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منظومه ی شمسی دیگر در نزدیکی ما !!!
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The young star TW Hydrae has long been a favorite astronomical
target as it is the nearest star to the solar system to play host to a
protoplanetary disk — the gas and dust collected around a young star
that goes on to form planets. It’s akin to an astronomer’s Petri dish —
all the ingredients are there for the formation of planets and it’s
‘only’ 176 light-years away, a prime location for our telescopes to
study.

However, TW Hydrae’s protoplanetary disk has been too small to
image directly and its size can only be inferred through spectroscopic
analysis (i.e. astronomers analyze the light from the system, deducing
what material it contains). Now, with the help of Europe’s Herschel
Space Observatory and the Atacama Large Millimeter/submillimeter Array
(ALMA) in Chile, a team of astronomers have made a lucky discovery. Not
only have they gained a more precise estimate of the mass of the
protoplanetary disk, they’ve also found that it may produce a system of worlds of comparable mass to the solar system.

Yes, TW Hydrae may look like the solar system did over 4 billion years ago.

PICTURES: Exquisite Exoplanetary Art

Previous mass estimates came from model assumptions of the
star’s protoplanetary material — creating huge margins for error — but
Herschel’s sensitivity to a certain wavelength of radiation from TW
Hydrae was a game changer.

Contained within the protoplanetary disk are hydrogen
molecules, but some contain deuterium (a hydrogen atom with an
additional neutron in its nucleus). These “hydrogen deuteride” molecules
emit a very specific radiation and because Herschel has such a
fine-tuned resolution to this specific wavelength, astronomers were able
to use this radiation as a guide. ALMA provided key information about
the temperature of the protoplanetary disk by detecting the temperature
of carbon monoxide. By combining these data, a precise ratio of hydrogen
deuteride to hydrogen could be made — a mass estimate could therefore
be attained.

It turns out that the baby TW Hydrae system is more massive
than other estimates predicted. Rather than ranging anything from 0.5 to
63 Jupiter masses, the material contained within the protoplanetary
disk has a lower limit of 52 Jupiter masses — this is more
material than what formed our solar system during its formative years.
Perhaps TW Hydrae will eventually host a similar system of planets as
our sun did.

ANALYSIS: Youngest Baby Exoplanet Discovered

“This project started in casual conversation … We realized that
Herschel was our only chance to observe hydrogen deuteride in this disk
— way too good an opportunity to pass up. But we also realized we would
be taking a risk. At least one model predicted that we shouldn’t have
seen anything! Instead, the results were much better than we had dared
to hope,” said Thomas Henning, of the Max Planck Institute for Astronomy
in Heidelberg.

“If there’s no chance your project can fail, you’re probably
not doing very interesting science. TW Hydrae is a good example of how a
calculated scientific gamble can pay off.”

Interestingly, although TW Hydrae is a “young” star in cosmic terms, it is also a star that would normally be considered too mature to host a protoplanetary disk.

“We did not expect to find so much gas around this
10-million-year-old star,” said lead researcher Edwin Bergin of the
University of Michigan.

“This star has significantly more mass than required to make
our own solar system and could make a much more exotic system with
planets more massive than Jupiter.”

This research will be published in the Jan. 31 issue of the journal Nature.

Further information: Max Planck Institute for Astronomy press release.

Image: Artist’s impression of the gas and dust disk around
the young star TW Hydrae. New measurements using the Herschel space
telescope have shown that the mass of the disk is greater than
previously thought. Credit: Axel M. Quetz (MPIA)



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  چگونگی رصد کردن غول منظومه ی شمسی! amir astronomer 0 191 04-02-2013، 03:16 PM
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