The mystery of a bloated but strangely cold star has been
resolved by Europe's Very Large Telescope.
The red supergiant in a nearby galaxy is actually about half
as massive as what astronomers previously thought, which explains its cool
temperature.
"Previous estimates gave an initial mass of 40 times
the mass of the sun to [the star] WOH G64," said Keiichi Ohnaka, lead
astronomer on the study at the Max-Planck Institute for Radio Astronomy in
Bonn, Germany. "But this was a real problem as it was way too cold, compared to
what theoretical models predict for such a massive star. Its existence couldn't
be explained."
Astronomers had assumed that a spherical cloud of gas and
dust partially hid the entire star, and adjusted their calculations of the
star's brightness and mass by overestimating from what they could see. However,
the Very
Large Telescope in Chile found the star ringed instead by a doughnut-shaped
torus of expelled gas and dust.
"We are looking into the torus from top," Ohnaka
told SPACE.com. The top-down view of the doughnut hole means astronomers
can see a lot more of the star's light than they had once thought.
The revised calculations suggest the star is half as bright
as previous estimates and has less mass — just 25 times as much mass as the
sun.
The star has also apparently undergone a crash
diet that has resulted in "heavy mass loss," said co-researcher
Markus Wittkowski from ESO at the Max-Planck Institute. That feeds the growing
doughnut of gas and dust surrounding the star.
"We estimate that the belt of gas and dust that
surrounds it contains between three and nine solar masses, which means that the
star has already lost between one tenth and a third of its initial mass,"
Wittkowski said.
The gas belt has expanded to almost a light-year across in
diameter, while the star still appears 2,000 times as large as our sun despite
its weight loss.
"Everything is huge about this system. The star itself
is so big that it would fill almost all the space between the Sun and the orbit
of Saturn," Ohnaka said.
Ohnaka and Wittkowski gathered the data by combining two
telescope units at the Very Large Telescope to form a VLT Interferometer, which
has a resolution equivalent to a 60-meter virtual telescope.
This represents the first time that any telescope has made
out the finer features of an individual star in a neighboring galaxy, peering
into the Large
Magellanic Cloud, which lies 163,000 light years away.
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