APOD: Flashes of the Crab Pulsar (2021 Feb 09)

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APOD: Flashes of the Crab Pulsar (2021 Feb 09)

Post by APOD Robot » Tue Feb 09, 2021 5:09 am

[img]https://apod.nasa.gov/apod/calendar/S_210209.jpg[/img] Flashes of the Crab Pulsar

Explanation: It somehow survived an explosion that would surely have destroyed our Sun. Now it is spins 30 times a second and is famous for the its rapid flashes. It is the Crab Pulsar, the rotating neutron star remnant of the supernova that created the Crab Nebula. A careful eye can spot the pulsar flashes in the featured time-lapse video, just above the image center. The video was created by adding together images taken only when the pulsar was flashing, as well as co-added images from other relative times. The Crab Pulsar flashes may have been first noted by an unknown woman attending a public observing night at the University of Chicago in 1957 -- but who was not believed. The progenitor supernova explosion was seen by many in the year 1054 AD. The expanding Crab Nebula remains a picturesque expanding gas cloud that glows across the electromagnetic spectrum. The pulsar is now thought to have survived the supernova explosion because it is composed of extremely-dense quantum-degenerate matter.

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Re: APOD: Flashes of the Crab Pulsar (2021 Feb 09)

Post by Ann » Tue Feb 09, 2021 5:20 am

The exact same video was posted here in the Recent Submissions video submissions thread a few days ago by Martin Fiedler, except that he called himself Subspacetransmitter here.

viewtopic.php?p=310477#p310477

Martin has written a detailed description of how he managed to capture the flashings of the pulsar in the Crab Nebula.

That's so well done, Martin! :clap:

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Re: APOD: Flashes of the Crab Pulsar (2021 Feb 09)

Post by Subspacetransmitter » Tue Feb 09, 2021 9:42 am

Thanks Anna. There is also the original GIF linked, which runs repetitively, so you can see the flashes much better.

Martin

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Re: APOD: Flashes of the Crab Pulsar (2021 Feb 09)

Post by sillyworm 2 » Tue Feb 09, 2021 1:12 pm

Thanks for the link Ann..I could not make out the flash in today's apod.

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Re: APOD: Flashes of the Crab Pulsar (2021 Feb 09)

Post by E Fish » Tue Feb 09, 2021 2:15 pm

I had to double check because I didn't realize when I started the video that it was only one second. :) But very cool. I'll be allowed to teach the intro to astronomy class again this summer and I might have to show this when we talk about pulsars.

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Re: APOD: Flashes of the Crab Pulsar (2021 Feb 09)

Post by smitty » Tue Feb 09, 2021 2:31 pm

Cool, but would have been helpful to have some sort of arrow or pointer pointing to the exact location of the flashes.

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Re: APOD: Flashes of the Crab Pulsar (2021 Feb 09)

Post by Ann » Tue Feb 09, 2021 3:03 pm

sillyworm 2 wrote:
Tue Feb 09, 2021 1:12 pm
Thanks for the link Ann..I could not make out the flash in today's apod.
Crab Nebula pulsar.png

The pulsar can be seen a little above center, center left.

Ann
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Re: APOD: Flashes of the Crab Pulsar (2021 Feb 09)

Post by orin stepanek » Tue Feb 09, 2021 3:04 pm

You had to be super alert to catch the flashes in todays video! At regular speed I barely caught the flashes; at 1/4 speed it was quite easy to see them! 8-)

hs-2005-37-a-large_web.jpg
What a beautiful Nebula the Crab is; even in regular light!
It is too bad the lady in 1957 didn't get her name credited
to spotting the flashes! :shock:
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Re: APOD: Flashes of the Crab Pulsar (2021 Feb 09)

Post by Chris Peterson » Tue Feb 09, 2021 3:07 pm

I designed a procedure to do this a number of years ago, using mostly conventional imaging techniques. Rather than adding short exposures, my plan was to utilize a shutter synchronized to the pulse rate. This allows for long exposures, and by adjusting the phase of the shutter, capturing different parts of the pulsation cycle.

