Three times eclipsing galaxies

Triple Eclipsing Galaxies

A schematic of a triple eclipsing stellar system seen from above the orbital plane. The green circle and green track mark the tertiary star, while the inner red/blue tracks are for the inner eclipsing binary star pair. Only about twenty triple-eclipse galaxies are known; astronomers have used TESS observations, combined with other data sets, to study six new ones. Credit: Rappaport, et al. 2022

Stars of the mass of the Sun or greater are usually accompanied by one or more companion stars. The system is created when gravity pulls the gas and dust of an interstellar cloud together until clumps develop that are so dense that they coalesce into stars. Multiple stellar systems evolve, according to one model, when the cloud has a slight spin. That generates a disk that then fragments to produce multiple stars.

In a competitive model, cloud turbulence causes clumps to break up into multiple systems. When the orbit of a pair of binary stars happens to fall along our line of sight, the stars form an eclipsing binary. Ordinary solar-mass eclipsing binaries have typical periods of days. Triplet stellar systems can also eclipse, but because the third star in a typical triplet orbits further out (it is further to keep the system relatively stable and not eject any of the stars), its period is closer to a year and longer monitoring is needed to recognize and study them. More than a million known to date obscuring binary systems are known, but only twenty triple-obscuring systems have been published.

Triple-obscure systems and binaries offer the benefit of enabling astronomers to reliably measure various otherwise degenerate physical features of the systems, including orbital inclinations and eccentricities and, in combination with other data, the stellar masses, rays, ages, temperatures and chemical compositions (“metallicity”). However, in eclipsing triples, complex dynamic interactions that take place over short time scales can also be studied. Last but not least, the statistics on obscuring triplets also shed light on the formation mechanisms of these systems, details that can be compared to simulations.

CfA astronomer Willie Torres was part of a team that used transit observations from TESS (the Transiting Exoplanet Survey Satellite) to spot about 50 new triple eclipse systems, 20 of them with reliable orbits for all three stars. The team reports on six of these eclipsing triplets for which additional data has enabled a more complete description of the stars’ characters. All six galaxies are relatively old, about a billion years. All six can be seen almost sideways, with the inner binary sometimes obscuring the outer tertiary star and sometimes vice versa.

The masses of all twelve stars in the inner binary system are in the range of 0.7 to 1.8 solar masses, and all stars are in the main sequence phase of their lives; the six tertiary stars are all larger, with masses ranging from 1.5 to 2.3 solar masses. The authors conclude with a discussion of the statistics of these systems and find that about 0.02% of nearby binary stars harbor a third star in a flat configuration like their current set – implying that there are probably several hundred thousand of them in our galaxy. . They also note possible connections between triplets and even more complex stellar systems such as the so-called “2 plus 2 compact quadruple systems”.

The research was published in Monthly Notices from the Royal Astronomical Society


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More information:
SA Rappaport et al, Six new compact triple blackout triples found with TESS, Monthly Notices from the Royal Astronomical Society (2022). DOI: 10.1093/mnras/stac957

Quote: Triple-eclipse stellar systems (2022, July 1), retrieved July 2, 2022 from https://phys.org/news/2022-07-triply-eclipsing-stellar.html

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