Explanation: Are your eyes good enough to see the Crab Nebula expand? The Crab Nebula is cataloged as M1, the first on Charles Messier's famous list of things which are not comets. In fact, the Crab is now known to be a supernova remnant, an expanding cloud of debris from the explosion of a massive star. The violent birth of the Crab was witnessed by astronomers in the year 1054. Roughly 10 light-years across today, the nebula is still expanding at a rate of over 1,000 kilometers per second. Over the past decade, its expansion has been documented in this stunningtime-lapse movie. In each year from 2008 to 2022, an image was produced with the same telescope and camera from a remote observatory in Austria. The sharp, processed frames even reveal the dynamic energetic emission surrounding the rapidly spinning pulsar at the center. The Crab Nebula lies about 6,500 light-years away toward the constellation of the Bull (Taurus).
The Crab Nebula is the remnant of a supernova explosion that was observed on Earth in the year 1054. The neutron star has a diameter of just around ten kilometers and rotates around its own axis approximately 30 times per second. Thus, it emits light pulses like a lighthouse, and these pulses stretch across the entire electromagnetic spectrum — from long radio waves to visible light and beyond, to the short waves of energetic gamma rays.
Ann
Re: APOD: M1: The Expanding Crab Nebula (2023 Mar 20)
Posted: Mon Mar 20, 2023 3:35 pm
by johnnydeep
So, over that 14 year period the Crab expanded about 0.046 ly, or about 1/20th of a lightyear.
Re: APOD: M1: The Expanding Crab Nebula (2023 Mar 20)
The Crab Nebula is the remnant of a supernova explosion that was observed on Earth in the year 1054. The neutron star has a diameter of just around ten kilometers and rotates around its own axis approximately 30 times per second. Thus, it emits light pulses like a lighthouse, and these pulses stretch across the entire electromagnetic spectrum — from long radio waves to visible light and beyond, to the short waves of energetic gamma rays.
Ann
So, about that "lighthouse" effect... Does every observer in the sphere surrounding a spinning pulsar get to see the pulse, or is it directional? And if everyone, is the strength of the pulse the same for all observers (at the same distance)?
Re: APOD: M1: The Expanding Crab Nebula (2023 Mar 20)
Posted: Mon Mar 20, 2023 3:52 pm
by Chris Peterson
johnnydeep wrote: ↑Mon Mar 20, 2023 3:35 pm
So, over that 14 year period the Crab expanded about 0.046 ly, or about 1/20th of a lightyear.
There's a good deal of uncertainty about how far away M1 actually is, as well as uncertainty about its shape. But we do know its expansion rate along our line of sight very accurately because of spectroscopic measurements of the Doppler shift, yielding an axial speed of 1500 km/s. Because the radial expansion can actually be measured given the visible expansion, a distance can be estimated if we assume the radial expansion rate is the same as the axial one. In which case the distance works out to about 6300 ly, which is consistent with some of the results obtained by other methods.
Re: APOD: M1: The Expanding Crab Nebula (2023 Mar 20)
johnnydeep wrote: ↑Mon Mar 20, 2023 3:35 pm
So, over that 14 year period the Crab expanded about 0.046 ly, or about 1/20th of a lightyear.
There's a good deal of uncertainty about how far away M1 actually is, as well as uncertainty about its shape. But we do know its expansion rate along our line of sight very accurately because of spectroscopic measurements of the Doppler shift, yielding an axial speed of 1500 km/s. Because the radial expansion can actually be measured given the visible expansion, a distance can be estimated if we assume the radial expansion rate is the same as the axial one. In which case the distance works out to about 6300 ly, which is consistent with some of the results obtained by other methods.
Note that I used the 1000 km/s expansion rate from the APOD text. So if it's really 1500 km/s, it would have expanded 50% more over that 14 year animation.
What's the difference between your use of radial, axial, and line-of-sight expansion rates here? I can imagine the expansion rate being different along many different directions from the nebula! Is axial the same as line-of-sight here? And is radial simply the expansion within the plane perpendicular to that line that we see visual evidence of in this animation?
Re: APOD: M1: The Expanding Crab Nebula (2023 Mar 20)
johnnydeep wrote: ↑Mon Mar 20, 2023 3:35 pm
So, over that 14 year period the Crab expanded about 0.046 ly, or about 1/20th of a lightyear.
There's a good deal of uncertainty about how far away M1 actually is, as well as uncertainty about its shape. But we do know its expansion rate along our line of sight very accurately because of spectroscopic measurements of the Doppler shift, yielding an axial speed of 1500 km/s. Because the radial expansion can actually be measured given the visible expansion, a distance can be estimated if we assume the radial expansion rate is the same as the axial one. In which case the distance works out to about 6300 ly, which is consistent with some of the results obtained by other methods.
Note that I used the 1000 km/s expansion rate from the APOD text. So if it's really 1500 km/s, it would have expanded 50% more over that 14 year animation.
