A very rare discovery: Failed star orbits a dead star every 71 minutes [View all]

[Judi Lynn]

June 9, 2017


An international team of astronomers using data from the rejuvenated Kepler space telescope have discovered a rare gem: A binary system consisting of a failed star, also known as a brown dwarf, and the remnant of a dead star known as a white dwarf. And one of the properties that makes this binary so remarkable is that the orbital period of the two objects is only 71.2 minutes. This means that the speeds of the stars as they orbit each other are about 100 km/sec (a speed that would allow you to travel across the Atlantic in less than a minute). Using five different ground-based telescopes across three continents, the team was able to deduce that this binary system consists of a failed star with a mass of about 6.7% that of the Sun (equivalent to 67 Jupiter masses) and a white dwarf that has a mass of about 40% of the sun's mass. They have also determined that the white dwarf will begin cannibalizing the brown dwarf in less than 250 million years making this binary the shortest-period pre-cataclysmic variable ever to have been discovered.


The hot white dwarf star had originally been identified by SDSS as WD1202-024 and was thought to be an isolated star. The fact that it is actually a member of a very close 71-minute binary was announced by Dr. Lorne Nelson of Bishop's University at the semi-annual meeting of the American Astronomical Society in Austin, TX on June 6th (see the link on the right for a concatenated version of the webcast of the press conference). Dr. Saul Rappaport (M.I.T.) and Andrew Vanderburg (Harvard Smithsonian Center for Astrophysics) were analyzing the light-curves of more than 28,000 K2 targets when one observation caught their attention. Unlike the transits of exoplanets that pass in front of their host stars and cause a small attenuation in the brightness of the star, this light curve showed reasonably deep and broad eclipses with a sinusoidal contribution to the brightness between eclipses that is thought to be due to an illumination of the cool component by the much hotter white dwarf.

The team quickly devised a model for the binary showing that it was consistent with a hot white dwarf composed of helium being eclipsed by a much cooler and lower-mass brown dwarf companion that is seen nearly edge-on.


Read more at: https://phys.org/news/2017-06-rare-discovery-star-orbits-dead.html#jCp