Hubble Space Telescope finds surprises around a star that erupted 40 years ago

Astronomers have used new information from NASA’s Hubble House Telescope and the retired SOFIA (Stratospheric Observatory for Infrared Astronomy) in addition to archival information from different missions to revisit one of many strangest binary star techniques in our galaxy—40 years after it burst onto the scene as a vivid and long-lived nova. A nova is a star that instantly will increase its brightness tremendously after which fades away to its former obscurity, often in just a few months or years.

The preliminary outcomes from the group’s analysis have been published in The Astrophysical Journal, and Sankrit is presenting analysis centered on the UV spectroscopy on the 244th meeting of the American Astronomical Society in Madison, Wisconsin.

Between April and September 1975, the binary system HM Sagittae (HM Sge) grew 250 occasions brighter. Much more uncommon, it didn’t quickly fade away as novae generally do, however has maintained its luminosity for many years. Just lately, observations present that the system has gotten hotter, however paradoxically pale a little bit.

HM Sge is a specific type of symbiotic star the place a white dwarf and a bloated, dust-producing large companion star are in an eccentric orbit round one another, and the white dwarf ingests gasoline flowing from the large star. That gasoline types a blazing sizzling disk across the white dwarf, which may unpredictably endure a spontaneous thermonuclear explosion because the infall of hydrogen from the large grows denser on the floor till it reaches a tipping level. These fireworks between companion stars fascinate astronomers by yielding insights into the physics and dynamics of stellar evolution in binary techniques.

“In 1975 HM Sge went from being a nondescript star to one thing all astronomers within the discipline have been taking a look at, and sooner or later that flurry of exercise slowed down,” stated Ravi Sankrit of the House Telescope Science Institute (STScI) in Baltimore. In 2021, Steven Goldman of STScI, Sankrit and collaborators used devices on Hubble and SOFIA to see what had modified with HM Sge within the final 30 years at wavelengths of sunshine from the infrared to the ultraviolet (UV).

The 2021 ultraviolet information from Hubble confirmed a robust emission line of extremely ionized magnesium that was not current in earlier printed spectra from 1990. Its presence exhibits that the estimated temperature of the white dwarf and accretion disk elevated from lower than 400,000 levels Fahrenheit in 1989 to larger than 450,000 levels Fahrenheit now. The extremely ionized magnesium line is considered one of many seen within the UV spectrum, which analyzed collectively will reveal the energetics of the system, and the way it has modified within the final three many years.

“After I first noticed the brand new information,” Sankrit stated, “I went, ‘Wow, that is what Hubble UV spectroscopy can do,’ I imply it is spectacular, actually spectacular.”

With information from NASA’s flying telescope SOFIA, which retired in 2022, the group was in a position to detect the water, gasoline, and dust flowing in and across the system. Infrared spectral information exhibits that the large star, which produces copious quantities of dust, returned to its regular conduct inside solely a pair years of the explosion, but additionally that it has dimmed in recent times, which is one other puzzle to be defined.

With SOFIA, astronomers have been in a position to see water shifting at round 18 miles per second, which they believe is the velocity of the scorching accretion disk across the white dwarf. The bridge of gasoline connecting the giant star to the white dwarf should presently span about 2 billion miles.

The group has additionally been working with the AAVSO (American Affiliation of Variable Star Observers), to collaborate with novice astronomers from all over the world who assist hold telescopic eyes on HM Sge; their continued monitoring reveals adjustments that have not been seen since its outburst 40 years in the past.

“Symbiotic stars like HM Sge are uncommon in our galaxy, and witnessing a nova-like explosion is even rarer. This distinctive occasion is a treasure for astrophysicists spanning many years,” stated Goldman.