Mira HM Sge. It’s a star system binarybinary located approximately 3,400 light years from Earth, in the constellation Arrow (Sagitta)). A system that intrigues astronomersastronomers for almost 50 years now. Since 1975 it has suddenly become 250 times brighter. And above all, that it did not then quickly fade away as a self-respecting nova should have done.
A symbiotic star that attracts attention
Astronomers say that Mira HM Sge corresponds to a particular star system. A symbiotic star, they say. Understand that the system is composed of only a white dwarf and a giant companion in orbitorbit eccentric around each other. The first ingests the gasgas coming from the second. This gas forms a burning disk around the white dwarf, which can unpredictably undergo a spontaneous thermonuclear explosion as the giant’s supply of hydrogen densifies on the surface.
And in the data of Hubble space telescopeHubble space telescope and of firefire the Stratospheric Observatory for Astronomy infraredinfrared (Sofia) as well as in archival data from other missions, researchers have discovered that the temperature of the star system has recently increased. Even though his brightnessbrightness has finally been decreasing since the mid-1980s. The Astrophysical Journalthe astronomers explain having evaluated using spectroscopy UVUV from Hubble, the temperature of the white dwarf at more than 250,000 °C. In 1989 it was only around 220,000°C. Enough to propel this white dwarf to the rank of the hottest ever observed. How did she get there? The question remains unanswered.
Still a lot of questions
The infrared spectral data revealed that thegiant stargiant star returned to its normal behavior – namely, periodic pulsations every approximately 534 days – just a few years after the explosion in novanova. However, it has steadily declined in recent years. For what ? Here again, the question remains unanswered.
In all the data collected, the researchers note a slow evolution of the Mira HM Sge system. Perhaps as the red giantred giant and the white dwarf are moving away. They conclude that the system was installed in a “new normal” after the nova explosion in 1975. The decrease in brightness could continue at its slow pace for many more years, until the white dwarf and the red giant approach each other again in their orbit, increasing the amount of mattermatter circulating between them and triggering another nova.
