Cosmic rays capable of destroying human DNA are hurtling through outer space like subatomic bullets, causing space crews radiation damage.
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LearningTranscript
00:00An invisible danger hurdles towards Earth at close to the speed of light.
00:08These are intergalactic alien interlopers on our Milky Way.
00:12Cosmic rays.
00:14Getting hit by a cosmic ray is like getting hit by a cosmic bullet.
00:19Cosmic rays are billions of times more energetic than any other types of particles.
00:24Vastly more energetic than anything we can even create in a laboratory,
00:27in a nuclear fusion reactor, anywhere.
00:30They pierce spaceships, putting our astronauts in danger.
00:34But the source of their power is a mystery.
00:37Are they coming from other galaxies? Are they coming from things in between the galaxies?
00:41Where do cosmic rays come from?
00:42Truth is, the most powerful ones, we haven't got a clue.
00:45The race is on to solve the mystery of the fastest particles in the universe.
01:00If I were to make a list of the dangers of space, it would be a long list.
01:10You know, there's hard vacuum, huge swings in temperatures, micrometeorites, all kinds of things.
01:16But probably at the very top of that list, cosmic rays.
01:20These space invaders are not what they seem.
01:24When you hear the name cosmic rays, you might think it's like a beam, like a laser beam of light.
01:29No, no, no, no, no, no, no.
01:30It's a tiny little death particle.
01:32To fight them, we must first understand them.
01:42April, 2019.
01:46NASA's Parker probe flies closer to the sun than ever before.
01:51We know the sun produces some of the cosmic rays that fill the solar system.
01:56But we don't know how.
01:58Our sun looks like a beautiful, glowing orb, bringing energy and light to Earth and allowing life to thrive.
02:09But if you look at it up close, you'll see a tumultuous storm of events.
02:16The amount of energy the sun is emitting every second is the equivalent of 100 billion one-megaton bombs.
02:24It's a dangerous neighborhood.
02:25Suddenly, the probe is caught head-on in a powerful blast.
02:35It's perfectly positioned to monitor the outburst from the inside.
02:39The entire outer third of the sun is a boiling cauldron.
02:46And tied up in that plasma are magnetic fields.
02:48They get tied and twisted.
02:50And energy is stored in them.
02:51So they rise toward the surface.
02:53And there, they rearrange.
02:55They reconnect.
02:56They twist.
02:57They spin.
02:58When the magnetic field lines snap, energy bursts out.
03:02And sometimes, that energy release is explosive.
03:08And that's what results in flares, which are these huge bursts of light.
03:11The probe discovers that after a solar flare, the sun's surface stores electrically charged particles.
03:20But sometimes, there's a second explosion called a coronal mass ejection, releasing superheated, electrically charged gas called plasma.
03:32These giant balls of plasma go flying off the surface of the sun.
03:38And in those balls of plasma are contained these charged particles.
03:42The charged particles move fast, but they hit a roadblock, a cloud of slower-moving particles that always surrounds the sun, the solar wind.
03:58Well, the coronal mass ejection is moving into the solar wind much faster than the wind is moving.
04:03So it sort of runs into it and creates the shock wave and ends up piling up particles at the edge.
04:09The shock wave and particles slam together.
04:14In the collision, the particles steal energy and speed, like a baseball accelerating off a bat.
04:21The particles transform into something far more powerful, a solar cosmic ray.
04:29They're light, but they're moving incredibly fast.
04:34The Earth is on average 93 million miles away from the sun.
04:38And these guys reach us in about an hour.
04:42That's 93 million miles an hour.
04:44That's pretty fast.
04:45The cosmic rays speed towards Earth.
04:49We're under attack.
04:51Cosmic rays are by far the most energetic particles that we know to exist in the universe.
04:58And when things with very high energy, no matter how small they are, impact something else, they deposit that energy, right?
05:06And so cosmic rays can be very dangerous.
05:09Solar cosmic rays aren't the only threat we face.
05:12Other space bullets arrive from beyond our solar system.
05:17There are different kinds of cosmic rays, just like there are different kinds of bullets.
05:21At the lowest end of the spectrum are these solar cosmic rays.
05:26These are like the BBs.
05:29And when a BB hits you, it might sting for a little bit, but you're not going to get too worried about it.
05:33A bigger concern?
05:35Galactic cosmic rays.
05:37If you thought galactic cosmic rays were bad, it's because you haven't met an ultra high energy cosmic ray.
06:06These are the biggest, baddest, meanest cosmic rays in the universe.
06:13These ultra high energy cosmic rays are like hypersonic missiles.
06:18They are screaming and they come from the most energetic events in the universe.
06:27The ultra high energy cosmic missiles are the rarest, but also the swiftest.
06:32These cosmic ray particles are moving fast.
06:38These mysterious particles are moving incredibly close to the speed of light.
06:42I'm not talking about 99% the speed of light.
