I asked this on the ‘movies’ stackexchange site but they suggested I ask here, it’s a purely hypothetical query based on a BBC drama show called ‘Hard Sun’, feel free to kill the question if it’s inappropriate here.

In the TV show’s series finale an expected ‘extinction level event’ happens and appears to be a black hole close to our sun, it already has developed a spiral of hot gas around it drawn from the sun.

Clearly this is fiction but I’m keen to understand just how badly-considered this is. Firstly the show is set in London and everyone seems amazed when the image below rises from the dusk yet clearly it's been in existence for the time taken to create the spiral (hours at least?) so nations east of the UK would have seen it for that time and reported on it globally surely?

My real question is more around is there any potential scenario where a black hole of that size could develop suddenly and get to that size quickly enough for that image to be a surprise? My understanding, very much as a scientific-layman, is that a black hole of that size would have to have the mass of at least one of our suns to get to that size (probably more) - is that a valid assumption? If so where has the mass come from? Also wouldn't the sudden existence of something else with at least the same mass as our sun suddenly appearing at the centre of our solar system have enormous gravitational impact on everything in the system, including Earth? We'd have massive volcanic/tectonic impact wouldn't we?

So again sorry if this is inappropriate, I was just incredulous at how badly-considered the scientific aspects of this fiction were and wanted to check that my understandings were correct.

Screengrab: enter image description here

  • A maybe for migrating to Worldbuilding SE, although it possibly doesn't quite fit there either. – StephenG Jan 18 at 11:37
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    This is actually kind of a fun question. The primary thing the show appeared to get wrong was gravitational effects from a distance and relative velocity. A black hole couldn't appear and stay near the sun, it would fly past, like Oumuamua and a black hole would throw our solar-system into chaos in the process.unless it was a theoretical micro black hole, but even so, that would just pass through, not eat the Sun. It's hugely improbable but the details on what specifically would happen and when we'd notice are kind of fun to discuss, whether worldbuilding or here. – userLTK Jan 18 at 12:08
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    isn't the sun a bit too big in that picture? – A. C. A. C. Jan 18 at 17:21
  • Yeaaahh, I thought that too – Chopper3 Jan 18 at 18:04
  • Probably the black hole had already reduced the earth sun distance. That's may be the only thing they somehow took into account :) – Alchimista Jan 18 at 18:57
up vote 2 down vote accepted

I'm not sure this needs another answer, but I got hooked on the show, so why not. (spoilers ahead).

Black Hole

We don't know that it's a black hole, even with the image. It kind of looks like a black hole drawing matter from the star, but there's a few problems with the image, and I'll get to that later.

A couple times in the show Elaine Renko (Agyness Deyn) says "I don't know what it is". She's presumably seen more of the data than anyone alive outside of the government insiders, so the show is careful not to commit to a specific scenario and the image only gives a little bit of information, so it could be a number of things. Because they never said what it is, it's harder to criticize the science.

Sudden appearance

Sudden appearances happen. That's not to say something suddenly appears out of thin air, er, space, or quantum improbability or some kind of other dimension nonsense, but "it suddenly appeared" is actually somewhat reasonable because space is big and dark and something going unnoticed until it's right on top of us, is in the realm of possible.

The Chelyabinsk meteor of 2013 is an example of a destructive object just "appearing" in the sky because, as a sun-side meteor it was harder to see and it was smaller than the meteors that NASA tracks, so nobody saw it coming until it was a bright flash in the sky.

Why NASA but nobody else.

NASA has the best telescopes, though there are some very good ones around the globe and numerous amateur astronomers, so that particular aspect may not be probable but it's theoretically possible.

Firstly the show is set in London and everyone seems amazed when the image below rises from the dusk yet clearly it's been in existence for the time taken to create the spiral (hours at least?) so nations east of the UK would have seen it for that time and reported on it globally surely?

I don't like the spiral. It's pretty but I don't like it. (I'll get to that shortly).

On the suddenness of the visual at the London sunrise, consider what we see. Two cops are chasing their suspect. Other cops are in the garage with their boss who was shot a bit before. Some paramedics are there, taking care of the shot person. The cops chasing grace aren't going to stop and check their phones, so it's entirely possible that images began flooding the internets minutes before and the people in the show weren't aware.

How long was it visible?

You're correct, if it's visible in London at sunrise, it's visible east of London earlier.

Basically everywhere on Earth where you see the sun, you're seeing the same side of the sun. The sun is in different parts of the sky but we all see the same side of the sun, so, unless there's clouds blocking the view, everyone east of London, still should have seen what they saw. That raises the question, how long was the object visibly affecting the sun because it couldn't have been long or word would have spread.

The object appears in that image to be about one solar radii distance from the Sun's surface, assuming the angle is somewhat straight on, not viewed sideways, then we can estimate it's distance from the sun to be about 1 solar radii or 700,000 km. The black dot is also quite small, maybe planet size, certainly smaller than Jupiter (which is 1/10th the diameter of the Sun), it appears larger than Earth (1/100th the diameter of the sun) and that would make it too large to be a black hole or neutron star, but perhaps a white dwarf, super earth, mini gas giant planet or planetary core fragment. There's a fair bit of wiggle room in there.

