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2010-07-22 04:48:29
By Jonathan Amos Science correspondent, BBC News
They are among the true monsters of space - colossal stars whose size and
brightness go well beyond what many scientists thought was even possible.
Continue reading the main story
Start Quote
Planets take longer to form than these stars take to live and die
End Quote Prof Paul Crowther Sheffield University, UK
One of the objects, known simply as R136a1, is the most massive ever found.
The star is seen to have a mass about 265 times that of our own Sun; but the
latest modelling work suggests at birth it could have been bigger, still.
Perhaps as much as 320 times that of the Sun, says Professor Paul Crowther from
Sheffield University, UK.
"If it replaced the Sun in our Solar System, it would outshine [it] by as much
as the Sun currently outshines the full Moon," the astronomer told BBC News.
The stars were identified by Crowther's team using a combination of new
observations on the Very Large Telescope facility in Chile and data gathered
previously with the Hubble Space Telescope.
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R136, a cluster of young, massive and hot stars (ESO). Astronomer Maggie
Aderin-Pocock explains why the discovery is significant
The group studied the NGC 3603 and RMC 136a clusters - regions of space where
thick clouds of gas and dust are collapsing into even denser clumps.
In these places, huge stars ignite to burn brief but brilliant lives before
exploding as supernovas to seed the Universe with heavy elements.
NGC 3603 is relatively close in cosmic terms - just 22,000 light-years distant.
RMC 136a (more often nicknamed R136) is slightly further away, and is sited
within one of our neighbouring galaxies, the Large Magellanic Cloud, some
165,000 light-years away.
The team found several stars with surface temperatures over 40,000 degrees -
more than seven times hotter than our Sun.
The research shows these young stellar objects to be unbelievably bright, truly
massive and also extremely wide - perhaps 30 times the radius of our Sun in the
case of R136a1.
How big is big? Star comparisons
Cluster of huge stars (Eso)
This artist's impression (L) shows the relative sizes (radius) of young stars,
from low mass "yellow dwarfs" such as our Sun, through "blue dwarf" stars that
are eight times more massive than the Sun, to a 300 solar-mass star like R136a1
(R). There are a number of low-density giants that are known to have an even
bigger radius than R136a1
Up close the stars would look a mess, however. Unlike our Sun which appears as
a defined disc on the sky, the giants identified by Professor Crowther and
colleagues would be losing so much material through powerful winds from their
puffed up atmospheres that they would have a fuzzy look about them.
One thing seems for sure - no planets would exist in orbit about them.
"Planets take longer to form than these stars take to live and die. Even if
there were planets, there would be no astronomers on them because the night sky
would be almost as bright as the day in these clusters," Professor Crowther
joked.
VLT (Eso) Europe's VLT facility is sited in Chile
"Some of these big stars are relatively close to each other, so even at 'night'
you'd have another very bright star shining on you."
Previously observed giants had been seen to get as big as 150 times the mass of
our Sun. The latest findings raise interesting questions about what the upper
limits on size might be.
Ordinarily, there should come a point where the pressure from all the radiation
emitted by a stellar behemoth pushes back against any further infall of gas and
dust. In other words, there ought to be a physical barrier to excessive star
growth.
But Professor Crowther adds a second factor - that of resource. There may not
exist in today's Universe places that have sufficient supplies of gas and dust
to feed ever more massive stars.
However, the new observations do give a tantalising glimpse of what the very
early Universe might have been like. Many objects in the very first population
of stars to shine shortly after the Big Bang are thought to have been monsters
like R136a1.
When these objects blew apart, their cataclysmic demise was so violent they may
not have left behind a remnant core of material as is often the case following
a supernova; or even a black hole which is another common consequence, too.
Instead, these giants may simply have dumped all their contents back into
space, dispersing heavy elements like iron equivalent to the mass of 10 of our
Suns.
"The bigger picture to this research is that it gives us confidence that there
were probably more of these really massive stars in much greater numbers early
on in the Universe," Professor Crowther told BBC News.
The new results appear in a paper in the journal Monthly Notices of the Royal
Astronomical Society.