What's the difference between your use of radial, axial, and line-of-sight expansion rates here? I can imagine the expansion rate being different along many different directions from the nebula! Is axial the same as line-of-sight here? And is radial simply the expansion within the plane perpendicular to that line that we see visual evidence of in this animation?
I'm using axial as line-of-sight. That's the only line we can measure Doppler shift along unambiguously. Regardless of the terms, the idea is that we can get an accurate measure of distance if we assume the expansion rate is uniform in all directions. And you are correct... that is just an assumption, although not entirely unreasonable, and it is significant that the resulting distance calculation is consistent with that produced by some other methods, and with with current consensus view of what is our best estimate to date.
Re: APOD: M1: The Expanding Crab Nebula (2023 Mar 20)
Posted: Mon Mar 20, 2023 5:03 pm
by Detlef Hartmann
From the images I have measured the maximal radial velocity of the red filaments, the result: 0.159+/-0.014 arcseconds.
Together with an axial velocity of 1500 km/sec. this gives a distance of 6500 lightyears (Crab Nebula (some simple science)).
The Gaia DR3 catalog shows a parallax of 0.5110+/-0.0788 milli arcseconds. This gives a distance of 6384+/-984 lightyears.
Re: APOD: M1: The Expanding Crab Nebula (2023 Mar 20)
Posted: Mon Mar 20, 2023 8:52 pm
by NateWhilk
This is a magnificent movie! I was just as impressed when Mr. Hartman released the 10-year version in 2017. (A humble suggestion: perhaps the next time APOD posts a short video like this, maybe make a single video that contains multiple copies of the source video, which would then be a rough simulation of a loop?)
Before Mr. Hartmann's work, we had only the Walter Baade image (from the 1940s?), but it was ground-breaking in its day. And a search didn't turn up any copies of it except on Phil Plait's website.
Re: APOD: M1: The Expanding Crab Nebula (2023 Mar 20)
Posted: Mon Mar 20, 2023 9:00 pm
by johnnydeep
NateWhilk wrote: ↑Mon Mar 20, 2023 8:52 pm
This is a magnificent movie! I was just as impressed when Mr. Hartman released the 10-year version in 2017. (A humble suggestion: perhaps the next time APOD posts a short video like this, maybe make a single video that contains multiple copies of the source video, which would then be a rough simulation of a loop?)
...
It might help I suppose, but you can also just right-click in the video and select "Loop" from the context menu, and replay it! (It's a Youtube feature.)
Re: APOD: M1: The Expanding Crab Nebula (2023 Mar 20)
Posted: Mon Mar 20, 2023 10:03 pm
by pferkul
What portion is expanding at the rate of 1000 km/s? Presumably the expansion rate falls off as radius squared from the source? So whatever feature is expanding at 1000 km/s it must have moved about 1/20th of a light-year in 14 years.
Re: APOD: M1: The Expanding Crab Nebula (2023 Mar 20)
NateWhilk wrote: ↑Mon Mar 20, 2023 8:52 pm
This is a magnificent movie! I was just as impressed when Mr. Hartman released the 10-year version in 2017. (A humble suggestion: perhaps the next time APOD posts a short video like this, maybe make a single video that contains multiple copies of the source video, which would then be a rough simulation of a loop?)
...
It might help I suppose, but you can also just right-click in the video and select "Loop" from the context menu, and replay it! (It's a Youtube feature.)
I have created a looped animated gif, which in the explanation is linked via time-lapse movie, the youtube movie has been created by the APOD team.
Re: APOD: M1: The Expanding Crab Nebula (2023 Mar 20)
Posted: Mon Mar 20, 2023 11:39 pm
by Uncle Jeff
Astronomers have been taking pictures of the crab for over 100 years. Using a little interpolation, there should be a longer movie out there somewhere.
Re: APOD: M1: The Expanding Crab Nebula (2023 Mar 20)
NateWhilk wrote: ↑Mon Mar 20, 2023 8:52 pm
This is a magnificent movie! I was just as impressed when Mr. Hartman released the 10-year version in 2017. (A humble suggestion: perhaps the next time APOD posts a short video like this, maybe make a single video that contains multiple copies of the source video, which would then be a rough simulation of a loop?)
...
It might help I suppose, but you can also just right-click in the video and select "Loop" from the context menu, and replay it! (It's a Youtube feature.)
Using your advice I got to see much more. And the white stuff clearly moves twice as fast as the red crunch.
Now what is all the talk of measuring the angular speed and the Doppler speed, when the ingredients are moving so independently?
Re: APOD: M1: The Expanding Crab Nebula (2023 Mar 20)
Posted: Tue Mar 21, 2023 3:14 am
by javachip3
How much of a visible supernova remnant like the Crab Nebula was actually ejected by the supernova, and how much was released before the supernova, during the progenitor star's Wolf-Rayet phase? I suspect most of what we see is Wolf-Rayet ejecta that has been ablated, excited, and accelerated by the extreme flux of photons and high-energy particles during the subsequent supernova. See, for example, the recent APOD photo of WR-124. Imagine the bright central star no longer there, imagine the WR ejecta eroded and attenuated, and the resulting pattern would resemble the Crab Nebula.
