TW Hydrae

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TW Hydrae is the nearest classical T Tauri star to the Sun, situated some 56 parsecs away in the constellation Hydra. TW Hydrae is similar in mass to the Sun, but is only about 5-10 million years old. The star appears to be accreting from a face-on protoplanetary disk of dust and gas, which has been resolved in images from the Hubble Space Telescope. TW Hydrae is accompanied by about twenty other low-mass stars with similar ages and space motions, comprising the "TW Hydrae association" or TWA, one of the closest regions of recent "fossil" star-formation to the Sun.

It is four-fifths the size of the Sun, and its surrounding disk has a radius equal to about 200 Astronomical Units.

1 Protoplanetary disk
2 TW Hydrae b
3 References
4 External links

[edit] Protoplanetary disk

David Wilner, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics, began examining Hydrae in the late 1990s, enabled by the new capabilities of telescopes. In 2005 he discovered that the gaseous disk surrounding TW Hydrae holds vast swaths of pebbles extending outward for at least one billion miles. The pebbles could be the stuff that future planets will be made of. The planet formation process, according to common theory, begins when dust grains in a disk collide and accrete to form larger and larger clumps. Eventually, after millions of years of colliding and combining, the clumps form planets.

Wilner and his colleagues used the National Science Foundation (NSF)-funded Very Large Array (VLA) radio telescope to measure the strength of radio waves emitted by TW Hydrae. Based on the relationship between wavelength and particle size, they determined the grainy materials surrounding the star to be centimeter-sized.

One of the collaborators, Mark Claussen of the National Radio Astronomy Observatory, thought the strong and variable emissions detected from TW Hydrae in previous x-ray detections indicated magnetic activity common in young stars. Claussen thought that if they monitored TW Hydrae at radio wavelengths for a period of a few months, they could determine if the emissions might be strong enough to image at a much higher resolution with the NSF-funded Very Long Baseline Array and study this activity. To their surprise, they found that the radio emissions did not vary significantly.

He decided to revisit the VLA. The observatory's twenty-seven operating antennae are spread throughout the plains of San Augustin, N.M., and arranged in one of four configurations that are changed every few months. Wilner found the pebbles using a larger configuration and higher angular resolution of the VLA. He enlisted the help of Nuria Calvet, a colleague at the Center for Astrophysics, who created a computer model of the disk surrounding TW Hydrae using previously published data.^[1]

Recently, Wilner collaborated with his graduate student, Meredith Hughes, and several other colleagues to identify a hole in TW Hydrae's dusty disk. Wilner says that the hole was probably created when a Jupiter-sized planet cleared that gap of much of its rocky material. This latest research was accepted for publication by the Astrophysical Journal in April 2007.

[edit] TW Hydrae b

In December 2007, a team led by Johny Setiawan of the Max Planck Institute for Astronomy in Heidelberg, Germany discovered a planet orbiting TW Hydrae, dubbed TW Hydrae b. It has a mass of 9.8±3.3 M_J, a period of 3.56 days, and an orbital radius of 0.04 AU (inside the inner rim of the protoplanetary disk).^[2]^[3] Since the star itself is so young, it is presumed this is the youngest extrasolar planet yet discovered, and essentially still in formation.^[4]