A spectacular trio of merging galaxies in the constellation Boötes takes center stage in this image from the NASA/ESA Hubble Space Telescope. These three galaxies are set on a collision course and will eventually merge into a single larger galaxy, distorting one another’s spiral structure through mutual gravitational interaction in the process. An unrelated foreground galaxy appears to float serenely near this scene, and the smudged shapes of much more distant galaxies are visible in the background. Image Credit: ESA/Hubble & NASA, M. Sun
When is 50,000 light-years only a small distance? When three galaxies are that close to one another. At that range, they’re fiercely interacting.
In the case of the three galaxies referred to as SDSSCGB 10189, they’re 50,000 light-years apart and growing closer as they merge into a single massive galaxy.
The trajectories of the Milky Way, Andromeda, and the Triangulam galaxies. Image Credit: E. Patel, G. Besla (University of Arizona), R. van der Marel (STScI)
Astronomers have known for some time that the Milky Way and the Andromeda galaxies will collide on some future date. The best guess for that rendezvous has been about 3.75 billion years from now. But now a new study based on Data Release 2 from the ESA’s Gaia mission is bringing some clarity to this future collision.
It was with great fanfare that Elon Musk announced SpaceX’s plans to colonize Mars with the Interplanetary Transport System.
I really wish they’d stuck to their original name, the BFR, the Big Fabulous Rocket, or something like that.
The problem is that Interplanetary Transport System is way too close a name to another really cool idea, the Interplanetary Transport Network, which gives you an almost energy free way to travel across the entire Solar System. Assuming you’re not in any kind of rush.
When you imagine rockets blasting off for distant destinations, you probably envision pointing your rocket at your destination, firing the thrusters until you get there. Maybe turning around and slowing down again to land on the alien world. It’s how you might drive your car, or fly a plane to get from here to there.
But if you’ve played any Kerbal Space Program, you know that’s not how it works in space. Instead, it’s all about orbits and velocity. In order to get off planet Earth, you have be travelling about 8 km/s or 28,000 km/h sideways.
Artist’s concept of a Bimodal Nuclear Thermal Rocket in Low Earth Orbit. Credit: NASA
So now, you’re orbiting the Earth, which is orbiting the Sun. If you want to get to Mars, you have raise your orbit so that it matches Mars. The absolute minimum energy needed to make that transfer is known as the Hohmann transfer orbit. To get to Mars, you need to fire your thrusters until you’re going about 11.3 km/s.
Then you escape the pull of Earth, follow a nice curved trajectory, and intercept the trajectory of Mars. Assuming you timed everything right, that means you intercept Mars and go into orbit, or land on its surface, or discover a portal to hell dug into a research station on Phobos.
If you want to expend more energy, go ahead, you’ll get there faster.
But it turns out there’s another way you can travel from planet to planet in the Solar System, using a fraction of the energy you would use with the traditional Hohmann transfer, and that’s using Lagrange points.
We did a whole article on Lagrange points, but here’s a quick refresher. The Lagrange points are places in the Solar System where the gravity between two objects balances out in five places. There are five Lagrange points relating to the Earth and the Sun, and there are five Lagrange points relating to the Earth and the Moon. And there are points between the Sun and Jupiter, etc.
Illustration of the Sun-Earth Lagrange Points. Credit: NASA
Three of these points are unstable. Imagine a boulder at the top of a mountain. It doesn’t take much energy to keep it in place, but it’s easy to knock it out of balance so it comes rolling down.
Now, imagine the whole Solar System with all these Lagrange points for all the objects gravitationally interacting with each other. As planets go around the Sun, these Lagrange points get close to each other and even overlap.
And if you time things right, you can ride along in one gravitationally balanced point, and the roll down the gravity hill into the grasp of a different planet. Hang out there for a little bit and then jump orbits to another planet.
In fact, you can use this technique to traverse the entire Solar System, from Mercury to Pluto and beyond, relying only on the interacting gravity of all these worlds to provide you with the velocity you need to make the journey.
Welcome to the Interplanetary Transport Network, or Interplanetary Superhighway.
Unlike a normal highway, though, the actual shape and direction these pathways take changes all the time, depending on the current configuration of the Solar System.
A stylized example of one of the many, ever-changing routes along the ITN. Credit: NASA
If you think this sounds like science fiction, you’ll be glad to hear that space agencies have already used a version of this network to get some serious science done.
