Special Guest:Elizabeth S. Sexton-Kennedy, who works at FermiLab as Compact Muon Solenoid (CMS) Offline Coordinator. CMS (at CERN/LHC) is a particle detector that is designed to see a wide range of particles and phenomena produced in high-energy proton collisions in the LHC.
Doesn’t it feel like the Universe is perfectly tuned for life? Actually, it’s a horrible hostile place, delivering the bare minimum for human survival.
Consider that incomprehensible series of events that brought you to this moment. In a way that we still don’t understand, a complex mix of chemicals came together in just the right combination to kick off the evolution of life.
Generation after generation of bacteria, insects, fish, lizards, mammals and eventually humans somehow successfully found a buddy and passed along their genetic material to another generation. Clever humans invented computers, the internet, YouTube, and somehow you found your way to this exact video, to hear these words. Whoa.
It’s amazing to consider the Universe we live in, and how it’s perfectly tuned for life. If just a single variable was a little bit different, life as we know it probably wouldn’t exist. Gravity might be a repulsive force. Pokemons might catch you.
Doesn’t it feel like the Universe was created especially for us? I mean, didn’t I already tell you that we’re all the center of the Universe?
I’m sad to say, but this couldn’t be further from the truth. The reality is that the Universe is 100% completely inhospitable. Well, apart from a thin layer on the surface of our Earth, but that’s got to be a rounding error. A fraction of a fraction of a fraction of the teeniest percent of the volume of the Universe. The rest of the Universe is bunk.
If I was plucked out of our cozy environment and dropped into the near vacuum of pretty much anywhere else, the only resource would be a handful of hydrogen atoms. And what can you do with a few hydrogen atoms? Nothing. It might even give Bear Grylls a run for his money. He might have a little more trouble on a star’s surface, crisping up in a heartbeat.
Into a black hole? Surface of a neutron star? Near an exploding supernova? Please enjoy the crushing pressures and hellish temperatures of Venus, or the freezing irradiated surface of Mars.
Earth itself is mostly a deathtrap. Travel down a few kilometers and you’d bake and crush from the rising temperatures of the Earth’s interior. Travel up and the air gets thin, cold and killy. In fact, without our technology heating, cooling, or helping us breathe, we wouldn’t last more than a few days on most of the planet.
Panorama of the part of Mars, from Sol 173. Credit: NASA/JPL/Caltech/Malin Space Science Systems. Image editing by
When you think about the landscape of time, we even live in a brief thumbnail of a moment when Earth is hospitable. Over the next few billion years, the Sun is going to heat up to the point that the surface of Earth will resemble the surface of Venus. And then the last hospitable hidey-hole in the entire Universe, that we know of, will wink out. The Universe is as inhospitable as it could possibly be. That is, without being completely inhospitable.
Especially when you consider the timeframes, and the long future when all the stars have died, where there’s nothing but black holes and frozen matter, and the Universe finally ditches that rounding error, and becomes 100% purely inhospitable.
Cosmologists use a term known as the anthropic principle to explain this very special moment we find ourselves in. There’s the greater anthropic principle that says the Universe wouldn’t be here without us to observe it, but that seems nutty and egotistical.
The lesser anthropic principle says that if the Universe turned out any differently, we wouldn’t be here to observe it.
First ever image of Earth Taken by Mars Color Camera aboard India’s Mars Orbiter Mission (MOM) spacecraft while orbiting Earth and before the Trans Mars Insertion firing on Dec. 1, 2013. Image is focused on the Indian subcontinent. Credit: ISRO
Imagine you threw a dart out the window of an airplane and it landed in a tiny spot on the surface of the Earth. What were the chances that it would land there? Almost zero. What a lucky spot.
You can imagine all kinds of other even more inhospitable Universes, where the conditions were never good enough for life to evolve, and so intelligent civilizations could never even ask the question, “Is Our Universe Perfect for Life.”
So when you look out across a meadow in the springtime. The birds are chirping, and there’s new growth everywhere, don’t forget about the boiling rock magma beneath your feet, the frigid air and then vacuum above your head, and the whole Universe of burning, radiating, impacting objects trying their best to kill you.
