Birth of a (Magnetic) Heavyweight
By Phil Berardelli
ScienceNOW Daily News
16 November 2009
Newborn. Astronomers have spied magnetic activity surrounding a massive young star in the Orion Nebula (inset), a hot spot of such activity in the Milky Way.
Credit: Bill Saxton, NRAO/AUI/NSF; (inset) NASA/ESA/M. Robberto (STScI/ESA)
Astronomers caught a glimpse of the emergence of a massive star for the first time. The observations confirm that magnetic fields play a strong role in the formation of these solar giants.Credit: Bill Saxton, NRAO/AUI/NSF; (inset) NASA/ESA/M. Robberto (STScI/ESA)
The death of massive stars is reasonably well known--most blow their innards across galaxies in titanic explosions called supernovae--but their birth is another story. Solar giants are relatively rare, and they form inside giant clouds of gas and dust that block the view of optical telescopes.
Lucky for astronomers, they managed to look at just the right patch of sky with a powerful new observing tool. That patch is located about 1300 light-years away, within the Great Nebula of the constellation Orion. Inside a vast cloud of dust and gas that is known as one of the Milky Way galaxy's premier star-hatcheries, the team found a zone emitting strong radio waves with the chemical signature of silicon monoxide gas, a strong indicator that the starmaking process is at work.
The researchers then trained the Very Long Baseline Array of radio telescopes--a line of dishes that stretches about 8000 kilometers, from Mauna Kea, Hawaii, to St. Croix in the U.S. Virgin Islands--on the source of the gas, an object they called Source I (pronounced "source eye"). The scopes picked out thousands of these silicon monoxide clouds, which they liken to lasers because they emit radio waves as bright pinpoints. Astronomers call them masers.
The researchers wanted to see if they could track the masers over time. So they took 21 monthly shots of the surrounding cloud and its masers between March 2001 and December 2002 and compiled a time-lapse movie.
The movie shows that some of the masers are swirling in toward the young massive star. But others are arcing up and away from the star--presumably from its north and south poles. That means, the team reports in an upcoming issue of The Astrophysical Journal, that the masers are following magnetic field lines, and therefore magnetic fields are controlling the star's evolution by pulling away material that otherwise would have been captured by the star's gravity.
Many astronomers had thought that magnetic fields would be too weak in young stars--particularly young massive stars--to influence their development. But lately some observational evidence has been collected, and Source I represents the first time that astronomers have caught a glimpse of the process at work.
Astronomer Daniel Apai of the Space Telescope Science Institute in Baltimore, Maryland, likens the tracks of the masers to "rising steam that reveals the boiling water as it swirls around a drain." The amount of detail and complexity in the images "will allow us to test in detail our models of the birth of the hottest and most massive stars," he says.