NASA greatly extended the mission of the International Sun/Earth Explorer 3, using these low energy transfers, it was able to perform its primary mission and then investigate a couple of comets.
The Japanese Hiten spacecraft was supposed to travel to the Moon, but its rocket failed to get enough velocity to put it into the right orbit. Researchers at NASA’s Jet Propulsion Laboratory calculated a trajectory that used the Lagrange points to help it move slowly and get to the Moon any way.
NASA’s Genesis Mission used the technique to capture particles from the solar wind and bring them back to the Earth.
There have been other missions to use the technique, and missions have been proposed that might exploit this technique to fully explore all the moons of Jupiter or Saturn, for example. Traveling from moon to moon when the gravity points line up.
It all sounds too good to be true, so here’s the downside. It’s slow. Really, painfully slow.
Like it can take years and even decades to move from world to world.
Imagine in the far future, there are space stations positioned at the major Lagrange points around the planets in the Solar System. Maybe they’re giant rotating space stations, like in 2001, or maybe they’re hollowed out asteroids or comets which have been maneuvered into place.
Exterior view of a Stanford torus. Bottom center is the non-rotating primary solar mirror, which reflects sunlight onto the angled ring of secondary mirrors around the hub. Painting by Donald E. Davis
They hang out at the Lagrange points using minimal fuel for station keeping. If you want to travel from one planet to another, you dock your spacecraft at the space station, refuel, and then wait for one of these low-energy trajectories to open up.
Then you just kick away from the Lagrange point, fall into the gravity well of your destination, and you’re on your way.
In the far future, we could have space stations at all the Lagrange points, and slow ferries that move from world to world along low energy trajectories, bringing cargo from world to world. Or taking passengers who can’t afford the high velocity Hohmann transfer technique.
You could imagine the space stations equipped with powerful lasers that fill your ship’s solar sails with the photons it needs to take you to the next destination. But then, I’m a sailor, so maybe I’m overly romanticizing it.
Here’s another, even more mind-bending concept. Astronomers have observed these networks open up between interacting galaxies. Want to transfer from the Milky Way to Andromeda? Just get your spacecraft to the galactic Lagrange point in a few billion years as they pass through each other. With very little energy, you’ll be able to join the cool kids in Andromeda.
I love this idea that colonizing and traveling across the Solar System doesn’t actually need to take enormous amounts of energy. If you’re patient, you can just ride the gravitational currents from world to world. This might be one of the greatest gifts the Solar System has made available to us.
A photo of the constellation Andromeda with all Bayer-designated stars marked and the IAU figure drawn in. Credit: Roberto Mura/Wikipedia Commons
In the 2nd century CE, Greek-Egyptian astronomer Claudius Ptolemaeus (aka. Ptolemy) compiled a list of the then-known 48 constellations. His treatise, known as the Almagest, would be used by medieval European and Islamic scholars for over a thousand years to come. Thanks to the development of modern telescopes and astronomy, this list was amended by the early 20th century to include the 88 constellation that are recognized by the International Astronomical Union (IAU) today.
Of these, Andromeda is one of the oldest and most widely recognized. Located north of the celestial equator, this constellation is part of the family of Perseus, Cassiopeia, and Cepheus. Like many constellation that have come down to us from classical antiquity, the Andromeda constellation has deep roots, which may go all the way back to ancient Babylonian astronomy.
Everything eventually dies, even galaxies. So how does that happen? Time to come to grips with our galactic mortality. Not as puny flesh beings, or as a speck of rock, or even the relatively unassuming ball of plasma we orbit.
Today we’re going to ponder the lifespan of the galaxy we inhabit, the Milky Way. If we look at a galaxy as a collection of stars, some are like our Sun, and others aren’t.
The Sun consumes fuel, converting hydrogen into helium through fusion. It’s been around for 5 billion years, and will probably last for another 5 before it bloats up as a red giant, sheds its outer layers and compresses down into a white dwarf, cooling down until it’s the background temperature of the Universe.
So if a galaxy like the Milky Way is just a collection of stars, isn’t that it? Doesn’t a galaxy die when its last star dies?
But you already know a galaxy is more than just stars. There’s also vast clouds of gas and dust. Some of it is primordial hydrogen left from the formation of the Universe 13.8 billion years ago.
All stars in the Milky Way formed from this primordial hydrogen. It and other similar sized galaxies produce 7 bouncing baby stars every year. Sadly, ours has used up 90% of its hydrogen, and star formation will slow down until it both figuratively, and literally, runs out of gas.
