Astronomers have confirmed the weight of the most massive
star in the galaxy.
This behemoth, estimated to be roughly 116 times the mass of
the sun, dwarfs most
other stars in the galaxy. In fact, the next most massive star is about 89
solar masses, and it is a gravitationally bound sister to the record setter.
The next most massive ever weighed is 83 solar masses.
Theory holds that stars can be up to about 150 solar masses.
Discovery of the record-setting stars were first announced
last year. The new measurements are rough, and the stars might turn out to
be considerably heavier or lighter.
"A star having a little over a hundred times more
material in it than the sun is rare," said researcher Anthony F. J. Moffat
of the Universite de Montreal. "For every star like it you get tens of
thousands of stars like the sun formed. So finding them is hard. That's why
very few have been known and measured."
Moffat, with Olivier Schnurr, Jules Casoli and Andre-Nicolas
Chene and Nicole St-Louis of the Universite de Montreal used measurements from
the European Southern Observatory's Very Large Telescope in Chile, and infrared
images from the Hubble Space Telescope to refine estimates of the two giant
stars' masses.
By measuring how the stars orbit around each other, the
researchers were able to calculate each one's mass, though the level of
uncertainty is still quite high (the larger weighs 116 plus-or-minus 30 solar
masses, while the smaller weighs 89 plus-or-minus 15 solar masses). The
astronomers hope to refine these calculations even further with future
observations.
The heavyweight binary, called A1, is in the star cluster
NGC 3603, which lies in the Carina spiral arm of the Milky Way, around 20,000
light-years away from our solar system.
The two A1 stars are thought be "Wolf-Rayet"
stars, which are very hot, heavy and evolved stars that appear to be losing a
large amount of mass in a stellar wind, similar to our sun's solar wind, but
stronger. These stars are so large and luminous that the pressure of their
outward-pouring radiation outweighs the inward pull of their gravity, so
material is constantly being blown away into space.
These stars can lose a significant portion of their mass —
ten of percent of their total bulk — to this process over their lifetimes. The
more massive a star is, the shorter its lifetime, since it tends to burn
through itself quicker. These very huge stars only live for 2 to 3 million
years before dying
in supernovae explosions.
Now that the researchers have found that the massive stars
in A1 are Wolf-Rayet stars, it may help them locate similar finds.
"We're on to something new, that the most massive stars
are probably like this," Moffat told SPACE.com "This is a new
revelation, I think. We should look for Wolf-Rayet stars like this."
Confirming the mass of these gigantors is important because
theories of star formation predict the existence of extremely massive stars
weighing up to 150 times the mass of our sun. Besides these two, though, no
other stars yet discovered have come close to that upper range.
The same research team previously
announced the discovery of this system in 2007, but the research had not
been published yet in a peer-reviewed journal. In the meantime, they have
further refined the measurements, and have recently detailed their findings in
the September 2008 issue of the journal Monthly Notices of the Royal
Astronomical Society.
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