We Found the Most Powerful Object in the Universe

0:00 From Earth, the night sky appears ethereal, peaceful.

0:05 It's so far removed from human civilization.

0:08 You'd be forgiven for thinking we're immune to anything going on up there.

0:13 But that couldn't be further from the truth.

0:16 We are under attack.

0:18 Cosmic rays are bombarding us from every direction.

0:22 tiny particles that collide with our planet's atmosphere,

0:25 setting off a chain reaction of ionization that can

0:28 render our satellites and other electronic machinery useless.

0:33 But where do they come from?

0:36 For hundreds of years, astrophysicists have searched in vain to find

0:40 the origin of these elusive attackers with little success.

0:44 Even the type of source has evaded their searches.

0:48 But now, thanks to a whole new field of research,

0:52 we're starting to find answers.

0:55 Not only do we now know what to look

0:57 for, but they are proving more powerful than we ever imagined.

1:03 What in the cosmos is possibly capable

1:06 of producing a quadrillion electron volts of energy?

1:11 I'm Alex Mccoan and you're watching Astramm.

1:14 Join me as we follow the trail of cosmic rays,

1:18 leading us right to the limits of physics as we know it.

1:21 We'll see how scientists detect the highest energy

1:24 particles in the universe and meet a new

1:27 class of astronomical objects whose extreme behavior until

1:32 recently seemed like the stuff of science fiction.

1:37 The Milky Way is full of energy,

1:40 but our eyes can only detect a tiny fraction of it.

1:44 Beyond the spectrum of visible light,

1:47 charged particles can give off higher energy radiation

1:49 in the form of X-rays and gamma rays,

1:52 creating a mess of energetic fingerprints throughout space.

1:57 Astronomers can forensically decode these cosmic clues

2:00 to understand the flow of energy through our galaxy.

2:04 But among these charged particles,

2:06 there is one group in particular that remains clouded in mystery.

2:12 Back in 1912, the Austrian physicist Victor

2:15 Hess made a historic air balloon ascent up to 5,300 m where he could measure

2:22 the rate of ionization in the upper atmosphere,

2:24 or how quickly atoms and molecules are becoming charged.

2:29 He expected to find that it decreased at higher altitudes,

2:33 confirming the prevailing theories at the time.

2:35 However, this was not to be.

2:38 Unexpectedly, Hess recorded a rate of ionization

2:42 that reached three times higher than at sea level.

2:46 This led to the realization that the ionizing radiation he had

2:49 dedicated his career to studying came not from Earth, but from space.

2:55 He had discovered cosmic rays and they did not come in peace.

3:02 Earth is under constant barrage from them.

3:06 These high energy particles, mostly protons,

3:09 travel at nearly the speed of light and collide with our planet's atmosphere,

3:14 sending a shower of secondary particles down onto its surface.

3:19 These attacks can do some serious damage.

3:22 The secondary particles produced in cosmic ray showers the likes of muons,

3:27 neutrons, electrons, posetrons and gamma rays can interact with living

3:32 organisms contributing to genetic mutations and radiation damage.

3:37 And when cosmic rays interact with satellites or other orbiting electronics,

3:42 they can trigger a bout of ionization that can

3:45 cause the circuits to degrade or even fail catastrophically.

3:50 And they are not only a nuisance to our best space equipment.

3:54 Cosmic rays have meddled with our best scientists, too.

3:58 For more than 100 years, the question of where cosmic rays come from has been

4:03 one of the major unsolved mysteries in high energy astrophysics.

4:07 Their physical properties make them almost impossible to track.

4:10 Magnetic fields bend their path before we can locate their origin,

4:14 and they break down into a shower

4:16 of particles before we can learn their identity.

4:20 These challenges are laid bare when scientists

4:23 try to measure the cosmic ray spectrum.

4:26 If you plot the number of incoming high

4:28 energy particles as a function of their energy,

4:31 you notice a distinct steepening point known as the knee beyond which the really

4:37 high energy cosmic rays above four pa electron volts are much less common.

4:45 At first, some scientists assumed that this knee must mark the boundary between

4:50 cosmic rays coming from inside our Milky Way and those coming from beyond.

4:55 Others simply didn't know.

4:57 But just as scientists were about to accept defeat,

5:01 one observatory stepped in to revolutionize

5:04 the search for these sneaky interlopers.

5:08 Before I start revealing the mystery, want to have a crack at it yourself?

