Can Nearby Binary Star Systems Mimic Planets?

The vast majority of the known exoplanets have been discovered by the radial velocity method. This method employs the effects of a planet’s gentle tug on its parent star which is perceived as a “wobble” in the star’s motion. A new study, conducted by Morais and Correia, looks at whether this effect can be mimicked by another, distinctly non-planetary, source: Binary stars.

Conceptually, the idea is rather straightforward. A star of interest lies in a triple star system. It is the third member and in a larger orbit around a tight binary system. As the tight binary system orbits, there will be periods in which they line up with the star of interest giving a minutely greater pull before relaxing the pull later in their orbit. This remote tug would show a distinctly periodic effect very similar to the effects expected from an inferred planet.

The obvious question was how astronomers could miss the presence of binary stars, close enough to have a notable effect. The authors of the paper suggest that if the binary pair orbited sufficiently close, it would be unlikely that they could be resolved as a binary. Additionally, if one member were sufficiently faint (an M dwarf), it may not appear readily either. Both of these instances are plausible given that some three fourths of nearby main sequence stars are M class, and about half of all stars are in binary system.

Next, the team asked how important these effects may be. They considered the case of HD 18875, a binary system in which a distant star (A) has a 25.7 year period around a tight binary (Ba + Bb) that orbit each other with a period of 155 days. This system was noteworthy because a hot Jupiter planet was announced around the A star in 2005, but challenged in 2007 when another team could not repeat the observations.

The new study attempted to use their understanding and modeling of three body systems to see if the binary interaction could have produced the spurious signal. Using their model, they determined that the effects of the system itself would have produced effects similar to those of a planet of 4 Earth masses located at 0.38 AU. A planet of such mass is well below the limit of a hot Jupiter and the distance is somewhat larger than usual as well. Thus, the nearby B-binary could not have been responsible. Furthermore, such minute effects of this type are generally interpreted as “super-Earths” and have only become prevalent in observations in the past few years.

Thus, while the unconfirmed planet around HD 18875 A might not have been caused by the nearby binary, the work in this new paper has shown that effects of nearby binaries will become increasingly important as we start detecting radial velocities indicative of less and less massive planets.

What did Isaac Newton Invent?

Classical Mechanics

Sir Issac Newton is best know for his laws of motion. Many people’s knowledge of his scientific contributions stops there. Issac Newtons inventions contributed a great deal to our current understanding of subjects from optics to theology and how early scientists were able to view their world.

In mathematics Isaac Newton inventions included laying the ground work for differential and integral calculus. His work was based on his insight that the integration of a function is merely the inverse procedure to differentiating it. Taking differentiation as the basic operation, he produced simple analytical methods that unified many separate techniques previously developed to solve apparently unrelated problems such as finding areas, tangents, the lengths of curves and the maxima and minima of functions.

Issac Newton inventions in mechanics and gravitation were summarized the Principia. His discoveries in terrestrial and celestial mechanics showed how universal gravitation provided an explanation of falling bodies on Earth and of the motions of planets, comets, and other bodies in the heavens. He explained a wide range of then unrelated phenomena: the eccentric orbits of comets, the tides and their variations, the precession of the Earth’s axis, and motion of the Moon as perturbed by the gravity of the Sun. This work includes Newton’s three famous laws of motion, fluid motion, and an explanation of Kepler’s laws of planetary motion.

Isaac Newton inventions in optics included his observation that white light could be separated by a prism into a spectrum of different colors, each characterized by a unique refractivity. He proposed the corpuscular theory of light. He was the first person to understand the rainbow. He was the first person to use a curved mirror in a telescope to prevent light form being broken up into unwanted colors.

Isaac Newton inventions and contributions to science were many and varied. They covered revolutionary ideas and practical inventions. His works in physics, mathematics and astronomy are still important today. His contributions in any one of these fields would have made him famous; taken as a whole, they make him truly outstanding.

We have written many articles about Isaac Newton’s inventions for Universe Today. Here’s an article about celestial mechanics, and here’s an article about Newton’s laws of motion.

If you’d like more info on Isaac Newton’s inventions, check out How Stuff Works for an interesting article about Isaac Newton’s inventions, and here’s a link to Isaac Newton’s Biography.

We’ve also recorded an entire episode of Astronomy Cast all about Gravity. Listen here, Episode 102: Gravity.

Sources:
How Stuff Works
University of Virginia
NASA