Of all the extreme environments in the Universe, which ones do you find most fascinating? Tell us in the comments below.
Black holes are created when stars die catastrophically in a supernova. So what in the universe is a white hole?
It’s imagination day, and we’re going to talk about fantasy creatures. Like unicorns, but even rarer. Like leprechauns, but even more fantastical!
Today, we’re going to talk about white holes. Before we talk about white holes, let’s talk about black holes. And before we talk about Black Holes, what’s is this thing you have with holes exactly?
Black holes are places in the Universe where matter and energy are compacted so densely together that their escape velocity is greater than the speed of light. We’ve done at least a million videos on them, but if you still want more info, you can start here with our Black Hole playlist.
Fully describing a black hole requires a lot of fancy math, but these are real objects in our Universe. They were predicted by Einstein’s theory of relativity, and actually discovered over the last few decades.
Black holes are created when stars, much more massive than our Sun, die catastrophically in a supernova.
So then what’s a white hole?
White holes are created when astrophysicists mathematically explore the environment around black holes, but pretend there’s no mass within the event horizon. What happens when you have a black hole singularity with no mass?
White holes are completely theoretical mathematical concepts. In fact, if you do black hole mathematics for a living, I’m told, ignoring the mass of the singularity makes your life so much easier.
They’re not things that actually exist. It’s not like astronomers detected an unusual outburst of radiation and then developed hypothetical white hole models to explain them.
White Hole. Image Credit: universe-review.ca
As my good friend and sometimes Guide to Space contributor, Dr. Brian Koberlein says, “If you start with five cupcakes and start giving them away, you eventually run out. At that point you can’t give away any more. In this case you can’t count down past zero. Sure, you can hand out slips of paper with “I O U ONE cupcake.” written on them, but it would be ridiculous to use the existence of negative numbers to claim that “negative cupcakes” exist and can be handed out to people.”
Now if white holes did exist, which they probably don’t, they would behave like reverse black holes – just like the math predicts. Instead of pulling material inward, a white hole would blast material out into space like some kind of white chocolate fountain. So generous, these white holes and their chocolate.
One of the other implications of white hole math, is that they only theoretically exist as long as there isn’t a single speck of matter within the event horizon. As soon as single atom of hydrogen drifted into the region, the whole thing would collapse. Even if white holes were created back at the beginning of the Universe, they would have collapsed long ago, since our Universe is already filled with stray matter.
That said, there are a few physicists out there who think white holes might be more than theoretical. Hal Haggard and Carlo Rovelli of Aix-Marseille University in France are working to explain what happens within black holes using a branch of theoretical physics called loop quantum gravity.
Artistic view of a radiating black hole. Credit: NASA
In theory, a black hole singularity would compress down until the smallest possible size predicted by physics. Then it would rebound as a white hole. But because of the severe time dilation effect around a black hole, this event would take billions of years for even the lowest mass ones to finally get around to popping.
If there were microscopic black holes created after the Big Bang, they might get around to decaying and exploding as white holes any day now. Except, according to Stephen Hawking, they would have already evaporated.
Another interesting idea put forth by physicists, is that a white hole might explain the Big Bang, since this is another situation where a tremendous amount of matter and energy spontaneously appeared.
In all likelihood, white holes are just fancy math. And since fancy math rarely survives contact with reality, white holes are probably just imaginary.
What other highly theoretical theories in space and physics would you like us to investigate? Tell us in the comments below.
Is there any possible way to take a black hole and terraform it to be a place we could actually live?
In the challenge of terraforming the Sun, we all learned that outside of buying a Dyson Spaceshell 2000 made out of a solar system’s worth of planetbutter, it’s a terrible idea.
Making a star into a habitable world, means first destroying the stellar furnace. Which isn’t good for anyone, “Hey, free energy! vs. Let’s wreck this thing and build houses!”
Doubling down on this idea, a group of brilliant Guidensians wanted to crank the absurdity knob all the way up. You wanted to know if it would be possible to terraform a black hole.
In order to terraform something, we convert it from being Britney Spears’ level of toxic into something that humans can comfortably live on. We want reasonable temperatures, breathable atmosphere, low levels of radiation, and Earthish gravity.