06:45They're moving through space at like 99.999999999999999999999999999999999999999999999999999999.
06:54Nine, nine, nine, nine, 21 nines.
06:56That's fast.
06:57That's wild, that's scary.
07:01All three types of cosmic rays
07:03are racing through the solar system.
07:06If I were to hold up a golf ball in the middle of space,
07:10almost 100 cosmic rays pass through that golf ball
07:16every single second.
07:19It's a deadly hail of particle bullets
07:22and out in space, our astronauts are caught in the crossfire.
07:27Cosmic rays represent one of the greatest dangers
07:31for human space flight.
07:33NASA plans to send astronauts back to the moon
07:36where radiation levels from cosmic rays
07:39are 200 times greater than on Earth.
07:42And that is just the start.
07:44One of NASA's big goals is to send humans to Mars
07:47and that is a long way away, at least a six month journey
07:51and more often about a nine month journey.
07:54That's a big problem.
07:55I am hoping that one day I can go to Mars as an astronaut,
08:00but I'm definitely afraid of cosmic rays.
08:03And the more that I read about it,
08:04the bigger of a threat it seems.
08:06So I think that NASA and other space organizations
08:11are going to need to work on how to protect their astronauts
08:15in these really dangerous situations.
08:17Only one group of people have been exposed
08:21to these high levels of cosmic rays.
08:25The crew members of the Apollo missions.
08:29July 1969.
08:32That's one small step for man,
08:35one giant leap for mankind.
08:39One of the astronauts, Buzz Aldrin,
08:42sees something strange.
08:44During Apollo 11, Buzz Aldrin reported
08:47seeing tiny little flashes sometimes
08:49when he was looking around.
08:51That's pretty weird, but what's weirder
08:54is that he saw them when his eyes were closed.
08:57Later missions also report seeing odd flashes of light.
09:03A streak in the lower left side of the left eye,
09:06moving down.
09:08The astronauts describe the flashes
09:10as spots, streaks, and clouds.
09:14Apollo 15 commander David Scott reported seeing one
09:17that was blue with a white cast, like a blue diamond.
09:21What's happening is that a cosmic ray
09:24is entering the eyeball
09:26and then striking molecules
09:29and giving off a flash of light.
09:33An alternative theory is that it triggers
09:35the layer of sensitive cells in your retina.
09:38So you perceive a streak of light,
09:41even though no light ever actually existed.
09:45The cosmic rays cause long-term damage.
09:48Inside of the eye's lens,
09:50there are these fiber cells that are transparent.
09:53Well, when a cosmic ray travels through them,
09:55it can damage those cells
09:56and make them cloudy, causing cataracts.
09:59When NASA examines the astronauts' helmets,
10:01they find tiny tracks etched through them.
10:05Evidence of cosmic ray impacts.
10:07When we say that cosmic rays
10:09are like tiny little bullets,
10:11we're not joking around.
10:13And some of these burrowed
10:15all the way through the helmet,
10:17which means it ended up
10:19in the astronaut's brain,
10:21which just makes me feel weird to think about.
10:24What might that long-term radiation do
10:27to your brain,
10:29to your ability to reason and problem-solve
10:32in one of the most dangerous environments
10:33that humanity's ever placed itself?
10:36The farther we venture from our home planet,
10:39the more danger we face.
10:51Cosmic rays, highly energetic space particles,
10:55may be the most serious threat
10:57to human space exploration.
10:59The Hollywood conception of outer space
11:02is it's full of dangers
11:04like aliens wielding ray guns
11:07or black holes or asteroid showers.
11:10But in reality,
11:11the biggest danger facing astronauts is invisible.
11:14It's the cosmic radiation.
11:16Cosmic rays damaged Apollo astronauts' eyes
11:20after just a few days' exposure.
11:23A one-way trip to Mars
11:24takes nine months.
11:27Future missions are going to be spending
11:29much longer times in space,
11:30which means we really need to consider
11:32how cosmic rays will impact us.
11:35We don't understand
11:37all the long-term effects
11:39from a steady rain of cosmic rays,
11:42but the astronauts are going to have to deal with it.
11:45To find out more,
11:47scientists bombarded human cells
11:50with man-made cosmic ray particles.
11:53They discovered cosmic rays
11:56physically cut through DNA,
11:59chopping it apart.
12:01Damage to DNA in your cell
12:03is by far the worst kind
12:07because your DNA is the cell's operating matter.
12:11It's the blueprint
12:11so the cell knows how it should be functioning
12:15normally.
12:16You can trigger that cell to turn tumerous,
12:19to start producing cancer.
12:22In 2019,
12:25scientists took the experiment further
12:27and simulated a trip to Mars
12:29for mice.
12:31For six months,
12:33they blasted the rodents
12:34with a steady stream
12:35of lab-made cosmic ray particles.
12:39The experiment found profound alterations
12:42to the mice's normal behaviour.
12:45They learnt new tasks
12:47much more slowly.