Re: APOD: M1: The Expanding Crab Nebula (2023 Mar 20)
NateWhilk wrote: ↑Mon Mar 20, 2023 8:52 pm
This is a magnificent movie! I was just as impressed when Mr. Hartman released the 10-year version in 2017. (A humble suggestion: perhaps the next time APOD posts a short video like this, maybe make a single video that contains multiple copies of the source video, which would then be a rough simulation of a loop?)
...
It might help I suppose, but you can also just right-click in the video and select "Loop" from the context menu, and replay it! (It's a Youtube feature.)
I have created a looped animated gif, which in the explanation is linked via time-lapse movie, the youtube movie has been created by the APOD team.
🗸
Re: APOD: M1: The Expanding Crab Nebula (2023 Mar 20)
NateWhilk wrote: ↑Mon Mar 20, 2023 8:52 pm
This is a magnificent movie! I was just as impressed when Mr. Hartman released the 10-year version in 2017. (A humble suggestion: perhaps the next time APOD posts a short video like this, maybe make a single video that contains multiple copies of the source video, which would then be a rough simulation of a loop?)
...
It might help I suppose, but you can also just right-click in the video and select "Loop" from the context menu, and replay it! (It's a Youtube feature.)
I have created a looped animated gif, which in the explanation is linked via time-lapse movie, the youtube movie has been created by the APOD team.
But it's confusing to new-comers like me to watch the Crab Nebula as a beating heart, made to go through reversed motions with no jumps that the YouTube looped playing has.
Even after I had tried to relate to the year count in the top right corner, I was still struggling to see what currents are the radial expansion and what are curly-whirly when they were reversing their tides all the time
Re: APOD: M1: The Expanding Crab Nebula (2023 Mar 20)
It might help I suppose, but you can also just right-click in the video and select "Loop" from the context menu, and replay it! (It's a Youtube feature.)
I have created a looped animated gif, which in the explanation is linked via time-lapse movie, the youtube movie has been created by the APOD team.
But it's confusing to new-comers like me to watch the Crab Nebula as a beating heart, made to go through reversed motions with no jumps that the YouTube looped playing has.
Even after I had tried to relate to the year count in the top right corner, I was still struggling to see what currents are the radial expansion and what are curly-whirly when they were reversing their tides all the time
You, sir, are hardly a newcomer (though you are apparently humble)! And I didn't even notice the year in the top right corner until you mentioned it! Also, you may already know this, but if needed for closer examination of a video, you can click the gear icon in the lower right on the YouTube screen and change the playback speed to .5x or .25x to get a better look. And you can also speed it up, up to 2x normal speed, which is great for getting though boring videos, or slow talkers, in short order.
Re: APOD: M1: The Expanding Crab Nebula (2023 Mar 20)
I have created a looped animated gif, which in the explanation is linked via time-lapse movie, the youtube movie has been created by the APOD team.
But it's confusing to new-comers like me to watch the Crab Nebula as a beating heart, made to go through reversed motions with no jumps that the YouTube looped playing has.
Even after I had tried to relate to the year count in the top right corner, I was still struggling to see what currents are the radial expansion and what are curly-whirly when they were reversing their tides all the time
You, sir, are hardly a newcomer (though you are apparently humble)! And I didn't even notice the year in the top right corner until you mentioned it! Also, you may already know this, but if needed for closer examination of a video, you can click the gear icon in the lower right on the YouTube screen and change the playback speed to .5x or .25x to get a better look. And you can also speed it up, up to 2x normal speed, which is great for getting though boring videos, or slow talkers, in short order.
I was trying to say that this APOD's YouTube video, if looped like you advise, carried more clear message to me than the smooth oscillating motions of the original timelaps. So I am thankful to APOD for stripping the coolness and making the picture more educational
Re: APOD: M1: The Expanding Crab Nebula (2023 Mar 20)
But it's confusing to new-comers like me to watch the Crab Nebula as a beating heart, made to go through reversed motions with no jumps that the YouTube looped playing has.
Even after I had tried to relate to the year count in the top right corner, I was still struggling to see what currents are the radial expansion and what are curly-whirly when they were reversing their tides all the time
You, sir, are hardly a newcomer (though you are apparently humble)! And I didn't even notice the year in the top right corner until you mentioned it! Also, you may already know this, but if needed for closer examination of a video, you can click the gear icon in the lower right on the YouTube screen and change the playback speed to .5x or .25x to get a better look. And you can also speed it up, up to 2x normal speed, which is great for getting though boring videos, or slow talkers, in short order.
I was trying to say that this APOD's YouTube video, if looped like you advise, carried more clear message to me than the smooth oscillating motions of the original timelaps. So I am thankful to APOD for stripping the coolness and making the picture more educational
M1: The Expanding Crab Nebula