The solar gravity, basically the escape velocity in reverse would have added about 430 km/s to whatever initial velocity relative to the sun that the object had as it approached the solar-system. Most near-by exo-solar system objects have a relative velocity to the sun in the 1s or 10s of km/s, at least for those objects that orbit in the same direction through the milkyway, but hyper accelerated objects can reach into the 100s of kms per second relative to the Sun. If that was a hyper-accelerated object approaching from the opposite side of the sun than the Earth, it's possible that it would be both difficult to see, and that it approached the solar-system very quickly. The slower something moves, the more time there is to see it and it's gravitational influence, but a hyper-velocity, behind the sun approach might work, either impacting or making a close pass by the sun.

Assuming that object is close to the sun, which it appears to be, even at hyper velocity, to the naked eye, it would appear largely still. If we give this object a relative velocity to the sun of lets say 700-1000 km/s. It would still take, from our perspective, 700-1,000 seconds (12-16 minutes), to travel one solar radii or 1/4 of 1 degree across the sky. That, in theory, means that it might have only been visible for 12-16 minutes, or less if it was traveling faster. That's a short enough time-frame that the cops could have chased their suspect unaware of the images that began flooding the internet. A 12-16 minutes actually works and is theoretically possible, if hugely improbable.

My real question is more around is there any potential scenario where a black hole of that size could develop suddenly and get to that size quickly enough for that image to be a surprise? My understanding, very much as a scientific-layman, is that a black hole of that size would have to have the mass of at least one of our suns to get to that size (probably more) - is that a valid assumption?

You're right. Black holes have a minimum mass of about 2 and change solar masses and that much mass simply wouldn't go unnoticed, even with it's tiny size, it's tidal effects on the orbiting planets would be noticed even by armature astronomers "Hey, Neptune isn't where it's supposed to be" - that kind of thing would get noticed. Also, as it passed close to the sun it wouldn't just draw a spiral off the sun but it would make the sun distinctly egg shaped. That much mass wouldn't work, but we don't know the objects mass. We don't know if it's a black hole or what it is.

Black holes don't suddenly develop either. They're made in the cores of very large stars when they go supernova. So your thinking is correct there too.

Where has the mass come from? Also wouldn't the sudden existence of something else with at least the same mass as our sun suddenly appearing at the centre of our solar system have enormous gravitational impact on everything in the system, including Earth? We'd have massive volcanic/tectonic impact wouldn't we?

The harm from a stellar mass object passing through the solar-system would be that it would change the planet's orbits and changing the Earth's orbit could be bad, pushing us outside our Goldilocks zone, but a 1 or 2 solar mass object would need to get pretty close to the Earth to cause the kind of tidal effects you're talking about. That object appears close to the sun, and we don't know it's mass so the kind of tidal effects you're talking about aren't a problem.

The Spiral

I don't like the spiral because it looks like the object is pulling gas away from the Sun, but it's not changed the shape of the sun. The spiral also appears well developed which would take some time. I don't want to say it's impossible but the spiral around the object, while pretty, seems the least scientific part of the event to me.


Apologies for the long answer, but I wanted to point out that an unnoticed, very fast effect is theoretically possible, just hugely improbable.

Firstly the show is set in London and everyone seems amazed when the image below rises from the dusk yet clearly it's been in existence for the time taken to create the spiral (hours at least?) so nations east of the UK would have seen it for that time and reported on it globally surely?

And we've kind of a large number of space based satellites that do nothing but monitor the Sun and all the people monitoring them would certainly spot this minor event.

My real question is more around is there any potential scenario where a black hole of that size could develop suddenly and get to that size quickly enough for that image to be a surprise ?

About the only way I can think of is someone creating a Kugelblitz, although it's pretty far fetched.

Maybe a very freak collision of two high mass objects head-on, but that would create far worse problems - essentially an absolutely huge explosion and we would not be looking at the result quietly afterward.

My understanding, very much as a scientific-layman, is that a black hole of that size would have to have the mass of at least one of our suns to get to that size (probably more) - is that a valid assumption ?

There's a minimum size for the formation of a black hole by gravitational collapse of a star and it's larger than our Sun's mass.

There is, however, no theoretical minimum for the size of a black hole if you can make one some other way.

If so where has the mass come from ?

Ask the writers. :-)

Also wouldn't the sudden existence of something else with at least the same mass as our sun suddenly appearing at the centre of our solar system have enormous gravitational impact on everything in the system, including Earth?

Yes that's a major issue.

Any black hole large enough to start siphoning off the Sun's outer layers would need a significant mass and it would have a significant impact on our orbit - and do so more or less immediately.

Our orbital speed is enough to maintain our almost circular orbit around the Sun.

With something as massive as a small star added close to the Sun, our orbital speed would no longer be enough for a circular orbit and we'd be in an elliptical orbit about the Sun-BH pair. It's more complicated than than that, but that's the broad strokes.