With temperatures inversely proportional to their mass, a solar mass black hole is about 60 billionths of a Kelvin. This is just a smidge over absolute zero. Otherwise known as “pretty damn” cold. Actively feeding black holes can be surrounded by an accretion disk of material that’s more than 10 million degrees Kelvin, which would also kill you. Make a note, fix the temperature.
There’s no atmosphere, and it’s either the empty vacuum of space, or the superheated plasma surrounding an actively feeding black hole. Can you breathe plasma? If the answer is yes, this could work for you. If not, we’ll need to fix that.
You’d be hard pressed to find a more lethal radiation source in the entire Universe.
Black holes can spin at close to the speed of light, generating massive magnetic fields. These magnetic fields whip high energy particles around them, creating lethal doses of radiation. There are high energy particle jets pouring out of some supermassive black holes, moving at nearly the speed of light. You don’t want any part of that. We’ll add that to the list.
Black holes are known for being an excellent source of vitamin gravity. Out in orbit, it’s not so bad. Replace our Sun with a black hole of the same mass, and you wouldn’t be able to tell the difference.
So, problem solved? Not quite. If you tried to walk on the surface, you’d get shredded into a one-atom juicy stream of extruded tubemanity before you got anywhere near the time traveling alien library at the caramel center.
Reduce the gravity. Got it.
Artist rendering of a supermassive black hole. Credit: NASA / JPL-Caltech.
As we learned in a previous episode on how to kill black holes, there’s nothing you can do to affect them. You couldn’t smash comets into it to give it an atmosphere, it would just turn them into more black hole. You couldn’t fire a laser to extract material and reduce the mass, it would just turn your puny laser into more black hole.
Antimatter, explosives, stars, rocks, paper, scissors…black hole beats them all.
Repeat after me. “Om, nom, nom”.
All we can do is wait for it to evaporate over incomprehensible lengths of time. There are a few snags with this strategy, such as it will remain as a black hole until the last two particles evaporate away. There’s no point where it would magically become a regular planetoid.
That’s a full list of renovations for the cast and crew of “Pimp my Black Hole”.
Let’s look at our options. You can move it, just like we can move the Earth. Throw stuff really close to a black hole, and you get it moving with gravity. You could make it spin faster by dropping stuff into it, right up until it’s rotating at the edge of the speed of light, and you can make it more massive.
With that as our set of tools, there’s no way we’re ever going to live on a black hole.
It could be possible to surround a black hole with a Dyson Sphere, like a star.
Freemon Dyson theorized that eventually, a civilization would be able to build a megastructure around its star to capture all its energy. Credit: SentientDevelopments.com
It turns out there’s a way to have a pet black hole pay dividends aside from eating all your table scraps, shameful magazines and radioactive waste. By dropping matter into a black hole that’s spinning at close to the speed of light, you can actually extract energy from it.
Imagine you had an asteroid that was formed by two large rocks. As they get closer and closer to the black hole, tidal forces tear them apart. One chunk falls into the black hole, the smaller remaining rock has less collective mass, which allows it to escape. This remaining rock steals rotational energy from the black hole, which then slows down the rotation just a little bit.
This is the Penrose Process, named after the physicist who developed the idea. Astronomers calculated you can extract 20% of pure energy from matter that you drop in.
There’s isn’t much out there that would give you better return on your investment.
Also, it’s got to have a similar satisfying feeling as dropping pebbles off a bridge and watching them disappear from existence.
Terraforming a black hole is a terrible idea that will totally get us all killed. Don’t do it.
If you have to get close to that freakish hellscape I do recommend surrounding your pet with a Dyson Sphere and then feeding it matter and enjoying the energy you get in return.
A futuristic energy hungry civilization bent on evil couldn’t hope for a better place to live.
Have you got any more questions about black holes? Give us your suggestions in the comments below.
Rogue stars are moving so quickly they’re leaving the Milky Way, and never coming back. How in the Universe could this happen?
Stars are built with the lightest elements in the Universe, hydrogen and helium, but they contain an incomprehensible amount of mass. Our Sun is made of 2 x 10^30 kgs of stuff. That’s a 2 followed by 30 zeros. That’s 330,000 times more stuff than the Earth.
