Planet 9 Where are You?

We’re still looking for the elusive body, we think it’s out there, lurking in the Kuiper Belt.

Refresher:  The Kuiper Belt is far-far away, at the edge of our solar system, composed of asteroids and some Dwarf Planets.  Remember Pluto?  Pluto is a Dwarf Planet at the beginning edge of the Kuiper Belt!  Think of the asteroid belt only 20 times as wide.

Astronomers have been on the hunt for a mysterious body, one that appears to be influencing the orbits of many Kuiper Belt objects.  A couple of years ago one group of investigators predicted its future position and waited until it might be detectable.  Nothing!  Now you might say if it’s so far away maybe we just cannot see it.  Well, we can see the objects it affects and how it affects them.  It is predicted to be massive,  maybe more massive than Earth.  I think a body as big or bigger than Earth should easily be seen with today’s telescopes.  Where is this planet nine?

The question might be then, what is planet nine?  Let me see, we can see the objects it’s gravity affects and how it affects them, but we can’t see it.  By analogy we can see the stars and how the supermassive black hole at our Milky Way’s center affects their orbits. Yet, we do not see the black hole.

Could planet nine be a black hole?  Well, it appears to be massive, but if it’s a black hole, would be quite small.  How small?  A black hole of Earth’s mass would be a sphere about the size of a marble, with gravitational influence equal to Earth’s.  If extrapolated to Uranus’s mass the black hole would be a biggie marble.  Still too small to find with today’s technology.  Sounds plausible in theory, but how does one make a mini black hole?

Turns out, the old-fashioned way, with immense gravity (mass/density) and temperature.  Turns out, that’s also the rub.  To achieve the pressure and temperature necessary for black hole formation, a mass at least 8-10 times that of our Sun is required.  In our known universe only very massive stars end up as black holes.  Those stars produce what we call stellar mass black holes.  While they are small, about 60 kilometers in diameter, their enormous gravity would influence the entire outer solar system and Kuiper Belt.  Easy to find.

A plausible concept comes from our early universe, not long after the big bang.  Density, pressure, and temperature were right.  Just needed a little perturbing to mix up a collection of little black holes.  Current thinking is this is what happened but most of them have evaporated by now.  Could a lonely little black hole still exist out there?

Maybe, but keep looking.

What’s in the Sky?

September 13-15; an hour before sunrise; east:  A waning crescent Moon slides past Venus then gets close to Regulus on the 15th.