12:49Their memory was affected
12:50and they forgot things
12:51they had already learnt.
12:53They were more anxious
12:55and prone to giving up on tasks
12:57they'd normally complete.
12:58If you put some of these irradiated mice
13:01into a swimming test,
13:03rather than trying to swim to safety,
13:06many of them just simply gave up.
13:09This is important
13:10because we need our astronauts
13:11to be fully functioning.
13:13The reason why you do crude missions
13:16is because the human brain
13:18is much better than any computer.
13:20The comments about the film?
13:21If even one of them has a problem,
13:23it can even put the mission
13:25and their lives in jeopardy.
13:27Other studies discover
13:29cosmic rays can accelerate aging,
13:32alter genes,
13:33and cause cardiovascular disease.
13:36That sounds bad enough,
13:39but there's a more immediate danger.
13:41When cosmic rays penetrate spaceships,
13:45they can fry electronic systems,
13:47and that's enough to jeopardize a mission.
13:49Our operations in space
13:52depend on electronics on computers.
13:55And the worst-case scenario
13:57is that the wrong cosmic ray
13:59comes at the wrong time
14:01and hits the wrong circuit.
14:04And it leads to a cascading series of failures
14:07that can totally jeopardize a mission.
14:10We see evidence of this onslaught
14:13in mission cameras.
14:15Even when we have a detector in space,
14:17like on the Hubble Space Telescope,
14:18if you saw a raw image,
14:20it doesn't look like the beautiful images
14:23that are shown to the public.
14:24They're just crossed with cosmic rays.
14:26And those cosmic rays
14:28are destroying that detector
14:29slowly over time.
14:33So how can we protect astronauts
14:35and their equipment?
14:37The obvious answer
14:38is to add shielding.
14:41That's one thing to say,
14:43like, oh, just add more stuff.
14:45But have you seen rocket launches
14:47and how hard they are,
14:49how expensive it is
14:50to get stuff up into space?
14:53NASA does have a plan.
14:56The spacecraft for the Artemis Moon landing mission
14:59will be packed
15:00for optimum cosmic ray protection.
15:02So one of the ways
15:04you can get around the mass limit
15:05is to basically get dual use
15:08out of everything,
15:09your supplies,
15:10your fuel,
15:11your water,
15:11and you can use those
15:13as shielding.
15:14But it's not that simple.
15:16Just as more powerful bullets
15:18penetrate armor,
15:19more energetic cosmic rays
15:21pierce the shielding
15:22on spaceships.
15:24The solar ones,
15:25yeah,
15:25you can just put up
15:26some material,
15:27some shielding,
15:27and it'll generally block them.
15:29But the higher energy ones,
15:31they can just burrow on through.
15:33If they hit one of the atoms
15:35in the shielding
15:37that is protecting our astronauts,
15:39it can create a shower of particles.
15:42That radiation particle
15:43might have missed
15:44any of the cells in your body,
15:46but you've now turned it into a blast,
15:49shredding through everything
15:50in the spacecraft.
15:52And so it turns out
15:53your shielding
15:54becomes the weapon
15:56that the cosmic rays
15:57use against you.
15:59But NASA is recruiting
16:01an unexpected ally,
16:03the sun.
16:04Can we protect our astronauts
16:06by fighting fire
16:08with fire?
16:19Powerful cosmic rays
16:20smash through spaceships.
16:23But how can objects
16:25smaller than an atom
16:26carry enough energy
16:28to be dangerous to astronauts?
16:31Moving objects
16:32carry energy.
16:34We call this kinetic energy.
16:35And when they strike something,
16:38they transform that energy.
16:41When I hit my hand,
16:43the kinetic energy of my fist
16:45transforms into sound
16:47and heat
16:48and vibration.
16:50My hand hurts a little
16:51from that impact,
16:53from the transformation of energy.
16:55It's the same thing
16:57with cosmic rays.
16:58When they slam
16:59into a human brain cell
17:01or a computer chip,
17:02they dump some energy,
17:04causing damage.
17:05How much damage
17:07depends on their
17:08kinetic energy.
17:10And that comes down
17:11to two things,
17:12mass and speed.
17:15Intuitively,
17:16things that are moving
17:17at the same speed,
17:19if they're more massive,
17:20they carry more energy.
17:22A bigger asteroid
17:23slamming into Earth
17:24will do more damage
17:25than a smaller asteroid.
17:27If you double the mass
17:28of an object,
17:29its kinetic energy
17:31also doubles.
17:33Although mass is important,
17:35it's not as important
17:36as speed.
17:40Speed matters
17:41even more than mass.
17:43The kinetic energy
17:44depends directly
17:45on the mass,
17:46but it depends
17:47on the square
17:48of the speed.
17:49Here's what that means.
17:50You double the mass,
17:51you have double
17:52the kinetic energy.
17:53You double the speed,
17:55you have four times
17:56the kinetic energy.