You would think it’d be a bit of challenge to throw around something that massive, but there are events in the Universe which are so catastrophic, they can kick a star so hard in the pills that it hits galactic escape velocity.
Rogue, or hypervelocity stars are moving so quickly they’re leaving the Milky Way, and never coming back. They’ve got a one-way ticket to galactic voidsville. The velocity needed depends on the location, you’d need to be traveling close to 500 kilometers per second. That’s more than twice the speed the Solar System is going as it orbits the centre of the Milky Way.
There are a few ways you can generate enough kick to fire a star right out of the park. They tend to be some of the most extreme events and locations in the Universe. Like Supernovae, and their big brothers, gamma ray bursts.
Supernovae occur when a massive star runs out of hydrogen, keeps fusing up the periodic table of elements until it reaches iron. Because iron doesn’t allow it to generate any energy, the star’s gravity collapses it. In a fraction of a second, the star detonates, and anything nearby is incinerated. But what if you happen to be in a binary orbit with a star that suddenly vaporizes in a supernova explosion?
That companion star is flung outward with tremendous velocity, like it was fired from a sling, clocking up to 1,200 km/s. That’s enough velocity to escape the pull of the Milky Way. Huzzah! Onward, to adventure! Ahh, crap… please do not be pointed at the Earth?
This artist’s impression shows the dust and gas around the double star system GG Tauri-A.
Another way to blast a star out of the Milky Way is by flying it too close to Kevin, the supermassive black hole at the heart of the galaxy.
And for the bonus round, astronomers recently discovered stars rocketing away from the galactic core as fast as 900 km/s. It’s believed that these travelers were actually part of a binary system. Their partner was consumed by the Milky Way’s supermassive black hole, and the other is whipped out of the galaxy in a gravitational jai halai scoop.
Interestingly, the most common way to get flung out of your galaxy occurs in a galactic collision. Check out this animation of two galaxies banging together. See the spray of stars flung out in long tidal tails? Billions of stars will get ejected when the Milky Way hammers noodle first into Andromeda.
A recent study suggests half the stars in the Universe are rogue stars, with no galaxies of their own. Either kicked out of their host galaxy, or possibly formed from a cloud of hydrogen gas, flying out in the void. They are also particularly dangerous to Carol Danvers.
Considering the enormous mass of a star, it’s pretty amazing that there are events so catastrophic they can kick entire stars right out of our own galaxy.
What do you think life would be like orbiting a hypervelocity star? Tell us your thoughts in the comments below.
Activity within the jet from NGC 3852 imaged by Hubble. Credit: NASA, ESA, and E. Meyer (STScI).
Even the Empire’s planet-blasting battle station has nothing compared to the immense energy being fired from the heart of NGC 3862, a supermassive black hole-harboring elliptical galaxy located 300 million light-years away.
And while jets of high-energy plasma coming from active galactic nuclei have been imaged before, for the first time activity within a jet has been observed in optical wavelengths, revealing a quite “forceful” collision of ejected material at near light speeds.
Using archived image data acquired by Hubble in 1994, 1996, and 2002 combined with new high-resolution images acquired in 2014, Eileen Meyer at the Space Telescope Science Institute (STScI) in Baltimore, Maryland identified movement in visible clumps of plasma within the jet emitted from the nucleus of NGC 3862 (aka 3C 264). One of the outwardly-moving larger clumps could be seen gaining on a slower, smaller one in front of it and the two eventually collide, creating a shockwave that brightens the resulting merged mass dramatically.
Such a collision has never been witnessed before, and certainly not thousands of light-years out from the central supermassive black hole.
Close-up image of the jet as seen in 2014. Credit: NASA, ESA, and E. Meyer (STScI).
“Something like this has never been seen before in an extragalactic jet,” Meyer said. “This will allow us a very rare opportunity to see how the kinetic energy of the collision is dissipated into radiation.”
Jets like this are created when infalling material around an active (that is, “feeding”) supermassive black hole gets caught up in its powerful spinning and twisting magnetic fields. This accelerates the material even further and, rather than permitting it to descend down past the black hole’s event horizon, results in it getting shot out into space at velocities close to the speed of light.
