Stars and planetary systems are born out of nebulae that swirl and contract out of their collective gravitational attraction—and yes, that means a nebula also crafted our own Solar System, with the Sun and all the planets along with it. These gas clouds, of course, are themselves born out of stars that reach the end of their life cycles in spectacular fashion in an event known as a supernova.
For years now, scientists had been constantly looking out for nebulae out in the universe. After all, the nebula that our planetary system sprung forth from is now long gone. As such, we must look elsewhere to find out just how exactly did our small patch of the neighborhood in the cosmos come to be.
However, there are instances where scientists look to the sky and find something new instead of something they’d already seen hundreds, if not thousands, of times before. Such is the case with YY Hya, a binary star composed of two dwarf stars that orbit around each other once every 8 hours and are only some 2.2 solar radii (1.5 million km; 951,000 mi) apart.
One part of the pair is a white dwarf with a temperature of about 66,000 °C (120,000 °F), while the other is a K dwarf, or otherwise known as an orange dwarf, with a temperature of only 4,400 °C (8,000 °F). Given the close proximity of one star to the other, the white dwarf is likely heating one side of its orange dwarf companion in such a way that it leads to “extreme phenomena in the spectrum of the [K dwarf] star,” according to the paper.
A couple of amateur astronomers aided a team of international scientists in tracking the curious stellar pair, and their collective efforts led to scientists discovering a new type of nebula known as a galactic emission nebula. Their results were published in the journal Astronomy & Astrophysics.
Said Stefan Kimeswenger, lead author and from the Department of Astro and Particle Physics at Innsbruck University: “Toward the end of their lives, normal stars inflate into red giant stars. Since a very large fraction of stars is in binary pairs, this affects the evolution at the end of their lives.”
Kimeswenger continued: “In close binary systems, the inflating outer part of a star merges as a common envelope around both stars. However, inside this gas envelope, the cores of the two stars are practically undisturbed and follow their evolution like independent single stars.”
The nebula in question is some 15 light-years across, which in normal circumstances would have left the gas cloud available for disturbance from nearby stars. YY Hya, however, is located above the galactic plane, or the plane along which a galaxy rotates; this means that most stars that would have otherwise disturbed YY Hya’s nebula are otherwise out of gravitational reach, leaving the gas cloud and the stars within it to themselves.
Interestingly, the binary star YY Hya may have had a role to play in the “Guest Star” observation of 1086 as reported by Chinese and Korean astronomers—a story quite similar to another Guest Star that occurred almost 100 years later.
Kimeswenger followed: “It is even possible that this system is related to a nova observation made by Korean and Chinese astronomers in 1086. In any case, the positions of the historical observations match very well with those of our object described here.”
References
- Gough, E. & Universe Today. (2022, January 9). Astronomers discover a brand new type of nebula, and it’s very cool. ScienceAlert. https://www.sciencealert.com/astronomers-discovery-a-brand-new-type-of-nebula-and-it-s-very-cool
- Kimeswenger, S., Thorstensen, J. R., Fesen, R. A., Drechsler, M., Strottner, X., Germiniani, M., Steindl, T., Przybilla, N., Weil, K. E., & Rupert, J. (2021). YY Hya and its interstellar environment. Astronomy & Astrophysics, 656, A145. https://doi.org/10.1051/0004-6361/202039787