5:12 Of course, you'll need the right equipment,

5:14 but even if you don't have a full observatory in your backyard,

5:17 you can still see the wonders of the universe,

5:20 galaxies, or the remnants of dead stars like the Crab

5:22 Nebula in incredible detail using the Dwarf Mini Telescope,

5:27 who've kindly sponsored this video.

5:29 Check out this image of the Crab Nebula taken by one user,

5:32 Julia Rash, using this book-sized ultra portable telescope.

5:37 Julia only had a small window to take this image as it had been

5:40 the first clear night in 4 weeks and there was work in the morning.

5:44 But just look at the result she achieved.

5:47 This was thanks to the Dwarf Min's ability to autotrack stars,

5:51 letting it quickly orient itself towards

5:53 your preferred target and its live stacking function.

5:55 By overlapping multiple photos, it produces these really clear images

5:59 of beautiful deep space objects in our cosmos.

6:02 I'm a big fan of this telescope and can't recommend

6:05 this enough for someone who's looking to get into astronomy.

6:09 So, scan our QR code or follow the link

6:11 in the description below to see for yourself.

6:13 Astronomy enthusiasts who use the code astron

6:16 5 at checkout get 5% off their purchase.

6:19 Now, enough waiting.

6:21 It's time to take a look at the observatory that's

6:23 helping solve the mysteries of these incredibly high energy cosmic rays.

6:29 The large high alitude air shower

6:31 observatory is a groundbased observatory located

6:34 nearly 4,500 meters above sea level in the mountains of Sichuan province, China.

6:42 It has one main objective to find the highest energy particles in the universe.

6:49 The chief scientist on this mission is Professor Ten

6:52 Cao who gave Astramm an exclusive interview about Lasso's work.

6:57 He said to make good measurements for the knee of the cosmic ray spectrum,

7:01 you need two things.

7:03 The detector must be big enough and it must be able

7:07 to identify the original particle from the air shower it creates.

7:12 Cosmic rays become more rare the higher the energy.

7:15 For the highest energy particles,

7:17 less than one per square kilometer per century is expected to hit Earth.

7:23 To combat this issue,

7:25 you need detectors spanning a whole lot more than a square kilometer,

7:29 which is why lasso covers an area the size of 190 football fields.

7:36 As for identifying the particles,

7:38 I mentioned that the cosmic rays produce a shower

7:41 of secondary particles when they collide with the atmosphere.

7:45 And this is what scientists use.

7:47 They must essentially piece the debris together to work

7:50 out whether the original particle was a proton,

7:53 a helium nucleus, or something heavier.

7:56 This is a tricky process as you need to make sure you catch all the fallout.

8:01 But Lasso is one of the most

8:03 welle equipped observatories to tackle the challenge.

8:06 It has at least three types of interconnected detectors in an array

8:11 to capture the shower and then identify the original cosmic ray particle.

8:16 This unparalleled ability pretty quickly led to the team's first big discovery.

8:23 Professor Cow said, "At the time, we only had around half of Lasso built.

8:28 We put it into operation for around half a year

8:31 and suddenly found that there were so many gamma rays.

8:35 By 2021, Lasso had detected gammaray photons with energies

8:39 exceeding one pa electron volt or one quadrillion electron volts.

8:46 and one at 1.4 quadrillion electron volts,

8:50 making it the highest energy photon ever observed.

8:54 For context, that's nearly 150 times more energy than

8:58 the fastest protons accelerated by the Large Hadron Collider.

9:03 Now, the laws of energy conservation tell us that PETA

9:06 electron volt particles don't just appear out of nowhere.

9:10 That colossal amount of energy has to be

9:13 transferred to the particles from a source.

9:16 Scientists had been theorizing about such a source for decades.

9:20 But Lasso's finding proved its existence once and for all.

9:25 The Pevatron.

9:28 Pevatrons are any source capable of accelerating

9:31 particles to a pael electron vault of energy.

9:34 And their existence promised to revolutionize the hunt for cosmic rays.

9:39 But how do we find them?

9:42 Luckily, Lasso wasn't finished.

9:44 Gamma rays are useful because they are neutral in terms of their charge,

9:49 so they can travel in straight lines throughout

9:50 the universe without being bent by magnetic fields.

9:54 This added a new dimension to Lasso's work.

9:57 It could trace back to where the gamma rays had come from.

