The days of the Sun are numbered. The Sun will become a white dwarf in about 5 billion years, when it will expand into a red giant.
Most sunlike stars are doomed, and the process is well understood. There are a few things we have to learn about dying suns.
A recent study looked at a star called V Hya. The red giant star is 1,300 light-years away and has a mass roughly the same as the Sun. It is what the Sun might look like in a billion years.
There are some differences that make it different from our home star.
It has a companion star. The companion is too faint for us to see, but based on the motion of V Hya, we know it is a red dwarf star.
V Hya seems to be dying in a strange way.
V Hya is a Mira variable star. It varies in brightness by about 2 magnitudes every 530 days. This is normal for red giant stars. Red giants enter a period of cooling and heating when they combine heavier elements in their core.
It is also a carbon star, which is more unusual. The atmosphere of the star has been dredged up to the core of the carbon. Astronomers see a strong presence of carbon when they look at V Hya's spectrum.
The atmosphere of the star is very shabby.
ALMA (ESO/NAOJ/NRAO)/S. Dagnello.
The outflowing rings and the diffuse arcs of the sixth ring can be seen in the 12CO carbon emission line and in views of the 13CO carbon isotopes.
V Hya is an Asymptomatic Giant Branch star. Most of the sunlike stars will enter an AGB period at the end of their lives.
The outer layers of the star are cast off over a period of 100,000 years in a gradual process of stellar death. The last core collapses into a white dwarf. V Hya shows that this is sometimes incorrect.
If an AGB gradually cast off its outer layers, we would see a planetary nebula surrounding most white dwarfs. Many planetary nebulae are remnants of sunlike stars.
The ALMA shows that V Hydrae isn't creating a nebula.
It has been casting off thick rings. The star has ejected rings for over two thousand years.
The jets of gas ejected from the star were observed by the team. V Hya undergoes an active period every few hundred years, which is very different from the common AGB model.
Astronomers are fortunate to have captured a dying star in this stage because this period of active bursts is likely short lived. It is not known whether most AGB stars experience active periods or not.
It will take more observations of dying red giant stars to solve that mystery.
The article was published by Universe Today. The original article is worth a read.
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