A Runaway Star in the Tarantula Nebula
In new observations released by the Hubble Space Telescope on May 11, 2010, a rogue star in outskirts of the 30 Doradus Nebula (Tarantula Nebula) in the Large Magellanic Cloud galaxy (170,000 light years from Earth) is examined. Although astronomers have known about this particular star for some time (it was first spotted in 2006 by the Anglo-Australian Telescope at Siding Spring Observatory, Australia), Hubble has confirmed the original finding that the star -- called "30 Dor #016" -- is a very, very long way from home. 30 Dor #016 is flying away from where it was born (a giant star cluster called R136) at a breakneck speed of 400,000 kilometers per hour and is currently 375 light-years away from its origin. By putting together all the pieces of evidence from Hubble and ground-based telescopes, astronomers are realizing that this is a rather special object.
Chaotic Star Birth
The Tarantula Nebula is a hothouse of stellar activity where the most massive stars in our local universe form, many of them exceeding 100 times the mass of our sun. In this image, the wide angle view was taken by the European Southern Observatory's (ESO) Wide Field Imager at the MPG/ESO 2.2-metre telescope on La Silla, Chile. The R136 star cluster -- the stellar nursery of these massive stars -- has been circled, and the runaway star can be seen some distance from the cluster to the right of the image. Inset is a Hubble image of the massive star -- weighing in at 90 solar masses -- obviously completely separated from its siblings in R136.
A Closer Look with Hubble
This is a close-up view of 30 Dor #016 as taken by Hubble's Wide Field and Planetary Camera 2 (WFPC2). The arrow in the right panel shows the direction the star has been traveling through the nebula. As is obvious in this Hubble image, the star is alone. But how did it get there?
A Gravitational Slingshot
There are two possible mechanisms that could have resulted in this speeding rogue star. The first mechanism is thought to occur when a binary system consists of one massive star and one smaller star. When the largest of the pair explodes as a supernova, the smaller star is flung away at high speed. It's not thought that 30 Dor #016 was accelerated in this way as most of the stars in the nebula are very young (only a couple of million years old), way too young to be ripe enough to explode as supernovae. The second mechanism entails a complex interaction with the gravity of other stars (as pictured here). In this case, a binary system is raided by a more massive star and its momentum transfered via a gravitational slingshot, hurling the least massive star out of the cluster. It is thought 30 Dor #016 was the least massive star of the trio.
A Spectroscopic Fingerprint.
Using data from Hubble's Cosmic Origins Spectrograph (COS), the elements that make up 30 Dor #016's stellar winds can be analyzed (top line). By comparing the star's spectrum with a similar star in the nebula (bottom line), astronomers realized 30 Dor #016 must be very young, much like the stars found in the R136 cluster. By gathering all of this evidence, astronomers are certain that the speedy stellar rogue originated in the R136 cluster. It also seems likely that it was flung out of the cluster by some kind of gravitational interaction with its more massive stellar siblings. And the drama hasn't finished for 30 Dor #016. Very massive stars live fast and die young and this particular star will explode as a supernova in a few million years time, forming a black hole. It's likely that the black hole will continue flying through the galaxy, eventually getting ejected from the Large Magellanic Cloud all together.
For more details, read "Hubble Spies Trailblazing Star Ripped from Stellar Nursery" on Discovery News.