When material approaches the black hole in even amounts the jets are fairly consistent. But if the inflow is uneven, the jets can consist of clumps or knots traveling outward at different speeds.
Because of the motion of the galaxy itself related to our own, the speed of the clumps can appear to actually move faster than the speed of light, especially when – as seen in NGC 3862 – a large clump has already paved the way within the jet. In reality the light speed limit has not been broken, but the apparent superluminal motion so far from the SMBH indicates that the material was ejected extremely energetically.
It’s expected that the combined clusters of material will continue to brighten over the next several decades.
You can see a video of the observations below, and watch a Google+ Hangout with Hubble team members about these observations here.
Nothing lasts forever, not even black holes. According to Stephen Hawking, black holes will evaporate over vast periods of time. But how, exactly, does this happen?
The actor Stephen Hawking is best known for his cameo appearances in Futurama and Star Trek, you might surprised to learn that he’s also a theoretical astrophysicist. Is there anything that guy can’t do?
One of the most fascinating theories he came up with is that black holes, the Universe’s swiffer, can actually evaporate over vast periods of time.
Quantum theory suggests there are virtual particles popping in and out of existence all the time. When this happens, a particle and its antiparticle appear, and then they recombine and disappear again.
When this takes place near an event horizon, strange things can happen. Instead of the two particles existing for a moment and then annihilating each other, one particle can fall into the black hole, and the other particle can fly off into space. Over vast periods of time, the theory says that this trickle of escaping particles causes the black hole to evaporate.
Wait, if these virtual particles are falling into the black hole, shouldn’t that make it grow more massive? How does that cause it to evaporate? If I add pebbles to a rock pile, doesn’t my rock pile just get bigger?
It comes down to perspective. From an outside observer watching the black hole’s event horizon, it appears as if there’s a glow of radiation coming from the black hole. If that was all that was happening, it would violate the law of thermodynamics, as energy can neither be created nor destroyed. Since the black hole is now emitting energy, it needs to have given up a little bit of its mass to provide it.
Let’s try another way to think about this. A black hole has a temperature. The more massive it is, the lower its temperature, although it’s still not zero.
From now and until far off into the future, the temperature of the largest black holes will be colder than the background temperature of the Universe itself. Light from the cosmic microwave background radiation will fall in, increasing its mass.
Viewed in visible light, Markarian 739 resembles a smiling face. Inside are two supermassive black holes, separated by about 11,000 light-years. The galaxy is 425 million light-years away from Earth. Credit: Sloan Digital Sky Survey
Now, fast forward to when the background temperature of the Universe drops below even the coolest black holes. Then they’ll slowly radiate heat away, which must come from the black hole converting its mass into energy.
The rate that this happens depends on the mass. For stellar mass black holes, it might take 10^67 years to evaporate completely.
For the big daddy supermassive ones at the cores of galaxies, you’re looking at 10^100. That’s a one, followed by 100 zero years. That’s huge number, but just like any gigantic and finite number, it’s still less than infinity. So over an incomprehensible amount of time, even the longest living objects in the Universe – our mighty black holes – will fade away into energy.
One last thing, the Large Hadron Collider might be capable of generating microscopic black holes, which would last for a fraction of a second and disappear in a burst of Hawking radiation. If they find them, then Hawking might want to the acting on hold and focus on physics.
The LHC. Image Credit: CERN
Nothing is eternal, not even black holes. Over the longest time frames we’re pretty sure they’ll evaporate away into nothing. The only way to find out is to sit back and watch, well maybe it’s not the only way.
Does the idea of these celestial nightmares evaporating fill you with existential sadness? Feel free to share your thoughts with others in the comments below.
Thanks for watching! Never miss an episode by clicking subscribe.
Our Patreon community is the reason these shows happen. We’d like to thank Dana Nourie and the rest of the members who support us in making great space and astronomy content. Members get advance access to episodes, extras, contests, and other shenanigans with Jay, myself and the rest of the team. Want to get in on the action? Click here.
