[The_Colonel]

That's likely a mistake in the article. "Small" black holes (i.e. smaller than supermassive) have star/stellar mass, but not size.

Micro black holes are only hypothesized so far, but they could get very small - e.g. a black hole with Earth mass would have less than 1 centimeter in diameter.

The size itself is not that important for spotting black holes, though. Even if it's as large as a star, all you see staring at the black hole "object" is nothing. What's important are the gravitational effects on the environment, and there the differences are stark. At a distance of 1000 light years, it will be difficult to spot a stellar-mass black hole floating through empty space, because its pull is strong enough only at stellar distances and won't produce enough disturbance in interstellar space for us to notice. OTOH supermassive blackholes will deform whole surrounding star systems because of its immense mass and gravitational pull. A micro black hole (e.g. Earth mass) passing through the solar systems would likely go undetected unless it collides with something (which is improbable). There could be a measurable disturbance, but it would be one-off and difficult to attribute to a black hole.

[ordu]

> A micro black hole (e.g. Earth mass) passing through the solar systems would likely go undetected unless it collides with something (which is improbable).

Solar wind? Would it generate some interesting effects when coming too close to a black hole? All these protons accelerated to a near light speed, probably hitting each other and running away into a black hole.

[The_Colonel]

An Earth-mass black hole will have a similar gravitational effect on solar winds as Earth. Can we detect these effects on solar winds from distance? Maybe if we watch for them in that particular direction of empty space, but will we? The effects would be localized and short-lived at each particular place on the trajectory.

[usbsea]

An earth mass black hole would surely peturb various orbits of planets in a solar system though?

[zesterer]

There are likely several > earth-mass objects in our solar system that are as-yet uncatalogued, and almost certainly many hundreds of dwarf planet-mass objects too. Granted, they are further out, but their influence is almost undetectable even over millions of years. It's pretty unlikely that the presence of an earth-mass black hole for just a few years (since it would likely be moving many times solar escape trajectory) would have much in the way of a measurable impact.