The Milky Way will die after it’s used all its star-forming gas, when all of the stars we have, and all those stars yet to be born have died. Stars like our Sun can only last for 10 billion years or so, but the smallest, coolest red dwarfs can last for a few trillion years.
The Andromeda Galaxy. Credit: Adam Evans
That should be the end, all the gas burned up and every star burned out. And that’s how it would be if our Milky Way existed all alone in the cosmos.
Fortunately, we’re surrounded by dozens of dwarf galaxies, which get merged into our Milky Way. Each merger brings in a fresh crop of stars and more hydrogen to stoke the furnaces of star formation.
There are bigger galaxies out there too. Andromeda is bearing down on the Milky Way right now, and will collide with us in the next few billion years.
When that happens, the two will merge. Then there’ll be a whole new era of star formation as the unspent gas in both galaxies mix together and are used up.
Eventually, all galaxies gravitationally bound to each other in this vicinity will merge together into a giant elliptical galaxy.
We see examples of these fossil galaxies when we look out into the Universe. Here’s M49, a supermassive elliptical galaxy. Who knows how many grand spiral galaxies stoked the fires of that gigantic cosmic engine?
Eta Carinae shines brightly in X-rays in this image from the Chandra X-Ray Observatory.
Elliptical galaxies are dead galaxies walking. They’ve used up all their reserves of star forming gas, and all that’s left are the longer lasting stars. Eventually, over vast lengths of time, those stars will wink out one after the other, until the whole thing is the background temperature of the Universe.
As long as galaxies have gas for star formation, they’ll keep thriving. Once it’s gonzo, or a dramatic merger uses all the gas in one big party, they’re on their way out.
What could we do to prolong the life of our galaxy? Let’s hear some wild speculation in the comments below.
When we look out into space, we’re also looking back into time. Just how far back can we see?
The Universe is a magic time window, allowing us to peer into the past. The further out we look, the further back in time we see. Despite our brains telling us things we see happen at the instant we view them, light moves at a mere 300,000 kilometers per second, which makes for a really weird time delay at great distances.
Let’s say that you’re talking with a friend who’s about a meter away. The light from your friend’s face took about 3.336 nanoseconds to reach you. You’re always seeing your loved ones 3.336 nanoseconds into the past. When you look around you, you’re not seeing the world as it is, you’re seeing the world as it was, a fraction of a second ago. And the further things are, the further back in time you’re looking.
The distance to the Moon is, on average, about 384,000 km. Light takes about 1.28 seconds to get from the Moon to the Earth. If there was a large explosion on the Moon of a secret Nazi base, you wouldn’t see it for just over a second. Even trying to communicate with someone on the Moon would be frustrating as you’d experience a delay each time you talked.
Let’s go with some larger examples. Our Sun is 8 minutes and 20 seconds away at the speed of light. You’re not seeing the Sun as it is, but how it looked more than 8 minutes ago.
On average, Mars is about 14 light minutes away from Earth. When we were watching live coverage of NASA’s Curiosity Rover landing on Mars, it wasn’t live. Curiosity landed minutes earlier, and we had to wait for the radio signals to reach us, since they travel at the speed of light.
When NASA’s New Horizons spacecraft reaches Pluto next year, it’ll be 4.6 light hours away. If we had a telescope strong enough to watch the close encounter, we’d be looking at events that happened 4.6 hours ago.
A Hubble Space Telescope image of Proxima Centauri, the closest star to Earth. Credit: ESA/Hubble & NASA
The closest star, Proxima Centauri, is more than 4.2 light-years away. This means that the Proxima Centurans don’t know who won the last US Election, or that there are going to be new Star Wars movies. They will, however, as of when this video was produced, be watching Toronto make some questionable life choices regarding its mayoral election.
The Eagle Nebula with the famous Pillars of Creation, is 7,000 light-years away. Astronomers believe that a supernova has already gone off in this region, blasting them away. Take a picture with a telescope and you’ll see them, but mostly likely they’ve been gone for thousands of years.
The core of our own Milky Way galaxy is about 25,000 light-years away. When you look at these beautiful pictures of the core of the Milky Way, you’re seeing light that may well have left before humans first settled in North America.