We hear that black holes absorb all the light that falls into them. And yet, we hear of black holes shining so brightly we can see them halfway across the Universe. What’s going on? Which is it?
I remember back to a classic episode of the Guide to Space, where I provided an extremely fascinating and concise explanation for what a quasar is. Don’t recall that episode? Well, it was super. Just super. Alright slackers, let’s recap.
Quasars are the brightest objects in the Universe, visible across billions of light years. Likely blanching life from everything in the path of the radiation beam from its lighthouse of death. They occur when a supermassive black hole is actively feeding on material, pouring out a mountain of radiation. Black holes, of course, are regions of space with such intense gravity where nothing, not even light itself, can escape.
But wait, not so fast “recap” Fraser Cain. I call shenanigans. If black holes absorb all the radiation that falls into them, how can they be bright?
You, Fraser Cain of days of yore, cannot have it both ways. It’s either a vortex of total destruction gobbling all the matter and light that fall into them OR alternately light can escape, which still sounds good. I mean, it could be WHERE NO STUFF CAN ESCAPE, except light.
If you’ll admit that you of the past was wrong, we’ll put you in the temporal cone of shame and move on with the episode. Right? Right? Wrong.
Let’s review. Black holes are freaky complicated beasts, with many layers. And I don’t mean that in some abstract Choprian “many connections on many different levels”. They’re a gobstopper from a Sam Neill Event Horizon style hellscape. Let’s take a look at the anatomy of a black hole, and everything should fall into place, including the terror.
At the very heart of the black hole is the singularity. This is the region of compressed matter that used to be a star, or in the case of a supermassive black hole, millions or billions of times the mass of a star. Astronomers have no idea what the singularity looks like or behaves, because our understanding of physics completely breaks down, along with the rest of our brains.
Illustration of Cygnus X-1, another stellar-mass black hole located 6070 ly away. (NASA/CXC/M.Weiss)
It’s possible that the singularity is a sphere of exotic matter, or maybe it’s constantly compressing down into an infinitely small size. It could also be a pork pie. We’ll never know, because nothing goes fast enough to escape from a black hole, not even light.
Maybe you’d need to be going 10 times the speed of light to escape. Or maybe a trillion times the speed of light. Which makes it easy; as far as we can tell, nothing can go faster than the speed of light, and so nothing is escaping.
As you get further from the singularity, the force of gravity decreases. Initially, it’ll still requires that you go faster than light. You’ll finally reach a very specific point where the escape velocity is exactly the speed of light. This is the event horizon, and it’s a different distance from the singularity with every black hole. That’s the line. Within the event horizon, the light is doomed, outside the event horizon, it can escape. This is the hard candy shell surrounding the chocolately unimaginable nightmare of physics.
So when see bright black holes, like a quasar, we’re not actually seeing light coming from inside the black hole itself or reflected of its surface. What we’re seeing is the material that’s piling up just outside the event horizon. For all its voracious hunger, a black hole’s gravitational eyes are much bigger than its stomach, and it can only feed so quickly. Excess stuff piles up around the black hole’s face and forms a vast disk of material, just like me at a Pizza Hut’s $5 all you can eat buffet. This pizza heats up until it’s like the core of a star, and starts blasting out radiation into space.
A WFPC2 image of a spiral-shaped disk of hot gas in the core of active galaxy M87. HST measurements show the disk is rotating so rapidly it contains a massive black hole at its hub.
Everything I’ve said is for non-spinning black holes, by the way. Physicists will always make this point with great emphasis. Stay your angry comments astrophysicists, for I have said the magic stone-cutter appeasement code-word, “Non-rotating”.
Of course, black holes do rotate, and can rotate at nearly the speed of light. And this rotation changes the nature of the black hole’s event horizon in ways that make difficult math even harder. All this spinning generates powerful magnetic fields around the black hole, which focuses jets of material that blast out for hundreds of thousands of light-years. When we see these bright quasars, we’re staring right at these jets with our delicate little eyeballs.
So how can we see light coming from black holes when black holes absorb all light? It’s not coming from black holes. It’s coming from the super-heated region of junk all around the black hole. And still, anything that falls through the event horizon, whether it be light, junk, you, me or Grumpy Cat it will never been seen again.
