Black holes don’t suck!

One of the advantages I feel we have to offer at the PVL is the diversity of experience of our individual members. I purposely recruit Astronomers, Engineers, Geologists, Physicists, Atmospheric Scientists or really anyone who has the interest and is holding a piece of the puzzle we call planetary science. Last weekend, Christina Smith spent some time going back to her roots as part of a panel hosted by a good friend of the lab, Jesse Rogerson of the Ingenium in Ottawa.

By Dr. Christina Smith

I may or may not have mentioned this in a previous blog post, but prior to joining the Planetary Volatiles Laboratory at YorkU, my research was in stellar astrophysics (my PhD and a short post-doc), primarily studying what small dying stars were made of and surrounded by (they have a tendency to shed bits of themselves all over the place). In fact prior to that, I dabbled in theoretical particle physics for a while (my undergraduate Masters’ project – simulating interactions of top quarks at the Large Hadron Collider to try and infer something about the physics of extra dimensions) but that’s a story for another day...

Anyway, a few weeks ago I was approached to be part of a Royal Canadian Institute of Science panel discussing back holes, which though not related to what I do now, is something I am familiar with in the grand scheme of stellar evolution from my PhD and short post-doc. Specifically, they wanted someone nerdy enough to talk about black holes as they are portrayed in popular culture. I am definitely nerdy enough and this was a really cool and interesting topic to talk about (and gave an excellent excuse for a lot of evenings spent in front of my TV binge watching sci-fi movies and TV shows).

I also figured this was a good topic to chat about – a tad outside the norm but I figured that was ok. So, before I delve into the world of black holes in popular culture, I’m going to digress a little into Black Holes 101.

So there are a few different types of black holes: stellar mass black holes (black holes that weigh a few times the weight of the Sun up to quite a lot of times the weight of the Sun), supermassive black holes (literally millions of times heavier than the Sun), and intermediate mass black holes (somewhere in-between). Now I’m not going to talk much about intermediate black holes for two reasons: 1) I don’t know much about them, and 2) they don’t really appear in pop culture. So you’ll just have to be satisfied with the fact that they exist.

Let’s start with stellar mass black holes. These are the little ones in Black Hole World. These guys are formed when a massive star goes supernova (the little ones I was studying make pretty planetary nebula and not black holes). Not all massive stars form black holes, some form pulsars, it just depends how much of the star gets blown off in the supernova, as there has to be enough of the star left that gravity forces it to collapse down and down and down until all that stellar matter is contained in an infinitely small area (a “singularity”). Supermassive black holes are much much bigger and not formed from the death of a star. There are a few different theories (as far as I know) about how these guys form. One is that they could be formed from lots of smaller black holes combining over a long period of time (and we have actually detected gravitational waves that we think are from stellar mass black holes combining – thanks LIGO and VIRGO! https://www.ligo.org/detections.php). Another way is that they could have formed from the collapse of an enormous gas cloud.

Side note thought experiment (this will be useful in a second, I promise – this thought experiment is borrowed without asking from Jesse Rogerson who was the excellent panel moderator): if you’re standing on the Earth (as I assume you are) and throw a ball up (outside, open air...), eventually the ball stops and comes back down. If you could throw it hard enough (say if you’re Superman), the ball (assuming it doesn’t burn up or anything) could escape the Earth. The minimum speed that something needs to be traveling at to escape a planetary body is known as its “escape velocity”.

Now, black holes have a LOT of gravitational pull. If you were inside a black hole (and not spaghettified or squished to death), and you wanted to throw a ball so it could escape the black hole, you would need to throw it hard enough that it was traveling faster than the speed of light. This is a huge no-no according to the laws of physics: nothing can travel faster than the speed of light in a vacuum, even if Superman throws it. Luckily, the gravitational pull of an object gets less the further away from the object you get. So around a black hole’s singularity, there is a horizon called the “event horizon”. Inside this horizon, EVERYTHING is trapped. Not even light can escape. So what we see when we look at black hole is a big dark patch.

There are other bits and pieces around a black hole that you could see though – outside the event horizon.  There’s something called an accretion disk which is a disk of material that’s been pulled apart by the black hole and is slowly spiraling into it. That’s the kind of thing that’s shown in movies and TV shows as a flat, spiraling disk (which isn’t far off reality).

As well as an accretion disk, some black holes (the supermassive ones that live at the centre of galaxies) have jets. These jets can so bright that they can be visible billions of light years away (take a look at “quasars” if you want to know more about these) - though these are pretty much never mentioned in pop culture so I won’t go any further into them.

So, onto how they are portrayed in pop culture...

I find there are three main features of black holes in the world of TV and movies: 1) black holes suck everything in,  2) they mess with time, and  3) even weirder stuff. So taking these one by one:

1) Black holes do have a pretty strong gravitational pull so I can see why they have this persona of the space version of a vacuum cleaner. However, as I mentioned earlier, gravitational pull decreases as you move further away from an object (its actually proportional to 1 over the square of the distance). So a fun fact is that if you could instantaneously magic away the Sun and replace it with a black hole of exactly the same mass, the the Earth would not be pulled into it. In fact it would just keep merrily going around the black hole as if it were still the Sun. It would, however, suddenly become pretty dark and cold. So whilst black holes do pull stuff in pretty strongly if you’re close to them, if you’re far away from them then they act just like any other massive space body.

