Suppose in ten decades time, a hyper velocity black hole estimated to be as massive a 3 Suns are approaching us at 1.5 millions mph (670000 m/s). Our Earth bounds telescope and orbiting satellites have been closely monitoring this HVBH since it was discovered using gravitational lensing.

My question is can we do anything about it or everyone regardless of species, race, religion, sex, age are going to finally be united for all of eternity until HVBH evaporates via hawking radiation?

  • $\begingroup$ I think the main question, as with every approaching problem, is: how much time do we have? $\endgroup$
    – Burki
    Jul 17, 2015 at 8:22
  • $\begingroup$ @Burki actually I intended to give humanity a millennium but I'm pretty sure a sci fi novel spanning hundreds of volumes don't qualify as killing boredom. So 100 years no bargain. $\endgroup$
    – user6760
    Jul 17, 2015 at 8:30
  • $\begingroup$ Please note the time and speed voyagers took to reach the heliosphere. $\endgroup$
    – user6760
    Jul 17, 2015 at 8:37
  • $\begingroup$ will Earth becomes a rogue planet? $\endgroup$
    – user6760
    Jul 17, 2015 at 10:56
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    $\begingroup$ @IsaacKotlicky chill down mate, my OP is saying the stellar black hole with nothing to feed will eventually evaporate on a quantum scale where do you get the idea of relativistic jet from? $\endgroup$
    – user6760
    Jul 17, 2015 at 11:18

6 Answers 6


As written, the answer is we can try, but it's unlikely to work.

There is no feasible way to deflect a stellar-mass black hole with modern-day technology - it's too big and has too much raw momentum; nothing we can throw at it would even have a measurable effect, let alone push it far enough off course to save the solar system. Changing the orbit of Earth meets the same problem - it's lighter, so 'theoretically' less difficult, but still too big to actually pull off.

Building a viable interstellar colony ship in time is going to be... difficult. It needs to be entirely self-sufficient, be able to survive and support a viable population in interstellar space for millenia - at least - and have sufficient delta-V to escape the oncoming black hole and (presumably) then match velocities with the target planet/star for colonisation. (Ideally, you'd want enough extra capacity to try multiple times, in case your first target turns out to be inhospitable).

Assuming that we managed to mobilise the entire world and turned 100% of our productive abilities to the task (no small task in-and-of-itself, even with the prospect of imminent extinction...), we'd probably be able to launch something; calculating how likely the mission is to actually succeed is beyond me, but I'd expect it to be low.

There is one potential ray of light, though - the black hole might not do as much damage as you'd expect. It's moving fast enough to cross the solar system in a bit less than a year - long enough for its gravity to mess up the planets' orbits pretty badly, but it's not going to swallow everything unless it scores a direct hit on the sun. Humanity would be strongly advised to have a colony fleet standing by, but it only needs to be good enough to get us from Earth to whichever planet looks most hospitable once the HVBH leaves. With a century to prepare, that should be well within our abilities.

Hard radiation might be an issue - accretion discs are some of the most active radiation sources in the universe - but it seems likely that this black hole doesn't have much of an accretion disc for some reason. (If it did, we'd expect to spot it much more easily than we have.) That means the only radiation-hazards are from matter it attracts and swallows during its flight through our solar system.

Running a back-of-the envelope calculation for a spherical iron asteroid 10km across gives an energy release equivalent to just under 3x10^20 kilotonnes of TNT. Radiation from a nuclear blast of that size would be lethal to roughly 6400km - which is about the radius of the Earth. We'd have to be very unlucky for a collision to occur that close, so unless the BH hits a planet or dwarf planet radiation shouldn't be a major issue.

(It' also worth running a sanity check on this scenario: we're talking about an object that is first detected less than a quarter of a light-year away from Earth. Implying, amoung other things, that it passed through the Oort cloud 400 years ago and still no-one noticed anything (gravitational effects included) till now...)

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    $\begingroup$ It's a black hole no wonder so difficult to see. $\endgroup$
    – user6760
    Jul 17, 2015 at 9:53
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    $\begingroup$ A black hole itself is essentially impossible to see, true - but the glowing ring of fire surrounding one is usually a little more obvious... en.wikipedia.org/wiki/Black_hole#Accretion_of_matter $\endgroup$
    – Toby Y.
    Jul 17, 2015 at 10:01
  • $\begingroup$ Johnny Cash would not agree with you @TobyY. $\endgroup$
    – Marv Mills
    Jul 17, 2015 at 13:02
  • $\begingroup$ @TobyY. black hole in the middle of interstellar space would have no accretion disk... $\endgroup$
    – Maciej
    Jul 25, 2017 at 10:05

can we do anything about it


...if you simply want to survive.

