An article published in “The Astronomical Journal” reports a study on the dimming of the red hypergiant star VY Canis Majoris. A team of researchers led by astrophysicist Roberta Humphreys of the University of Minnesota, USA, used observations conducted with the Hubble Space Telescope to study not only the star but also huge clumps of materials around it. The conclusion is that VY Canis Majoris had moments where it ejected huge amounts of materials that formed those clumps and obscured it for various periods, detected over time.
About 3,900 light-years from Earth, VY Canis Majoris has a mass estimated to be around 30-40 times the Sun’s. Its brightness is estimated to be around 300,000 times the Sun’s, but from the Earth, it’s variable with dimming episodes recorded during the 19th and the 20th century. At its lowest, its brightness dropped to a sixth of its normal. For these reasons, it’s been the subject of many studies with various instruments: for example, an article published in the journal “Astronomy & Astrophysics” reported a study conducted with the SPHERE instrument on the VLT.
Over the past few years, Roberta Humphreys and her collaborators have studied VY Canis Majoris and other red giants to better understand the processes taking place in these stars that are going through the last phase of their life before exploding into supernovae. The ejection of large masses of materials is a characteristic, and this star had various ejection episodes over the last few centuries, traced thanks to observations conducted with the Hubble Space Telescope. Some of the ejected clumps have masses that are twice the planet Jupiter’s.
In this new study, Roberta Humphreys’ team focused on the clumps closest to VY Canis Majoris, the ones ejected less than a century ago from the Earth’s point of view. The calculation of their movements links many of those clumps to episodes in which this star’s brightness visibly decreased. Even today it’s less bright than in the past, so you need to use a telescope to locate it while astronomical records indicate that in the past it was visible to the naked eye.
The dimming of VY Canis Majoris has been compared to that of Betelgeuse, the protagonist of recent research also because between November 2019 and February 2020 its brightness dropped to about a third of its normal. A cloud of dust composed of materials ejected from the star itself was considered the culprit of the phenomenon as well. VY Canis Majoris is much larger and more massive than Betelgeuse, so all the ongoing processes are more violent.
Among the known red supergiants and hypergiants, VY Canis Majoris is the one that shows the greatest complexity in its activity. We’re seeing it within a period of its life that is very short from an astronomical point of view, as it lasts a few thousand years. As far as we know, it might have already exploded. Studying VY Canis Majoris will help understand how these stars lose materials during the last stage of their life. Those materials could help form new stars and the elements that will be generated by the supernova can help form new planets.
The image right below (NASA, ESA, and R. Humphreys (University of Minnesota), and J. Olmsted (STScI)) shows on the left the large nebula surrounding VY Canis Majoris seen from Hubble, at the center a detail of the area central with the zone near the star, and on the right an artistic representation of the star.