10:01 Mapping these traces across the sky,

10:03 scientists identified 12 distinct sources capable

10:06 of producing ultra high energy gamma rays,

10:10 several of which showed signs of accelerating

10:12 particles to a quadrillion electron volts.

10:16 There was a catch though.

10:17 Lasso may have identified the general direction of these gammaray sources,

10:22 but scientists had no idea how far away they were.

10:26 12 lines of sight stretching out endlessly

10:28 into space isn't exactly a narrow search field.

10:32 Except scientists knew something else about

10:34 these gamma rays that would tighten the net.

10:38 The universe has been full of photons since the big bang.

10:41 And these photons are very cold with low energies.

10:45 Gamma rays at ultra high energies are

10:47 very likely to collide with these background photons.

10:50 And when they do, they vanish.

10:53 This means that gamma rays simply can't travel vast distances through space.

10:58 So if lasso was detecting them here on Earth,

11:02 then they couldn't have traveled very far.

11:05 In fact, there is no way that these 12

11:07 high energy sources could be extra galactic.

11:11 They must be inside our Milky Way.

11:14 Not only did this tell scientists that the knee,

11:17 the bend in the graph we saw earlier,

11:19 had nothing to do with cosmic rays coming from outside the Milky Way,

11:23 but it brought the search for them much closer to home.

11:27 The race was on.

11:31 Now, before Lassa's work,

11:33 astrophysicists had developed theories about the production of cosmic

11:36 rays and which type of source could be responsible.

11:40 After all, space is a weird and wonderful place,

11:44 home to several unusual objects displaying extreme behavior.

11:48 But which of these oddities were

11:50 capable of producing the highest energy particles?

11:53 And how?

11:55 For the past 70 years, a popular idea was that supernova remnants

12:00 played a key role in producing cosmic rays.

12:03 They certainly have enough energy for it.

12:05 In fact, calculations show that if they converted just

12:09 10 to 20% of their kinetic energy into accelerated particles,

12:14 supernova remnants could supply most of the cosmic rays we see in our galaxy.

12:20 See, when a star goes supernova, it drives material out into interstellar space,

12:26 forming a collisionless shock wave just ahead of it,

12:29 where there is a sharp change in density, magnetic fields, and pressure.

12:35 When a particle hits this shock wave,

12:37 it gets bounced back and forth across the shock front, gaining energy each time.

12:43 Particles can propagate here for some time up to thousands of years.

12:48 And the longer they spend there, the higher the energy can become.

12:52 This process is known as diffusive shock acceleration or the the mechanism.

12:58 But although supernova remnants can accelerate particles in this way,

13:02 reaching better electron volt energies may still be tricky.

13:06 Theoretical models suggest that supernova

13:08 remnants are only capable of accelerating

13:11 particles to these extremes during the first 100 years of their life.

13:16 And all the supernova remnants we know of are much older.

13:21 However, there might be one scenario where supernova remnants can

13:25 act as a source for ultra high energy gamma rays.

13:29 If they gain enough energy to overpower the magnetic forces that confine them,

13:34 some accelerated particles may escape the supernova remnant

13:38 and get trapped in nearby giant molecular clouds.

13:42 Here, they can interact with the dense gas and produce

13:45 gamma rays with energies up to one quadrillion electron volts.

13:49 even if the supernova remnant itself is

13:52 no longer capable of pael electron fault acceleration.

13:56 So supernova remnants show some potential as cosmic ray producers.

14:01 Up to six of the 12 lasso candidates could be associated with them,

14:07 but they're not the main type of source we should be looking at.

14:11 There's another source capable of creating even higher energies, pulsars.

14:18 We've covered pulsars on the channel before,

14:21 so feel free to check out some of the previous videos for more information,

14:24 but as a quick recap, pulsars are highly magnetized rotating

14:29 neutron stars created in supernova explosions.

14:32 We have now detected over 1,500 pulsars.

14:36 But how could they create such high power gamma rays?

14:40 Well, they're already proven to be

14:42 capable of accelerating electrons and posetrons

14:45 since the dense and highly magnetized

14:47 structure rotates to produce powerful electric fields.

14:51 These electric fields can strip electrons from the stars surface

14:54 forming a wind of particles that expands outwards at rapid speeds.

14:59 And once this wind reaches the surrounding material,

15:02 like the gas or dust from a nebula,

15:05 it suddenly slows down, forming a termination shock.

15:09 At this shock point, the particles are accelerated to extremely high energies.

15:16 You can think of it like water flowing in a stream.

