Submitted by MistWeaver80 t3_yp8a4b in science
Reply to comment by [deleted] in Bizarre star may have a solid surface, according to X-ray observations. Astronomers have now spotted a super strange one that seems to have a solid surface. Its intense magnetic field is strong enough to overcome its blistering temperatures and “freeze” its outer layers into a solid crust. by MistWeaver80
Wow. So if it’s giving off enough light to be a star how is that energy being generated and how does it ‘get out’ of the solid surface?
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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
Space is so tight
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Thats exceptionally cool.
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Does the black body spectrum change for a neutron star, given there are significantly less electrons and protons than in normal matter?
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.
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?
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.
But where do the photons come from?
From the electromagnetic field
They just poof into existence? I'm assuming I just don't understand what a photon actually is.
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.
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?
Photons do not have mass. They do carry momentum though.
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!
Photons are made of photons. They are fundamental particles
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.
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?
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.
Cool thanks for your reply
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?
Thanks. Makes sense. So this is an immensely hot solid ball slowly cooling.
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.
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.
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.
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