What happened after the thermonuclear explosion? binary star System observed approximately 3,400 light-years away Hubble space telescope.
HM Sagittae, or HM Sge for short, is a system known as the symbiotic system. white dwarf feeding on a friend red giant star. The stolen material forms an accretion disk orbiting the white dwarf. If too much material falls from the disk onto the white dwarf at the same time, the pressure and temperature increase so much that a thermonuclear explosion occurs on the surface of the white dwarf.
Although this explosion is not enough to destroy the white dwarf in a supernova, it releases enough energy to cause the system to glow in a formation called a “nova.”
Between April and September 1975, HM Sge went nova in the constellation Sagittarius the Arrow. enlightened within night sky Magnitude six through magnitude +17 (visible only by telescopes with apertures larger than about 305 mm/12 inches) to magnitude +10.5; At this point it became more easily visible to telescopes with smaller apertures equal to about 102 mm/4 inches, allowing amateurs to view astronomers need to follow this. This equals an increase in brightness. brightness 250 times.
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Since turning into Nova, HM Sge has not been following the rules. Most novae fade out after a few days; HM Sge remained at its peak brightness for many years until the mid-1980s, when it gradually began to fade, punctuated by more notable dimming events. Even now it has only faded to magnitude +12.
“In 1975, HM Sge went from being an ordinary star to something that all astronomers in the field were looking at, and at some point the activity slowed down,” said Ravi Sankrit of the Space Telescope Science Institute (STScI). expression.
“Symbiotic stars like HM Sge are rare on our Earth. galaxyand witnessing a nova-like explosion is even rarer,” added Steven Goldman, also of STScI. “This unique event has been a treasure trove for astrophysicists for decades.”
Observations with numerous telescopes over the years have attempted to get to the bottom of what is happening at HM Sge. Now Goldman and Sankrit have reached new conclusions with their team, based on the 2021 Hubble Space Telescope observations and collected data. NASAno longer valid SOFIA (Stratospheric Observatory for Infrared Astronomy), with an infrared telescope at the back Boeing’s 747 aircraft in 2021 and 2022.
The onset of dimming in the system since 1985 was attributed, at least in part, to the behavior of the red giant. It’s called Mira variable (after the prototype of the class, Mira – omicron Ceti – the Whale in the constellation Ceti) and is based on periodic vibrations approximately every 534 days. The beginning of the system’s blackout in the mid-1980s was attributed to one of two things. This event may have been triggered either by a larger-than-typical mass loss event associated with the red giant’s pulsations; This event may have created a dust shower that blocked some of the light, or it may have been the result of a mass loss of 90 percent. The non-circular orbits of the white dwarf and red giant around each other push them further apart, reducing the amount of material flowing between the two. Currently the separation between the two components of the system is approximately 40. astronomical units (AU), where 1 AU is defined by the average distance between them. Soil And our sun149.6 million kilometers (93 million miles). For comparison, Neptune It is 30 AU away from the Sun.
Hubble’s observations also revealed a strong emission line from ionized magnesium. This emission line was not present in the spectrum of HM Sge dating back to 1990, when the temperature of the white dwarf was 200,000 degrees Celsius (about 400,000 degrees Fahrenheit). For strongly ionized magnesium to be present in abundance, the temperature of the white dwarf would have to have risen to 250,000 degrees Celsius (about 450,000 degrees Fahrenheit) at that time. This makes it one of the hottest known white dwarfs, despite the overall decrease in luminosity of the system. What causes this increase in temperature is currently a mystery.
Additionally, for the first time, SOFIA was able to detect emission lines from water vapor in the disk in a symbiotic binary system and use its signal as a proxy to measure the properties of the accretion disk. Water molecules appear to be moving at 29 kilometers (18 miles) per second, which is attributed to the speed at which they flow over the edge of the disk.
However, most of the emission lines in HM Sge’s spectrum are weakening compared to 1990; This probably shows that the system is slowly changing and evolving as the red giant and white dwarf move away from each other.
Goldman and Sankrit’s team concluded that the HM Sge system settled into a “new normal” fairly quickly after the nova explosion in 1975, with only a slow decline in average brightness over the years (there was some increase and decrease in brightness, as well as optical and infrared and not always the same time, again attributed to the behavior of the red giant). The overall extinction may continue at a slow pace for many more years until the white dwarf and red giant come closer in orbit again, increasing the amount of material flowing between the two and igniting another nova.
Finally, a preview of what fate has in store for the white dwarf, red giant companion. Both were once like the sun stars In a binary system, one star has slightly more mass than the other. The more massive star consumed its nuclear fuel more quickly and eventually collapsed into a red giant, shedding its dispersed outer shell to reveal its exposed, dormant core, the white dwarf. The other star evolved a little slower but is now following the same path as its sibling; It first evolves into a red camel and then, about a million years later, into a white dwarf.
The gravitational change caused by the transformation of the red giant could bring the two white dwarfs closer together. If they collide one day, they will explode as Type Ia. supernovabut this will not happen for hundreds of millions, perhaps even billions, of years.
Findings of Hubble and SOFIA published Astrophysical Journal.