MSGID: 1:317/3 64002671   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Ultracool dwarf binary stars break records    
    Astrophysicists discover the closest and oldest ultracool dwarf binary   
   ever observed    
      
     Date:   
         March 1, 2023   
     Source:   
         Northwestern University   
     Summary:   
         Astrophysicists have discovered the tightest ultracool dwarf binary   
         system ever observed. The two stars are so close that it takes   
         them less than one Earth day to revolve around each other. In   
         other words, each star's 'year' lasts just 17 hours.   
      
      
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   FULL STORY   
   ==========================================================================   
   Northwestern University and the University of California San Diego (UC   
   San Diego) astrophysicists have discovered the tightest ultracool dwarf   
   binary system ever observed.   
      
      
   ==========================================================================   
   The two stars are so close that it takes them less than one Earth day   
   to revolve around each other. In other words, each star's "year" lasts   
   just 17 hours.   
      
   The newly discovered system, named LP 413-53AB, is composed of a pair of   
   ultracool dwarfs, a class of very low-mass stars that are so cool that   
   they emit their light primarily in the infrared, making them completely   
   invisible to the human eye. They are nonetheless one of the most common   
   types of stars in the universe.   
      
   Previously, astronomers had only detected three short-period ultracool   
   dwarf binary systems, all of which are relatively young -- up to 40   
   million years old. LP 413-53AB is estimated to be billions of years old --   
   similar age to our sun -- but has an orbital period that is at least three   
   times shorter than the all ultracool dwarf binaries discovered so far.   
      
   The research was published on March 1 in the Astrophysical Journal   
   Letters.   
      
   "It's exciting to discover such an extreme system," said Chih-Chun "Dino"   
   Hsu, a Northwestern astrophysicist who led the study. "In principle, we   
   knew these systems should exist, but no such systems had been identified   
   yet."  Hsu is a postdoctoral researcher in Northwestern's Center for   
   Interdisciplinary Exploration and Research in Astrophysics(CIERA). He   
   began this study while a Ph.D. student at UC San Diego, where he was   
   advised by Professor Adam Burgasser.   
      
   The team first discovered the strange binary system while exploring   
   archival data. Hsu developed an algorithm that can model a star based   
   on its spectral data. By analyzing the spectrum of light emitted from   
   a star, astrophysicists can determine the star's chemical composition,   
   temperature, gravity and rotation. This analysis also shows the star's   
   motion as it moves toward and away from the observer, known as radial   
   velocity.   
      
   When examining the spectral data of LP 413-53AB, Hsu noticed something   
   strange.   
      
   Early observations caught the system when the stars were roughly aligned   
   and their spectral lines overlapped, leading Hsu to believe it was just   
   one star.   
      
   But as the stars moved in their orbit, the spectral lines shifted in   
   opposite directions, splitting into pairs in later spectral data. Hsu   
   realized there were actually two stars locked into an incredibly tight   
   binary.   
      
   Using powerful telescopes at the W.M. Keck Observatory, Hsu decided to   
   observe the phenomenon for himself. On March 13, 2022, the team turned   
   the telescopes toward the constellation Taurus, where the binary system   
   is located, and observed it for two hours. Then, they followed up with   
   more observations in July, October and December as well as January 2023.   
      
   "When we were making this measurement, we could see things changing over   
   a couple of minutes of observation," Burgasser said. "Most binaries we   
   follow have orbit periods of years. So, you get a measurement every few   
   months. Then, after a while, you can piece together the puzzle. With this   
   system, we could see the spectral lines moving apart in real time. It's   
   amazing to see something happen in the universe on a human time scale."   
   The observations confirmed what Hsu's model predicted. The distance   
   between the two stars is about 1% of the distance between the Earth and   
   the sun. "This is remarkable, because when they were young, something   
   like 1 million years old, these stars would have been on top of each   
   other," said Burgasser.   
      
   The team speculates that the stars either migrated toward each other   
   as they evolved, or they could have come together after the ejection of   
   a third -- now lost -- stellar member. More observations are needed to   
   test these ideas.   
      
   Hsu also said that by studying similar star systems researchers can learn   
   more about potentially habitable planets beyond Earth. Ultracool dwarfs   
   are much fainter and dimmer than the sun, so any worlds with liquid water   
   on their surfaces -- a crucial ingredient to form and sustain life --   
   would need to be much closer to the star. However, for LP 413-53AB,   
   the habitable zone distance happens to be the same as the stellar orbit,   
   making it impossible to form habitable planets in this system.   
      
   "These ultracool dwarfs are neighbors of our sun," Hsu said. "To   
   identify potentially habitable hosts, it's helpful to start with our   
   nearby neighbors.   
      
   But if close binaries are common among ultracool dwarfs, there may be   
   few habitable worlds to be found."  To fully explore these scenarios,   
   Hsu, Burgasser and their collaborators hope to pinpoint more ultracool   
   dwarf binary systems to create a full data sample.   
      
   New observational data could help strengthen theoretical models for   
   binary-star formation and evolution. Until now, however, finding ultracool   
   binary stars has remained a rare feat.   
      
   "These systems are rare," said Chris Theissen, study co-author and a   
   Chancellor's Postdoctoral Fellow at UC San Diego. "But we don't know   
   whether they are rare because they rarely exist or because we just don't   
   find them.   
      
   That's an open-ended question. Now we have one data point that we can   
   start building on. This data had been sitting in the archive for a long   
   time. Dino's tool will enable us to look for more binaries like this."   
       * RELATED_TOPICS   
             o Space_&_Time   
                   # Stars # Galaxies # Astrophysics # Black_Holes #   
                   Extrasolar_Planets # Astronomy # Solar_Flare #   
                   Solar_System   
       * RELATED_TERMS   
             o Gravitational_wave o Light-year o Extrasolar_planet o Planet   
             o Neptune's_natural_satellites o Pluto o Globular_cluster   
             o Open_cluster   
      
   ==========================================================================   
   Story Source: Materials provided by Northwestern_University. Original   
   written by Amanda Morris. Note: Content may be edited for style and   
   length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Chih-Chun Hsu, Adam J. Burgasser, Christopher A. Theissen. Discovery   
      of   
         the Exceptionally Short Period Ultracool Dwarf Binary LP   
         413-53AB. The Astrophysical Journal Letters, 2023; 945 (1): L6 DOI:   
         10.3847/2041-8213/ acba8c   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/03/230301162706.htm   
      
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