Will Our Black Hole Eat the Milky Way? Putting Supermassive Black Holes in Their Place

As soon as you learn about the supermassive black hole at the center of the Milky Way, your next thought is: is that thing going to destroy our galaxy? In the short term, no, in the long term… maybe?

Follow us on Twitter: @universetoday

Team: Fraser Cain - @fcain
Jason Harmer - @jasoncharmer

Created by: Fraser Cain and Jason Harmer
Edited by: Chad Weber
Music: Left Spine Down - “X-Ray”

Want to hear something cool? There’s a black hole at the center of the Milky Way. And not just any black hole, it’s a supermassive black hole with more than 4.1 million times the mass of the Sun.

It’s right over there, in the direction of the Sagittarius constellation. Located just 26,000 light-years away.

And as we speak, it’s in the process of tearing apart entire stars and star systems, occasionally consuming them, adding to its mass like a voracious shark.

Wait, that doesn’t sound cool, that sort of sounds a little scary. Right?

Don’t worry, you have absolutely nothing to worry about, unless you plan to live for quadrillions of years, which I do, thanks to my future robot body. I’m ready for my singularity, Dr. Kurzweil.

Is the supermassive black hole going to consume the Milky Way? If not, why not? If so, why so?

The discovery of a supermassive black hole at the heart of the Milky Way, and really almost all galaxies, is one of my favorite discoveries in the field of astronomy. It’s one of those insights that simultaneously answered some questions, and opened up even more.

Back in the 1970s, the astronomers Bruce Balick and Robert Brown realized that there was an intense source of radio emissions coming from the very center of the Milky Way, in the constellation Sagittarius.

They designated it Sgr A*. The asterisk stands for exciting. You think I’m joking, but I’m not. For once, I’m not joking.

In 2002, astronomers observed that there were stars zipping past this object, like comets on elliptical paths going around the Sun. Imagine the mass of our Sun, and the tremendous power it would take to wrench a star like that around.

The only objects with that much density and gravity are black holes, but in this case, a black hole with millions of times the mass of our own Sun: a supermassive black hole.

With the discovery of the Milky Way’s supermassive black hole, astronomers found evidence that there are black holes at the heart of every galaxy.

At the same time, the discovery of supermassive black holes helped answer one of the big questions in astronomy: what are quasars? We did a whole episode on them, but they’re intensely bright objects, generating enough light they can be seen billions of light-years away. Giving off more energy than the rest of their own galaxy combined.

It turns out that quasars and supermassive black holes are the same thing. Quasars are just black holes in the process of actively feeding; gobbling up so much material it piles up in an accretion disk around it.

Once again, these do sound terrifying. But are we in any danger?

In the short term, no. The black hole at the center of the Milky Way is 26,000 light-years away. Even if it turned into a quasar and started eating stars, you wouldn’t even be able to notice it from this distance.

A black hole is just a concentration of mass in a very small region, which things orbit around. To give you an example, you could replace the Sun with a black hole with the exact same mass, and nothing would change. I mean, we’d all freeze because there wasn’t a Sun in the sky anymore, but the Earth would continue to orbit this black hole in exactly the same orbit, for billions of years.

Same goes with the black hole at the center of the Milky Way. It’s not pulling material in like a vacuum cleaner, it serves as a gravitational anchor for a group of stars to orbit around, for billions of years.

In order for a black hole to actually consume a star, it needs to make a direct hit. To get within the event horizon, which is only about 17 times bigger than the Sun. If a star gets close, without hitting, it’ll get torn apart, but still, it doesn’t happen very often.

The problem happens when these stars interact with one another through their own gravity, and mess with each other’s orbits. A star that would have been orbiting happily for billions of years might get deflected into a collision course with the black hole. But this happens very rarely.

Over the short term, that supermassive black hole is totally harmless. Especially from out here in the galactic suburbs.

But there are a few situations that might cause some problems over vast periods of time.

[-dimar-]

Can a galaxy have more than one supermassive black hole?
Could there be a galaxy that, instead of stars, planets, moons, etc, would have only black holes?

[magzire]

so a black hole gains mass when it consumes stars, so that means matter is not disappearing from existence but rather storing it below the event horizon

[mjgholdings]

FINALLY a kindred spirit! I've NEVER heard of any one else who wanted their (conciousness) to be around to see stuff like that! From a human [more or less] perspective! I would love to make my body last that whole time and REALLY see those things from my human perspective!! Who knows? Wish me luck!

[ImGerald]

Dammit. I was looking forward to meeting that black hole. Now my dream is ruined!

[alternatehistorypt]

I have a telescope and today I saw several planets, awesome video as usual :)

[MusiCaninesTheMusicalDogs]

My mother-in-law eats so much she almost glows like a quasar.

[xiZverx]

Hey fraser, here's one for you, not strictly astronomy, but you could do a video on different telescopes and why visible light requires lenses, while other wave spectrums only needs antennas

[seandonnelly]

Question: How close are the stars orbiting around Sagittarius A? How fast do they get going when they zip around at their closest proximity?

[txc]

So glad you explained that black holes are not huge vacuum cleaners and quasars are black holes which something has crossed over into its event horizon, correct? Yea?

[lauscho]

Do you buy into the idea of string theory's "fuzzballs" as an explanation for black holes? It's supposed to be an extension of the idea of neutron stars being so compressed that all of the matter is turned into neutrons, quark stars being the same thing with quarks, but black holes being matter compressed down until it's just a ball of the "strings" that make up all matter.

It's kind of an interesting idea, and it almost kind of makes sense, but it's pretty out there and wacky.

[FirefoxisredExplorerisblueGoog]

1:23 I've never seen a Canadian this intimidating, haha.

Nonetheless, it's always * to learn something new :).

[SharmarkejamalVEVO]

I learned so much from you, I wish I could donate

[HalfAhBean]

existence is so amazing! its so overwhelming how amazing everything is. i just want to run around screaming amazing!! with my hands waving in the air like a mad man, everyday of my ego life!

[Iksperial]

Another fantastic videos. I love our universe and I am so scared when I think about the how big and scary it is.

[tsareric]

one idea since this series is called guide to space you sort of glossed over a major part of space travel the ship/vessel and life movement options so could do a video on that

[jerbiebarb]

I remember reading that there's a very old jet, quite faint now, coming out of the galactic center and detectable behind the stars of Cassiopeia. We're heading that way, but as the galaxy rotates the jet will be staying ahead of us. This jet reached that far out, almost to the Perseus Arm, so that's probably when a quasar was last active in this galaxy.

[DamianReloaded]

It'd be cool if you could revisit different methods to terraform Mars and Venus. Like asteroid bombardment to alter their rotation and or reactivate their magnetic fields and or put water on them. Or the technological feats required to bring a significant asteroid on a collision course with a planet. Could we do it today? Could we send enough fuel and engines to move them?

[Badyours]

What would happen if Sagittarius A* evaporated?

[ligore]

Hey Fraser, love these videos you guys make. One small request though, would it be possible to add links to the annotated links in the video to the description as well in the future (or add them to the more info card for mobile)... you know for when I'm watching these videos in bed.

[tzarius]

What would happen if the black holes collide. Would the fusion of matter cause a mini big bang and restart the events over again.