Is ‘Planet Nine’ actually a grapefruit-sized black hole?

Credit: NASA

Could there even be more than one black hole? The search for a significant extra planet has drawn a blank so far.
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A coming sky survey will help test a wild idea — that a grapefruit-sized black hole lurks undiscovered in the outer solar system, says Mike Wall @ Space.com.

Over the past few years, researchers have noticed an odd clustering in the orbits of multiple trans-Neptunian objects (TNOs), which dwell in the dark depths of the far outer solar system.

Some scientists have hypothesized that the TNOs’ paths have been sculpted by the gravitational pull of a big object way out there, something 5 to 10 times more massive than Earth (though others think the TNOs may just be tugging on each other).

This big “perturber,” if it exists, may be a planet — the so-called “Planet Nine,” or “Planet X” or “Planet Next” for those who will always regard Pluto as the ninth planet.

But there’s another possibility as well: The shepherding object may be a black hole, one that crams all that mass into a sphere the size of a grapefruit.

Astronomers are already scanning the heavens for any sign of Planet Nine, and they should soon be able to hunt for the putative black hole as well, a new study reports.

The highly anticipated Vera C. Rubin Observatory, a big telescope under construction in the Chilean Andes, is scheduled to begin a wide-ranging, decade-long survey of the southern sky called the Legacy Survey of Space and Time (LSST) in late 2022.

Continued here.