The Andromeda Galaxy. Credit: Adam Evans
And don’t get me started on Andromeda. That galaxy is more than 2.5 million light-years away. That light left Andromeda before we had Homo Erectus on Earth. There are galaxies out there, where aliens with powerful enough telescopes could be watching dinosaurs roaming the Earth, right now.
Here’s where it gets even more interesting. Some of the brightest objects in the sky are quasars, actively feeding supermassive black holes at the cores of galaxies. The closest is 2.5 billion light years away, but there are many much further out. Earth formed only 4.5 billion years ago, so we can see quasars shining where the light had left before the Earth even formed.
The Cosmic Microwave Background Radiation, the very edge of the observable Universe is about 13.8 billion light-years away. This light left the Universe when it was only a few hundred thousand years old, and only now has finally reached us. What’s even stranger, the place that emitted that radiation is now 46 billion light-years away from us.
So crack out your sonic screwdrivers and enjoy your time machine, Whovians. Your ability to look out into space and peer into the past. Without a finite speed of light, we wouldn’t know as much about the Universe we live in and where we came from. What moment in history do you wish you could watch? Express your answer in the form of a distance in light-years.
There’s a supermassive black hole in the center of our Milky Way galaxy. Could this black hole become a Quasar?
Previously, we answered the question, “What is a Quasar”. If you haven’t watched that one yet, you might want to pause this video and click here. … or you could bravely plow on ahead because you already know or because clicking is hard.
Should you fall in the latter category. I’m here to reward your laziness. A quasar is what you get when a supermassive black hole is actively feeding on material at the core of a galaxy. The region around the black hole gets really hot and blasts out radiation that we can see billions of light-years away.
Our Milky Way is a galaxy, it has a supermassive black hole at the core. Could this black hole feed on material and become a quasar? Quasars are actually very rare events in the life of a galaxy, and they seem to happen early on in a galaxy’s evolution, when it’s young and filled with gas.
Normally material in the galactic disk orbits well away from the the supermassive black hole, and it’s starved for material. The occasional gas cloud or stray star gets too close, is torn apart, and we see a brief flash as it’s consumed. But you don’t get a quasar when a black hole is snacking on stars. You need a tremendous amount of material to pile up, so it’s chokes on all the gas, dust, planets and stars. An accretion disk grows; a swirling maelstrom of material bigger than our Solar System that’s as hot as a star. This disk creates the bright quasar, not the black hole itself.
Quasars might only happen once in the lifetime of a galaxy. And if it does occur, it only lasts for a few million years, while the black hole works through all the backed up material, like water swirling around a drain. Once the black hole has finished its “stuff buffet”, the accretion disk disappears, and the light from the quasar shuts off.
Sounds scary. According to New York University research scientist Gabe Perez-Giz, even though a quasar might be emitting more than 100 trillion times as much energy as the Sun, we’re far enough away from the core of the Milky Way that we would receive very little of it – like, one hundredth of a percent of the intensity we get from the Sun.
This annotated artist’s conception illustrates our current understanding of the structure of the Milky Way galaxy. Image Credit: NASA
Since the Milky Way is already a middle aged galaxy, its quasaring days are probably long over. However, there’s an upcoming event that might cause it to flare up again. In about 4 billion years, Andromeda is going to cuddle with the Milky Way, disrupting the cores of both galaxies. During this colossal event, the supermassive black holes in our two galaxies will interact, messing with the orbits of stars, planets, gas and dust.
Some will be thrown out into space, while others will be torn apart and fed to the black holes. And if enough material piles up, maybe our Milky Way will become a quasar after all. Which as I just mentioned, will be totally harmless to us. The galactic collision? Well that’s another story.
It’s likely our Milky Way already was a quasar, billions of years ago. And it might become one again billions of years from now. And that’s interesting enough that I think we should stick around and watch it happen. How do you feel about the prospects for our Milky Way becoming a quasar? Are you a little nervous by an event that won’t happen for another 4 billion years?
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I don’t want to freak you out, but you should be aware that there’s a gigantic galaxy with twice our mass headed right for us. Naw, I’m just kidding. I totally want to freak you out. The Andromeda galaxy is going to slam head first into the Milky Way like it doesn’t even have its eyes on the road.
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Transcript
I don’t want to freak you out, but you should be aware that there’s a gigantic galaxy with twice our mass headed right for us. Naw, I’m just kidding. I totally want to freak you out. The Andromeda galaxy is going to slam head first into the Milky Way like it doesn’t even have its eyes on the road.