What’s your favorite sci-fi black hole? Tell us in the comments below.
Thanks for watching! Never miss an episode by clicking subscribe. Our Patreon community is the reason these shows happen. We’d like to thank Marcel-jan Krijgsman and the rest of the members who support us in making great space and astronomy content. Members get advance access to episodes, extras, contests, and other shenanigans with Jay, myself and the rest of the team. Want to get in on the action? Click here.
This artist's rending shows "before" and "after" images of a changing look quasar. Credit: Yale University.
Last week, astronomers at Yale University reported seeing something unusual: a seemingly stedfast beacon from the far reaches of the Universe went quiet. This relic light source, a quasar located in the region of our sky known as the celestial equator, unexpectedly became 6-7 times dimmer over the first decade of the 21st century. Thanks to this dramatic change in luminosity, astronomers now have an unprecedented opportunity to study both the life cycle of quasars and the galaxies that they once called home.
A quasar arises from a distant (and therefore, very old) galaxy that once contained a central, rotating supermassive black hole – what astronomers call an active galactic nucleus. This spinning beast ravenously swallowed up large amounts of ambient gas and dust, kicking up surrounding material and sending it streaming out of the galaxy at blistering speeds. Quasars shine because these ancient jets achieved tremendous energies, thereby giving rise to a torrent of light so powerful that astronomers are still able to detect it here on Earth, billions of years later.
In their hey-day, some active galactic nuclei were also energetic enough to excite electrons farther away from the central black hole. But even in the very early Universe, electrons couldn’t withstand that kind of excitement forever; the laws of physics don’t allow it. Eventually, each electron would drop back down to its rest state, releasing a photon of corresponding energy. This cycle of excitation happened over and over and over again, in regular and predictable patterns. Modern astronomers can visualize those transitions – and the energies that caused them – by examining a quasar’s optical spectrum for characteristic emission lines at certain wavelengths.
A simple example of an atomic spectrum, showing emission lines at particular wavelengths. Broad humps correspond to brighter emission lines, while lines that arise from narrow, lower-intensity emissions appear dimmer. Credit: NASA
Not all quasars are created equal, however. While the spectra of some quasars reveal many bright, broad emission lines at different energies, other quasars’ spectra consist of only the dim, narrow variety. Until now, some astronomers thought that these variations in emission lines among quasars were simply due to differences in their orientation as seen from Earth; that is, the more face-on a quasar was relative to us, the broader the emission lines astronomers would be able to see.
But all of that has now been thrown into question, thanks to our friend J015957.64+003310.5, the quasar revealed by the team of astronomers at Yale. Indeed, it is now plausible that a quasar’s pattern of emission lines simply changes over its lifetime. After gathering ten years of spectral observations from the quasar, the researchers observed its original change in brightness in 2010. In July 2014, they confirmed that it was still just as dim, disproving hypotheses that suggested the effect was simply due to intervening gas or dust. “We’ve looked at hundreds of thousands of quasars at this point, and now we’ve found one that has switched off,” explained C. Megan Urry, the study’s co-author.
How would that happen, you ask? After observing the comparable dearth of broad emission lines in its spectrum, Urry and her colleagues believe that long ago, the black hole at the heart of the quasar simply went on a diet. After all, an active galactic nucleus that consumed less material would generate less energy, giving rise to fainter particle jets and fewer excited atoms. “The power source just went dim,” said Stephanie LaMassa, the study’s principal investigator.
LaMassa continued, “Because the life cycle of a quasar is one of the big unknowns, catching one as it changes, within a human lifetime, is amazing.” And since the life cycle of quasars is dependent on the life cycle of supermassive black holes, this discovery may help astronomers to explain how those that lie at the center of most galaxies evolve over time – including Sagittarius A*, the supermassive black hole at the center of our own Milky Way.
“Even though astronomers have been studying quasars for more than 50 years, it’s exciting that someone like me, who has studied black holes for almost a decade, can find something completely new,” added LaMassa.
The team’s research will be published in an upcoming issue of The Astrophysical Journal. A pre-print of the paper is available here.
