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Alright, I'm confused. How does this square with Hawking radiation? How can a black hole shrink without shrinking? The article mentions both in the context tha
by eximius 5y ago
Alright, I'm confused. How does this square with Hawking radiation? How can a black hole shrink without shrinking?
The article mentions both in the context that they are reconciled but not how they are reconciled.
- rakkhi 5y agoExactly what I came here to ask. Is Hawking's theory that the area never decreases or that it does not decrease in a black hole merger as was tested here. "central law for black holes predicts that the area of their event horizons — the boundary beyond which nothing can ever escape — should never shrink" this seems to imply the former to me. Does that mean with Hawking radiation the black hole effectively evaporates by loosing mass (?) from the inside without the boundary area never shrinking?
- jleahy 5y agoThey're not reconciled, it's just garbage reporting. The 'area theorem' they are referring to was by Bekenstein and others, not Hawking. It's basically the equivalent of the second law of thermodynamics for black holes (dA/dt>=0 instead of dS/dt>=0). Hawking's insight was that this formula was wrong and the area could decrease due to radiation.
- aliasEli 5y agoIt is a pity about the reporting. But it is a fascinating area of research. I never expected that we could measure gravitational waves in our life time.
- Cthulhu_ 5y agoI'm amazed - to the point of skepticism - that with such minute forces they can extrapolate so much information and prove theories. I mean I'm no astrophysicist, I like the "pop sci" bits, but when I look closer I'm seeing a lot of small numbers and statistics that imply something - e.g. exoplanets based on minute wobbles and brightness variations, water on said exoplanets based on spectrography. It's theories based on tiny but statistically significant data. The pop sci then comes in and makes statements like "second Earth found!11", which is like, whoa hold on, when you look closer all they found is a wobble or dimness variation that kind of implies there might be a planet at a certain distance from its host star. Anyway I don't dispute the findings or that there are exoplanets or whatever, I'm just impressed that they are able to make confident claims on what little information we can receive from here.
- eru 5y agoIt's fascinating what's possible. For example, we know more about the chemical composition of other galaxies than we know about the centre of the earth. Just because we can infer so much from their light spectrum. (For empirical information about the centre of the earth, we are basically limited to seismic data and perhaps the magnetic field and bumps in gravity?)
- DSingularity 5y agoWhy not launch a probe and point its sensors at earth?
- db48x 5y agoThe Earth is opaque. I don’t have a source to cite for this, but I think you can check it easily enough.
- eru 5y agohttps://www.answers.com/Q/Is_the_earth_opaque https://www.answers.com/Q/Is_the_earth_opaque
- nine_k 5y agoWe hardly resolve any individual stars in other galaxies (maybe some giant stars inside Andromeda?), so our idea of chemical composition of other galaxies is very... averaged. We barely can resolve largest and closest exoplanets into a few pixels.
- floxy 5y ago>We barely can resolve largest and closest exoplanets into a few pixels For now... https://arxiv.org/abs/1802.08421 https://arxiv.org/abs/1802.08421 https://www.youtube.com/watch?v=NQFqDKRAROI https://www.youtube.com/watch?v=NQFqDKRAROI
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- untoxicness 5y agoWhile I agree that the article should have mentioned black hole evaporation, I would like to point out that "dA/dt > 0" is commonly referred to as "Hawking's area theorem" as a quick online search can verify and Stephen Hawking certainly did publish on this topic.
- Florin_Andrei 5y agoI think what they really meant in the article is that it can never decrease through processes other than the radiation. E.g., BH mergers and so on, the area always increases.
- morebortplates 5y agoYes, black holes shrink because of Hawking radiation, but in reality this doesn't really happen because black holes are much colder than their surrounding space. Actually they are the coldest objects in nature. Stellar black holes have a temperature of a few Nanokelvins and the average temperature of space is 2.7 K so there's a net gain of energy/mass from absorbed photons from CMB radiation vs emitted photons via Hawking radiation. In order to have a higher temperature than the CMB a black hole would have to be really small with a mass about half of that of the moon.
- eru 5y ago> In order to have a higher temperature than the CMB a black hole would have to be really small with a mass about half of that of the moon. Either that, or you just wait a couple eternities for the CMB to cool down enough.
- morebortplates 5y agoOr primordial black holes with such a small mass actually do exist, who knows...
- sandworm101 5y agoOr you make a smaller one and watch it shrink. It is theoretically possible to construct a smaller black hole by cramming the necessary mass/energy into a small enough space. (Plug a death star into the LHC's big brother.) Such a hole would be very hot and short-lived.
- phkahler 5y agoFrom the outside they must look cold since they can't radiate heat any more than light. That doesnt imply anything about the inside.
- ttul 5y agoThe inside is empty space.
- edem 5y agoIf you drain your bathwater while also running the bath you can have a bathtub that's slowly filling up.
- streamofdigits 5y agoThis might help https://physics.stackexchange.com/questions/169886/black-hole-area-theorem-and-hawking-radiation https://physics.stackexchange.com/questions/169886/black-hol... A black hole merger of this size is unlikely to have any significant quantum aspect