> According to Albert Einstein’s general theory of relativity, the behavior of a black hole depends on two numbers: how heavy it is, and how fast it is rotating. And that’s it. Black holes are said to have “no hair” — no features that distinguish them from their fellows with the same mass and spin.
As far as I know, there's a third property that black holes have - electric charge. Would a sufficiently strong electric charge between two black holes be detectable, whether they both have the same charge, or opposing charges?
I suppose based on the article, the effects would only take places once the black holes got within 40km of each other...
fsmv · 45m ago
Black holes can have charge but a charged black hole would attract ions of the opposite charge strongly and would quickly neutralize. So it would be quite difficult to get a non-negligible charge on a black hole.
BurningFrog · 28m ago
So some very advanced and bored civilization could take black holes and shoot gigantic numbers of protons into it, and get a very positively charged black hole.
If you pump in enough charge that the electrical repulsion is stronger than the gravity attraction, you can then store them safely next to each other, for when you might need one.
marcosdumay · 20m ago
It also allows you to move the black hole around, somewhat freely.
It may be a very useful thing if it turns out that we can make small ones.
Terr_ · 14m ago
> move freely [...] small ones
At the risk of spoiling the mystery of a 50-year-old short story, this happens in the The Borderland of Sol by Larry Niven.
momoschili · 1h ago
It has been proposed and is often studied in different contexts, but it seems unlikely that we will be able to measure it any time soon.
raverbashing · 47m ago
I think you might just need a comb and some pieces of paper
renewiltord · 1h ago
Judging by what the article says they can't be different
> In theory, there’s a third defining property: electric charge. But real, astrophysical black holes have negligible net charge.
FergusArgyll · 4m ago
This reminds me of something I mull over; Greek style philosophy seems so smart, rational and correct until you actually observe the world. Imo the perfect example is elementary particles - the Greeks (mostly) were convinced that it's impossible for something physical to be elementary (cannot be further split) and logically it is hard to understand why can't we continue to split the particle?! but hey, we can't.
Physical beings which cannot be distinguished from one another would have made their heads spin...
xeonmc · 58m ago
The question of hairy black holes is intimately connected to the greatest puzzle in modern physics: How can general relativity be merged with quantum theory?
Consider the situation where an object crosses a black hole’s point of no return, called the event horizon. According to general relativity, all outsiders will see is how the swallowed object contributes to the two numbers that describe the black hole: how much mass the object adds, and how much faster or slower it makes the black hole rotate.
The idea that anything within the event horizon should be treated as an opaque black box -- could it be reinterpreted as saying that any property which has dependence on spatial or temporal distribution within becomes an unknowable quantity? If so, can it be tied somehow to Quantum Mechanic’s idea of the removal of degrees of freedom by observation, since now certain quantities are not unobserved but rather unobservable in principle? I am asking this from a naive laymen’s point of view, so I may be conflating entirely unrelated ideas.
gus_massa · 24m ago
No. The "no hair theorem" has a condition that says "after a while", but people ignore it because it's a short time. So intermediately after the object entered the black hole will have bump and will emit gravitational waves and after a while it will be a perfect sphere (if it's not rotating, or a similar round elongated shape if rotating).
As far as I can understand, it totally unrelated to Quantum Mechanics.
layer8 · 25m ago
For one, observers inside the event horizon can still observe each other. From the point of view of an observer falling into a black hole, nothing unusual happens when they cross the event horizon. They still observe stuff falling in with them in the same way as before (assuming a large enough black hole so that the local curvature is negligible).
If Hawking radiation is real, it might also expose information from inside the black hole, possibly solving the information paradox. In that sense, the inside of a black hole would still be “observable” from the outside in the QM sense. But since we don’t know how quantum gravity works, that is an open question.
trjordan · 29m ago
Not exactly. Black holes are not lopsided, for instance. There isn't anything on "one side" of them, once the matter has crossed the event horizon.
An interesting consequence of having "no hair" on them is that information on everything that falls in them is lost forever, which leads us to an information loss paradox. Not nice.
datadrivenangel · 27m ago
Another blow against string theory.
behnamoh · 1h ago
Yet another clickbait title by the quantamagazine. I'm afraid these "science popularization" techniques only make it more confusing for the general public. Just say the exact, scientific word and cut this bs.
mr_mitm · 28m ago
This is the first time I heard quanta magazine being accused of click bait. They show no ads and don't sell anything. What would be their motivation for using click bait?
Click bait used to mean things like "five reasons you always get sick - number three will SHOCK you" or "doctors hate this one weird trick!".
The title of this article isn't click bait at all. Black holes having hair or not is almost the technical expression, as evidenced by the "no hair" theorem. Physicists are quirky like that sometimes.
ordu · 37m ago
Yeah. The photo of a hairy astrophysicist claiming that if black holes have hair, it is shorter than 40 km seems like a petty way to spark a public interest.
jleyank · 46m ago
If they finds "casual" names for scientific principles, they're going to just LOVE the names for genes. hERG activity is a bad thing that gets drugs taken off the market (cardiac arrhythmia). hERG means "human ether-a-go-go-related gene". Scientists are human, and obviously playful at times.
It's not a recent thing. Check out quark names and their associated properties.
As far as I know, there's a third property that black holes have - electric charge. Would a sufficiently strong electric charge between two black holes be detectable, whether they both have the same charge, or opposing charges?
I suppose based on the article, the effects would only take places once the black holes got within 40km of each other...
If you pump in enough charge that the electrical repulsion is stronger than the gravity attraction, you can then store them safely next to each other, for when you might need one.
It may be a very useful thing if it turns out that we can make small ones.
At the risk of spoiling the mystery of a 50-year-old short story, this happens in the The Borderland of Sol by Larry Niven.
> In theory, there’s a third defining property: electric charge. But real, astrophysical black holes have negligible net charge.
Physical beings which cannot be distinguished from one another would have made their heads spin...
As far as I can understand, it totally unrelated to Quantum Mechanics.
If Hawking radiation is real, it might also expose information from inside the black hole, possibly solving the information paradox. In that sense, the inside of a black hole would still be “observable” from the outside in the QM sense. But since we don’t know how quantum gravity works, that is an open question.
Rotating black holes are pretty well modeled as a spinning ring: https://en.wikipedia.org/wiki/Ring_singularity
Barber goes "You're kidding me, right?"
Click bait used to mean things like "five reasons you always get sick - number three will SHOCK you" or "doctors hate this one weird trick!".
The title of this article isn't click bait at all. Black holes having hair or not is almost the technical expression, as evidenced by the "no hair" theorem. Physicists are quirky like that sometimes.
It's not a recent thing. Check out quark names and their associated properties.
https://www.wikipedia.org/wiki/List_of_unusual_biological_na...
https://en.wikipedia.org/wiki/List_of_chemical_compounds_wit...
https://en.m.wikipedia.org/wiki/No-hair_theorem