Neutron star

So when that supernova happens, the remnant, the core of that star that did the implosion, it can go a couple of different ways.

So it can either become a neutron star or a black hole.

And I'm going to say a little bit about neutron stars first, because neutron stars are these really amazing objects.

So if the star is less than something like 20 times the mass of the sun, but more than eight, then when that supernova happens and the core collapses...

It's too massive to be held up by even electron degeneracy pressure, even this white dwarf thing.

Wow.

Yeah.

And one cool thing about neutron stars is a lot of times when they're formed, when they're compressed that way, the magnetic fields of the star are kind of compressed and twisted around and the star is born like spinning really rapidly.

And you could imagine, you know, putting that somewhere on the periodic table.

Astronomers call these things neutron stars, and they exist.

They were discovered in the 1960s.

And a typical neutron star, a couple times the mass of the Sun, has mass equals 2 times the mass of the Sun, radius of about 10 kilometers.

Now, in fact, during the course stars' life, one of the things I glossed over is stars tend to lose mass as they live, and so they don't end up with the same mass they started with.

But stars with initial masses at the beginning of their lifetime, greater than, oh, I don't know, something like thirty times the mass of the Sun, will end up with masses greater than three times the mass of the Sun, and then there's nothing to stop their collapse.

What happens is, they turn into neutron stars, but they turn into neutron stars whose radii are smaller than the Schwarzschild radius, and that is a black hole.

So, they collapse down into black holes.

Which is, uh, a very formal way of saying that we are finally figuring out how to optimize our telescopes to see one of the most violent, spectacular flashes of light in the entire universe.

Because we know black holes eat neutron stars, right? Like, we can literally hear them doing it through gravitational waves, those ripples stretching and squeezing space time.

But despite having world-class telescopes scanning the skies every night, we've never actually seen the visual flash of light that this collision makes.

Yeah.

That wider baseline across the globe gives physicists a much sharper angle to measure those minute time delays, which shrinks that massive cosmic haystack down to a highly targeted patch of sky.

And the numbers in the paper are incredible for this.

They modeled a specific population of neutron star black hole mergers, they call it population one, which assumes the neutron stars are a bit squishy.

Squishy, yeah.

But do these objects truly exist? What evidence do we have for them? And if they are real, could they be the production site for the most dangerous material in the universe? Self-replicating strange matter.

To understand the Quark star, we first have to understand the neutron star.

When a star heavier than about 8 solar masses reaches the end of its life, the outward pressure from radiation fizzles out and so gravity tries to compress the star down into a single point.

The core becomes so compressed that it reaches a critical density where it's able to resist further collapse, causing the outer layers to bounce off the core in a dramatic supernova event, specifically here a type known as a core collapse supernova.

With the outer layers gone, the core is left naked in space, and it's called a stellar remnant.

If that remnant exceeds about three solar masses, then it will collapse all the way down into a black hole.

But for remnants lighter than this, they instead will become neutron stars.

A neutron star is able to avoid collapsing all the way down to a black hole because it has enough internal strength to resist the power of gravity.

The arrow of time.

Scientists recently broke down the math of neutron stars and compared it to our existing paradigm for the forward moving arrow of time, the idea that time moves exclusively forward.

They found in certain conditions a neutron star's specific extremely high gravity turns this math inside out, creating a separate arrow of time traveling the opposite of its usual direction.

When it comes to the math, at least, these neutron stars are collapsing backward in time.

The researchers' work appears now in the European Physical Journal C.

Their investigation focuses on what are known as epoch functions, which accounts for key aspects of space-time.

Cosmologists who study the tiny period of time directly after the Big Bang have long tried to reconcile high, though much lower than today, entropy of the early universe with the fact that we still appear to be on the later end of the time's arrow today.

Could the answer be that some pockets or processes have always been winding the clock back? To investigate, the researchers basically chose to set two different ends of math equations opposite each other, epic functions of gravitational collapse and epic functions of space-time curvature and structure.

Smarty pants, do you know what object I'm talking about? Is it A, black holes; B, nebuli; or C, asteroids? The answer is A.

But unlike black holes, we can actually see neutron stars.

Right now, all I'm seeing is a lot of flashing light.

Yes, pulsars give off streams of light that look like flashes because the star is spinning around like a super-fast lighthouse.

They appear around white dwarfs in cataclysmic variable star systems, periodically erupting in spectacular outbursts called novae when accumulated hydrogen ignites in thermonuclear flashes on the white dwarf's surface.

They surround neutron stars in X-ray binary systems, where the disk becomes so intensely hot, reaching tens of millions of degrees, that it radiates primarily in X-rays detectable only by orbiting telescopes above Earth's atmosphere.

And most dramatically, accretion disks encircle the supermassive black holes at the centres of galaxies, forming the blazing cores of active galactic nuclei and quasars, that can outshine the entire surrounding galaxy of hundreds of billions of stars by factors of hundreds or even thousands.

The supermassive black hole at the center of the galaxy, M87, famously imaged by the Event Horizon Telescope in 2019, is surrounded by a glowing asymmetric ring of accreting material, a disk of gas spiraling inward at a significant fraction of the speed of light, heated to billions of degrees by compression and friction.

Every pulse of the Crab Pulsar is an echo of the angular momentum that existed in the progenitor star before it died, preserved and magnified by the conservation law through one of the most violent events in astrophysics.

But 30 rotations per second is modest by neutron star standards.

Some neutron stars spin far faster, reaching speeds that strain the imagination.

These are called millisecond pulsars, and they achieve their extraordinary rotation rates not through collapse alone but through a second mechanism.

Yeah, without a doubt.

Because we are quite literally inside the mantle of a neutron star.

Okay, let's unpack this.

Because the sheer imagination of this source material is blowing my mind, but frankly my brain is already hurting just trying to visualize the physics of it.

Right.

But before we even get to the people, I feel like we need a reality check.

You said we are inside a neutron star.

Yes, we are.