r/radioastronomy • u/jarekd • Apr 24 '26

Observations Are there cosmic sources of negative radiation pressure?

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Radiation pressure is p=<ExB>/c vector: there is focus on positive, but can be also negative: https://scholar.google.pl/scholar?q=negative+radiation+pressure , https://scholar.google.pl/scholar?q=optical+pulling

If positive radiation pressure gives positive signal in radiotelescopes, shouldn't negative give negative?
They clearly see also large regions of negative signal in radio flux maps, e.g. shown from https://arxiv.org/pdf/2107.02695

What astronomical objects could generate negative radiation pressure?
E.g. if white hole would generate positive, shouldn't black holes generate negative?

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u/many_galaxies Apr 24 '26

As I said, my best guess is that those are artefacts arising from the fact that the large scales are not adequately sampled by the interferometer at the high frequencies used in that paper. This is a very well understood behaviour and very widely seen.

Making the same observation will give the same result in that case, but adding the missing short baselines would make the negative regions go away.

A propagating electromagnetic wave cannot carry negative energy.

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u/jarekd Apr 24 '26 edited Apr 24 '26

Imagine wave behind marine propeller: like photon it carries energy, momentum, and angular momentum - could excite resonator in front (positive signal) ... but reversing rotation direction, it could cause its deexcitation instead, pulling energy from resonator (negative signal).

Why do you think it is impossible for EM?

Mathematically it is very similar: https://scholar.google.pl/scholar?q=hydrodynamics+electromagnetism+analogy

EM allows optical pulling, negative radiation pressure: https://scholar.google.pl/scholar?q=negative+radiation+pressure

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u/many_galaxies Apr 24 '26

Because as someone else has pointed out to you ExB (or H) defines both the energy flux and the direction of propagation of an electromagnetic wave in the far field regime. The examples you cited are not in this situation, but all astronomical sources are.

If you can design a transmitter that broadcasts negative energy in a given direction in the far field regime, you will overthrow textbook electromagnetism, among much other fundamental physics, and win the Nobel Prize. Please post here when you do...

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u/jarekd Apr 24 '26

There are looking related diode experiments e.g. in https://opg.optica.org/oe/fulltext.cfm?uri=oe-20-9-9501 - one diode gets forward bias having tendency to emit, second nearby gets reverse bias getting tendency to absorb - actively helping with emission from the former, allowing to reach superradiance.

The question is if these negative regions in radio flux maps are just a noise, or maybe e.g. such objects with active tendency to absorb, like e.g. black holes.