An incredibly bright star system that has long baffled astronomers could soon brighten the sky with the glow of thousands of solar cores, a new study suggests. If that happens, the results could be visible to the naked eye from Earth day and night.
The system, called Sagittarius V, consists of a white dwarf (the dense core of a dead Sun-like star) and a companion to a more massive star located in the constellation Sagittarius’ arrow, about 10,000 light-years away. The voracious white dwarf is devouring material from its companion “at a rate never seen before,” the research team said in a statement.
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“The material accumulating in the white dwarf is likely to cause a nova explosion within the next few years, during which time V Sagitta will become visible to the naked eye,” Pablo Rodríguez Gil, a professor at Spain’s Institute of Astrophysics in the Canary Islands and co-author of the study, said in a statement.
understand the beast
In a study published in November in the journal Monthly Notices of the Royal Astronomical Society, an international team of researchers led by the University of Turku in Finland analyzed the light emitted by V. sagittae to better understand what kind of beast they are.
These data were collected over a 120-day observation period by the X-Shooter spectrometer on the European Southern Observatory’s Very Large Telescope, located 8,600 feet (2,600 meters) atop Cerro Paranal Mountain in Chile’s Atacama Desert.
A spectrometer like the X-Shooter collects incoming light from a celestial object and separates it into its constituent wavelengths. Because each atom and molecule absorbs and reflects light at specific wavelengths, this yields a spectrum that reveals an object’s chemical composition. To gain perspective, consider how a prism splits white light into its constituent colors to produce a rainbow.
This spectral data helped researchers reanalyze the properties of V Sagittae. Previously, in a 1965 study, astronomers calculated that the two stars had solar masses of 0.7 and 2.8, a controversial conclusion.
To constrain the star’s size, this more recent study, taking into account factors such as orbital period, suggests that the entire system may be less than 2.1 solar masses, with the white dwarf and its companion star each about 1 solar mass.
Phil Charles, emeritus professor of astronomy at the University of Southampton and co-author of the study, explained the confusion surrounding this “very important system”. This uncertainty stems from V Sagittarius’ complex and constantly fluctuating light emission, which is “likely due to rapid outflow” rather than the star’s orbital motion, making it difficult to determine its magnitude.
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“Our study shows that no one has yet been able to uniquely determine the orbital motion of each component, so we still do not have precise measurements of the mass of each star,” Charles told Live Science in an email.
orbiting nuclear weapons
The researchers also identified V Sagittarius as a supersoft X-ray source (SSS). This means that they produce lower-energy X-rays compared to hard sources such as active black holes or colliding neutron stars. A classic SSS consists of an accreting white dwarf and a more massive star whose gas spills out and falls onto the white dwarf.
V Sagittae’s incredible gravitational appetite causes sustained thermonuclear reactions on the white dwarf’s surface, turning it into an orbiting core and the brightest SSS in the galaxy, the researchers said in a statement.
In fact, V Sagittarius is 100 times brighter than other variable star systems, even in its fainter phase. The rate of material falling into a white dwarf’s accretion disk changes dramatically and unpredictably, sometimes in just a few days, as it struggles to consume all the material it steals from its partners, the researchers said in a separate statement.
As a result, a significant amount of material escapes, forming a ring of gas, or halo, surrounding both stars, forming an “orbiting disk” with a radius that spans about two to four times the distance between the two stars.
daytime supernova
V Sagitte’s chaotic accretion and extreme brightness are signs of its impending violent death, preceded by an explosive appetizer, so to speak, offering hopeful stargazers a promising scenario: a nova explosion.
Novaes occur when an accreting white dwarf swallows large amounts of material and ejects it explosively from its surface. Although these stellar explosions don’t destroy white dwarfs, they’re still amazing: the average nova shines hundreds of thousands of times brighter than the Sun. Because they do not destroy white dwarfs, these novae can recur over thousands or millions of years.
But this spectacular sight is only a prelude to the main event. When the stars spiral into each other, they create “supernova explosions that are so bright that they can be seen from Earth during the day,” Rodríguez-Gil added.
This ultimately glorious finale could occur as early as 2067, according to a 2020 study from Louisiana State University, which predicted V Sagitte’s demise based on a decrease in the star’s orbital period. Charles concludes:[observed] That should happen if the periodic decline continues, but that could easily change, as it is difficult to accurately predict stellar evolution!”
So mark your calendars to keep an eye out for a nova in the constellation Sagittarius, a supernova that will bring one of our galaxy’s most fascinating star systems to a spectacular end.
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