star is also interesting because of its jets," adds Dr. David Devine of Goddard. "Protostellar jets are a byproduct of the accretion of material onto a young star, and are thought to have lifetimes of a few hundred thousand years or so. It came as a big surprise to find them associated with a 4 million year old star. One possible explanation for these 'old' jets is that the formation of planets in the disk results in periodic 'meteor showers' of material falling onto the central star, which rejuvenates the jets. In simpler terms, the star gets the hiccups while eating dessert." Grady and Devine will present their results at the winter meeting of the American Astronomical Society (AAS) in Atlanta, Georgia, Jan. 12, and the research will be published in the Astrophysical Journal.

The star, designated HD163296, is approximately 400 light years away from Earth in the direction of the constellation Sagittarius (one light year is almost six trillion miles). It is about twice as massive as the Sun and has an estimated age of 2-10 million years. This is relatively young, as stars of its type have lives spanning up to one billion years.

If the gap in the disk is due to a single planet, the planet has an estimated mass 1.3 times that of Saturn. It is likely that the planet will gain additional mass as it continues to pull material from the disk.

It would have been very difficult to detect the jets and the gap in the disk without the use of a coronagraph. Normally, a young star's bright light prevents astronomers from seeing material that is close to it (imagine a match next to a spotlight). However STIS has a coronagraph that blocks the star's light and allows the study of the much fainter surrounding material. Unfortunately, the inner part of the disk can't be directly seen, because it is obscured by the coronagraph. However the astronomers were able to trace the disk to within about 180 AU of the star (1 AU is the distance from the Earth to the Sun, about 93 million miles (150 million kilometers) ).

Structures in the jets provide hints of what is happening in the inner disk blocked from view by the coronagraph. "We do see dense clumps in the jet," said Devine. "They are regularly spaced, and appear to be ejected about once every five years."

"One exciting, but speculative, possibility is that there is another planet forming in the inner part of the disk," said Grady. "As the planet progresses in its orbit, it may periodically disrupt the disk and toss material on the star, some of which is ejected as denser clumps of material in the jets."

"The five-year spacing of the knots in the star's jets may be related to a five-year orbital period for any potential companion object," said Grady. "This is in the habitable zone for the star, where liquid water could exist. However, since the system is young and the object is still forming, there is likely a constant rain of meteorites on its surface. I wouldn't want to spend a vacation there."

"On the other hand, the knots in the jets may have nothing to do with planet formation, and may be due to some unobserved feature of the star or disruptions caused by a low-mass companion like a brown dwarf. A brown dwarf is an object not quite massive enough to shine by nuclear fusion like a star but instead glows dimly with heat left over from its formation. If the companion were a low-mass star, it should produce X-rays, but other observatories sensitive to X-rays have not seen any nearby. However, we can't yet rule out a brown dwarf," said Grady.

"We have only recently had observatories powerful enough to tell us something about planet formation, so the field is very young," said Grady. "We don't yet know the full diversity of solar systems -- if a star with fast, remote planet formation and jets is common or rare. Recent observations of stellar disks, announced at last January's AAS meeting, indicate that at least one other star (HD141569) may have planets forming rapidly at great distances. If this were a rare occurrence, we would not expect to find two examples so quickly."

"We will use Hubble to take longer exposures of HD163296 in the summer to see if there is anything else going on in its faint, outer disk, and we plan similar observations of 8-10 other stars by September. We are very fortunate to be exploring this new frontier, and are tremendously excited by future observatories, such as the Space Interferometry Mission and the Terrestrial Planet Finder, that promise to tell much more," said Grady.

In addition to taking pictures, STIS separates light into its component colors, much like a prism separates white light into a rainbow. It turns out that each element can only emit light of certain colors, so by analyzing the light emitted by an object astronomers can figure out its composition. Astronomers can also learn about its motion because light from an object that is moving toward us is shifted to more energetic, bluer colors, and light from an object moving away is shifted to less energetic, more red colors. The effect is similar to the way the pitch of the siren on a speeding ambulance appears to rise as it approaches and fall as it rushes away.

The disk exhibits a surprising amount of structure. There is a bright dust ring at 350 times the Earth-Sun distance which can be seen on either side of the star's location, together with a darker lane just inside it. The dark lane is 0.4" or 50 times the Earth-Sun distance across. If this lane is cleared by a single body, the inferred mass of the body is 1.3 Saturn masses. Inside the dark lane the disk becomes as bright as the outer bright ring, but does not continue to brighten with decreasing distance from the star. This suggests that there may be a region between 300 and 180 times the Earth-Sun distance which is partially cleared. The coronagraphic image also reveals three regions of nebulosity (the fuzzy, bright features) aligned perpendicular to the disk. These features were completely unexpected in a star this old, and are more typically detected in association with really young protostars which are 10 times younger than HD 163296.

The middle figure shows a spectral image of the vicinity of the star in the light of glowing hydrogen gas. In this image, we sample material along a 0.2" (24 times the Earth-Sun distance) wide slit passing through the nebulosities (vertical axis of the middle image). Along the horizontal axis we see the light of the star spread out into its constituent colors. The nebulosities above the star (NE in the coronagraphic image) are displaced toward the red, indicating that the gas is moving away from us at velocities of 250 miles/second (400 km/s). Below the star, the data reveal a jet of material moving toward us at 250 miles/second (400 km/s). This velocity information enables us to determine the three-dimensional space orientation of the disk and jet system. A cartoon combining the information from the coronagraphic image and the spectrum is shown on the right. The nebulosities seen in both the image and the spectrum have been identified as ejected gas features termed Herbig-Haro objects and collectively are cataloged as HH409.

Photo credits: NASA and C.A. Grady and David Devine (NOAO, NASA Goddard Space Flight Center), B. Woodgate and R. Kimble (NASA Goddard Space Flight Center), F.C. Bruhweiler and A. Boggess (Catholic University of America), J.L. Linsky (JILA, University of Colorado and NIST), P. Plait (Advanced Computer Concepts), M. Clampin and P. Kalas (Space Telescope Science Institute).

Space Telescope Imaging Spectrograph

Community
Email This Article
Comment On This Article

Related Links
Space

Memory Foam Mattress Review

SPACE MEDIA NETWORK PROMOTIONS Solar Energy Solutions Tempur-Pedic Mattress Comparison ... Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News

SPACEDAILY

Satellite Launch To Boost DTH In India
Calcutta, India (SPX) Dec 28, 2005
The successful launch Thursday of India's heaviest satellite from spaceport of Kourou in French Guyana may have boosted the country's space research efforts to yet another level, but it has also lifted the spirits of at least three Direct-To-Home televisions broadcasters, one of which has been waiting for years to launch its services in India.

---------------------------------------------------------
New from Telescopes.com!

It's new. And it's downright terrific!

Celestron's CPC Schmidt-Cassegrain telescope is the scope you've been waiting for! It offers new alignment technology, advanced engineering, and bold new design at a new, low price!

In fact, Celestron's Professional Computerized (CPC) scope with revolutionary SkyAlign Alignment Technology redefines everything that amateur astronomers are looking for. It offers quick and simple alignment, GPS technology, unsurpassed optical quality, ease of use, advanced ergonomics, enhanced computerization and, most important, affordability.

Want to view M-31 tonight? One button takes you there!

Shop for telescopes online at Telescopes.com! today!
------------------------------------------------------------