15:19 Normally, the flow is smooth, but if you place an obstacle in the way,

15:23 some water will spill out, and this water will be flowing much faster.

15:28 The Lasso team believed that more than 30%

15:31 of the candidate Everrons they detected could be associated with pulsars,

15:36 making them a key player in the search for cosmic rays.

15:41 The final type of cosmic ray source came as a bit of a surprise to scientists.

15:46 If we take another look at the spectrum and zoom into the knee shape,

15:50 you see not a smooth line, but a hump.

15:54 In other words, an anomaly.

15:57 The properties of these cosmic rays didn't fit with them coming

16:01 from a known source like a supernova remnant or a pulsar,

16:05 which meant they must have been created by another type of source.

16:10 This required scientists to think outside the box and proposed

16:14 some other less traditional ways that particles could be accelerated.

16:18 And with that, they recognized what could be

16:21 described as nature's ultimate particle accelerators, black holes.

16:27 The idea that black holes could produce high

16:29 energy particles had been discussed way back in 2009.

16:34 Named the Bardos Silk West effect after the scientists who came up with it.

16:38 It describes a phenomenon where if two particles move

16:41 towards a black hole and collide near the event horizon,

16:45 they could reach near unlimited energies.

16:49 However, this theory was thought to be effectively useless since the particles

16:53 would no doubt be sucked into the black hole and lost forever.

16:57 That was until more recent years when newer models revealed that a fraction

17:02 of the particles would more likely be ejected back out into space.

17:07 Free of the black hole,

17:08 these particles could travel through space as none other than cosmic rays.

17:14 Now, we've discussed some of the theory behind cosmic rays

17:17 and where they come from, but it begs the question, what have we actually found?

17:24 The main thing to understand about this search is that it's really hard.

17:28 Lasso may have identified 12 candidate Hevatrons in our galaxy,

17:33 but finding the actual object responsible is a whole other task.

17:38 That aside, the search is still ongoing, and a few sources have been found.

17:44 So, without further ado, let's take a look.

17:48 One of the first objects pinned down may be familiar to you.

17:52 The Crab Nebula, known as Messia 1, it's a supernova remnant found around 6,500

17:59 lighty years away in the constellation Taurus.

18:02 Although stunning to look at, Messia 1 is not just a pretty face.

18:07 It's capable of accelerating electrons

18:09 to a quadrillion electron volts of energy.

18:13 And as one of the best studied objects in the known universe,

18:16 observing Messia 1 gives astronomers a good

18:19 insight into how nature's particle accelerators work.

18:23 In the gammaray domain, Messia 1 shows some extreme variability.

18:29 It produces intense flares which can last anywhere

18:32 between a few hours to a few days.

18:35 And with our new understanding of pevetrons,

18:38 scientists realized that these flares were

18:40 the photons resulting from some serious electron acceleration.

18:45 Exactly how this happens has been debated.

18:49 It could be DSA at the boundary between

18:51 the particle wind and the medium surrounding the pulsar,

18:55 energy released by magnetic field lines breaking and reconnecting,

18:59 or a more complex mechanism within the particle wind itself.

19:04 For context, electrons at high energies transfer

19:07 part of their energy to background photons,

19:09 boosting them to gamma rays that scientists can detect.

19:12 However, accelerating electrons is really difficult

19:15 because they lose energy very quickly.

19:18 To produce gamma rays with energies of a quadrillion electron volts,

19:22 the electrons themselves must have had several times that energy.

19:27 This proves that Messia 1 is undoubtedly

19:30 a Pevotron and an impressive one at that.

19:34 However, this has only been proven for electrons,

19:37 making Messia 1 what scientists call electronic accelerator.

19:42 But pevetrons are capable of accelerating any charged particle.

19:47 And if you remember, cosmic rays are mostly protons.

19:51 So, it's these pevetrons, otherwise known as hydronic accelerators,

19:55 that scientists are most keen to find.

20:00 I mentioned that lasso detected a photon at 1.4 peta electron volts,

20:05 the highest energy photon ever observed.

20:09 With such mindblowing energy,

20:11 scientists were keen to see where it came from, which

20:14 led them to our next candidate, the Signis region.

20:19 The Signis constellation is one of the most recognizable in the northern sky,

20:24 spanning more than 800 square degrees or 4,000 full moons.

20:29 And it was here that scientists found some seriously interesting stuff.

20:34 Lasso found lots of petal electron vault photons inside the Signis Cocoon,

20:39 a huge superb bubble which surrounds a region of massive star formation.

