The Space Explosion So Powerful, It Compressed Our Atmosphere from 2 Billion Light Years Away

In October 2022, a brilliant flash pierced  the cosmos, brighter and more intense than anything human civilization had ever seen.  And that’s not an exaggeration. The strength of the blast blinded our gamma ray detectors  the world-over, and unleashed more energy in a matter of seconds than our sun will emit  over its entire 9-billion-year lifespan.

Over the 18 months that followed,  it became the most widely studied gamma-ray burst in history, creatively dubbed  the BOAT, for “brightest of all time”. As researchers began to decipher its cause, their  findings unravelled one mystery after another. Scientists have been cataloguing gamma-ray  bursts for decades, but this one was closer, brighter, and unexplainably devoid of  some key signatures you’d expect to see.

It also raises some far-reaching  questions about our Standard Model, the possibility of a dark matter particle,  and how heavy elements like gold are made. I’m Alex McColgan, and you’re watching  Astrum. Join me today as we dive into the mystery of the biggest and brightest  gamma-ray burst of all time.

What caused such a colossal explosion? How is it different  from other gamma-ray bursts before it? And what can it teach us about our understanding of the  universe and the particles that constitute it?

— Gamma-ray bursts are brief, intense flashes of high-energy gamma radiation lasting  from milliseconds to several minutes. The first of its kind was detected in 1967,  when American satellites designed for detecting covert Soviet nuclear testing picked up an  unusual pattern of electromagnetic energy. Since then, gamma-ray bursts have been of  tremendous interest to the cosmological community, as they allow scientists to study states of matter  and physics that are not reproducible on Earth.

Essentially, they provide researchers  with a glimpse of how stars are formed and evolve across the whole  timeline of the universe. There are two different kinds of gamma-ray bursts.  Short gamma-ray bursts last less than two seconds, and are attributed to either the  collision of two neutron stars, or the merger of a neutron star and a black  hole.

They can be followed by a kilonova, an emission of bright light resulting from the  radioactive decay of chemical elements. This decay creates even heavier elements, an important  feature of novae which we’ll discuss more later. Anything lasting longer than two seconds  is classed as a long gamma-ray burst.

These are thought to be caused by the  explosive deaths of massive stars, and their subsequent supernovae. The collapsed  core may form either a neutron star or a black hole. These typically occur close to  the edges of the observable universe, because they are characteristic of low-metallicity  stars which formed when there were less heavy elements around.

When we see one of these, we’re  witnessing events from billions of years ago! In the case of both long and short gamma-ray  bursts, the newly-formed black hole blasts out jets in opposing directions, containing  particles accelerated close to the speed of light. When these particles interact with surrounding  matter, they emit the gamma rays we detect.

So what made the BOAT so special? Let’s start  by analysing some of its key characteristics. Firstly, the BOAT lasted 10 whole  minutes, and was detectable for 10 hours after-the-fact.

It occurred in the Sagitta  constellation, only 2 billion light years away, which is much closer than other gamma-ray  bursts we’ve detected, until now. In fact, such a bright explosion so close to  Earth is thought to be a 1 in 10,000 year event, meaning the last time one happened,  humans had barely started farming. As is the case with other long  gamma rays, we know a collapsing and exploding star was behind it - but  this is where things start to get fuzzy.

— A supernova alone isn’t enough to explain the  magnitude of the gamma rays emitted - the BOAT was a whopping 70 times stronger than any  other gamma-ray burst detected. Initially, the theory was that this must be  the supernova of a ginormous star, the likes of which we rarely see. However,  upon closer inspection of the afterglow, scientists found that the supernova  behind the BOAT was shockingly…ordinary.

To get a clearer picture, astronomers  pointed the James Webb Space Telescope in the BOAT’s direction. Webb’s  near-infrared spectrograph revealed that the supernova behind the BOAT was  actually pretty average. It wasn’t nearly as bright as you’d expect given the  gamma-ray burst that accompanied it.

