bad astronomy | An exoplanet around GJ 896 is as strange as it comes

It’s rare that every bit of an astronomy news story is so great, but here we go. You will want to continue with all of this.

A planet-sized telescope has observed a binary red dwarf star system for 14 years, pinpointing the two stars’ positions with incredible accuracy, and the discovery of a planet larger than Jupiter orbiting one of them in a dramatically inclined plane. to the orbits of stars around each other.

Yes, of course. This is my type of story [link to paper].

The star system is called GJ 896, and it’s a pair of low-mass red dwarfs 20.37 light-years from Earth — and yes, as I’ll get to it, the distance is known precisely. The larger of the two, GJ 896A, is about 0.44 times the mass of the Sun, and its companion star, GJ 896B, is much smaller at 0.165 solar masses. So both are neat. Although they are among the closest known stars to the Sun, they are so faint that you need a telescope to see them at all.

Between 2006 and 2011, and again in 2020, these stars were observed using the Very Long Baseline Array, an array of radio dishes spread across the Earth. They observe at the same time, and then their data is combined in such a way that their vision is as keen as if they were a single dish the size of a planet. This technique is called Interferometryhas been in use for decades, and is perhaps best known today as the Event Horizon Telescope uses it to look at black holes in the center of the Milky Way and M87.

A telescope’s accuracy—its ability to measure an object’s position very precisely, or the separation of two objects in the sky—depends in part on its size, so a telescope over 10,000 km wide has Unusual Precision. GJ 896’s observations have an accuracy of about 60 microarcseconds, which is a very small angle in the sky. There are 60 arcseconds in a degree, for example, and the moon is 0.5 degrees = 1800 arcseconds. A microsecond is a million of arcseconds, so that resolution is like being able to see a cell phone sitting on the moon.

Even older, less precise observations were accurate enough to see the two stars’ orbital motions around each other. The orbital period is about 229 years, and they are about 4.5 billion km apart, which is the same distance as Neptune from the Sun.

The new measurements are easily enough to capture the view caused by the Earth’s movement around the sun. As we go around the sun, we see the stars from one angle and then from a different angle six months later. this is the view It is the same idea of ​​holding your thumb in front of your face and closing one eye and then the other; Your thumb will appear to be moving on the background. This technique is used to get distances to the stars, which is why the distance to GJ 896 is determined so well.

Once you subtract that effect, and subtract the orbital motions of the two stars around each other, something very strange can be seen: the primary star, GJ 896A, is rotating through space, making one revolution every 284.4 days. The reason must be something small orbiting it, its gravity pulling the star and causing it to spin through the galaxy. Looking at the period of the clouds, astronomers have determined that it is a planet with a mass about 2.3 times the mass of Jupiter.

The planet itself is not visible, but traces of its gravity can be seen at GJ 896A positions over time. The process of measuring the position of a star is called astronomyIt is very rare to find a planet this way. This one, called GJ 896Ab, is one of very few that have been found in this way.

And it gets better: very accurate measurements of the planet’s orbit show It orbits the star in a strongly inclined plane to the orbital plane of the two stars, tilted by 148 degrees. It’s weird. Likes, truly amazing.

All the major planets in the orbit of the solar system rotate in approximately the same plane. A handful of exoplanets have been found rotating at large angles to other planets on their systems, and it’s not clear why. One planet may have migrated too close to another and the gravitational interaction pushed it into an inclined orbit. Perhaps over time the gravitational influence of the second star pumped up the tilt of the planet’s orbit until its tilt changed to where it is now. Or maybe it had something to do with the way the planet and stars were formed in the first place. We don’t know yet.

And remember, the planet itself is strange. We know a lot of planets orbiting red dwarf stars, but most of them are far from small Earth-sized planets. Very few gas giants, not to mention More than twice the mass of Jupiter. This system is peculiar in almost all respects, which of course makes studying much more fun.

This is the first time that the full 3D motions of a binary star and an exoplanet orbiting one have been determined. That in itself is pretty cool, but when you add everything else into it, this becomes one of the most interesting star/planetary systems that we know of. And the cherry on top is that it’s so close to us that we can actually study it in some detail.

Its proximity also makes me wonder. If such systems were very rare in a galaxy, you would expect the nearest system to be thousands of light years away. The fact that GJ 896 is one of the closest star systems to the Sun in the entire galaxy indicates that these kinds of things are common. The only way we can detect it is to study as many binary red dwarfs as possible, and continue to keep a close eye on GJ 896. Hopefully, long-term observations will solve the mystery of the planet’s tilted orbit, why it is so big, and how this wonderful and brutal system emerged.

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