Rho Ophiuchus

Rho Ophiuchus – an inconspicuous star near the border with the constellation Scorpio. It appears in our latitudes as low and briefly as Antares, but with its brightness (about 5m) within the city limits it is practically invisible to the eye – only through optics.

But it is in optics that the most interesting things begin.

This star is famous for the beautiful nebula that surrounds its birthplace. Astronomers call it the “Rho Ophiuchi cloud complex,” which is superimposed on another cloud complex called the “Antares Nebula.” But Rho Ophiuchi (and the nebula surrounding it) is one and a half times closer to Antares, and very different from it.

This is a pair of young blue and very hot giants, 360 light years away from us – a good target for amateur telescopes of medium power, because the components are separated by only 3 seconds of arc – a rather close and beautiful stellar pair. How far these stars are from each other in real geometry – this can only be guessed, but the minimum estimates are from 3 hundred astronomical units – 10 times further than Neptune from the Sun. This is far, but not too far. And even our backward space technologies could deliver a parcel from one star to another.

But there are many more stars in this system.

In the region of the sky around Rho Ophiuchi (with a diameter of about 3 arc minutes), astronomers have identified several stars that, although fainter than Rho Ophiuchi, are at the same distance from us, and are also inside this gas-dust nebula complex, from which they were apparently born. Among them, there are also close pairs, but at least 6 stars are gravitationally bound to each other and actually form a small open star cluster.

The hazy region of the sky around the stars Antares and Rho Ophiuchi has recently been very took a spectacular photo Steeve Body – a French amateur astronomer, currently living in Australia (the astroclimate there is much better). Interestingly, Steve's main profession is a composer. But I haven't listened to his music yet. I voiced the video clip based on his astrophotograph his.

But where in this picture – among the unimaginable stellar scatterings – is Rho Ophiuchi?

It is worth mentioning right away that the image is upside down – relative to what is visible to the eye, binoculars, a telescope or on a star map. Telescopes flip the image (although not all and not always), and for astro cameras there is no such concept at all – there the orientation of the photo depends entirely on the whim of the photographer. But Steve Badie wanted it this way – after all, he lives in Australia. And the star, located in the northern part of this region, ended up at the very bottom of the frame.

It will be more understandable if we say that the star Rho Ophiuchi is located exactly 3 degrees north of Antares (and the famous globular cluster M4, which is nearby, and, by the way, another globular cluster – M80 – is located 2 degrees west of Rho Ophiuchi – this region of the sky is very interesting!).

If you look at this star through binoculars (or a spotting scope), it may seem that this star is triple (or even quadruple!). But this is an illusory neighborhood. Fainter stars visible near Rho Ophiuchi are located 100 light years further away. For an advanced galactic civilization, 100 set stars is not that much, but gravitational forces cannot bind these stars into a single system.

The stars behind Rho Ophiuchi are quite close to each other on the scale of interstellar distances. Whether they are related in themselves is a question for a separate study. But both are binary systems, and one of them is also very good for careful examination in a small telescope.

This star company looks beautiful, but to get to the gravitationally bound components, you need to use a larger magnification – 80-100 times. Binoculars or a tube will not be enough. But the most inexpensive telescope with an objective diameter of 80 mm will already show you Rho Ophiuchi separately.

In the picture, Rho Ophiuchi are the two stars that have almost merged together, but a small telescope shows them exactly like that. A larger telescope will show the duality of Rho Ophiuchi more clearly. But in reality, the stars in this system are separated by a distance of 50 billion kilometers and make one revolution around their common center of mass in two and a half thousand years. The more distant participants in this system, invisible to amateur telescopes, spend tens or even hundreds of thousands of years to make one revolution around these two luminaries. For stars, this is not much at all, but we, of course, will not live to see it.

This is a fairly young star system – only a few million years old. The mass of each of the two main stars is about 10 times greater than the mass of the Sun. This means that in a few million years there will be something shining here like the double Antares, only brighter, because Rho Ophiuchi is closer. And it is approaching us – at a speed of 11 km per second. If the velocity vector were directed directly at us, then just at the moment of the supernova explosion (and such stars end their lives only in this way) – in 10 million years, Rho Ophiuchi would be in the immediate vicinity of the Solar System, and our distant descendants would be in danger. Fortunately, Rho Ophiuchi has a significant lateral velocity – more than 20 milliseconds per year. This corresponds to a spatial velocity of about 9 km / sec to the side. As a result, they will miss by a large margin.

Video of the flight to the star Rho Ophiuchi, based on astrophotography by Steve Body

But in any case, during its lifetime, this system of 6 stars will move far from the places where it was born as an extended gas and dust nebula. Now we see this nebula around Rho Ophiuchi, but only the part that the star illuminates, and the full size of the nebula is enormous, as is its mass, which is estimated at least at 3,000 solar masses. And many more bright stars will emerge from these shining interstellar clouds.