17:57When it comes to speed,
18:03cosmic rays
18:04are the elite.
18:06An ultra-high-energy
18:07cosmic ray
18:08detected in 1991
18:10hit the atmosphere
18:11so fast,
18:13scientists called it
18:14the oh-my-god particle.
18:18This particle
18:19was higher energy
18:21than they thought
18:23they would ever,
18:24ever see.
18:24Until this fluorescent
18:26streak in the Utah sky,
18:28no one believed
18:29a particle could
18:30reach the Earth
18:30traveling so close
18:32to the speed of light,
18:33making cosmic ray
18:34particles far more
18:36dangerous than expected.
18:38As you approach
18:39the speed of light,
18:40energy, momentum,
18:42mass, they start
18:43to act a little bit
18:44differently.
18:45Einstein's equations
18:46of relativity
18:47become important.
18:48The physics changes
18:49and the energy it has
18:50becomes much,
18:51much, much stronger.
18:53If a particle
18:54is moving at close
18:55to the speed of light,
18:56that means that
18:57its energy is almost
18:59at the maximum
19:00allowed by the laws
19:01of physics.
19:04It's amazing to think
19:06that something as tiny
19:07as a proton
19:07could actually be
19:08dangerous to a human
19:09being.
19:10But amazingly,
19:11that proton is moving
19:12so fast,
19:13it carries as much
19:14energy as a baseball
19:15thrown at 100 miles
19:17an hour.
19:17A baseball contains
19:19over a trillion,
19:20trillion protons.
19:21Imagine all that energy
19:23carried by just one
19:24particle.
19:25So now you get a sense
19:26of just how risky
19:27these can be.
19:29Ultra-high energy
19:30cosmic rays,
19:31like the Oh My God
19:33particle,
19:33are like supersonic
19:34missiles.
19:36They are the fastest,
19:37but they're so rare,
19:39astronauts are unlikely
19:40to be hit by one.
19:42Solar cosmic rays
19:43are like BB pellets,
19:45abundant,
19:46but our spacecraft
19:47can block them.
19:49The biggest threat
19:50to our astronauts,
19:51however,
19:51are galactic cosmic rays.
19:53They come from elsewhere
19:55in the Milky Way.
19:56The combination
19:57of their speed
19:58and frequency
19:59makes them
20:00the most dangerous.
20:01These galactic
20:03cosmic rays
20:04are much more powerful
20:05than the solar
20:06cosmic rays,
20:07and they've traveled
20:08enormous distances
20:10to mess you up.
20:14Luckily,
20:15our astronauts
20:15have a surprising
20:17protector,
20:18a guardian
20:19of the solar system,
20:21the sun.
20:23As well as spitting
20:24out these
20:25high-energy
20:26solar cosmic ray
20:28particles,
20:29the sun is also
20:30streaming out
20:32lots of much
20:32lower energy particles
20:34of the solar wind.
20:36That outward-moving
20:37solar wind
20:38acts as a force field,
20:40and the cosmic rays
20:41have to work
20:42their way upstream
20:43to get to Earth,
20:45far inside this bubble.
20:47The solar wind
20:49extends 11 billion miles
20:52around the solar system,
20:53generating a magnetic field
20:55that repels
20:56incoming galactic
20:58cosmic rays.
20:59It's almost like
21:00the deflector shield
21:02of the starship
21:03Enterprise.
21:04So the sun's
21:06magnetic field
21:06partially helps
21:08protect the Earth
21:10and any astronauts
21:11from the incoming radiation.
21:13Not long ago,
21:15our Voyager spacecraft
21:16made it to that
21:17boundary between
21:18the sun's bubble
21:20and the galaxy
21:21and was able
21:21to study that region.
21:23And we see the difference
21:24between inside
21:25the sun's bubble
21:26and what's going on
21:27outside the sun's bubble.
21:29The sun has our back
21:31billions of miles away,
21:33and that's pretty cool.
21:35The Voyager space probes
21:37discovered a moving
21:39battlefield.
21:39The solar wind
21:42behaves a bit
21:43like a storm front
21:43on Earth.
21:45Sometimes it advances,
21:47sometimes it retreats.
21:49When the sun's activity
21:51is the highest,
21:52it's spitting out
21:53more solar energetic proton.
21:55But those solar cosmic rays
21:57are much less damaging
21:59than the galactic ones.
22:00So the net
22:01is a benefit.
22:02So actually,
22:04ironically,
22:05you might find
22:06that for astronauts,
22:07it is safer
22:08to launch missions
22:09to Mars
22:10during a period
22:11of higher solar activity.
22:13Because although
22:14you have more
22:15of the solar particle
22:17radiation,
22:18you also get
22:20a better shielding
22:21effect
22:22from the solar wind.
22:24The sun's activity
22:25goes through
22:26an 11-year cycle
22:27of highs and lows.
22:29The protective bubble
22:30follows the same cycle.
