Scientists have studied the yellow supergiant HD 144812, which has increased emission in the infrared. Scientists believe that this luminary once turned into a red supergiant and then reverted back to its original state.
Yellow supergiants
Astronomers from the Czech Republic and Argentina used the Gemini South telescope to study the star HD 144812. They have found evidence that it represents a rare case where a luminary has evolved to a red supergiant and then returned to its previous state. A paper on this is published in arXiv.
Yellow supergiants are extremely rare stars. The reason for this lies in the peculiarities of their evolution. They are born with masses of 10-40 solar masses and as the rest of the luminaries begin to deplete their hydrogen reserves.
However, the more massive the luminary, the sooner it will move to the last stage of its existence — its outer shells swell and get colder. In the case of yellow supergiants, this process begins almost immediately after birth. They evolve rapidly into red supergiants and stay in this stage much longer than in their original state.
That’s why scientists see so few of them throughout the Galaxy compared to the giant red luminaries. Yellow supergiants exist for too short a time, and there is only one way out of their red stage — supernova, after which only a neutron star or black hole remains.
Evolution in reverse
However, scientists have known for some time that the evolution of supermassive stars is even more improbable than it may seem. It can even go in the opposite direction in terms of general ideas about astrophysics.
This is particularly true for yellow supergiants. Scientists have long known that some stars whose spectrum has a so-called galactic emission line are actually yellow supergiants that have reverted back to their original state. This is thought to occur when the star loses most of its mass.
That is HD 144812, discovered back in 1978 and located 2500 light-years away. All this time, scientists knew that its spectrum contains a galactic emission line and there is still excess radiation in the red part of the spectrum, but that it is a post-red supergiant has not yet been confirmed.
However, it has been suspected for a long time and that’s why scientists have been investigating it as part of a program to find yellow supergiants. Spectral analysis confirmed that the star had indeed returned from the red giant stage. Moreover, there is a gas-dust disk around it, and a companion is also present.
We can see that all of this has something to do with the fact that the evolution of HD 144812 has turned back and now this luminosity is “blueing”. The gas-dust disks are traces of the giant emissions that caused this. But the connection to the companion has not been established yet.
According to phys.org
