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The Nobel Prize in Physics 2020

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Re: The Nobel Prize in Physics 2020

#21

Post by me_me_me »

frereubu wrote: post #9
tchalla wrote: post #2

The press release has a popular science background - https://www.nobelprize.org/uploads/2020/10/popular-physicspr... Highly recommend the illustrations on the press release for a quick overview Cross section of a black hole (pdf) - https://www.nobelprize.org/uploads/2020/10/fig2-phy-en-cross... The Milky Way - https://www.nobelprize.org/uploads/2020/10/fig3-phy-en-milky... Stars closest to the centre of the Milky Way…

An illustration in the press release contains this phrase: "When a massive star collapses under its own gravity, it forms a black hole that is so heavy that it captures everything that passes its event horizon. Not even light can escape. At the event horizon, time replaces space and points only forward. The flow of time carries everything towards a singularity furthest inside the black hole, where density is infinite…

https://www.youtube.com/watch?v=mht-1c4wc0Q

I hope it helps. I think this is the cleanest explanation with actual visual representation.

Edit: Sorry this one is even better.

How Time Becomes Space Inside a Black Hole | Space Time

https://www.youtube.com/watch?v=KePNhUJ2reI

Re: The Nobel Prize in Physics 2020

#23

Post by potiuper »

tchalla wrote: post #2

The press release has a popular science background - https://www.nobelprize.org/uploads/2020/10/popular-physicspr... Highly recommend the illustrations on the press release for a quick overview Cross section of a black hole (pdf) - https://www.nobelprize.org/uploads/2020/10/fig2-phy-en-cross... The Milky Way - https://www.nobelprize.org/uploads/2020/10/fig3-phy-en-milky... Stars closest to the centre of the Milky Way…

The PR seems like a double dig on Hawking. "Nothing, not even light, can escape." except Hawking radiation?

Re: The Nobel Prize in Physics 2020

#24

Post by Sharlin »

SiempreViernes wrote: post #10
frereubu wrote: post #9

Earlier quoted context omitted.

An illustration in the press release contains this phrase: "When a massive star collapses under its own gravity, it forms a black hole that is so heavy that it captures everything that passes its event horizon. Not even light can escape. At the event horizon, time replaces space and points only forward. The flow of time carries everything towards a singularity furthest inside the black hole, where density is infinite…

Honestly, "time replaces space" is probably intentionally dramatic: I don't think anyone really means more than that the light-cone is so tilted it lies completely outside of where it started. In practice it just means that wherever you try to go you'll end up in the same place, basically you're going down a funnel and the exceptional thing is that the funnel is made out of spacetime itself.

Well, time does very concretely swap roles with one of the spatial dimensions, namely the radial one. They change signs in the metric, making the radial dimension timelike and the old temporal dimension spacelike.

Re: The Nobel Prize in Physics 2020

#25

Post by stargazer-3 »

fsnowdin wrote: post #16

I thought we already knew there was a supermassive black hole in the center of the Milky Way for a while now? What specifically did Genzel and Ghez do to expand on that knowledge? I'm curious to know.

Back in the day they each led research to detect irrefutable evidence of it. This isn't anything new and groundbreaking.

Re: The Nobel Prize in Physics 2020

#26

Post by SiempreViernes »

potiuper wrote: post #23
tchalla wrote: post #2

The press release has a popular science background - https://www.nobelprize.org/uploads/2020/10/popular-physicspr... Highly recommend the illustrations on the press release for a quick overview Cross section of a black hole (pdf) - https://www.nobelprize.org/uploads/2020/10/fig2-phy-en-cross... The Milky Way - https://www.nobelprize.org/uploads/2020/10/fig3-phy-en-milky... Stars closest to the centre of the Milky Way…

The PR seems like a double dig on Hawking. "Nothing, not even light, can escape." except Hawking radiation?

Hawking radiation is emitted from the outside, if you start beyond the barrier it's usually not counted as an escape.

Re: The Nobel Prize in Physics 2020

#27

Post by Sharlin »

tannhaeuser wrote: post #15
frereubu wrote: post #9

Earlier quoted context omitted.

An illustration in the press release contains this phrase: "When a massive star collapses under its own gravity, it forms a black hole that is so heavy that it captures everything that passes its event horizon. Not even light can escape. At the event horizon, time replaces space and points only forward. The flow of time carries everything towards a singularity furthest inside the black hole, where density is infinite…

Worth noting that the "BH so massive even light can't escape" meme, a staple of popular science, wouldn't make sense since photons don't have mass. What's happening is that space is skewed (according to Schwarzschild if I got it right). It can be better groked with a modern depiction of a BH such as in eg "Interstellar" where the far end of the accretion disk is observed as a second disk.

Light has mass-energy, and mass-energy both affects and is affected by the gravitational field. Indeed it is theoretically possible to make a black hole out of nothing but photons [1].

[1] https://en.wikipedia.org/wiki/Kugelblitz_(astrophysics)

Re: The Nobel Prize in Physics 2020

#28

Post by xioxox »

fsnowdin wrote: post #16

I thought we already knew there was a supermassive black hole in the center of the Milky Way for a while now? What specifically did Genzel and Ghez do to expand on that knowledge? I'm curious to know.

Have a look at the linked documents giving the popular science background.

They led the teams that gave the decisive proof that there is black hole at the galactic centre. The teams developed techniques to precisely measure the orbits of the stars which orbit the central black hole. Looking at the speed of the stars, particularly as they pass close to the object, you can measure its mass and put a constraint on its size. The only thing which is small enough and heavy enough is a black hole. Doing this required lots of advances in data analysis and adaptive optics to be able to measure the stars orbits to enough precision.

Re: The Nobel Prize in Physics 2020

#29

Post by nabla9 »

fsnowdin wrote: post #16

I thought we already knew there was a supermassive black hole in the center of the Milky Way for a while now? What specifically did Genzel and Ghez do to expand on that knowledge? I'm curious to know.

We already know it because Genzel and Ghez discovered it.

Their work goes back 30 years.

Re: The Nobel Prize in Physics 2020

#30

Post by xioxox »

stargazer-3 wrote: post #25
fsnowdin wrote: post #16

I thought we already knew there was a supermassive black hole in the center of the Milky Way for a while now? What specifically did Genzel and Ghez do to expand on that knowledge? I'm curious to know.

Back in the day they each led research to detect irrefutable evidence of it. This isn't anything new and groundbreaking.

I think that's rather unfair. The measurements are still ongoing with ever-increasing accuracy. In 2018 they managed to record the closest approach of the star S2, measuring a velocity of 7000 km/s at its maximum. This was after mapping the full 16 year orbit. I know that Genzel is still actively researching this topic with his group, see e.g. https://www.mpe.mpg.de/7433286/news20200416
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