# Is it possible to have a perfectly black material?

After reading this NASA article about the "blackest material", the following stuck out to me.

The tiny gaps between the tubes absorb 99.5 percent of the light that hits them

Is it possible to create a material that absorbs, not just all visible light, but all electromagnetic radiation?

• In general, it is not possible to have anything "perfect". – jinawee Jun 23 '14 at 22:31
• Do keep in mind that electromagnetic energy comes in 'packets' (photons) and that the energy of a photon is proportional to the frequency (or inversely proportional to the wavelength). So, unless there is a material that can, in principle, absorb a photon of arbitrarily large energy without being destroyed, then the answer is no. – Alfred Centauri Jun 23 '14 at 23:15
• @jinawee: That might be true most of the time, but not all. We do have superconductors. – Gerard Jun 24 '14 at 15:06
• A possibly related answer; note that the material in the article seems to be versatile enough to be applied like paint and to be black from all angles of incidence, constraints which might limit the total absorption you can achieve. – rob Jun 24 '14 at 16:57

We can make it absorb a lot of energy but if you read about black-body radiation effect you will notice that as energy is introduced into the object it will similarly radiate a small amount of the energy back, at room temperature appears black, as most of the energy it radiates is infra-red and cannot be perceived by the human eye. At higher temperatures, black bodies glow with increasing intensity and colors that range from dull red to blindingly brilliant blue-white as the temperature increases.

This means that later even if we did have an $100$ percent absorbing materials of all electro-magnetic radiation the object will radiate some energy due to heating or other similar process. That in mind, it will always leak out some energy.To conclude, we could say it will only absorb radiation for short-time before releasing enough photons which could be detected by an photon detector, therefore "breaking" the truly blackest or absorbing material due to this effect.

As a summary as long as the object absorbs some form of energy it can never be completely black.

Furthermore, an blackhole is very black however it even is not as the power in the Hawking radiation (if it was proven, currently it is hypothesized) from a solar mass $M$ which is equal to $1.98855\pm 0.00025 * 10^{30}$ black hole turns out to be a minuscule 9 × 10−29 watts. It is indeed an extremely good approximation to call such an object 'black'. As $$P =\hbar c^2/15360\pi G^2M^2 = 9.004 * 10^{-29}$$

That being said, even black-holes one of the strongest objects cannot escape being truly black.

I believe user43495's answer to be quite accurate, and right, but I will add something here just as food for thought.

It has been hypothesised that the LHC could create miniature black holes. Even if it can't, there are many in space[citation needed]. These would be able to "absorb" all kinds of electromagnetic radiation. Within a black hole's event horizon, escape velocity is higher than the speed of light. Black holes are black bodies, but even their own radiated photons cannot escape past their event horizon. That should be as dark as you can get.

Stephen Hawkings has some works where he describes a kind of radiation emanated from black holes. Editions in italic: the existence of this Hawkings Radiation has been not been proved true or false yet. But supposing it exists, it is a kind of black body radiation. However, its energy is not proportional to temperature as in most black bodies. Rather, it's inversely proportional to the black hole's mass. I think with sufficient mass, a black hole may be darker than the material quoted in the question.

(Thanks user43495 for reminding me that Hawkings Radiation is still hypothetical.)

• Hawking radiation is still hypothesized and never had been seen in laboratories or even observed (except in Mathematics) therefore I edited your answer to express its hypothesized stage as it could confuse individuals as they could be misled into thinking Hawking Radiation has been detected. – LogicProgrammer Jun 24 '14 at 15:17
• Like to point out that while it is sufficiently black, a black hole's event horizon is not something I would classify as a "material" – Jim Jun 24 '14 at 17:25
• @Jim I mean the whole black hole as a material, not just its event horizon. – Renan Jun 24 '14 at 18:16
• @Jim Im sure Renan was attempting to show the closest thing to an truly dark object – LogicProgrammer Jun 24 '14 at 18:19
• I suppose it depends on your definition of "material". While I was looking for something tangible enough to create something out of (clothing, car, spaceship, synthetic planet, etc.) I do appreciate the offer of "blackest" possible thing. – David Starkey Jun 24 '14 at 18:28