News Space 11 September 2018

Stand down. Binary star system is not about to explode


A 2017 prediction of twin-star self-destruction turns out to be based on a 20 year-old mistake. Andrew Masterson reports.


An artist's impression of a binary star system in close mutual orbit.

An artist's impression of a binary star system in close mutual orbit.

Mark Garlick / Science Photo Library / Getty Images

A typographical error has been blamed for a spectacular 2017 prediction that the stars comprising a binary system 1800 light-years from Earth were about to merge and create a titanic explosion.

The prediction, made by a team led by astrophysicist Lawrence Molnar from Calvin College in Grand Rapids, US, was published in The Astrophysical Journal.

The scientists looked at a binary system dubbed KIC 9832227, in the constellation of Cygnus. Using data gathered by Calvin College’s own observatory between 2013 and 2016, backed up by archival measurements taken since 2007, and anchored on a 1999 finding from a long-running observation project known as the Northern Sky Variability Survey (NSVS), Molnar and colleagues found that the two stars in the system were orbiting each other ever faster.

With the stars circling each other every 11 hours, the scientists said, they were set to merge into what is called a red nova, at some point in the year 2022.

Since publication, the team has continued to take measurements using the Calvin College Observatory, and found nothing to contradict the initial findings.

Now, however, a second team, headed Quentin Socia from San Diego University, US, has taken another look at the original data and concluded that long-ago human error distorted the picture, and led to an inaccurate prediction.

KIC 9832227, it seems, is not about to self-destruct.

To make their findings, Socia and colleagues looked first at the gap in the Molnar research, covering the years 1999 to 2007. Using data from the NASA Vulcan Ames Project they discovered that the system’s eclipses – the point at which either star blocks the other out, from the point of view of Earth – were consistently half an hour later than the original hypothesis predicted.

Although, the Molnar group’s post-2007 readings were spot on, the anchoring NSVS 1999 measurement was an hour off. Further investigation found that the paper from which this NSVS value was derived had in fact got the time wrong by a whole 12 hours.

This meant that Molnar’s subsequent measurements were out of whack by one entire orbit – 11 hours – plus one hour. Revised in the light of this finding, the original study did not support the conclusion that the binary was close to going nova.

“This is arguably the most important part of the scientific process,” says Socia.

“Knowledge advances the most when bold predictions are made, and people question and test those predictions. Often the most exciting discoveries happen when our expectations are not met.

“This is a good example of how scientists from different parts of the world can work together to better understand how our universe works, bringing with them new pieces to the puzzle.”

For his part, Molnar is comfortable with being proven wrong. It’s all part of the way good science proceeds, he says.

“Good science makes testable predictions,” he notes.

“There have been a few other papers that have tried to poke at our project, and we’ve been able to poke back – criticisms that just don’t fly. But this one does fly, and I think they have a good point. This illustrates how science can be self-correcting.”

The new work is published in The Astrophysical Journal Letters.

  1. http://iopscience.iop.org/article/10.3847/1538-4357/aa6ba7/meta
  2. http://inspirehep.net/record/642510/
  3. http://vulcan.project.asu.edu/index.php
  4. http://iopscience.iop.org/article/10.3847/2041-8213/aadc0d
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