Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: chris on 18/06/2016 09:49:33
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VY Canis Majoris is in our cosmic neighbourhood and is massive. But how did it get that big, and what's its ultimate fate?
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how did VY Canis Majoris get that big?
It is thought that stars (and their surrounding planets) condense out of a cold molecular cloud consisting of dust and gas.
Different parts of the cloud will condense at different rates, forming stars with a wide range of masses - our Sun is thought to be a bit larger than average, and VY Canis Majoris is far larger than average, with an estimated mass 17 times the Sun.
It is currently thought to be in its red giant phase, which means that it has already burnt up all its hydrogen in the core (turning it into Helium), and is probably now producing elements heavier than Helium in the core.
VY Canis Majoris has already shed its outer layers of atmosphere, forming a large nebula around the star. Effectively the outer edges of the star are so far from the center that they are just drifting off into interstellar space. The pressure of gas at the visible surface of the star is far less than the pressure of Earth's atmosphere (about 100,000 times less than the pressure at Earth sea level).
what's its ultimate fate?
The luminosity of VY Canis Majoris is estimated to be around 270,000 times brighter than the Sun.
Since it only has about 17 times as much fuel as the Sun, this means that it is burning through its fuel enormously fast. It is much younger than the Sun, and it will be gone long before the Sun starts to turn into a red giant.
Stars this large are rare, and their lives are very short (in astronomical terms), so astronomers don't have a good sample of stars of this type in order to make a detailed prediction of its future. So there are some different ideas about it.
Once it has produced iron atoms in its core, it will not be generating any heat to sustain it against its enormous gravity, and it will start to shrink catastrophically, exploding as a supernova.
The mass of VY Canis Majoris is large, but shedding its outer layers will continue. It is more likely that the remnant will be a neutron star (although if the mass is at the upper end of the estimated range, it may form a black hole).
See: https://en.wikipedia.org/wiki/VY_Canis_Majoris
https://en.wikipedia.org/wiki/Supernova#Core_collapse