2) Black holes mess with time. This is true. Time is a funny thing that isn’t actually the same everywhere. Thanks to Einstein’s theories of relativity, we know (and have shown through experiments) that time flows at different rates depending on how fast you are traveling and whether you are close to something very large. If you are traveling very quickly or if you are standing close to something very large (say for example, a black hole) then time – from the perspective of someone stationary or a long way away from the something very large – appears to move more slowly for you than the that other person. This effect is called “time dilation” and there are a whole host of TV shows and movies that play around with this as a plot device. Interstellar has lots of fun with that, as does Stargate SG 1’s “A Matter of Time” (I particularly appreciate the violations of the laws of physics in the latter, to the confusion of the military scientist character: “from everything I think I know about General Relativity, that can’t happen!”).

3) Even weirder stuff. By this I’m mostly talking about the what-happens-when-you-cross-the-event-horizon scenarios. Lots of TV shows and movies have all sorts of fantastical things happen to their characters as they pass through (and survive...) the event horizon – travel to other dimensions, travel back in time, travel to another part of the Universe, getting caught in a weird time loop, and the list goes on. There are lots of theories as to what could be beyond the event horizon of a black hole but we can’t see beyond it (as light is trapped) and if you could travel over the event horizon and survive, you wouldn’t be able to send signals out to tell anyone what you found – unless there was a huge shift in our understanding of the laws of physics. So I can completely see why the idea of crossing the event horizon opens up this area of creativity and I, for one, appreciate it.

Now I’m going to move on to some major nerding out about Interstellar’s visuals.

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Interstellar wanted to be as scientifically accurate (or in some cases justifiable speculation) as possible. Some things are deemed unlikely to happen in nature, but plausible, and that was ok for Interstellar too. I should also mention that a lot of what I’m talking about below comes from Kip Thorne’s book on the Science of Interstellar and the papers that were published about visualizing Gargantua and the wormhole by James et al. 2015 (https://iopscience.iop.org/article/10.1088/0264-9381/32/6/065001 and https://aapt.scitation.org/doi/10.1119/1.4916949d).

The thing that caught my eye is the visual representation of Gargantua, the supermassive black hole at the centre of the planetary system Cooper and crew travel to. Some fun facts: the writers wanted Miller’s Planet (which orbits as close as it physically could to Gargantua without being torn apart) to have a 1-hour-on-Miller’s-Planet-equals-7-years-on-Earth time dilation. That set not only the size of the black hole (100 million times the mass of the Sun) but also meant the black hole had to spin really fast – almost the maximum possible. They also knew that they didn’t want Gargantua to have jets so it had to be a black hole that was fairly quiet, hadn’t been fed in a long time (the one at the centre of the Milky Way doesn’t have jets either so it’s very plausible). But it would have an accretion disk. So they ran simulations to see what it would look like to the outside observer. And if you want to see what it looks like, take a look here: https://cdn.iopscience.com/images/0264-9381/32/6/065001/Full/cqg508751f16_online.jpg (a figure from the paper written about the simulations).

First thing -  it’s 3D which I love. Black holes are actually spherical (or flattened spheres if they are spinning), but often are shown as an actual hole in space. They also showed the wormhole as a sphere which I also really really appreciate (https://aapt.scitation.org/na101/home/literatum/publisher/aip/journals/content/ajp/2015/ajp.2015.83.issue-6/1.4916949/production/images/medium/1.4916949.figures.f11.gif).

Secondly, Gargantua has a stripe through the middle, and a sort of glowing halo round the outside of it. This is a warped view of the accretion disk. To orientate yourself, you’re looking just a smidge off directly in line with the disk (think looking at a DVD edge-on rather than face on, so it almost disappears, or looking at Saturn when the rings almost disappear). The stripe through the middle is where the disk crosses in front of Gargantua. The dark flattened sphere is Gargantua (its flattened because it’s spinning – though they actually slowed it down for the visuals in Interstellar to make it look nicer). The glowing halo-ish thing is actually also the disk, but the part of the disk that is behind Gargantua. Think of Saturn: when you look at Saturn, the rings behind Saturn are hidden by Saturn itself. Gargantua is so massive that it actually bends light around itself so the back of the disk form the halo-y thing above and below Gargantua. How cool is that? This phenomenon is called “gravitational lensing” and we see it quite often when looking at galaxies – foreground galaxies are massive enough that they cause lensing of background galaxies. Here’s a handy artists impression animation that might help you visualize it: https://www.spacetelescope.org/videos/hubblecast70c/.

Anyway, I think I’ve rambled on enough about black holes. Back to the Solar System for me!