Is there a black hole in our backyard?
In Part One we discussed a proposed space mission called "Breakthrough Starshot," whose objective is to send a spacecraft the size of a grain of rice to the nearest star system, Alpha Centauri. All of us will be keen to get the first "up-close" photos of planets around a new star system. One would like to add that the journey may prove to be just as interesting as the destination.
This is because there is a growing consensus the nanocraft will pass by an object en route that is 5-10 times more massive than the Earth called "Planet 9." This enigmatic object was discovered by its pull on nearby metal-rich icy bodies (aka "dirty snowballs") in its immediate vicinity. Planet 9 is larger than expected for its placement in the outskirts of the Solar System, and on top of that has not yet been directly imaged. Because it may be dark and massive, it was recently proposed that Planet 9 might be a small and very old "primordial" black hole.
Wait a minute: if Planet 9 is a black hole, then will it suck up the entire solar system, including Earth?! While, it is the case that black holes do not let material that falls onto them escape, they are also not vacuum cleaners. So Earth is safe for now.
An interesting question to ask is can we confirm, or rule out, this seemingly preposterous idea? The Breakthrough Starshot nanocraft could potentially make a measurement that would support the black hole interpretation, but it would also be a challenge to obtain the necessary data set.
Another idea to search for icy bodies impacting onto Planet 9. In such a case, the impactor would heat up as it hits the accretion disk of the black hole and then would shine brightly in optical blue light just before disappearing into the black hole.
A new telescope coming on line soon called the LSST will have the ability to make such a detection and in doing so, give us some definitive answers as to what is lurking in our backyard.