Questions tagged [black-hole]

Questions regarding points of extremely high mass density, which creates an extremely strong gravitational field from which light cannot escape.

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How can firewalls stay put on the event horizon?

Firewalls in black holes were introduced in relation with the information paradox. In Wikipedia we can read: A black hole firewall is a hypothetical phenomenon where an observer falling into a black ...
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How well conserved is etendue in extreme gravitational lensing scenarios?

This excellent answer to Could dark matter exist in the Universe in the form of sufficiently dense objects? includes the following image and description: Light from the background galaxy circles a ...
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New Object Formation at Stellar Collapse [closed]

Assume QM degeneracy pressures exist beyond neutron degeneracy pressure. Under this assumption, what would the sequencing be for new object formation upon the collapse of a massive star whose ...
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If a black hole was headed for our solar system and would arrive within a year, would we necessarily know of it?

Basically, is our observational technology and coverage sufficient enough to pretty much always spot incoming objects like a black hole when they're a year from arriving? If so, within what time frame ...
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Primordial black holes microlensing

Could the movement of a PBH found in the outer solar system by microlensing be totally unpredictable and impossible to track after it was first detected?
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Has gain in mass from accretion onto a black hole been observed?

Have we observed a black hole directly gain mass via accretion? That is, have we observed the black hole to have mass $m_1$ at time $t_1$ and then observed its mass to be $m_2 > m_1$ at a later ...
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why did big bangs take place [duplicate]

why did the big bangs take place? The question of ‘why’ is impossible for us to answer, and leads into much deeper philosophical and metaphysical questions. All we are able to do is determine what ...
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What if wormholes were created when a black hole and white hole collide? [closed]

Scientists have discovered black holes, white holes and wormholes but I am still unsure how they came to life. Did the black holes collide with the white hole causing a mixture of both or is there ...
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Why black holes are extremely cold?

"The most massive black holes in the Universe, the supermassive black holes with millions of times the math [sic] of the Sun will have a temperature of 1.4 x $10^{-14}$ Kelvin. That's low. Almost ...
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How can a black hole have a charge, or be charged?

So-called 'hairless' black holes (no-hair theory, or theorem?) , which is what real black holes are, can be described by just three characteristics: Mass, spin, and charge. It is easy enough to ...
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What is the thickness of black holes event horizon?

I would premit that I am just an enthusiast, so don't expect a good background or a deep mathematical knowledge about the topic. I just read an article about how light is reflected by a black hole (...
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Could we detect a globular cluster consisting entirely of black holes?

A paper recently came out in Nature simulating the evolution of the $\sim10^4M_{\odot}$ globular cluster Palomar 4 (Gieles et al. 2021, arXiv link). The authors argue that in ~1 billion years, a ...
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Can dark matter be normal matter after all? [duplicate]

MACHO's and RAMBO's are both baryonic (and leptonic) forms of matter that can't be observed by their nature. They barely emit or reflect light. Black holes, neutron stars, or brown dwarfs (or groups ...
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Would the stars look different if many primordial black holes were present?

Suppose that there are many primordial black holes. These are point masses which have a small probability to collide with stars let alone themselves. They are formed in the early universe and could ...
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If a black hole is spinning, does its singularity have a new name and what is the name? [duplicate]

Think of a spinning black hole. (Kerr black hole) Every black hole has a point of infinite density, called a singularity. When a singularity is spinning, does it have a different name? But when a ...
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Medium sized Black Holes

For many years the existence of medium sized Black Holes (IMBH$^1$) have eluded scientists. BH of several times the mass of our sun have been found, as well as SMBH with millions of sun masses. SMBH's ...
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Black Holes: More Than One Entry Point?

Most animations and drawings of Black Holes that I've seen usually depict some kind of funnel which is the "entrance" to the black hole; let's call this the front. Are there more than one ...
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Would time go by infinitely fast when crossing the event horizon of a black hole?

If you were to fall into a black hole, my understanding is that from your reference point, time would speed up (looking out to the rest of the universe), approaching infinity when approaching the ...
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Whats the deal with black holes and “no information from inside the event horizon can leave”?

I don't know if this would fall under the other questions but I have always been confused by this... Information has left the black hole; its mass, rotation, location, and a few other properties. My ...
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What would I experience on a planet orbiting close to a black hole? [closed]

I can't get my head around it completely. I am standing on an Earth-sized planet circling a black hole. Let's assume the planet to be an incompressible one. It is observable that matter is sucked in ...
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Does this black hole mass/galaxy stellar mass relation hold for extremely low-mass galaxies?

I read a preprint last week (Palmese & Conselice 2020) that suggested that the recent gravitational wave detection GW190521 could be the end result of a merger of two extremely low-mass galaxies. ...
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Binaries consisting of a black hole and a non-black hole?

Are there any known binary systems in which one member is a black hole and the other is not a black hole (main sequence star, giant, neutron star, white dwarf, whatever)? Googling seems to turn up ...
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How far away was the binary black hole that produced GW170729?

GW170729 was gravitational wave signal's detected by the Virgo and LIGO detectors. I read the following in a news report: Known as GW170729, in accordance with the date of its discovery (in US ...
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How does Hawking Radiation work exactly?

I know that a particle and anti particle, virtual particles, spawn at the edge of an event horizon, and one particle falls into the black hole, and the other goes out, but how does the other know how ...
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If all stars rotate, why was there a theory developed that requires non-rotating stars?

According to Penrose's research, a non-rotating star would end up, after gravitational collapse, as a perfectly spherical black hole. However, every star in the universe has some kind of angular ...
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What would happen if a medium -sized black hole passed the Earth?

