The Approach: A Hard Science Fiction Thriller. The Black Hole Trilogy, #1

Dr. Naomi Ingram's job is to know where everything is. Four times a year she publishes the reference frame that every measurement on Earth is quoted against, and this quarter it will not close. There is a residual of three millimeters that has no cause. She applies a correction, signs the release, and goes home. Then a satellite fleet in Auckland starts burning propellant nobody budgeted. Atomic clocks in Paris drift apart by four parts in a hundred quadrillion.
A probe eighty-four astronomical units out needs a course correction with no known cause. Separately, every anomaly has an explanation. Together they have a direction. What is approaching cannot be seen, only inferred, and when the solution finally converges it converges on a black hole of four solar masses falling toward the Sun. The good news arrives first: it will miss Earth by a wide margin. The bad news takes longer, because missing Earth was never the question.
An object that heavy passing that close does not disturb the solar system. It rearranges it, and where Earth ends up depends on where every gram of mass sits when it happens. Humanity has been moving mass for a hundred and ninety-one years. Mining the belt, stripping the Moon, parking stations at the exact gravitational points where small changes matter most. The total is nothing. The placement is everything.
And when the world finally acts, when it commits the largest engineering operation in history to fixing what it did by accident, Naomi finds the reason it fails written in a correction model that has carried her signature since she was thirty-three. Something enormous is coming. It is not aiming at us. We have already made it worse.