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Blocking out the sun

Speed read
  • Multi-institution astronomy team locates record-setting stellar eclipse that lasts for over three years at a time.
  • Eclipse caused by opaque cloud from nearby stripped down red giant star.
  • Telescope advances should enable scientists to home in when the next eclipse comes in 2080.

Imagine living on a world where, every 69 years, the sun disappears in a near-total eclipse that lasts for three and a half years.

That is just what happens in a binary star system nearly 10,000 light years from Earth, a system recently discovered by US National Science Foundation (NSF) and National Aeronautics and Space Administration -funded researchers.

The new system — TYC 2505-672-1 — sets a new record for both the longest duration stellar eclipse and the longest period between eclipses in a binary system. Epsilon Aurigae, a giant star eclipsed by its companion every 27 years for periods ranging from 640 to 730 days, is the previous record holder.

<strong> Taking the long view.</strong> Joey Rodriguez combed through over 14,000 images taken since 1890 to find a star system with the longest observed eclipse on record. Situated 10,000 light years from Earth, this system eclipses every 69 years for 3.5 years at a time. The culprit: A large opaque cloud stripped from one of the nearby red giants. Courtesy Vanderbilt University.

“TYC 2505-672-1 has the longest enduring stellar eclipse and the longest orbit for an eclipsing binary ever found — by far,” says the paper’s first author Joey Rodriguez, a doctoral student at Vanderbilt University. “Epsilon Aurigae is only about 2,200 light years from Earth – and much brighter, which has allowed astronomers to study it extensively.”

Rodriguez discovered the system’s extraordinary properties with the assistance of colleagues from Vanderbilt, Harvard, Lehigh, Ohio State, Pennsylvania State universities, Las Cumbres Observatory Global Telescope Network, and the American Association of Variable Star Observers.

The collaboration began when Rodriguez heard a lecture by Sumin Tang of the Harvard-Smithsonian Center for Astrophysics who presented results gleaned from thousands of photographic plates taken by Harvard astronomers between 1890 and 1989. Searching the Kilodegree Extremely Little Telescope (KELT) system database, Rodriguez found about 9,000 corresponding images of the obscure system taken in the last eight years to combine with the 1,432 images taken at Harvard.

His resulting analysis revealed a system similar to the one at Epsilon Aurigae, with some important differences. It appears to consist of a pair of red giant stars, one of which has been stripped down to a relatively small core and surrounded by an extremely large disk of material that produces the extended eclipse.

“About the only way to get these really long eclipse times is with an extended disk of opaque material. Nothing else is big enough to block out a star for months at a time,” Rodriguez says.

<strong>Star pupils. </strong> The newly discovered eclipse will recur in 2080, enabling scientists using the better telescopes from that era to add to our knowledge about stellar environments, says Keivan Stassun, professor of physics and astronomy at Vanderbilt . Courtesy Vanderbilt University.

Combined temperature and size estimates lead the astronomers to conclude TYC-2505-672-1 is a red giant with its outer layers stripped away. They suspect this stripped material may account for the obscuring disk. In order to produce the 69-year interval between eclipses, the astronomers calculate that they must be orbiting at an extremely large distance, about 20 astronomical units, which is approximately the distance between the Sun and Uranus.

Even though the most powerful telescopes can’t independently resolve the two objects, the astronomers hope technological advances will make that possible by 2080 when the system’s next eclipse occurs.

“One of the great challenges in astronomy is that some of the most important phenomena occur on astronomical timescales, yet astronomers are generally limited to much shorter human timescales,” says co-author Keivan Stassun, professor of physics and astronomy at Vanderbilt.

“Here we have a rare opportunity to study a phenomenon that plays out over many decades and provides a window into the types of environments around stars that could represent planetary building blocks at the very end of a star system’s life.”

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