29

It is quite likely there is an astrophysical upper limit to the mass of a black hole that can be produced during the core collapse of a massive star, caused by the pair instability supernova phenomenon. There isn't an observational bias against detecting more massive black holes in the range of 100 to a few hundred $M_{\odot}$. Details: The frequency of ...


24

The picture isn't a "colour" picture - it is monochrome. i.e. It is obtained at a single microwave wavelength of 1.3 mm, and so not at any wavelength you could see (Akiyama et al. 2019). There isn't therefore any spectral information that would reveal the expected Doppler effect. Any difference of colour in the "false-colour picture" is ...


22

I think, that's a bit semantics, and a question of what do you call 'I see something': If you see the shadow cast by an object on a bright background - do you see the object? Do you see Mercury or Venus when it passes in front of the disk of our sun? Similarly, if you look an object through an atomic force microscope - do you see the object, or do you just ...


21

Gravitational waves are efficiently emitted by massive black holes orbiting each other - the power emitted increases with mass. Hawking radiation on the other hand is a process that increases with decreasing mass. As a result only very tiny black hole binaries would emit more power in Hawking radiation than they do in gravitational waves; at least towards ...


16

This is the Newtonian model of gravity. It is a very good model, it is used for accurate calculating the motion of objects in the solar system to a very high degree of accuracy. However, for very strong gravitational fields you need to use Einstein's model, which accounts for things like the constant speed of light for all observers. I'm not going to go into ...


16

Part of the answer is easy. The strain measured in that event was about $0.25\times 10^{-21}$. That is an object $1m$ long would be squeezed by $0.25\times 10^{-21} m$ in one direction and stretched by the same amount in the orthogonal direction. The strain drops off linearly with distance from the black hole, so to achieve a distortion of 1mm in something ...


13

It is not well known, but a paper by M. Brightman et al gives a value of $10^{6.3\pm0.4}$ or between 8 hundred thousand and 5 million solar masses, while noting that this estimate is lower than previous estimates which had $10^{6.95}$ or about 9 million masses. It seems that, although the galaxy is face-on to us, its black hole is viewed from the edge. This ...


12

No, you cannot "see" a black hole, only the way that it interacts with objects or light in its vicinity. In terms of interacting with other objects, the classic observations that betray the presence of a black hole are the very rapid motions of stars and gas close to an object with a large mass, but which cannot be directly seen. Examples include low- and ...


12

Not enough to worry about. Most neutrinos we detect on Earth come from the sun. The black hole at the centre of the galaxy is not so close to a star as the Earth is so you would expect the neutrino flux to be lower than on Earth, let's assume it is similar: about $10^{11}$ neutrinos per $\text{cm}^2$ per second. But each neutrino is light, even including ...


12

We can currently only detect gravitational radiation when it is extremely intense: in the last fraction of a second. For example the first gravitational wave detection lasted less 0.15 seconds. The black holes are releasing gravitational radiation with every orbit, but that radiation is too weak for us to detect. It takes a colossal amount of energy being ...


11

M87 is an active galaxy with an accreting, rotating central black hole of mass $M\simeq6.5\times10^9M_{\odot}$ (Akiyama et al. 2019). It is the inner disk surrounding this black hole that produces, among radiation, the 1.3 mm synchrotron emission observed by the Event Horizon Telescope, as well as the relativistic jets emitted perpendicular to the disk's ...


10

Applying a numerical density to a black hole isn't possible. The material inside the event horizon will fall to a "singularity" (or some other ultrahigh density state that we currently have no adequate theory to describe) on a relatively short timescale. What you can do, is exactly what you have done, which is divide the gravitational mass of a black hole ...


10

The Schwarzschild metric can be written as $$ c^2 d\tau^2 = \left( 1 - \frac{r_s}{r}\right)\ dt^2 - \left(1 - \frac{r_s}{r}\right)^{-1}\ dr^2 - ...,$$ where $r$ is the radial coordinate, $t$ is the coordinate time, $\tau$ is the proper time (that measured on an observer's own clock) and $r_s = 2GM/c^2$ is the Schwarzschild radius. I have left out the angular ...


10

Black holes formed after the epoch of primordial nucleoynthesis would be part of the baryonic matter, since they would be mostly formed of baryons. It is possible or even probable that every black hole must contain some non-baryonic matter too, since there is nothing to prevent it being accreted, in small amounts, directly into black holes. However, the ...