I assume your specie wants to live and the black hole is going to collide with us. According to this I think the best option is to merely fly away from the HVBH's path and settle in some other safer place far away. But when you asked the question, if you were thinking of re-routing the black hole or even making it disappear you're certainly optimistic too much.

Maybe you could find a way to make it orbit around some other massive object but... if you were able to do such an enormity I assume you would have all the necessary technology to quit the Earth safely and it's either way a much preferable option.

If the people of your world can build rockets and space-station I think they should stop gazing at the black hole and start packing their things. A viable space colony would require around 5000 inhabitants so the specie will keep growing and not degenerate.

  • Number of a second in $100$ years: $3.942\times10^{8}$ s
  • Speed of your black hole: $670000$ m/s

Assuming (from your comment) that $100$ years is what needed to quit the solar system, your black hole has to be at least at a distance of $2.11318 \times 10^{15}$ meters away from the Earth which is totally plausible since the observable Universe is $8.8 \times 10^{26}$ meters long.

everyone regardless of species, race, religion, sex, age are going to finally be united for all of eternity til HVBH evaporates via hawking radiation?

According to the heat death of the Universe (which you are obviously referring to here) we are all going to evaporate via Hawking radiations whether your black hole hits us or not.

  • $\begingroup$ True but according to my setup there shouldn't be any safe heaven within our solar system. $\endgroup$
    – user6760
    Jul 17, 2015 at 8:23
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    $\begingroup$ It does not matter, depending on your civilization you could target another stellar system and take more than 5000 inhabitants to keep humanity evolving properly while flying to its next heaven. If you do not have access to advanced technology then... I'm very sad to say that your civilization is doomed. $\endgroup$
    – Ephasme
    Jul 17, 2015 at 8:25
  • $\begingroup$ I'm pretty sure my calculation eliminated any interstellar travel, unless you can invent a boomtube within the next century. $\endgroup$
    – user6760
    Jul 17, 2015 at 8:28
  • $\begingroup$ How far is it from us? Because if it is far enough so we still have time to fly away my scenario stay plausible. Could you explain your calculations? $\endgroup$
    – Ephasme
    Jul 17, 2015 at 8:39
  • $\begingroup$ ETA is approximately 100 years, velocity is roughly 1,500,000 mph and the voyagers unloaded and compact traveling at break neck speed took 25 years maybe to escape solar system. Either I was hoping for an ingenious solution to this calamity or should I take the red pill?(ref The Matrix) $\endgroup$
    – user6760
    Jul 17, 2015 at 8:49

Your Hawking Radiation isn't going to be a problem. It's the theoretical radiation from the evaporation of the black hole due to virtual particle pairs spawned at the event horizon. The accretion disc is a more substantial problem, as that's where the lethal radiation would be coming from.

BUT you're assuming there's no accretion disc. Which means that the radiation wouldn't be lethal. And as other answers have noted, the event horizon for a black hole of 3 solar masses is relatively tiny - less than 10 kilometers. Unless this hits us dead on (very unlikely) then we'll be safe from getting "sucked in."

So what's the problem?

You're introducing a large, heavy object very suddenly into the orbits of all bodies in the solar system. Orbital mechanics are a delicate balance (as anyone playing Kerbal Space Program could tell you), and the pull of such a large object over time would shift everything in the solar system.

Since gravity falls off by the square of the distance, the pull of this 3 solar mass hypervelocity black hole would outweigh the pull of the sun at ~1.7 AU. For reference, at 1.5 million miles per hour, the black hole would cross that distance in ~106 hours. Considering that the Hill Sphere of our sun is 1-2 light years out, this black hole would affect us even before it officially enters the solar system.

At best, it crosses our orbital disc perpendicular to the plane of rotation, causing minimal disruption. Depending on where it intersects and the positions of the other planets (the disc is ~3.75 lightyears across, which would take our BH 837 years to cross), there would be perturbations of orbits in some of the outer planets, the Oort cloud thrown into disarray, etc. We might see more comets and the like being sent into the inner solar system.

At worst, we get slingshotted around a black hole and it kicks the planet entirely out of its current orbit, sending us tumbling through space on a long, cold voyage.

Can we do anything about it?

