The behemoth has a thick belt

May 27, 2008
The behemoth has a thick belt
The position of the supergiant star WOH G64 in the Large Magellanic Cloud, one of the Milky Way's neighbouring galaxies, is shown in this Spitzer image (left). On the right, an artist's impression is provided of the thick, massive torus of matter surrounding the star as inferred from observations made with ESO's Very Large Telescope Interferometer. This is the first time that MIDI resolves an individual star in a neighbouring galaxy. Credit: ESO

Talk about a diet! By resolving, for the first time, features of an individual star in a neighbouring galaxy, ESO's VLT has allowed astronomers to determine that it weighs almost half of what was previously thought, thereby solving the mystery of its existence. The behemoth star is found to be surrounded by a massive and thick torus of gas and dust, and is most likely experiencing unstable, violent mass loss.

WOH G64 is a red supergiant star almost 2 000 times as large as our Sun and is located 163 000 light-years away in the Large Magellanic Cloud, one of the Milky Way's satellite galaxies.

"Previous estimates gave an initial mass of 40 times the mass of the Sun to WOH G64. 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," says Keiichi Ohnaka, who led the work on this object.

New observations, made with ESO's Very Large Telescope Interferometer, conclude that the gas and dust around the star is arranged in a thick ring, rather than a spherical shell, and the star is thus less hidden than had been assumed. This implies that the object is in fact half as luminous as previously thought, and thus, less massive. The astronomers infer that the star started its life with a mass of 25 solar masses. For such a star, the observed temperature is closer to what one would expect.

"Still, the characteristics of the star mean that it may be experiencing a very unstable phase accompanied by heavy mass loss," says co-author Markus Wittkowski from ESO. "We estimate that the belt of gas and dust that surrounds it contains between 3 and 9 solar masses, which means that the star has already lost between one tenth and a third of its initial mass."

To reach this conclusion, the team of astronomers used the MIDI instrument to combine the light collected by three pairs of 8.2-m Unit Telescopes of the VLT. This is the first time that MIDI has been used to study an individual star outside our Galaxy.

The observations allowed the astronomers to clearly resolve the star. Comparisons with models led them to conclude that the star is surrounded by a gigantic, thick torus, expanding from about 15 stellar radii (or 120 times the distance between the Earth and the Sun - 120 AU!) to more than 250 stellar radii (or 30 000 AU!).

"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," says Ohnaka. "And the torus that surrounds it is perhaps a light-year across! Still, because it is so far away, only the power of interferometry with the VLT could give us a glimpse on this object. "

Source: ESO

Explore further: 'Perfect storm' quenching star formation around a supermassive black hole

add to favorites email to friend print save as pdf

Related Stories

Hunting for dark matter in a gold mine

Dec 09, 2014

"What really impressed me was the trip down," said astrophysicist James Buckley, PhD, speaking of the vertical mile he traveled to get to the site of an underground dark-matter experiment. "You can see you're ...

Hubble spies charming spiral galaxy bursting with stars

Dec 09, 2014

(Phys.org) —The NASA/ESA Hubble Space Telescope observes some of the most beautiful galaxies in our skies—spirals sparkling with bright stellar nurseries, violent duos ripping gas and stars away from ...

Recommended for you

The hot blue stars of Messier 47

17 hours ago

Messier 47 is located approximately 1600 light-years from Earth, in the constellation of Puppis (the poop deck of the mythological ship Argo). It was first noticed some time before 1654 by Italian astronomer ...

Why is space black?

Dec 16, 2014

Imagine you're in space. Just the floating part, not the peeing into a vacuum hose or eating that funky "ice cream" from foil bags part. If you looked at the Sun, it would be bright and your retinas would ...

Confirmation bias in studies of gamma ray bursts

Dec 16, 2014

Our understanding of gamma ray bursts (GRBs) – flashes of gamma rays from explosions in distant galaxies – since they were discovered more than 50 years ago may not be as solid as first thought.

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

omatumr
1 / 5 (2) Jul 31, 2009
YET ANOTHER MYSTERIOUS COSMIC OBSERVATION

This doesn't sound like the stories of stellar evolution described in astronomy textbooks:

"Still, the characteristics of the star mean that it may be experiencing a very unstable phase accompanied by heavy mass loss," says co-author Markus Wittkowski from ESO. "We estimate that the belt of gas and dust that surrounds it contains between 3 and 9 solar masses, which means that the star has already lost between one tenth and a third of its initial mass."

Something is wrong with astronomy and astrophysics when almost every observation is a new mystery. I think the answer is recorded in the rest masses of every known nucleus except one, the single neutron.

With kind regards,
Oliver K. Manuel
http://myprofile....anuelo09

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.