22:32Allowing NASA
22:33to predict
22:34the safest times
22:35to launch.
22:37This is a thorny problem
22:38and, you know,
22:39we have very smart people
22:40working on it.
22:41But we want to explore space
22:43as much as we can.
22:44But we have to lower
22:45the risk to the astronauts
22:47as much as possible.
22:50NASA's fight
22:51against the cosmic invaders
22:52continues.
22:54But the biggest mystery remains.
22:57What exactly is launching
22:58the deadliest galactic
23:00cosmic rays?
23:02Every second,
23:12quadrillions of bits
23:13of space shrapnel
23:14race towards Earth
23:15at close to the speed
23:16of light.
23:18Galactic cosmic rays.
23:21The galactic cosmic rays
23:23are like a rifle bullet.
23:25You do not want
23:26to get hit by one of these.
23:27They are invaders
23:29from outside the solar system.
23:32We know they're made
23:33by something powerful
23:34within our galaxy,
23:36so the source
23:36should be easy to detect.
23:39You'd think if one of them
23:41hits a detector on Earth
23:44that we'd just be able
23:44to point back
23:45in a straight line
23:46and say it came
23:47from over there
23:47and then look,
23:48is there something else
23:49over there,
23:49like a supernova explosion
23:51that could explain
23:52the source of this.
23:53The problem is
23:54that cosmic rays
23:55get bent
23:56as they move
23:57by magnetic fields.
24:00The electric charge
24:01on a cosmic ray
24:02makes it act
24:03like a little magnet.
24:05And the Milky Way
24:06is full of other magnets.
24:09If I'm a cosmic ray
24:10just barreling
24:11through the galaxy
24:12and I encounter
24:13a magnetic field,
24:15I'm going to slightly
24:16change directions.
24:17Maybe here,
24:18maybe there,
24:19maybe up there.
24:20My trajectory
24:21is going to become
24:22scrambled.
24:24And after a few
24:25million years or so,
24:26basically all the information
24:28about where it started
24:29has been lost.
24:29It's going in a completely
24:30random direction
24:32for all practical purposes.
24:34But galactic cosmic rays
24:36also have a sidekick,
24:38one that is far less
24:40elusive,
24:42gamma rays.
24:43When a galactic cosmic ray
24:46hits a regular atom
24:47out in space,
24:48it causes this big reaction.
24:51It emits all sorts
24:53of other particles,
24:54including gamma rays,
24:55which are basically
24:56extremely energetic
24:57photons of light.
24:59Critically,
25:00gamma rays don't get
25:01bent by magnetic fields
25:03because they don't have
25:03an electric charge.
25:05So they just beeline off
25:06in a straight line
25:07along whatever direction
25:08the cosmic ray
25:09was moving in
25:09in the first place.
25:11So we can look back
25:12at where gamma rays
25:14are coming from
25:15in the sky
25:16and that tells us
25:17where there are a lot
25:18of cosmic rays
25:19having collisions.
25:21And they've led us
25:22to a prime suspect.
25:27Supernovas.
25:27Supernova are some
25:32of the most powerful
25:33explosions in the universe,
25:35and so they're ripe grounds
25:36for these highly energetic,
25:38extremely fast particles
25:39to be created.
25:41When a giant star
25:43runs out of fuel,
25:44it can no longer
25:45support its own weight.
25:47It collapses inward,
25:49triggering a huge explosion,
25:53powerful enough
25:54to smash atoms
25:55into tiny pieces.
25:58The explosion pushes out
26:00an expanding cloud
26:01of gas and dust,
26:03the supernova remnant.
26:05And that material,
26:06as it's moving out
26:07at a thousand miles a second,
26:08generates an incredibly
26:10powerful shock wave.
26:12And that shock wave
26:13could be where a particle
26:15swept up in the shock
26:16gets accelerated.
26:19The magnetic fields
26:21inside the cloud
26:22trap the subatomic particles.
26:24cosmic rays
26:26inside of the supernova
26:27remnant
26:27are a lot like
26:28being in a pinball machine.
26:32So you have
26:33the shock wave
26:34as the flipper,
26:35and then your magnetic fields
26:37are these bumpers
26:38prohibiting it
26:38from actually leaving.
26:41They're bouncing
26:42back and forth
26:42across this incredibly
26:44energetic shock,
26:45and each time
26:46they bounce back and forth,
26:47the key is they pick up
26:48a little more energy.
26:50When a galactic cosmic ray
26:52gains enough energy,
26:54the magnetic fields
26:55can no longer
26:56hold on to it.
26:57It escapes.
27:01The supernova theory
27:02explains the birth
27:04of many of these
27:05cosmic bullets.
27:06But then we discovered
27:08a super gamma ray
27:09so powerful,
27:11it must have
27:12a completely different
27:13origin story.
27:15So this gamma ray
27:16was incredibly high energy,
27:18which means that
27:19the cosmic ray
27:20responsible for it
27:21was probably also
27:22extremely high in energy.