20:44 Inside the bubble is a massive young

20:47 star cluster known as the Signis OB2 Association.

20:52 This is a very active place and the many young

20:56 massive stars can create a strong wind which accelerates particles.

21:01 Signis OB2 is found nearly 5,000 lightyears from Earth and it lines

21:05 up pretty well with some of the gamma rays observed by Lasso.

21:09 But as I mentioned, these gamma rays only indicate

21:12 the general direction of a pevetron, not its distance.

21:16 So scientists can often struggle to identify

21:19 the origin of a signal among several possible sources.

21:23 And in the case of Signis, there are plenty of energetic objects to choose from.

21:28 In a similar direction to OB2, but further away,

21:32 there is an X-ray binary known as Signis X3.

21:36 It consists of a donor star and a compact

21:39 object likely a black hole or neutron star.

21:43 The donor is a wolf ray star meaning it is extremely hot

21:47 and massive and it feeds material

21:50 into the compact object through strong stellar winds.

21:53 This combined with the compact object which releases powerful

21:57 jets of plasma creates the perfect conditions for particle acceleration.

22:03 At first, it seemed impossible to tell which

22:05 system Lasso was detecting PA electron volt signals from.

22:09 But on taking a closer look at the signal itself,

22:12 scientists noticed something unique.

22:15 There was a temporal feature of the signals.

22:18 A pattern that repeated every 4.8 hours, seen not just in the gamma rays,

22:24 but in the X-rays and the infrared radiation, too.

22:28 But where was the pattern coming from?

22:30 On further investigation, scientists realize the truth.

22:34 Every 4.8 hours, the black hole of Signis X3 orbits its massive donor star.

22:42 Suddenly, scientists could be certain the gamma rays were coming

22:45 from Signis X3 and that they had found another Pevotron.

22:50 Signis X3 was a particularly intriguing object.

22:54 For one thing, the highest energy photons

22:57 from this object already measured 3.7 pa electron volts.

23:02 And since photons are radiated by accelerated protons,

23:06 the energy of the proton must be several times larger.

23:10 What that suggests is that Signis X3 is not just a pevatron,

23:15 but a super pevetron capable of accelerating

23:19 protons to at least 10 pa electron volts.

23:24 We've had a whistle stop tour of some

23:26 of the most exciting pevatrons we found so far,

23:30 but what does the future hold for this ultra powered search?

23:35 And where will it take us?

23:37 Hunting 12 candidate pevetrons seemed hard enough,

23:41 but since Lasso's first finding, that number has boomed.

23:45 Lasso published the first global catalog of galactic pevatrons

23:49 in 2023 detailing 43 ultra high energy gammaray sources.

23:56 But now 2 years later and with continued monitoring from observatories around

24:02 the world the number of sources has risen to more than 75.

24:07 With so many candidate pevatrons hiding in our Milky Way,

24:11 we need to seriously rethink our perception

24:13 of the galaxy and what it's capable of.

24:16 Many thought that the Milky Way was a relatively peaceful place since

24:20 it lacks the massive black holes

24:22 typical of galaxies with violent energetic pasts.

24:26 However, Lasso's work has proven this to be an outdated

24:29 assumption and is changing the landscape of our non-thermal universe,

24:34 starting with our own cosmic home.

24:38 It's definitely an exciting time to be hunting cosmic rays.

24:41 Lasso is collaborating with several other observatories

24:44 detecting high energy gamma rays around the world,

24:48 including the US, Germany, Namibia, and Spain.

24:52 This international network has fostered an open

24:55 and collaborative approach to their experiments,

24:58 sharing data and cooperating evidence.

25:01 Their goal is to build up a comprehensive spectrum of photons across

25:06 different energies as well as measuring

25:09 X-rays and gamma rays above Earth's atmosphere.

25:13 I want to give a huge thanks to Professor K

25:16 for his expertise on the world of high energy astrophysics.

25:20 As I'm sure you'll agree,

25:21 studying peveratrons is a dynamic and rapidly developing field,

25:26 and observatories like Lasso are on the front line.

25:29 Their work so far has transformed our galaxy from a tranquil place to a violent,

25:34 energetic mess filled with particle accelerators,

25:38 more powerful than anything we can build here on Earth.

25:41 We may still be under attack from cosmic rays,

25:44 but now we're ready to chase them back to their hiding places.

25:51 Thanks for watching.

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