Probably not. Any solutions to "save the planet" barring an "interstellar" type generational ship (currently not possible) would probably knock us out of orbit anyhow. If we can predict when, where, and at what angle it will intersect our system, we can roughly gauge just how bad it will be for us. If it hits the outskirts of the system (very likely - it's the largest target) than we'll be fine. if it's going straight through the center (bullseye!) than the we'll probably be pulled off orbit to spiral into the sun over a few million years.

A few million years?

Yeah, we'll have 1000+ years of the blackhole affecting our orbit, and with the perturbations it will take quite some time for us to be sucked in, but LONG before that the earth will have been scoured clean of life due to massive environmental destruction. I'd give it a few millenia or so. Plenty of time for humans to work on tech to move us to a different solar system.

  • $\begingroup$ 1.5M miles per hour leading to crossing 1.7 AU in 106 seconds? Can that really be right? 1.7 AU is 255M km, and 1.5M mph is 2.4M km/h. My math says you're looking at 106 hours. $\endgroup$
    – user
    Jul 17, 2015 at 12:01
  • $\begingroup$ Thanks, you're right. I got switched around on the units. Fixing... $\endgroup$ Jul 17, 2015 at 12:02

Using a pulsed Orion spacecraft you could launch a viable population of humans and a number of other species to another star at a reasonable velocity using current or near current tech.

Moving the earth outside of the solar system in a 100 years would require tech well-beyond our current level. Ideally you would also want to keep earth warm for the trip to a nearby star and that task is also unrealistic for the near future.

Stars are rather energetic, so you can tap that to produce thrust in various ways, but they are all too slow to make a difference in 100 years (total energy of 100 years of sunlight does not provide enough delta-v to escape).

If you can figure out the proper triggering explosion, you could perhaps use a pulsed Orion drive where the surface of the sun provides the bulk of the nuclear fuel, but I don't know if this is actually possible though I think it would be if you arranged a set of explosion in the form of a shaped charge -- this is still well beyond our current tech, but perhaps not excessively so.


Ok, 3 suns, so this thing has an event horizon at a radius of about 8859 meters, call it a little under 18km across.

670,000 m/s

The suns orbital velocity around the milky way is 220,000 m/s so this thing is whizzing past the sun pretty fast.

So it's going pretty fast on a galactic scale but it's still going to be within the orbit of pluto for about 203 days or to be more accurate our solar system is going to be close to it for that long.

I was working this out to see if it was going to just whip through so fast that it doesn't do too much damage but this thing would disrupt the orbit of every planet. Even if it misses the earth and stays closer to mars the earths biopshere is going to be wrecked.

If it was on a direct collision course with the earth it's easier to move the planet earth out of the way than to try to do anything about the black hole.

There's going to be a lot of very hard radiation from the Accretion disc for months so missing the earth isn't even much help, hard xrays still kill everything.

If it hits the earth I don't know how to calculate the expected energy released but there's still going to be one hell of a burst of very hard radiation so I'm not even sure you could run given 100 years. You might have your big colony ship headding for the outer solar system only for the survivors to get bathed in the gamma radiation from the dying earth.

  • $\begingroup$ Hard radiation from the accretion disc is only a problem if the disc exists - there's nothing theoretically impossible about a BH with nothing orbiting it. I find it hard to believe that every astonomer on earth missed a hard-radiation source that powerful at a distance of less than a light-year until now... $\endgroup$
    – Toby Y.
    Jul 17, 2015 at 10:38
  • $\begingroup$ I've been thinking of gravity boom lately but let's keep this as simple as possible, agree? no gravitational anomaly? $\endgroup$
    – user6760
    Jul 17, 2015 at 10:42
  • $\begingroup$ @TobyY. again, I don't know how to calculate the radiation output but even picking up dust, rocks and the occasional asteroid from our own system is going to be pretty bad. it's going to stir up the ort cloud and asteroid belt as well so if the earth survives there's going to be a lot of asteroid impacts. $\endgroup$
    – Murphy
    Jul 17, 2015 at 10:54
  • $\begingroup$ @Murphy back-of-the-envelope calculations (using nuclear-explosion dynamics and raw mass-energy of the asteroid) suggest that radiation from a 10-km asteroid hitting the BH would be lethal at ~6400 km - around the radius of the earth. If the BH is that close, we've got bigger problems... $\endgroup$
    – Toby Y.
    Jul 17, 2015 at 11:23

There is a documentary that describes similar situation : A neutron star is going to reach our solar system in some 80 years. The result will be completely wiped out solar system. Humans try to create a generation ship and send it to closest assumed habitable planet.

Even though I disagree with most of the design of the spaceship, I believe it is more than possible to build a generation ship to send refugees out into space to guarantee survival of our species.


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