I asked already a similar question about the Earth orbiting a black hole but it was closed. So I ask a new one. What if the solar system passes a black hole? Say it has a mass of ten suns and the hole ...
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Can Quantum tunneling be possible within Blackhole ? And if so, could that be the source of Dark Energy?

Quantum tunneling starts happening when there are empty energy states available for the electrons to occupy and the energy barrier is of the order of the wavefunction of the electrons. Could there be ...
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What does it mean that a black hole has a magnetic field?

Black holes have a magnetic field around them. What does this mean for the interior of the holes? That a net electric charge is "flowing in one direction?" Or at least a net current was ...
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Spaghettification of hard-things/Elements

Is it possible for a Black Hole to easily stretch or turn any hard object (Like: Diamond, Gold bar, Platinum bar, Brass) into spaghettification state in just a fraction of seconds or minute once it ...
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Can a small black hole orbit a large star?

I recently read about the discovery of a tiny black hole (with only three times the mass of the sun) nicknamed ‘The unicorn’ about 1500 light years from earth. This got me thinking, can this black ...
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What did Hawking mean when he said “things can get out of a black hole”?

I was wondering about this quote I read the other day, by Stephen Hawking: "Black holes ain’t as black as they are painted. They are not the eternal prisons they were once thought. Things can ...
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Can the other side of the observable universe be seen as a black hole?

When looking at the objects near the horizon of the observable universe, the objects seem to emit radiation that is red-shifted. Time seems to advance at a slower rate than our own and at the horizon ...
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Would a possible accretion disk around a primordial black hole 500 au from the Sun be visible in present telescopes?

If the hypothetical two-inch black hole 500 au from the Sun had an accretion disk, might current telescopes detect it already or do we have to wait till the Vera Rubin Observatory starts work?
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Do photons slow down as they approach the event horizon of a black hole?

So, if a black hole is so dense, that light cannot escape, what happens to the photons as the approach and go past the event horizon (or some other horizon, about which I am ignorant)? Do photons ...
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Do black holes have “age” when they form?

I was thinking about black holes, and I know that they form by the death of massive stars. I was wondering, though, do they technically have an "age" when they're born? Do they begin at 0 ...
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What is Lawrence Krause's theory of total energies?

Does Lawrence Krauss theory say that the total energy in the universe is equal to zero or that the energy in the entire universe remains constant and the mass in the entire universe also remains ...
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Do the orbits of 14 TNOs even need an explanation (a planet mass) or is it just for historical reasons (how they formed)?

From Uranus' orbit we concluded there must be another planet beyond Uranus, eventually discovered and named Neptune. The same happened when Pluto was about to be discovered (though on false premises). ...
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Can an entire star pass through the event horizon of a black hole unharmed?

Can there be any black hole big enough that a regular sized star can pass through its event horizon unharmed?
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Understanding various conditions where a star and a black hole meet and there is no tidal disruption; what all can we infer from this diagram?

Can an entire star pass through the event horizon of a black hole unharmed? is a one sentence HNQ with an amazing (to me at least) answer: for supermassive black holes larger than roughly 100 million ...
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Why did astronomers believe most or all stellar black holes had masses no greater than 15 solar masses?

The so-called 'mass gaps' for black holes, according to theoretical models, are between 2-5 solar masses and 50 to 150 solar masses. (Actually, I have read that there is no good theoretical reason ...
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If the spacetime singularity at a black hole's event horizon is an artificial one then how can it be real?

If the metric belonging to the spacetime of a black hole is expressed as the Schwarzschild metric, it turns out that there is a coordinate singularity at the event horizon. If we use an alternative ...
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If a black hole has the same mass as me, then why dont i suck everything at my center of mass?

So, a black hole is very dense that you can get really close to its center of mass that it has a strong pull, well, if i have the mass of a black hole that has a really small event horizon, why doesnt ...
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Can Hawking Radiation ever be detected and does it exist? [duplicate]

I'm researching black hole Hawking radiation for a contest, and so far I get the overall gist of how the process works. But as far as I've searched, there hasn't been any confirmed observational ...
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How do we know that supermassive black holes can gain mass by means other than merging with other supermassive black holes?

I just stumbled across the following answer "update" from 2013: This just in, recent observations have ruled out the possibility that SMBHs gain mass only through merging with other black ...
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If a black hole has a mass similar to a star, why does it have a different gravitational pull?

Say there is a black hole with 1 solar mass, having the sun's mass, it would have the same gravity as the sun, right? But it still has an event horizon, so why does it have such a strong gravitational ...
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Astrophysical Jet Size?

I am wondering about what is the estimated size of astrophysical jet that shoots out from a black hole, I don’t know if it is determined by the size of a black hole. What would classify a black hole ...
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How deep and shaped is the depth of a black hole?

A common representation of a black hole is a black circle which if I'm correct, indicates its breadth. This representation depicts it as a 'plate', so a really small depth compared to its breadth. ...
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Which came first: black holes or galaxies?

In other terms, did galaxies grow around black holes at their center?
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What is the Inner Horizon of a rotating black hole?

My understanding is that any object with non-zero angular momentum which undergoes gravitational collapse to a black hole will become a rotating black hole. In reality all black holes will be rotating ...
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Can Newton's gravity equation explain why black holes are so strong?

I was just wondering why black hole's gravitational forces are so powerful. I know it's usually explained by Einstein's relativity which states that when an object becomes infinitely dense (a compact ...

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