A duo of dancing stars

Small stars like our Sun die in great beauty, surrounded by beautiful shrouds of multi-colored gases that were once their outer layers, leaving only their relic cores as silent testimony to the Universe that they once existed. Our Sun, like other small stars, will first become a swollen red giant It will grow in size to the frightening point that its flames will engulf the inner planets Mercury, Venus, and possibly Earth. Then it will wither into a small, dense white dwarf-its train core. In March 2020, an international team, led by astronomers from the University of Warwick (UK), reported that they had discovered a strange phenomenon involving a duet of these dead stars dancing closely. Scientists detected a huge white dwarf star with a strange carbon-rich atmosphere that could actually be two white dwarfs that merged while performing their strange macabre dance in the space between the stars, narrowly escaping explosive destruction.

Astronomers detected an unusual ultra massive white dwarf located about 450 light years from Earth with an atmospheric composition never seen before. This important observation marked the first time that a fused dance duo of white dwarfs it had been discovered by astronomers using its atmospheric composition as a clue to solve the mystery of its true identity.

The discovery, published in the March 2, 2020 issue of the magazine Nature astronomy, could shed new light on the nagging question of how massive white dwarf the stars evolve, as well as the number of supernovae that inhabit our barred spiral Milky Way.

Tea ultramassive white dwarf, called WD J0551 + 4135, was detected in a survey of data derived from the European Space Agency (ESA) Gaia telescope. The astronomers followed their discovery with a spectroscopy obtained using the William Herschel Telescope. The scientists focused on those white dwarfs identified as especially massive, an achievement that was made possible by the Gaia mission. By breaking the light emitted by the strange star, astronomers were able to determine the chemical composition of its atmosphere and found that it contained an unusually high level of carbon.

Lead author Dr Mark Hollands from the Department of Physics at the University of Warwick explained on a March 2, 2020 University of Warwick Press Release that “This star stood out as something we’ve never seen before. Expect to see an outer layer of hydrogen, sometimes mixed with helium, or just a mixture of helium and carbon. You don’t expect to see this combination of hydrogen and carbon at the same time there should be a thick layer of helium in the middle that forbids it. When we looked at it, it didn’t make sense. “

The majority white dwarfs They are relatively light, weighing about 0.6 times the mass of our Sun. However, WD J0551 + 4135 weighs 1.14 times the impressive solar mass, making it almost twice the average mass of other white dwarfs. Despite being more massive than our Sun, it is compressed into a small dense ball that is only two-thirds the diameter of Earth.

To solve the intriguing mystery, the astronomer-detectives decided to discover the true origins of the star. The age of WD J0551 + 4135 it also provided an important clue. Older stars orbit our Milky Way much faster than younger ones, and this strange white dwarf around our galaxy faster than 99% of the others nearby white dwarfs with the same cooling age. This means that this dead star is much older than it appears.

Dr. Hollands continued to explain on March 2, 2020. University of Warwick Press Release that “We have a composition that we cannot explain through normal stellar evolution, a mass twice the average of a white dwarf, and a kinematic age greater than that inferred from cooling. We are pretty sure how a star forms a white dwarf and it shouldn’t do this. The only way to explain it is if it was formed by merging two white dwarfs “.

The death of a small sun-like star

White dwarfs they are all that is left of the stars, like our own Sun, after they have finished burning all their necessary supply of nuclear fusion fuel. At this fatal point, the tiny dying star has spewed its outer gaseous layers into space. A little star Grand finale it contrasts with the noisy and explosive disappearance of more massive stars, which die in violent and catastrophic supernova explosions. Little stars like our Sun “gently enter that good night” and perish with great beauty and relative peace. In fact, their adorable multi-colored gaseous shrouds have inspired astronomers to refer to them as the “butterflies of the Universe,” in homage to their celestial beauty.

Little lonely stars like our Sun die softly. However, if there is another star actor in the drama, horrible complications develop. If a small star resides in a binary system with another star, a wild party will inevitably occur. When the first of the duo “dies”, leaving his dense white dwarf core behind, the stellar corpse will gravitationally suck up material from its still-living companion star, and victim. Like the vampire dwarf He continues to steal more and more material from his unfortunate companion, finally drinking enough material to reach enough mass to “become critical.” At this point, the white dwarf he pays for his crime and explodes, just like the greats. This explosion is called Type Ia supernova, and differs from type II supernovae with core collapse experienced by more massive stars.

The proposal that WD J0551 + 4135 is actually an object that was formed as a result of the merging of a duo of white dwarfs it is based on a related, but not identical, theory of its formation. In this case, how one of the two stars expanded at the end of its life into a swollen red giant, engulfed its companion star, drawing its orbit closer and closer as the first star faded in its white dwarf practices. Then there was a repeat performance when the other star turned into a bloat red giant. Over billions of years, the emission of gravitational waves further shortened the orbit, to the point where the stellar waltz-dancing duo merged to form a single object.

The dancers and their dance

Although white dwarf Mergers are predicted to occur, which involves the unusual WD J0551 + 4135 it’s stranger than expected. This is because most of the mergers in our Milky Way occur between stars that have different masses, while this strange merger likely occurred between a duo of stars of similar size. There is also a limit to the size of the resulting single. white dwarf change. This is because, if the resulting stellar corpse weighs more than 1.4 times the solar mass, it will “become critical” and shatter in a Type Ia supernova explosion. However, it is possible that such fatal stellar explosions could be unleashed at slightly lower masses, so this strange white dwarf is especially useful because it demonstrates how massive a white dwarf can get and still “live” to tell the story.

Because the merger restarts the star’s cooling process, astronomers find it difficult to calculate the star’s true age. The stellar corpse likely merged about 1.3 billion years ago, but the original dead star duo may have existed for many billions of years prior to that event.

WD J0551 + 4135 is important because it is one of the few white dwarfs to be identified, and it is the only one that has been identified so far on the basis of its composition.

Dr. Hollands explained on March 2, 2020. University of Warwick Press Release that “there are not so many white dwarfs this massive, although there are more than one would expect, which implies that some of them were probably formed through mergers. “

“In the future, we may be able to use a technique called astroseismology to learn about him White dwarf composition of the nucleus from its stellar pulsations, which would be an independent method to confirm that this star was formed from a merger. Perhaps the most exciting aspect of this star is that it must have failed to explode as a supernova – these gigantic explosions are really important for mapping the structure of the Universe, as they can be detected at very great distances. However, there is still a lot of uncertainty about what kind of star systems reach the supernova stage, “he added.

“As strange as it may sound, measuring the properties of this ‘failed’ supernova and future views tells us a lot about the pathways to thermonuclear self-annihilation,” continued Dr. Hollands.

This research appears in the March 2, 2020 issue of the journal Nature astronomy under the title Year Ultramassive white dwarf with a mixed hydrogen and carbon atmosphere as a probable fusion remnant.

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