So what could’ve caused such a flash? One idea is that we simply  perceive the flash as bigger and brighter because of Earth's  relative position to the blast. Imagine a flashlight shining in the dark - diffuse  and soft, it lights the path 1-2 metres ahead of you.

Now, imagine capturing all that light  and focusing it into a singular laser beam. It wouldn’t illuminate the path as widely,  but it would reach hundreds of metres into the distance. And if Earth was in the direct  path of that laser, it would register a super bright reading.

That doesn’t mean the laser  released more energy than the flashlight - it just means the way it was concentrated and  then detected resulted in a higher reading. The same concept can be applied to these  gamma-ray bursts. If a massive star is spinning super fast when it collapses, then  the shape and structure of the near-lightspeed jets it emits will be more narrow and  focused, and therefore brighter.

In fact, the jets seen from the BOAT are  some of the narrowest ever seen. — But not only were these particle jets brighter  than expected, scientists also detected way more of them going way faster than expected. They  travelled with such fervour, that after 2 billion years traversing the cosmos, they arrived here  and momentarily disrupted the Earth’s atmosphere.

Sitting just 50 - 1,000 km above the surface  of our planet, Earth’s ionosphere is rich in electrically charged particles. When the BOAT  struck, it left a mark comparable to that of a major solar flare - pushing the ionosphere  down into lower altitudes. If photons from an explosion 2 billion light years away can  have this kind of effect on our planet, I don’t really want to think about what happens  if something in our neighbourhood explodes.

The Large High Altitude Air Shower  Observatory (LHAASO) in Daocheng County, China, managed to capture data on tens of  thousands of photons over the course of the initial blast and into the afterglow.  This is a quantity unlike anything seen before in gamma-ray astronomy. In fact,  it is so far out of pocket, that some astrophysicists think they might be pointing  towards something missing from our models.

According to our current understanding, it’s  very unlikely these super high-energy photons are travelling for 2 billion years.  Cosmic microwave background radiation, interactions with intergalactic dust, or  redshifting caused by the expansion of the universe are all factors that can interfere  with a photon’s trajectory. One hypothesis put forward is that photons convert themselves  into a hypothetical particle called an axion, and then convert back into gamma rays  upon reaching our galaxy’s magnetic field.

Axions are thought to be an ultralight particle  responsible for dark matter. Their existence is currently purely hypothetical - we have  no evidence for them, and even if we did, they would lie outside the Standard Model of  particle physics. We don’t have time to dive into detail in today’s video, but let me know if you’d  enjoy a separate video on this in the comments.

— Ok - so far, we’ve established that BOAT was  caused by a massive star collapsing and turning into a black hole - which, incidentally, is  known as a collapsar. Aside from generating a long gamma-ray burst, collapsars are also  known for generating something else - gold. Wait, wait, how is gold connected  to gamma rays?

Good question. To understand that, let’s take a minute  to discuss how elements are made. The core of a star is a super  high-pressure environment - some 200 billion times higher than atmospheric  pressure on Earth.

In these conditions, nuclear fusion reactions create heavier  elements out of lighter ones. For example, one helium atom comes from fusing  four hydrogen atoms together. Elements 2 through 26 on the periodic table  - that’s helium to iron - are made this way, a process known as stellar nucleosynthesis. 

However, once you get to iron, it isn’t energetically favourable to continue  making bigger and bigger elements this way. So how do we account for the rest of the periodic table? Where do these heavier  elements like gold come from?

At the moment, we know of two different ways  these elements are formed. The first was recently confirmed by the James Webb Space Telescope.  When two ultra-dense neutron stars collide, they emit an immense amount of neutron particles. 

Surrounding material captures these neutrons, making their atoms temporarily  unstable. In order to stabilize, the neutrons undergo radioactive decay into  protons, creating new, heavier elements. This process is known as rapid neutron capture, or  r-process nucleosynthesis.