27:24If you fire a bullet
27:25into a pinball machine,
27:26it's not going to
27:26bounce back and forth.
27:29It's just going to
27:29break through the machinery.
27:31And the problem is
27:32that these are vastly
27:33more energetic
27:34than that.
27:35So there's no way
27:36they could have been
27:37bouncing around
27:38all the way up
27:39to their current energies
27:40inside of that
27:42particular pinball machine.
27:43There must be
27:46something else
27:47in the Milky Way
27:48creating
27:48galactic cosmic rays.
27:51Something
27:52more powerful
27:53than a supernova.
27:56The question is,
27:57what?
28:01January 2021.
28:03At an observatory
28:05high up on the side
28:06of a Mexican volcano,
28:08blue light
28:09zaps through
28:10water tanks.
28:11signs of
28:14incoming gamma rays.
28:16Their trail
28:17stretches back
28:18across the Milky Way,
28:20crossing billions
28:21of miles,
28:22but suddenly
28:23goes cold.
28:25Instead of originating
28:27in a huge explosion,
28:29the trail ends
28:30in a cold,
28:31sparse cloud
28:32of dust.
28:34Molecular clouds
28:35at first glance
28:36seem like
28:37one of the most
28:37boring,
28:39innocuous
28:39places in the universe.
28:41You can barely
28:42even see them
28:43without an
28:44infrared telescope.
28:46They're not
28:46events like
28:47supernova
28:48that have
28:49enormously
28:49high energies,
28:50so you wouldn't
28:51expect to create
28:52super energetic
28:53particles.
28:54Something must
28:55be hidden
28:56in the cloud.
28:57Something powerful
28:58enough to
28:59accelerate
29:00the cosmic rays.
29:02We just
29:02don't know
29:02what.
29:03We can't
29:04see inside
29:05the molecular
29:06clouds,
29:06so it
29:07could be
29:08that
29:09deep inside
29:10them there
29:10are clusters
29:11of newborn
29:12stars that
29:12are cranking
29:13out these
29:14cosmic rays.
29:15But we
29:15don't know
29:16if even
29:16the crankiest
29:18of stars
29:18are capable
29:19of producing
29:20cosmic rays
29:21at these
29:21energies.
29:24Just two
29:25months later,
29:25in March
29:26of 2021,
29:27we get
29:28another clue.
29:29Scientists
29:30detect gamma
29:31rays coming
29:32from the
29:32Cygnus
29:33Cocoon
29:33nebula.
29:35It's a
29:36dense,
29:36molecular
29:37cloud
29:37with a
29:38difference.
29:40At the
29:40center is
29:41a cavity.
29:42Hundreds
29:42of closely
29:43packed stars
29:44push against
29:46the dust
29:47and gas,
29:48including
29:48huge,
29:49bright stars
29:50called
29:51spectral
29:51type O
29:52and B.
29:54Spectral
29:55type O
29:55and B
29:56stars are
29:56some of
29:57the hottest
29:57stars in
29:58our universe.
29:59The
30:00massive stars
30:01blast out
30:02solar winds
30:02far stronger
30:03than the wind
30:04produced by
30:04our sun.
30:06When you
30:07think about
30:07all these
30:08stars forming
30:08together,
30:09they are all
30:10putting off
30:10a wind of
30:11high-energy
30:12particles from
30:13their surfaces.
30:14These winds
30:14collide and form
30:15big shock
30:16structures between
30:17all of these
30:18young stars.
30:19You're getting
30:19so much energy
30:20from so many
30:21different winds
30:22coming from
30:23so many
30:23different directions
30:24that it forms
30:25a boiling mass
30:27of shock waves
30:28and magnetic
30:29fields.
30:30It's a pinball
30:30machine on a
30:31far bigger scale.
30:33The magnetic
30:34fields are
30:35stronger than
30:35the supernovas,
30:37trapping and
30:37accelerating the
30:39more energetic
30:39cosmic rays for
30:41longer.
30:42One important
30:43thing about
30:43star clusters is
30:44that they're
30:45around for
30:45millions and
30:46millions of
30:47years.
30:47It's not just
30:48a one-off
30:48event like a
30:49supernova.
30:50And so you've
30:51got this magnetic
30:52field and these
30:53shocks happening
30:54over a long
30:55period of time,
30:56and that may be
30:57what you need to
30:57accelerate cosmic
30:58rays.
30:58Molecular clouds
31:01may shoot out
31:02galactic cosmic
31:03rays, but what
31:05fires the
31:06hypersonic space
31:07missiles, the
31:08ultra-high-energy
31:09cosmic rays?
31:11The culprit may
31:12be hiding out in
31:13distant galaxies,
31:15supermassive black
31:17holes.
31:17ultra-high-energy
31:26cosmic rays are
31:28the hypersonic
31:29missiles of the
31:30particle world.
