[geordief (OP)]

What if the Sun became a black hole almost  instantaneously?

Suppose  we were living in a Solar System where the Sun was much smaller but equally  massive.

The planets were orbiting  this Sun in almost the same way  as in ours   and then ,one day the Sun tipped over into  a black hole for whatever reason ( not including the arrival of a foreign body but presumably  something that caused its radius to shrink )

In that scenario what would happen to    the orbits of the planets?

Would things continue as if nothing had  changed in that regard?

[Halc]

What if the Sun became a black hole almost  instantaneously?

It would get very cold in short order. Humanity would survive perhaps a couple months in a few places, more if they're given time to prepare for the calamity, but what would be the point of such preparation?
A nuke sub, heavily stocked and lightly crewed, would be my choice of places to last the longest.

The people on Jupiter and further out would probably not notice since local energy is far greater than the pittance given by solar radiation.

In that scenario what would happen to    the orbits of the planets?

Nothing of course. You seem to know this already.  The orbits are determined by acceleration=GM/r² and period=√(4π²r³/GM) and none of those values are changing in your scenario.

[geordief (OP)]

Nothing of course. You seem to know this already.  The orbits are determined by acceleration=GM/r² and period=√(4π²r³/GM) and none of those values are changing in your scenario

No ,I was genuinely unsure.On account of an ongoing discussion over at scienceforums.net where Markus Hanke is being quizzed by MigL and now myself about BHs  EHs and causality

[Petrochemicals]

The black hole would presumably be oriented in a  coplaner manner with the solar system and would emmit radiation?

[Janus]

The black hole would presumably be oriented in a  coplaner manner with the solar system and would emmit radiation?

How?  Radiation from Black holes can have limited sources:
Radiation produced by  collisions between matter in the accretion disk.
Particles spiraling in through its rotating magnetic field and then shot out at the poles
Hawking radiation.

Anything outside of the Sun's present radius is either in orbit around it or flying away from it (solar wind)
So the entire region of the Sun's present volume would be empty of matter if the present Sun suddenly collapsed into a black hole. Nothing to form an accretion disk.
And while, on a occasion, a comet does crash into the Sun, the newly formed Black hole would be an extremely small target to hit.
With Hawking radiation, the Hawking temperature of a solar mass black hole would be less than the that of the cosmic background radiation.

[Petrochemicals]

The black hole would presumably be oriented in a  coplaner manner with the solar system and would emmit radiation?

How?  Radiation from Black holes can have limited sources:
Radiation produced by  collisions between matter in the accretion disk.
Particles spiraling in through its rotating magnetic field and then shot out at the poles
Hawking radiation.

Yeh, that.

[geordief (OP)]

while, on a occasion, a comet does crash into the Sun, the newly formed Black hole would be an extremely small target to hit.

So the Sun turning into a BH would affect the orbit of a comet but not (as @Halc  says) that of the planets?

[Halc]

while, on a occasion, a comet does crash into the Sun, the newly formed Black hole would be an extremely small target to hit.

So the Sun turning into a BH would affect the orbit of a comet but not (as @Halc  says) that of the planets?

No, it would not alter the orbit of a comet or any other object. The sun squashed down to a 3 km black hole merely becomes a much smaller target, so a comet that might have hit the sun would miss the black hole.