Some calculations suggest one neutron star collision can produce  up to three Earth masses worth of heavy elements. However, this explanation alone isn’t  sufficient to account for all the heavy elements in the universe.  Neutron star collisions are rare, and take a long time to happen - in the  order of billions of years.

On top of that, observations of very old stars show that heavy  elements were already present in parts of the universe well before most binary neutron  stars would have had the chance to collide. So how do you explain that? There must be  another source of heavy elements in the cosmos.

Which brings us back to our BOAT. There’s another theory that collapsars like the BOAT could be another source  of r-process nucleosynthesis. In their dying stages, massive stars like the  one that caused the BOAT are surrounded by layers of exploding gas.

These explosions leave disks  of matter swirling around the resulting infant black hole. As the black hole begins devouring  the surrounding matter, it can only ‘ingest’ so much at a time. What it cannot manage is  swept away in a neutron-dense wind.

Here, the same r-process nucleosynthesis occurs - forming  heavier elements like gold, silver, and platinum. Seems promising, but unfortunately,  even factoring in these kinds of supernovae still isn’t enough to account  for the abundance of gold in the universe. To make matters worse, analysis of the  BOAT spectrum didn’t show any traces of heavy elements - raising questions about the  validity of this collapsar gold-making theory.

Some scientists suggest the BOAT’s host galaxy  might have something to do with the lack of heavy elements in the explosion. Upon modelling the  host galaxy’s spectrum, researchers discovered it has the lowest metallicity of all previous host  galaxies where gamma-ray bursts were detected. In other words, maybe the environment didn’t have the  right building blocks to make heavier elements.

How do we know how much gold should be out  there in the first place? How do scientists predict something like the relative  abundance of elements in the universe? There are two main methods of calculating this - the spectroscopy of stellar  photospheres, and meteorite analysis.

By analyzing the absorption  lines in the spectra of stars, astronomers can determine the relative abundances  of elements in the photosphere of those stars. The composition of meteorites - remnants  of an early solar system - are analysed in parallel to determine the relative  abundances of elements. Meteorites are especially useful for measuring the  abundances of volatile elements like hydrogen, helium, and noble gases that are  underrepresented in stellar photospheres.

The results of both of these methods are  usually congruent, indicating we’re probably doing something right. But this is physics,  so of course nothing is so cut and dry. One famous exception to this rule is  lithium.

According to the standard Big Bang nucleosynthesis theory, the early universe  should have produced about three times more lithium-7 than is actually observed. The plot  thickens when we consider its isotope lithium-6, where we observe 1,000 times more  than our predictions can account for. This discrepancy is known as the "lithium problem"  and remains unresolved, presenting a significant challenge to the standard cosmological model. 

It highlights the importance of understanding the processes that shape the relative  abundances of elements in the universe, and suggests that our current understanding  of nucleosynthesis might be incomplete. — Just because the BOAT didn’t yield  gold as expected doesn’t mean we should discard these kinds of extreme gamma-ray bursts as places where heavy elements could  be made. Observations of nearby stars have provided strong evidence for an early r-process  that enriched the universe with heavy elements.

But the BOAT findings cannot be ignored,  as they suggest there may be alternative, currently unknown processes responsible for  this elemental enrichment of our cosmos. The results may call into question our entire model of understanding regarding collapsars and  their role in creating heavy elements. This discovery is much bigger than just the  BOAT, or gamma rays.

It is about the literal building blocks of our universe as we know  it. Where do our different atoms come from, and why do they exist in the proportions  they do? How much of our model is accurate, and how much is missing?

What role does  dark matter play in all of this? We need more time and research before we know for  sure, but the BOAT is a great example of how new findings keep our understanding of physics  ever-evolving … just like the universe itself. Thanks for watching!

If you like this video, you  may like my others about stars in this playlist. A big thanks to my patrons and members. If you  want to support and have your name added to the end of every Astrum video, check the links  below.

All the best and see you next time.