This artist’s concept shows the nova system HM Sagittae (HM Sge), where a white dwarf star is pulling material from its red giant companion. This forms a blazing hot disk around the dwarf, which can unpredictably undergo a spontaneous thermonuclear explosion as the infall of hydrogen from the red giant grows denser and reaches a tipping point. These fireworks between companion stars are fascinating to astronomers by yielding insights into the physics and dynamics of stellar evolution in binary systems. Credit: NASA, ESA, Leah Hustak (STScI)
Hubble Telescope Revisits a Star System That is Still Extraordinarily Hot
If we could gaze down upon the magnificent spiral structure of our
A Hubble Space Telescope image of the symbiotic star Mira HM Sge. Located 3,400 light-years away in the constellation Sagitta, it consists of a red giant and a white dwarf companion. The stars are too close together to be resolved by Hubble. Material bleeds off the red giant and falls onto the dwarf, making it extremely bright. This system first flared up as a nova in 1975. The red nebulosity is evidence of the stellar wind. The nebula is about one-quarter light-year across. Credit: NASA, ESA, Ravi Sankrit (STScI), Steven Goldman (STScI), Joseph DePasquale (STScI)
Hubble Space Telescope Finds Surprises Around a Star That Erupted 40 Years Ago
Astronomers have revisited one of the strangest binary star systems in our galaxy – 40 years after it burst onto the scene as a bright and long-lived nova – using new data from
SOFIA soars over the snow-covered Sierra Nevada mountains with its telescope door open during a test flight. SOFIA is a modified Boeing 747SP aircraft. SOFIA achieved full operational capability in 2014 and concluded its final science flight on September 29, 2022. Credit: NASA/Jim Ross
Data From SOFIA
With data from NASA’s flying telescope SOFIA, which retired in 2022, the team was able to detect the water, gas, and dust flowing in and around the system. Infrared spectral data shows that the giant star, which produces copious amounts of dust, returned to its normal behavior within only a couple years of the explosion, but also that it has dimmed in recent years, which is another puzzle to be explained.
With SOFIA astronomers were able to see water moving at around 18 miles per second, which they suspect is the speed of the sizzling accretion disk around the white dwarf. The bridge of gas connecting the giant star to the white dwarf must presently span about 2 billion miles.
The team has also been working with the AAVSO (American Association of Variable Star Observers), to collaborate with amateur astronomers from around the world who help keep telescopic eyes on HM Sge; their continued monitoring reveals changes that haven’t been seen since its outburst 40 years ago.
A Hubble Space Telescope image of the symbiotic star Mira HM Sge with compass and scale bar. Located 3,400 light-years away in the constellation Sagitta, it consists of a red giant and a white dwarf companion. The stars are too close together to be resolved by Hubble. Material bleeds off the red giant and falls onto the dwarf, making it extremely bright. This system first flared up as a nova in 1975. The red nebulosity is evidence of the stellar wind. The nebula is about one-quarter light-year across. Credit: NASA, ESA, Ravi Sankrit (STScI), Steven Goldman (STScI)
The Rarity and Significance of HM Sge
“Symbiotic stars like HM Sge are rare in our galaxy, and witnessing a nova-like explosion is even rarer. This unique event is a treasure for astrophysicists spanning decades,” said Goldman.
The initial results from the team’s research were published in the DOI: 10.3847/1538-4357/ad12c9
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