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Hyper-Giant Star Reveals More of Its Secrets

New observations of the star using the SPHERE instrument on the VLT have clearly revealed how the brilliant light of VY Canis Majoris lights up the clouds of material surrounding it, and have allowed the properties of the component dust grains to be determined better than ever before. (Image:  ESO)
New observations of the star using the SPHERE instrument on the VLT have clearly revealed how the brilliant light of VY Canis Majoris lights up the clouds of material surrounding it, and have allowed the properties of the component dust grains to be determined better than ever before. (Image: ESO)

The most detailed images have now been taken of the hyper-giant star, VY Canis Majoris, using the European Southern Observatory (ESO) Very Large Telescope. While the giant star prepares for its life-ending supernovae, astronomers have discovered new insights on the necessary processes gigantic stars — like VY Canis Majoris — go through before they meet their explosive demises.

The astronomers’ observations show how the unexpectedly large size of the particles of dust surrounding the star enable it to lose an enormous amount of mass as it begins to die.

The star VY Canis Majoris is a red hypergiant, one of the largest known stars in the Milky Way. It is 30–40 times the mass of the Sun and 300 000 times more luminous. In its current state, the star would encompass the orbit of Jupiter, having expanded tremendously as it enters the final stages of its life. New observations of the star using the SPHERE instrument on the VLT have clearly revealed how the brilliant light of VY Canis Majoris lights up the clouds of material surrounding it and have allowed the properties of the component dust grains to be determined better than ever before. In this very close-up view from SPHERE the star itself is hidden behind an obscuring disc. The crosses are artefacts due to features in the instrument.

The star, VY Canis Majoris, is a red hyper-giant, one of the largest known stars in the Milky Way. It is 30-40 times the mass of the Sun, and 300,000 times more luminous. In its current state, the star would encompass the orbit of Jupiter, having expanded tremendously as it enters the final stages of its life. New observations of the star using the SPHERE instrument on the VLT have clearly revealed how the brilliant light of VY Canis Majoris lights up the clouds of material surrounding it, and have allowed the properties of the component dust grains to be determined better than ever before. In this very close-up view from SPHERE, the star itself is hidden behind an obscuring disc. The crosses are artifacts due to features in the instrument. (Image: ESO)

To put things into perspective, the stellar goliath is 30-40 times larger than our Sun. So if we were to replace VY Canis Majoris with our Sun, it would reach out and encompass the orbit of Jupiter; VY Canis Majoris is also 300,000 times brighter than the Sun. The red hyper-giant is located in the constellation Canis Major, which is over 3,800 light-years away.

This video sequence takes you on a voyage from a broad vista of the sky into a close-up look at one of the biggest stars in the Milky Way, VY Canis Majoris. The final image comes from the SPHERE instrument on ESO’s Very Large Telescope in Chile:

Astronomers used an instrument called the Spectro-Polarimetric High-contrast Exoplanet Research instrument (SPHERE), which is on the Unit 3 Telescope. The adaptive optics system of this instrument corrects images to a higher degree than earlier adaptive optics systems. This allows features very close to bright sources of light to be seen in great detail, according to ESO.

Using SPHERE, astronomers were able to see how VY Canis Majoris was lighting up clouds of material that surround it. When the researchers used the ZIMPOL mode of SPHERE, they were able to see further into the heart of the cloud, which is made up of gas and dust, and were also able to see how the starlight was scattered and polarized by the surrounding material.

This chart shows the location of the very brilliant red hypergiant star VY Canis Majoris, one of the largest stars known in the Milky Way. Most of the stars visible to the naked eye on a clear and dark night are shown and the location of VY Canis Majoris is marked with a red circle. This star is visible in a small telescope and has a strikingly red colour.

This chart shows the location of the very brilliant red hyper-giant star, VY Canis Majoris, one of the largest stars known in the Milky Way. Most of the stars visible to the naked eye on a clear and dark night are shown, and the location of VY Canis Majoris is marked with a red circle. This star is visible in a small telescope, and has a strikingly red color. (Image: ESO)

How the material in the upper atmospheres of these giant stars’ is pushed away into space before the host explodes has remained a mystery, until now. The most likely explanation has always been radiation pressure, which is the force that starlight exerts. Because this pressure is extremely weak, it relies on larger grains of dust; this ensure a broad enough surface area to have an appreciable effect.

The large grains of dust observed close to the star mean that the cloud can effectively scatter the star’s visible light and be pushed by the radiation pressure from the star. The size of the dust grains also means much of it is likely to survive the radiation produced by VY Canis Majoris’ inevitable dramatic demise as a supernova. This dust then contributes to the surrounding interstellar medium, feeding future generations of stars and encouraging them to form planets, ESO wrote.

This wide-field view shows the sky around the very brilliant red hypergiant star VY Canis Majoris, one of the largest stars known in the Milky Way. The star itself appears at the centre of the picture, which also includes clouds of glowing red hydrogen gas, dust clouds and the bright star cluster around the bright star Tau Canis Majoris towards the upper right. This picture was created from images forming part of the Digitized Sky Survey 2.

This wide-field view shows the sky around the very brilliant red hyper-giant star VY Canis Majoris, one of the largest stars known in the Milky Way. The star itself appears at the center of the picture, which also includes clouds of glowing red hydrogen gas, dust clouds, and the bright star cluster around the bright star, Tau Canis Majoris, towards the upper right. This picture was created from images forming part of the Digitized Sky Survey 2. (Image: ESO)

Peter Scicluna, from the Academia Sinica Institute for Astronomy and Astrophysics in Taiwan, and lead author of a new paper that will be published in the journal Astronomy & Astrophysics, wrote in an press release:

“Careful analysis of the polarization results revealed these grains of dust to be comparatively large particles, 0.5 micrometers across, which may seem small, but grains of this size are about 50 times larger than the dust normally found in interstellar space.”

The ESO notes: “The dust particles must be large enough to ensure the starlight can push it, but not so large that it simply sinks. Too small, and the starlight would effectively pass through the dust; too large, and the dust would be too heavy to push. The dust the team observed about VY Canis Majoris was precisely the right size to be most effectively propelled outwards by the starlight.”

Every year, VY Canis Majoris loses 30 times the mass of the Earth, expelled from its surface in the form of dust and gas through its expansion. The cloud of material is then pushed outward before the star explodes.

After the powerful supernova blast, some of the dust is destroyed, with the rest being forced out into space.

This leftover material, and the heavier elements that were created during the supernova explosion, will then be used by the next generation of stars.

“Massive stars live short lives,” says Scicluna. “When they near their final days, they lose a lot of mass. In the past, we could only theorize about how this happened. But now, with the new SPHERE data, we have found large grains of dust around this hyper-giant. These are big enough to be pushed away by the star’s intense radiation pressure, which explains the star’s rapid mass loss.”

VY Canis Majoris will eventually build up enough heavier elements at its core to implode; scientists believe it will likely take hundreds of thousands of years. During the massive supernova, it will be seen from Earth, and may be as bright as the moon.

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