But that ellipse would be with our current distance as an aphelion, whereas we'd have a smaller perihelion distance. So we'd get warmer. And it would not take much to raise temperatures here uncomfortably. Very roughly if we were to have a closest approach of 0.72 AU (Venus's current orbit) we'd find our temperatures rise by perhaps 24 degrees Celsius, which would be enough to make the planet unlivable for us - ( maybe 60 C at the equator and enough to melt significant parts of the polar ice and permafrost ). And as this change would happen every six months as we orbited moving from close in to far out, we'd be permanently shifting climate. And that ignores greenhouse effects - we could end up with a runaway greenhouse effect that raised temperatures to lethal levels everywhere.

We'd have massive volcanic/tectonic impact wouldn't we?

That's a hard one to call. This would depend on how far apart they Sun and the BH were and how massive the BH was.

But we'd have lots to worry about.

  • Thank you for humouring me, I know this isn't right place to ask this kind of thing but I was keen to ensure my limited knowledge of physics wasn't completely wrong and that in this case the writers are just a bit poo/lazy :) – Chopper3 Jan 18 at 12:50
  • I think this show was on a few decades back. The BH doesn't appear stationary in the solar system; rather it was somehow flying freely and undetected through the ISM and then happened to enter our solar system and have a near miss with our sun. As it swings around, it pulls the sun towards the Earth or vice versa. The time scale was a month or so between "oh look, there's a BH" and "we're all cooked and dead". I don't suppose anyone did the orbital calculations to see if this was feasible. I remember because even at the time it seemed faintly ridiculous. – Calchas Jan 20 at 23:21
  • there's a movie with the same thing and a Neutron star here: youtube.com/watch?v=v-hSfKn9DrY and there was another movie where a small black hole punctures the earth back a forth a few times. – com.prehensible Jan 22 at 6:58

Well... maybe it's not a black hole.

If some kind of magnetic anomaly in the Sun was pushing plasma out in one direction, the object wouldn't have to be more massive than the sun to catch the spray. The black spot could even be Mercury - any mass would capture an outbound plasma jet if the jet reached high enough. This either pairs well with the sun being much too big or doubles down on the farce, depending on how much you know about stellar mechanics.

Of course, that doesn't explain why it's black. Maybe it's a small black hole. I suppose if it was a small black hole, lighter than the sun, the Earth could have something like a conventional orbit. But even in the absence of a plasma stream, I'm pretty sure the gravitational lens effect would mess about in visible ways.

Or maybe flat earth theory is true in the show, and what we're really seeing is some kind of damage in the projection dome that encircles the earth! It's not a black hole, it's the mother of all dead pixels.

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    Props on the Mercury suggestion.. The picture in this question isn't quite the same as what they showed in the finale. There was a black dot in the finale, roughly the size of Mercury. – userLTK Mar 23 at 14:01

I've thought a lot about the series finale, and it's confusing to say the least. It is possible that the black hole could be some sort of micro singularity, theorised to be possible but never found. That way it's mass isn't sufficient to throw all the planets into chaos the moment it comes near the solar system. That being said, they had a timer on the end of the world since the first episode, so the question begs, how did they know it was coming? Personally the most logical answer is that it's artificial in nature, perhaps a human space station experiment gone very, very wrong. That would explain the timer, perhaps they knew all along that it was destined from that point to consume the sun.

Ignoring that, it isn't beyond science possibility that a naturally occurring micro black hole could be travelling at a slow enough speed, relative to the speed of our own solar system, to be captured within the gravity well of the star. It's accretion disk would also likely slow down its speed as it sucks up matter from the star and increases its mass. Needless to say, it's all extremely unlikely, but not impossible, that we could snag our own terrifying sun-eater by sheer chance.

It really doesn't look good for the people of Earth in this series. As the mass of the black hole increases, and the two orbit each other, it's going to play hell on the organisation of the planets within the solar system, likely shifting the orbit of Earth to a position far less pleasant for life here. Truly, an awesome "end of days". Can't wait to see how it all pans out!

  • Thanks for the response. The writer has said that he's got a full five year plan marked out that definitely ends with the end of the Earth. The problem with this is that the show's not considered to have been a strong critical or viewer success so they may not get to make all five seasons - to be fair only Agyness Deyn stood out, most of the rest of the cast were either asleep or massively overacting, that didn't help. – Chopper3 Jan 26 at 12:12

You guys are all hinting about the effects of a black hole on the solar system, but you are forgetting about the effects on time that gravity creates. The gravity of a black hole would slow time. As such, the gravitational time dilation effect would let us see a slow death spiral of the solar system, even though to an external observer, the solar system would already be gone. The sun would indeed become egg-shaped, but the spiral we see at the end of the Hard Sun miniseries would be the first sign of it. The five year timetable would be how long it would take for the earth to actually experience the full effects of the black hole, because as we got closer to the black hole, time would continue to slow down and we would feel time dragging out even farther than before.

As for it suddenly appearing and nobody noticing, the fact is that someone did notice. That is the reason the flash drive existed. Remember, NASA still only monitors NEOs over 140m across. A black hole is actually much smaller than that - and it is virtually undetectable except in the presence of matter.

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