Smoke Rings | by Brian Koberlein



8 April 2022

Artist view of V Hya in its death throes.
Artist view of V Hya in its dying throes.

Our Solar’s days are numbered. In about 5 billion years the Solar will broaden right into a purple big, getting rid of its outer layers earlier than settling right down to turn into a white dwarf. It’s the inevitable destiny of most sunlike stars, and the method is nicely understood. However as a latest examine reveals, there are nonetheless a number of issues now we have to study dying Suns.

This latest examine appears at a star often known as V Hydrae or V Hya for brief. It’s a purple big star about 1,300 light-years away with a mass roughly the identical because the Solar. It’s what the Solar may seem like in a number of billion years. There are, nevertheless, a few issues that make it completely different from our residence star.

For one, it has a companion star. The companion is simply too faint for us to see, however based mostly on the movement of V Hya, we all know it’s doubtless a purple dwarf star that orbits V Hya as soon as each 8.5 years. For one more, V Hya appears to be dying in an uncommon means.

In its present state, V Hya is categorized as a Mira variable star. It varies in brightness by about 1 – 2 magnitudes each 530 days, give or take. That is typical for dying purple big stars. As they fuse heavier parts of their core attempting to outlive, purple giants typically enter a interval of oscillation, pushed by the heating and cooling of the core. What’s extra uncommon is the truth that it’s also a carbon star. Because of this carbon fused in its core has been dredged as much as the ambiance of the star. So when astronomers take a look at V Hya’s spectrum, they see a powerful presence of carbon. Mainly, the star’s ambiance could be very “sooty.”

These two traits mixed make V Hya an Asymptomatic Large Department star or AGB. About 90% of sunlike stars will enter an AGB interval towards the top of their life. Astronomers have usually thought that the AGB epoch is a gradual means of stellar dying, the place the outer layers of the star are forged off over a interval of about 100,000 years. After which, the remaining core collapses right into a white dwarf. However V Hya reveals that is both partly or typically incorrect.

ALMA image of V Hydrae and its smoke rings.
ALMA picture of V Hydrae and its smoke rings.

If an AGB regularly forged off its outer layers, then we might anticipate to see an ever-expanding nebula often known as a planetary nebula surrounding most white dwarfs. And we do see many planetary nebulae because the remnants of sunlike stars. However observations by the Atacama Giant Millimeter/submillimeter Array (ALMA) present that V Hydrae isn’t creating such a nebula. As an alternative, it has been getting rid of thick rings wealthy in carbon. The star has ejected six rings over the course of about 2,100 years. The staff additionally noticed jets of gasoline ejected from the star perpendicular to the rings. This implies that V Hya undergoes an unusually energetic interval each few hundred years, which could be very completely different from the widespread AGB mannequin.

This era of energetic bursts is probably going quick lived in comparison with the complete AGB epoch, so astronomers are lucky to seize a dying star on this stage. It isn’t recognized whether or not most AGB stars expertise such energetic intervals, or whether or not V Hya is especially uncommon. To unravel that thriller, it is going to take extra observations of different dying purple big stars.

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