31:31If a photon of
31:32light, the fastest
31:33thing in the
31:34universe, had a
31:35race with an
31:36ultra-high-energy
31:36cosmic ray, it
31:38would be so close
31:39that after 200,000
31:41years, that photon
31:43would be half an
31:44inch ahead of the
31:45ultra-high-energy
31:45cosmic ray.
31:47They appear to
31:49come from beyond
31:50our Milky Way
31:50galaxy.
31:52Our galaxy is
31:53100,000 light
31:55years across.
31:56The next nearest
31:57galaxy to us is
31:582 million light
31:59years away.
32:00So these are
32:01traveling to us
32:02across millions
32:03and billions of
32:04light years.
32:06How do you
32:07accelerate this
32:09tiny little
32:10particle to such
32:11insane
32:12velocities?
32:14What is the
32:16power source?
32:16What in the
32:17universe has
32:18that kind of
32:19capability?
32:20Where's the
32:21Death Star here?
32:23Their speed
32:23makes them
32:24dangerous, but
32:26it also makes it
32:26easier to find
32:28their source.
32:29Ultra-high-energy
32:30cosmic rays are
32:31moving so rapidly
32:32that they're really
32:33not affected that
32:34much by magnetic
32:35fields.
32:36It's like a bullet
32:36going through a
32:37fisherman's net.
32:38And so they're
32:39coming mostly in a
32:40straight line.
32:42When they're coming
32:43in a straight line,
32:44we can point back
32:45to their origin.
32:46And that's something
32:47we can use to figure
32:48out where and how
32:50they're getting
32:50accelerated.
32:53In the Argentinian
32:54desert, the
32:55Pierre Auger cosmic
32:56ray detector completes
32:58a 12-year study of
33:00the sky.
33:02It confirms that most
33:04galaxies have a
33:05supermassive black
33:06hole at their center,
33:08but only a few are
33:09active, shooting out
33:11energy.
33:11These active
33:13supermassive black
33:14holes also blast
33:16out ultra-high-energy
33:17cosmic rays.
33:20Supermassive black
33:21holes are already
33:22extremely powerful, so
33:24it makes a lot of
33:24sense to me that the
33:25ultra-high-energy
33:26cosmic rays could
33:27originate at
33:28supermassive black
33:29holes.
33:30The M87 galaxy is
33:3354 million light-years
33:35away.
33:36It's famous because
33:37we took a photo of
33:39the supermassive black
33:40hole at its
33:41core.
33:42So the Event Horizon
33:43Telescope image of
33:45the swirling vortex of
33:46gas around that
33:47central black hole, that
33:48shadow that you can't
33:50actually see, that
33:51could be a site for
33:53the unbelievably
33:55energetic acceleration
33:56of cosmic rays.
33:58In March 2021,
34:01scientists analyzed
34:02the data further.
34:04This new image of
34:05M87 shows very clear
34:07magnetic field lines,
34:09which is really
34:09stunning and reminds us
34:11of how much energy
34:12could be contained
34:13close to the
34:14supermassive black
34:15hole.
34:15Black holes have
34:17enormous power, but
34:18how do they transfer
34:19some of that energy to
34:21a tiny particle?
34:23One possibility for how
34:24supermassive black
34:25holes could accelerate
34:26such enormously
34:27energetic cosmic rays is
34:29that they actually drag
34:31or capture via their
34:32gravity pre-existing
34:34normal cosmic rays,
34:36which are already
34:37extremely energetic, and
34:38then give them an extra
34:39boost to even higher
34:41energies.
34:42So supermassive black
34:43holes bend the fabric of
34:45space-time around them,
34:47and even light particles
34:48can get stuck.
34:50And cosmic rays are no
34:51different.
34:51They can also be attracted
34:53by the supermassive black
34:54holes and get drawn into
34:56their orbit.
34:56It makes sense that the
34:59black hole captures passing
35:01cosmic rays, but how do
35:03the particles escape its
35:05clutches and hurdle
35:06towards us?
35:09M87 has a fearsome weapon
35:11in its arsenal.
35:13Enormous jets of energy
35:14blast out of its poles.
35:16So M87's jets are
35:19spectacularly large, larger
35:22than the entire galaxy that
35:23houses this black hole that's
35:24launching those jets.
35:26The powerful jets may give
35:27the cosmic rays a speed
35:29injection, transforming them
35:31from galactic rifle bullets
35:33into ultra-high-energy
35:35hypersonic missiles.
35:37So imagine if you had a
35:40regular bullet that you fired
35:42out of a gun at high speed,
35:43and as it's flying, a little
35:47rocket motor in the bullet
35:48kicks in and takes it up
35:50to even higher speed.
35:53That's sort of what's
35:54happening to the cosmic rays
35:56in these jets.
35:58Black holes may be the
36:00supervillains we've been
36:01looking for, firing out the
36:03fastest cosmic bullets.
36:05But cosmic rays have a
36:07superpower of their own.
