The Hypergiant red star VY Canis Majoris, one of the largest stars in our galaxy, is going to die soon, new study suggests. Will it impose some risks to our planet as it dies in violent supernovae explosion?
If you watch the sky these nights you would probably easy identify the brightest star in the sky, Sirius. Located in the constellation Canis Major, Sirius is however not as imposing as you might think. It’s only a binary star system in which the largest is about twice as massive as the Sun. Sirius system appears bright because its proximity to Earth, at just 8.6 light years, its literally one of ours near neighbors.
However, VY Canis Majoris, it is not visible to the naked eye. Located in the same small constellation Canis Major, it is one of the most massive known stars, a red hypergiant: if it placed at the center of the Solar System, VY Canis Majoris’s surface would extend beyond the orbit of Jupiter. It is 300,000 times brighter than our own star. But since it is 3900 light years, it takes you at least a small telescope to see it.
Hypergiant stars like VY Canis Majoris have the shortest lives because they burn massive amounts of nuclear fuel. A star exists because of a balance between gravity and some counteracting force — nuclear reactions are kept under control due to the forces exerted by gravity.
In the case of a hypergiant, this equilibrium seems precarious: they lose significant amounts of material in the upper atmospheres. It is estimated that each year, VY Canis Majoris loses about 30 times the Earth’s mass. The dust and gas expelled from its surface forms clouds around the star and its remain surrounding it until the inevitable explosion that marks the end. But the exact process by which this type of star “die” was unclear. It has been assumed that radiation pressure is behind the process — the force that starlight exerts. But this pressure is very weak to have such efftects.
Though, the latest observations may change our understanding of this mass-loss mechanism. Astronomers used the new extreme-adaptive-optics instrument SPHERE at the VLT, to make the first direct detection of submicron dust grains in VY’s ejecta. After they analyzed the dust of these clouds in depth, they found evidence for varying grain sizes throughout the ejecta: some grains are about 50 times larger than normally dust found in the interstellar space. So what is that actually mean?
These grains are sufficiently large to derive a significant amount of radiative acceleration from scattering. The increased size of the grains also makes them resistant to sublimation in the supernova that will eventually consume VY CMa. This may result in VY CMa injecting upwards of 1% Sun’s masses of pre-supernova dust into the interstellar medium.
said Ralf Siebenmorgen ~ co-author of the study, which will be published in the journal Astronomy & Astrophysics.
In other words, VY Canis Majoris is coming to the end of its life.
Massive stars live short lives,
said Peter Scicluna, lead author of the paper.
When they near their final days, they lose alot of mass. In the past, we could only theorise about how this happened. 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.
VY Canis Majoris is going to continue “dieting” until the end. Its end will come as a violent supernova explosion, which should happen, cosmologically speaking, very soon. Maybe in a thousand year or, maybe, in a few hundred thousand. When it dies the bright explosion will be viewable from Earth. Our descendants will attend a good show and see VY illuminate the sky.