THE SOLAR SYSTEM'S BLACK HOLE

As the hunt for a mysterious world at our solar neighbourhood’s edge steps up, something more exotic might also fit the bill

- James Romero

It’s been four years since Mike Brown, the astronomer who removed Pluto’s status as a planet, added a hypothetical one back in to explain strange orbits in the outer Solar System. In another two years the Vera C. Rubin Observatory will map those celestial backwaters to help find Brown’s Planet Nine. But what if this target can’t be seen? It’s a possibility that hit the headlines last year when Planet Nine was replaced, at least in excited media headlines, by an ancient black hole. Brown himself addressed the possibility, writing on Twitter: “P9 could definitely be a black hole, as long as it is the right mass. In fact, it could also be a six-Earth-mass hamburger.” So is a black hole lurking in the outer Solar System a statistical possibility worth considering? Or a whopper of a stab in the dark?

FINDING THE PHANTOM PHOTOBOMBERS

By monitoring a billion stars, we are finding the fingerprints of rogue planets, stars and possibly black holes

1 Like a converging lens

When an object of mass passes in front of a distant star, it can actually make the star brighter. While some stellar radiation will be blocked, more light rays become bent towards Earth by the foreground object’s gravity.

2 Setting stars aflicker

A number of objects are capable of producing the microlensing effect. These include rogue planets, brown dwarfs, white dwarfs, neutron stars and possibly PBHs.

3 A mysterious gravitational fingerprint