36:09They're time travelers.
36:13Cosmic rays race through the
36:20universe at close to the
36:21speed of light.
36:23Like subatomic bullets,
36:25they can pierce spaceships
36:26and harm astronauts.
36:32But down on Earth, we're
36:34protected.
36:36Out of all of the rocky
36:39inner planets in the solar
36:41system, the Earth is the only
36:44one to generate its own
36:45deflector shield against
36:46this cosmic radiation.
36:49That's amazing, and that's
36:50where life is.
36:51I don't think that's actually
36:52all that much of a
36:53coincidence.
36:54The Earth creates its own
36:56magnetic field.
36:58The Earth has this
36:59wonderful active molten
37:00core of metal.
37:02All of that metal is moving
37:03around inside the Earth, and
37:05that moving metal generates a
37:06strong magnetic field.
37:08These cosmic rays are
37:09electrically charged.
37:10They follow a magnetic field.
37:12So our magnetic field deflects
37:14most of the cosmic rays
37:15around it.
37:16The shield is not perfect.
37:19Some cosmic rays do get
37:20through, but then they hit our
37:23second line of defense, the
37:25atmosphere.
37:27One of the things we have to be
37:27thankful for is our atmosphere.
37:29Not only does it give us air to
37:30breathe, but it protects us from
37:32these space bullets.
37:33The atmosphere is like a missile
37:36defense system.
37:37cosmic rays collide with air
37:40molecules, shattering into safer,
37:43smaller particles.
37:45The most common ones are called
37:48muons.
37:49The muons are the children of the
37:53cosmic rays.
37:54They're produced by these high-energy
37:57collisions in our upper atmosphere
37:59that create these showers of muons
38:01that then come down to the surface.
38:03There's as many as four of these
38:05cosmic rays passing through my hand
38:07every second.
38:08They're passing through your body
38:09right now.
38:10Muons are so abundant, we don't need a
38:13high-tech observatory to detect them.
38:15Just a few things you'd find in a high
38:17school science lab.
38:19A small aquarium that I've attached a
38:22small piece of felt to the bottom.
38:25Some frozen carbon dioxide, some dry ice,
38:28hence the safety gloves.
38:30A flat piece of metal like this.
38:34Some isopropyl alcohol.
38:37Then I flip the whole thing over onto
38:41the bottom and I wait.
38:45So what's happening is that the alcohol
38:48in the felt is evaporating and sinking
38:51down.
38:52And because that bottom layer is so cold
38:55from the dry ice, it forms a super-saturated
38:58cloud of alcohol vapor.
39:02When the charged particles pass through
39:04the cold vapor, they create tiny, ghostly
39:08trails.
39:10What we're looking for are the muons,
39:13the subatomic particles generated when a
39:16cosmic ray strikes the upper atmosphere.
39:19Each silvery thread in the cloud chamber
39:22is the sign of a cosmic ray.
39:25These muons should never make it down to
39:28Earth at all.
39:29They only live for 2.2 microseconds
39:32before breaking up.
39:34Not enough time to travel through six miles
39:37of Earth's atmosphere.
39:39Naively, we would think there's no way that a muon
39:41could make it from the upper atmosphere
39:43to where we are now without decaying.
39:46It turns out they do.
39:47And the only way they do this is they
39:48effectively time travel.
39:50The muons move at 98% the speed of light.
39:56They move so fast, they experience what
39:59Einstein called time dilation.
40:03Albert Einstein taught us that we live in a
40:05space-time.
40:06And so that means that all measurements of
40:08lengths and durations of time are relative.
40:12From a muon's perspective, we humans move
40:15incredibly slowly.
40:18They're moving so fast that for them,
40:21time is stretched out.
40:24What we found by measuring the energy
40:27and the lifetime of muons is that as muons
40:31got closer to the speed of light,
40:33their lifetime increased because to them,
40:38time is slowing down exactly the way
40:40Einstein predicted.
40:42Their lifespan is extended by more than 20 times
40:45from our perspective.
40:47So they make it to the ground.
40:52Cosmic rays are the ultimate space travelers.
40:56Their awe-inspiring speed allows us
40:59to unlock hidden processes
41:01and test our theories of physics.
41:05They're way more energetic than anything
41:07we can do in a laboratory on Earth.
41:09So that means we can unlock all kinds of new domains
41:11about physics at the highest, most extreme energies.
41:15They're our best link
41:17to the farthest reaches of the cosmos.
41:20To me, it's really exciting
41:22that we're actually sampling pieces of matter
41:25from distant stars, from distant galaxies,
41:29and we're getting them here at Earth
41:31and studying them.
41:34There are so many amazingly violent events
41:37in the universe,
41:38the birth of black holes, exploding stars.
41:40These cosmic rays that are going through your body
41:42right now are messengers from those events.
41:46In some way, you're still connected to those events
41:48millions of light years away.
41:52These are messengers from the universe
41:54telling us about how it works.
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