This collision will tear the structure of our galaxy apart. The two galaxies will coalesce into a new, larger elliptical galaxy, and nothing will ever be the same again, including your insurance premiums. There’s absolutely nothing we can do about it. It’s like those “don’t text and drive commercials” where they stop time and people get out and have a conversation about their babies and make it clear that selfish murderous teenagers are really ruining everything for all of us all the time.
The Andromeda Galaxy will collide with the Milky Way in the future. Credit: Adam Evans
And now that we know disaster is inbound, all we can do is ask WHY? Why this is even happening? Isn’t the Universe expanding, with galaxies speeding away from us in all directions? Shouldn’t Andromeda be getting further away, and not closer? What the hay, man!
Here’s the thing, the vast majority of galaxies are travelling away from us at tremendous speed. This was the big discovery by Edwin Hubble in 1929. The further away a galaxy is, the faster it’s moving away from us. The most recent calculation by NASA in 2013 put this amount at 70.4 kilometers per second per megaparsec. At a billion light-years away, the expansion of the Universe is carrying galaxies away from us at 22,000 km/s, or about 7% of the speed of light. At 100 million light-years away, that speed is only 2,200 km/s.
Which actually doesn’t seem like all that much. Is that like Millenium Falcon fast or starship Enterprise Warp 10 fast? Andromeda is only 2.5 million light-years away. Which means that the expansion of the Universe is carrying it away at only 60 kilometers per second. This is clearly not fast enough for our purposes of not getting our living room stirred into the backyard pool. As the strength of gravity between the Milky Way and Andromeda is strong enough to overcome this expansive force. It’s like there’s an invisible gravity rope connecting the two galaxies together. Dragging us to our doom. Curse you, gravity doom rope!
The Hubble Space Telescope’s extreme close-up of M31, the Andromeda Galaxy. Picture released in January 2015. Credit: NASA, ESA, J. Dalcanton, B.F. Williams, and L.C. Johnson (University of Washington), the PHAT team, and R. Gendler
Andromeda is speeding towards us at 110 kilometers per second. Without the expansion of the Universe, I’m sure it would be faster and even more horrifying! It’s the same reason why the Solar System doesn’t get torn apart. The expansion rate of the Universe is infinitesimally small at a local level. It’s only when you reach hundreds of millions of light-years does the expansion take over from gravity.
You can imagine some sweet spot, where a galaxy is falling towards us exactly as fast as it’s being carried away by the expansion of the Universe. It would remain at roughly the same distance and then we can just be friends, and they don’t have to get all up in our biz. If Andromeda starts complaining about being friend-zoned, we’ll give them what-for and begin to re-evaluate our friendship with them, because seriously, no one has time for that.
The discovery of dark energy in 1998 has made this even more complicated. Not only is the Universe expanding, but the speed of expansion is accelerating. Eventually distant galaxies will be moving faster away from us than the speed of light. Only the local galaxies, tied together by gravity will remain visible in the sky, eventually all merging together. Everything else will fall over the cosmic horizon and be lost to us forever.
This annotated artist’s conception illustrates our current understanding of the structure of the Milky Way galaxy. Image Credit: NASA
All things in the Universe are speeding away from us, it’s just that gravity is a much stronger force at local levels. This is why the Solar System holds together, and why Andromeda is moving towards us and in about 4 billion years or so, the Andromeda galaxy is going to slam into the Milky Way.
So, if by chance you only watched the first part of this video, freaked out, sold your possessions and joined some crazy silver jumpsuit doomsday cult, and are now, years later watching the conclusion… you may feel a bit foolish. However, I hope that you at least made some lifelong friendships and got to keep the jumpsuit.
Really, there’s nothing to worry about. Stars are spread so far apart that individual stars won’t actually collide with each other. Even if humanity is still around in another 4 billion years or so, which is when this will all go down. This definitely isn’t something we’ll be concerned with. It’s just like climate change. Best of luck future generations!
What do you think, will humans still be around in 4 billion years to enjoy watching the spectacle of the Milky Way and Andromeda collide?
Host: Fraser Cain (@fcain) Special Guest:Andy Weir , author of “The Martian”
Andy was first hired as a programmer for a national laboratory at age fifteen and has been working as a software engineer ever since. He is also a lifelong space nerd and a devoted hobbyist of subjects like relativistic physics, orbital mechanics, and the history of manned spaceflight. “The Martian” is his first novel.
