Catch a Star Exploding in Action in 2022

As photon energy is inversely proportional to wavelength, they're also very weak and so even if the noise weren't there you'd have a helluva time detecting them - and you may have to wait a long time. Photons of wavelength 10⁸ metres (freq about 3 Hz) aren't especially hard to detect, actually, and you can choose which component to detect - whether its electric field or magnetic component, or both. Easily within the range of many ELF receivers (one I built recently, for example, starts rolling-off at about 9.3 Hz [λ ~ 32,000 km]).

But you're quite right, noise can make things a bit difficult down in the EM basement. Not only 1/f noise, but thermal noise as well. Loop antennas, for example, benefit greatly from low resistance, to help keep thermal noise down. As I don't have the money (nor inclination) to use cryogenics, the next best thing is to throw a boatload of copper at it. My loop uses about 15 kg' worth. I could use less and significantly increase the loop's area, but this is a portable loop (about 2 m in diameter) for field work (pun intended ).

What about magnetic monopole antenna? Is that any use at low wavelength?

They work right down to DC - except that the Universe isn't old enough yet to produce a frequency that low and, as far as anyone knows, magnetic monopoles neither.

Maybe I mis-stated. Friend of mine has some sort of radio antenna that is pretty directional, and is magnetic field selective rather than electric field selective. Maybe that is what I meant to say. I am not a ham radio operator, but I am sure his antenna cannot pick up anything near that low.

It's a loop aerial no doubt (which are directional), but most loops don't go that low due to their combination of wire resistance and loop inductance. At ham-radio frequencies they are typically also part of a tuned circuit - I'd bet that somewhere in your friend's design there is a (possibly-variable) capacitor across its terminals for tuning the antenna.

ELF (extremely low frequency) loops for faint-signal reception put pretty stringent demands on the design; ones that are largely absent at ham-radio frequencies (certain signals I'm interested in, for example, peak at around 1 pico-Tesla), but the basic idea is the same except that mine aren't tuned - the output is amplified and sent straight to a spectrum analyser. It is also receive-only*. The loop is so sensitive to magnetic fields that even slight motion/vibration from the wind can saturate the output amplifier. The wind induces spurious currents to flow due to the loop's motion in the Earth's magnetic field, and so the loop has to be protected from that. Were this a permanent installation I'd bury the loop. Lots of fun stuff your friend doesn't have to deal with.

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* Practical transmitting antennas at these frequencies are extremely inefficient because of the enormous wavelengths and so would take tens of megawatts of input power just to radiate one or two watts. At 7 Hz for example an efficient, quarter-wavelength transmitting antenna would be about 6000 miles high.

Yeah, that whole picture is a little bit insane.

Throw in 50 & 60 Hz mains noise (and their harmonics, which can exceed 5 kHz), atmospheric noise (especially in local summer) and yeah, it's a difficult EM environment in which to work. The mains peaks are so strong that a colleague in Finland can not only detect the 60 Hz signal from North America's power grids (Finland's mains are 50 Hz) but can tell when various N.A. utilities buy and sell power from each other. Fun stuff! About the only places you can get away from it are in the middle of the oceans and in Antarctica well away from research stations and their generators. Earth is a noisy place!

One of the first times seeing Milla in action!