A star thought to have passed the age at
which it can form planets may, in fact, be creating new worlds. The disk
of material surrounding the surprising star called TW Hydrae may be massive enough to make even more planets than we have in our own solar system. The findings were made using the European Space Agency's Herschel Space Telescope,
a mission in which NASA is a participant. At roughly 10 million years
old and 176 light years away in the Hydra, or Sea Serpent,
constellation, TW Hydrae is relatively close to Earth by astronomical
standards.
TW Hydrae is relatively young but, in theory, it is past the age at
which giant plants already may have formed. "We didn't expect to see so
much gas around this star," said Edwin Bergin of the University of Michigan in Ann Arbor. Bergin led the new study appearing in the journal Nature.
"Typically stars of this age have cleared out their surrounding
material, but this star still has enough mass to make the equivalent of
50 Jupiters," Bergin said.
In addition to revealing the peculiar state of the star, the findings
also demonstrate a new, more precise method for weighing planet-forming
disks. Previous techniques for assessing the mass were indirect and
uncertain. The new method can directly probe the gas that typically goes
into making planets. Planets are born out of material swirling around
young stars, and the mass of this material is a key factor controlling
their formation. Astronomers did not know before the new study whether
the disk around TW Hydrae contained enough material to form new planets
similar to our own.
In 2011, astronomers used the Herschel space observatory to detect
copious amounts of cool water vapor, illustrated in blue, emanating from
the star's planet-forming disk of dust and gas. Credit: NASA/JPL-Caltech
"Before, we had to use a proxy to guess the gas quantity in the
planet-forming disks," said Paul Goldsmith, the NASA project scientist
for Herschel at NASA's Jet Propulsion Laboratory
in Pasadena, Calif. "This is another example of Herschel's versatility
and sensitivity yielding important new results about star and planet
formation."
Using Herschel, scientists were able to take a fresh look at the disk
with the space telescope to analyze light coming from TW Hydrae and
pick out the spectral signature of a gas called hydrogen deuteride.
Simple hydrogen molecules are the main gas component of planets, but
they emit light at wavelengths too short to be detected by Herschel. Gas
molecules containing deuterium, a heavier version of hydrogen, emit
light at longer, far-infrared wavelengths that Herschel is equipped to
see. This enabled astronomers to measure the levels of hydrogen
deuteride and obtain the weight of the disk with the highest precision
yet.
"Knowing the mass of a planet-forming disk is crucial to
understanding how and when planets take shape around other stars," said
Glenn Wahlgren, Herschel program scientist at NASA Headquarters in
Washington. Whether TW Hydrae's large disk will lead to an exotic
planetary system with larger and more numerous planets than ours remains
to be seen, but the new information helps define the range of possible
planet scenarios. "The new results are another important step in
understanding the diversity of planetary systems in our universe," said
Bergin. "We are now observing systems with massive Jupiters, super-Earths,
and many Neptune-like worlds. By weighing systems at their birth, we
gain insight into how our own solar system formed with just one of many
possible planetary configurations."
For more information: "An old disk that can still form a planetary
system," by E. Bergin et al, is published in Nature, 31 January 2013.
www.nature.com/nature/journal/v493/n7434/full/nature11805.html Journal
reference: Nature.
Source: The Daily Galaxy via NASA
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