9

All the binary mergers chirp, but the overall timescale of the event depends on the total system mass (or rather the chirp mass - see below). The more massive the system, the more rapid the evolution of the amplitude and frequency and the lower the orbital frequency when it finally merges. What you observe is also governed by the response of the detector - ...


8

There are of the order of tens of millions of stars we can observe with telescopes. We can see, in all these observations, the various stages of development of similar classes of stars (which we can classify using stellar spectra - a highly developed science). So we have observed all the stages of development in different, but similar stars. Think of it ...


8

The Brightest Cluster Galaxy (BCG) in Abell 2261 ("Abell 2261-BCG") is a massive elliptical; these almost always seem to have supermassive black holes in their centers. In addition, the center of the galaxy has a large region of relatively low stellar density (a "core"), something usually thought to be produced by the merger of two SMBHs ...


7

We don't know for sure. It is possible that random fluctuations in the density of matter of the early universe created black holes that could be much smaller than regular black holes formed by stellar collapse. These would have formed in the moments after the big bang. Otherwise the first stars formed about 400 million years after the big bang, and some of ...


7

You are essentially asking the following: if someone falls from the Earth from some way beyond the event horizon of a black hole, how long after they have left can an observer on Earth still signal to them with a light beam? The answer of course depends on exactly how far the Earth is from the black hole. It is also often forgotten that it is not just light ...


7

Just a supplement to @JamesK's excellent answer. The image below (from Caltech/MIT by way of New Sciencist) shows what was detected for one collision. On the left (at the start) the blackholes orbit one another about every 0.03 seconds, but the waveform is too faint to detect. At about 0.3 seconds on the Time axis the waves start being detectable and the ...


7

The duration of a gravitational wave detection is not particularly important in detecting electromagnetic counterparts, although the fact that they are not recurrent or repeating sources is. Binary systems continually emit gravitational waves, up until the time that they merge, predominantly at twice the orbital frequency. At the same time, the power emitted ...


7

The answer is that there is a limited rate at which matter that can be crammed into a black hole of this size. That rate is small enough that the black hole will traverse through the Sun hardly picking up any mass (when expressed as a fraction of its original mass). Details: You could use the Bondi-Hoyle accretion rate: $$\dot{M} = \frac{dM}{dt} = \pi \rho \...


6

M87 was actually the easiest black hole for the Event Horizon Telescope (EHT) to attempt, and was thus sensibly its first target. For the EHT to work you need 1) an active BH accreting matter such that it is a strong radio source, and 2) that it be close and massive enough to be angularly large. While M87 is some 20x further away than, say M31 or M33, it ...


6

Yes, we can, indeed, "see" a black hole and we just did not too long ago. You see, being able to "see" an object is not solely about "reflection" alone: rather, you "see" things by them interacting in any way with the light that reaches your eye (or other "seeing" instrument), and then by your eye interacting with that object-interacted radiation. ...


6

These questions turn on an even more fundamental one. "Are stars governed by the same laws of physics that we observe in the laboratory on Earth?" If the answer is "yes" then, for example, stars can't shine forever because their energy source will run out; large clouds of warm gas cannot just remain because they will collapse under their own gravity; and ...


5

The observation did indeed confirm general relativity, see e.g. Lisa Grossman wrote in October 2020 for ScienceNews: The first black hole image helped test general relativity in a new way That iconic image, of the supermassive black hole at the center of the galaxy M87 about 55 million light-years away, showed that the shadow closely matched general ...


5

“We think that ‘The Cow’ is the formation of an accreting black hole or neutron star,” said Northwestern’s Raffaella Margutti, who led the research. “We know from theory that black holes and neutron stars form when a star dies, but we’ve never seen them right after they are born. Never.” ... Another team of astronomers, led by Paul Kuin from, an ...


5

This article explains what the image shows. This distinct structure is a result of the warped spacetime around massive objects like black holes. The ring of light is comprised of photons from the hot, radiating gas that surrounds the black hole, whose paths have been bent around the black hole before arriving at our telescopes. The dark region in the ...


5

We've certainly seen supernovae, and in at least one case we've seen the star before the supernova (and its not there afterwards) Stars are not born from black holes [I wonder where you got that idea from. A little better prior research would help you ask better questions] Black holes are formed at the end of the life of some stars (those much larger than ...


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