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Post Info TOPIC: TW Hydrae Association
Blobrana


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TW Hydrae b
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TW Hydrae b.kmz
Google Sky file (2kb, kmz)

-- Edited by Blobrana at 16:50, 2008-01-12

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Astronomers have detected the youngest planet so far, a newborn world located in the planetary nursery of a distant star only 10 million years old.
Scientists at the Max Planck Institute for Astrophysics in Germany used a telescope in Chile to pick up indirect evidence of the planet orbiting a star 180 light years from the solar system, in the constellation Hydra the snake.
The solar system is at least 4.5 billion years old, but until now the average age of planets discovered outside the solar system has been about two billion years.

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The planet is the youngest yet discovered and is in a solar system still being formed from cosmic dust and gas. Despite being a baby, chronologically speaking, it is vast in comparison with Earth and has been classified as a giant planet. Astronomers reckon that it has a mass 3,115 times that of our own planet and 9.8 times that of Jupiter.
Previously the youngest planet to have been identified was an estimated 100 million years old. Earth is calculated to be 4.5 billion years old.

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A team led by Johny Setiawan, an Indonesia-born astronomer at the Max Planck Institute in Heidelberg, Germany, found a massive gas giant, between 5.5 and 13.1 times the size of Jupiter, orbiting within the dust disc of a well-studied star called TW Hydrae.
It takes a mere three and a half Earth days to zip around the star, at a distance of just 600,000 kilometres.
Light from the star suggests that it is between only eight and 10 million years old, which implies that planets can form even before the disc has been dissipated by stellar particles and radiation.

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Astronomer David Wilner of the Harvard-Smithsonian Center for Astrophysics (CfA) and his colleagues have discovered that the gaseous protoplanetary disk surrounding TW Hydrae holds vast swaths of pebbles extending outward for at least 1 billion miles. These rocky chunks should continue to grow in size as they collide and stick together until they eventually form planets.

"We're seeing planet building happening right before our eyes. The foundation has been laid and now the building materials are coming together to make a new solar system" - David Wilner.


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Wilner used the National Science Foundation's Very Large Array to measure radio emissions from TW Hydrae. He detected radiation from a cold, extended dust disk suffused with centimetre-sized pebbles. Such pebbles are a prerequisite for planet formation, created as dust collects together into larger and larger clumps. Over millions of years, those clumps grow into planets.

"We're seeing an important step on the path from interstellar dust particles to planets. No one has seen this before" - Mark Claussen (NRAO), co-author on the paper announcing the discovery.


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Position(2000): RA 11h 01m 52.00s Dec -34 42' 16.00"

A dusty disk like that in TW Hydrae tends to emit radio waves with wavelengths similar to the size of the particles in the disk. Other effects can mask this, however. In TW Hydrae, the astronomers explained, both the relatively close distance of the system and the stage of the young star's evolution are just right to allow the relationship of particle size and wavelength to prevail.
The scientists observed the young star's disk with the VLA at several centimetre-range wavelengths.
"The strong emission at wavelengths of a few centimetres is convincing evidence that particles of about the same size are present" - Mark Claussen.

Not only does TW Hydrae show evidence of ongoing planet formation, it also shows signs that at least one giant planet may have formed already. Wilner's colleague, Nuria Calvet (CfA), has created a computer simulation of the disk around TW Hydrae using previously published infrared observations. She showed that a gap extends from the star out to a distance of about 400 million miles - similar to the distance to the asteroid belt in our solar system. The gap likely formed when a giant planet sucked up all the nearby material, leaving a hole in the middle of the disk.

Located about 180 light-years away in the constellation Hydra the Water Snake, TW Hydrae consists of a 10 million-year-old star about four-fifths as massive as the Sun. The protoplanetary disk surrounding TW Hydrae contains about one-tenth as much material as the Sun - more than enough to form one or more Jupiter-sized worlds.

"TW Hydrae is unique. It's nearby, and it's just the right age to be forming planets. We'll be studying it for decades to come" - David Wilner.

This research was published in the June 20, 2005, issue of The Astrophysical Journal Letters.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Press release


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Exploring Terrestrial Planet Formation in the TW Hydrae Association

Authors: F. J. Low (1), P. S. Smith (1), M. Werner (2), C. Chen, (2 and 3), V. Krause (4), M. Jura (5), D. C. Hines (6) ((1) Steward Observatory, (2) JPL, (3) NOAO/KPNO, (4) California Institute of Technology, (5) UCLA, (6) Space Science Institute)

Spitzer Space Telescope infrared measurements are presented for 24 members of the TW Hydrae association (TWA). High signal-to-noise 24-micron (um) photometry is presented for all of these stars, including 20 stars that were not detected by IRAS. Among these 20 stars, only a single object, TWA 7, shows excess emission at 24um and at the level of only 40% above the star's photosphere.
TWA 7 also exhibits a strong 70um excess that is a factor of 40 brighter than the stellar photosphere at this wavelength. At 70um, an excess of similar magnitude is detected for TWA 13, though no 24um excess was detected for this binary.
For the 18 stars that failed to show measurable IR excesses, the sensitivity of the current 70um observations does not rule out substantial cool excesses at levels 10-40x above their stellar continua. Measurements of two T Tauri stars, TW Hya and Hen 6-300, confirm that their spectacular IR spectral energy distributions (SEDs) do not turn over even by 160um, consistent with the expectation for their active accretion disks.
In contrast, the Spitzer data for the luminous planetary debris systems in the TWA, HD 98800B and HR 4796A, are consistent with single-temperature blackbody SEDs. The major new result of this study is the dramatic bimodal distribution found for the association in the form of excess emission at a wavelength of 24um, indicating negligible amounts of warm (less than 100 K) dust and debris around 20 of 24 stars in this group of very young stars.
This bimodal distribution is especially striking given that the four stars in the association with strong IR excesses are >100x brighter at 24um than their photospheres.

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