New observations from the Very Large Telescope at ESO’s Paranal Observatory in Chile show how enormous size of dust particles surrounding the hypergiant star VY Canis Majoris enable it to lose a huge amount of mass as it enters the final stages of its life.
In this image from ESO’s Very Large Telescope (VLT) the red hypergiant star VY Canis Majoris is hidden behind an obscuring disc; the crosses are artifacts due to features in VLT’s SPHERE instrument. Image credit: ESO.
VY Canis Majoris, also known as VY CMa, HD 58061 or HIP 35793, is a red hypergiant located in the constellation Canis Major.
This star is 3,840 light-years distant from Earth and is one of the largest known stars.
According to astronomers, VY Canis Majoris has a radius of approximately 1,420 solar radii. It is about 35 times the mass of our Sun and 300,000 times more luminous.
Throughout their expansion, giant stars like this shed large amounts of material. For example, VY Canis Majoris sees 30 times the mass of Earth expelled from its surface in the form of dust and gas every year.
This cloud of material is pushed outwards before the star explodes, at which point some of the dust is destroyed, and the rest cast out into interstellar space. This material is then used, along with the heavier elements created during the supernova explosion, by the next generation of stars, which may make use of the material for planets.
To observe VY Canis Majoris, Dr Peter Scicluna of Kiel University’s Institute of Theoretical Physics and Astrophysics and his colleagues used Very Large Telescope’s SPHERE instrument.
The instrument revealed how the light of this distant hypergiant was lighting up clouds of material surrounding it. The astronomers could also see how the starlight was scattered and polarized by the surrounding dust particles.
Analysis of the polarization results revealed these particles 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.
“Massive stars live short lives. When they near their final days, they lose a lot of mass. In the past, we could only theorize about how this happened,” said Dr Scicluna, who is the lead author of a paper published today online in the journal Astronomy & Astrophysics (arXiv.org preprint).
“But now, with the new SPHERE data, we have found large grains of dust around this hypergiant.”
“These are big enough to be pushed away by the star’s intense radiation pressure, which explains the star’s rapid mass loss.”
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P. Scicluna et al. Large dust grains in the wind of VY Canis Majoris. A&A, published online November 25, 2015; doi: 10.1051/0004-6361/201527563
