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[deleted] t1_ivjjq26 wrote



Rodot t1_ivjua01 wrote

It's black body radiation, usually taught in stat mech classes when deriving the Planck distribution (distribution of energies in a gas of photons). It's low level mechanism comes from what are called "continuum" interactions. They are called that because they produce a continuous spectrum unlike atomic interaction which are discrete.

Some examples of continuum interactions include Thomson/Compton scattering (photons bouncing off electrons, Thomson scattering is the low energy approximation and Compton is the relativistic case), Bremsstrahlung radiation (electrons scattering off ions), photoionization (electrons being kicked out of their atoms), collisional interactions (atoms and ions bumping into eachother), and autoionization (atoms with multiple excited electrons reconfiguring to shoot off an outer most electron through quantum tunneling). For those for who it's not clear where exactly the light comes from in all of these, accelerating charged particles emit light.

All of these interactions together create the Black-body (or Planck) distribution.

Source: I'm one of the developers of an astrophysical radiative transfer code


flyingpanda1018 t1_ivkifab wrote

Does the black body spectrum change for a neutron star, given there are significantly less electrons and protons than in normal matter?


Rodot t1_ivl46ap wrote

It's spectrum is much more complicated because it's very high energy and you need to consider how the light interests with the protons and the structure of the magnetic fields.


OfLittleToNoValue t1_ivmrwnd wrote

I'm not an astrophysicist, but are you saying electrons are moving so fast they generate light? Isn't light a photon? Where are they coming from?


Rodot t1_ivmvufb wrote

According to Maxwell's equations, a changing electric field creates a magnetic field, and a changing magnetic field creates an electric field. If you set this up as a set of differential equations you get perpendicular propagating waves in the electric and magnetic fields.

A charged particle moving at a constant speed makes a constant magnetic field. An accelerating charge makes a changing magnetic field which makes a changing electric field etc. which makes an electromagnet wave. The quantization of this field results in the waves propagating as photons.


OfLittleToNoValue t1_ivoeg6p wrote

But where do the photons come from?


Rodot t1_ivojlpk wrote

From the electromagnetic field


OfLittleToNoValue t1_ivoop6h wrote

They just poof into existence? I'm assuming I just don't understand what a photon actually is.


Rodot t1_ivopmiw wrote

Think of a photon as similar to a musical note when you play an instrument. For a string instrument, you pluck the string and it causes it to vibrate at a specific frequency depending on the length (i.e. it's boundary conditions). This is kind of like a photon but instead of plucking a string you are "plucking" the electromagnetic field and it makes a vibration at a certain frequency depending on the boundary conditions (electrons, ions, etc) of the system.


OfLittleToNoValue t1_ivorr0q wrote

I understand sound to be the consecutive vibration of atoms which is why sound cannot traverse a vacuum. For light to traverse space is my understanding that is that photos are some kind of discrete particle with mass and that's why things like solar sails work.

From what you're saying, the interaction of the fields creates photons. Is this energy converting into matter and the genesis of a discrete particle?


Rodot t1_ivorv7u wrote

Photons do not have mass. They do carry momentum though.


OfLittleToNoValue t1_ivosz7x wrote

Man I feel dumb. What is a photon made of then? It's just energy that flows and glows until it dissipates? Thanks for humoring my ignorance!


Rodot t1_ivqj6cx wrote

Photons are made of photons. They are fundamental particles


Bonesmash t1_ivm5n5j wrote

You got some good “how” replies. I just wanted to point out that when a neutron star is made, it’s an extremely energetic event, in addition to it having just been a nuclear fusion reactor. So that’s where the initial heat for the black body radiation came from.


KenHutchenson t1_ivkc7vj wrote

Wait whaaat!? Neutron stars don’t radiate photons!? Today I learned…that’s so cool.

So to see neutron stars do I need a special telescope?


8Eternity8 t1_ivkf3rt wrote

X-Rays are photons. Just with higher energy and outside the visible spectrum.

But yes you would need a special telescope to see something that only radiates in the x-ray spectrum.


SandyDelights t1_ivjmts5 wrote

Objects don’t need to continuously generate energy to produce light – white dwarves are the “dead” cores of stars, but it takes an extraordinary long time for them to radiate away the remnant heat.

The distinction here being they don’t need to generate energy because they already have generated that energy (in the form of heat), so the light (in the case of white dwarves) is just the heat radiating into space as the dead star slowly cools (or causes the star to cool, whichever you prefer).

Good example is a stove burner: turn it on, crank it up to high so it’s burning hot and glowing red, then turn it off, pull the plug if you want to. Does the red go away instantaneously, or does it slowly darken as it cools?


go_half_the_way t1_ivjn27l wrote

Thanks. Makes sense. So this is an immensely hot solid ball slowly cooling.


SandyDelights t1_ivjnutq wrote

Oh, not going to say that – I was explicitly answering the general question of “if it’s giving off enough light to be a star now is that energy being generated and how does it ‘get out of the solid surface’”, i.e. you don’t need to produce energy to produce light (you just need some form of energy present for it).

That said, yes, but there are a lot of caveats – this article covers it really well and in fairly simple terms.


thr33pwood t1_ivjne32 wrote

Despite being very different in nature Both neutron stars and white dwarfs are the remnants of former stars and both emit electromagnetic radiation (light, heat, x-rays, gamma rays) which is left over from the time they were actively undergoing fusion processes.

White dwarfs are the remnants of smaller stars, they are essentially the solid hyper-hot iron core of stars. They radiate heat and light for many millions of years before they eventually cool off. (Note that this will last longer than the universe is old now).

Neutron stars are the remnants of more massive stars. The moment the fusion fuel burns out, there is no force pushing outwards to counteract the immense gravoitational force - and in the case of these stars the gravitational force is strong enough to overcome the repelling force of protons that keeps atoms apart. The force crushes the nucleons together into a neutron soup. This crush generates immense "heat" energy which is being radiated in the form of gamma rays, radio waves and in other electromagnetic spectra until eventually these neutron stars too cool off in the distant future.

Stars that have had even more mass before the fusion reaction stopped, turn into black holes.


Deafcat22 t1_ivlnmk1 wrote

They also tend to spin real quick! Conservation of angular momentum, coupled with a drastic reduction in radius, greatly increases whatever spin the star previously had.