What If a Quasar Appeared In The Milky Way? | Unveiled

What if a Quasar Appeared in the Milky Way?

Few things are as strange and unusual as quasars. They’re some of the most vast and unpredictable structures in all of space; a weird phenomenon first observed in the 1950s and that physicists only even began to understand in the ‘60s. But wondrous as they are, would we really want to see one up close and personal?

This is Unveiled, and today we’re answering the extraordinary question; what if a quasar appeared in the Milky Way?

The term “quasar” is short for “quasi-stellar object”, and key traits like their incredible luminosity and radiation did have the scientists who first viewed them confused into thinking they were some kind of never-before-seen “super star”. But, in fact, a quasar isn’t a star at all… Instead, it’s an Active Galactic Nucleus, existing at the centre of some galaxies. These cosmic giants are so big that they actually hold one or more supermassive black holes within their centre… and yet they’re still some of the brightest objects in the universe, thanks to the enchanting light they emit via vast accretion disks.

So, how do they happen? Standard black holes are characterised by their incredible gravitational pull, seemingly sucking things up and then condensing and destroying them to feed their singularities. But they can only “eat” as quickly as gravity can pull, and sometimes they get backed up. An excess of debris and matter is what forms an accretion disk, which glows and becomes incredibly hot… And it’s this process that turns a black hole into a quasar. A quasar needs a supermassive black hole specifically, though, which is a black hole with a mass often more than a billion times the mass of our sun. And the only places those really occur are at the centre of galaxies, which is why quasars only occur at the centre of galaxies, too.

Not every supermassive black hole turns into a quasar, but when they do it’s quite the light show. And, once they’ve formed, the effect remains until they’ve finished devouring everything in their accretion disk… no one’s really sure how long that takes, but it’s potentially billions of years. Were a quasar to appear in the Milky Way then all of the action would play out around Sagittarius A-star.

Sagittarius A-star is the site of the supermassive black hole at the centre of our galaxy. Right now, we only have one existing photograph of a black hole, and it isn’t of this one, so radio waves provide most of our evidence determining that a black hole is even out there. But, if Sagittarius A-star were a quasar, our telescopes would suddenly be able to see and detect it, thanks to the light pouring from it - in this way, we at least know the Milky Way doesn’t currently have a quasar.

Quasars typically only form when a galaxy still has plenty of excess matter, at the start of its life; which our galaxy isn’t. So, if one did show up in our corner of the universe then it’d be unexpected, to say the least. But there is, theoretically, a way it could happen. Something we know for sure is that in around 4.5 billion years the Milky Way is going to collide with the Andromeda Galaxy. So, the wealth of new galactic material brought with this collision could feasibly cause a quasar at the heart of our Milky Way-Andromeda merger system.

Galaxies colliding in this way is actually relatively common, and we do know of quasars that possess binary black hole systems – or two black holes orbiting each other. The black holes of those two different galaxies don’t cease to exist, and neither would the Milky Way’s or Andromeda’s, they’d simply be interacting with the surrounding space in a dramatically different way. It’s thought that the closest quasar to Earth right now, Markarian 231 about 581 million lightyears away, might actually have a binary black hole system too… when it comes to quasars, it’s a popular set-up!

All of that said, while a quasar at the centre of the Milky Way would certainly be very bright, and definitely bright enough for us to see in the night sky, it wouldn’t really affect us here on Earth outside of it just being visible. So, what if a quasar appeared a little closer to home, in, say, our very own solar system? The situation suddenly (and drastically) changes!

Sure, it would be exciting for physicists to see a quasar up close, but ultimately, with our star system completely dismantled by its gravitational pull, we wouldn’t last long at all. For one, the accretion disk of a quasar is often bigger than the entire solar system even is, so if one showed up here then we’d almost certainly find ourselves trapped inside it. The damage wouldn’t necessarily be instant, and it could still take centuries before we’re devoured by the black hole itself, but we’d now have a constant reminder of our imminent and inescapable doom because of the permanent, ultra-bright quasar-light we’d be bathed in. And that’s only if we don’t burn up in the intense heat of an accretion disk first, which we more than probably would do.

Thankfully, it is impossible for this to happen, since our sun has nowhere near enough mass to even become a regular black hole when it dies, let alone a supermassive one. Instead, our star will turn into a red giant and eventually fizzle out. If humans are still living on Earth when that happens, then we’d still be in a lot of trouble - just a different type of trouble… but we’d most likely have died out or else relocated long before our own sun starts to threaten.

Thankfully, again, we’re also much too far away from the galactic centre of the Milky Way for a true quasar to ever drag us across the galaxy to our inevitable demise. And the chances of the universe’s other quasars in some way affecting us are very, very low as well.

There is a “but”, though. Because it is a little misleading to say that quasars only form from supermassive black holes. Regular quasars do, but micro-quasars are also a thing, and these can form from normal black holes. The V616 Mon, our closest regular black hole, is just 3,000 lightyears away - much closer than Markarian 231, our closest supermassive quasar - and, if V616 Mon somehow gained enough fresh material to consume, it could turn into a micro-quasar. While micro-quasars are smaller and have a weaker gravitational pull, their accretion disks burn hotter, a lot hotter, at up to a few million degrees. So, if a micro-quasar ever found its way into our solar system (an only slightly more plausible prospect than a true quasar appearing here), it would also bathe us in light and then also fry us, before also sending what was left of us on a gradual journey into the black hole itself. But, again, the chances of that actually happening are exceptionally low.

Any supermassive black hole can become a quasar, and any normal black hole can become a micro-quasar… But if any kind of quasar were to ever appear anywhere even relatively close to us, it would be all eyes on Sagittarius A-star, and even then, it would hardly affect Earth at all. A quasar in the Milky Way would be a wondrous and unique sight for sure, and we’d be lucky to see something that usually only happens once in the lifetime of a galaxy… Even luckier still, though, we’d be watching it all unfold at a more than safe viewing distance. And that’s what would happen if a quasar appeared in the Milky Way.