I ran into some problems procuring an appropriate LCD shutter, and didn't proceed. But such shutters are now readily available and inexpensive. I guess I should take another go at it.
Chris

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Re: APOD: Flashes of the Crab Pulsar (2021 Feb 09)

Post by johnnydeep » Tue Feb 09, 2021 4:53 pm

Ann wrote:
Tue Feb 09, 2021 3:03 pm
sillyworm 2 wrote:
Tue Feb 09, 2021 1:12 pm
Thanks for the link Ann..I could not make out the flash in today's apod.
Crab Nebula pulsar.png

The pulsar can be seen a little above center, center left.

Ann
I saw it straight away, but only saw 2 flashes in the two second long video. I was expecting having to attempt to see 30 flashes per second, which is the actual pulse rate. Somewhat disappointed I am. Are there more flashes that I'm failing to discern, even at .25 speed?

EDIT: well, 2 bright flashes, and perhaps one dim one between those two. Though that could just as well be an artifact.
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Re: APOD: Flashes of the Crab Pulsar (2021 Feb 09)

Post by neufer » Tue Feb 09, 2021 6:01 pm

johnnydeep wrote:
Tue Feb 09, 2021 4:53 pm

I saw it straight away, but only saw 2 flashes in the two second long video. I was expecting having to attempt to see 30 flashes per second, which is the actual pulse rate. Somewhat disappointed I am. Are there more flashes that I'm failing to discern, even at .25 speed?
https://en.wikipedia.org/wiki/Photosensitive_epilepsy wrote:
Click to play embedded YouTube video.
<<Photosensitive epilepsy (PSE) is a form of epilepsy in which seizures are triggered by visual stimuli that form patterns in time or space, such as flashing lights; bold, regular patterns; or regular moving patterns. PSE affects approximately one in 4,000 people (1 in 20 of those with epilepsy). The visual trigger for a seizure is generally cyclic, forming a regular pattern in time or space. Flashing lights or rapidly changing or alternating images (as in clubs, around emergency vehicles, near overhead fans, in action movies or television programs, etc.) are examples of patterns in time that can trigger seizures, and these are the most common triggers.

When functioning correctly, mains-powered fluorescent lighting has a flicker rate sufficiently high (twice the mains frequency, typically 100 Hz or 120 Hz) to reduce the occurrence of problems. However, a faulty fluorescent lamp can flicker at a much lower rate and trigger seizures. Newer high-efficiency compact fluorescent lamps (CFL) with electronic ballast circuits operate at much higher frequencies (10–20 kHz) not normally perceivable by the human eye, though defective lights can still cause problems.

An animated segment of a film promoting the 2012 Summer Olympics was blamed for triggering seizures in people with photosensitive epilepsy. The charity Epilepsy Action received telephone calls from people who had seizures after watching the film on television and online. In response, the London 2012 Olympic Committee removed the offending segment from its website.

The 2018 Pixar film Incredibles 2 contains scenes with flashing lights starting about an hour into the film, in which a villain called the Screenslaver hypnotizes other characters. After concerns over possible triggering of seizures due to this scene, theatres posted warnings for audiences with this condition.

Cyberpunk 2077, a video game released in December 2020, contains a "braindance" sequence with red and white flashing lights which reportedly resembles the patterns produced by medical devices used to intentionally trigger seizures. Liana Ruppert, a journalist for Game Informer who has photosensitive epilepsy, experienced a grand mal seizure while reviewing the game days before its release. After criticism from epilepsy advocacy groups that the game's disclaimers were insufficient, CD Projekt Red stated that it would work on a "more permanent solution.">>
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Re: APOD: Flashes of the Crab Pulsar (2021 Feb 09)

Post by bystander » Tue Feb 09, 2021 6:02 pm

Ann wrote:
Tue Feb 09, 2021 5:20 am
...
viewtopic.php?p=310477#p310477
...
Subspacetransmitter wrote:
Tue Feb 09, 2021 9:42 am
...
There is also the original GIF linked, which runs repetitively, so you can see the flashes much better.
...
johnnydeep wrote:
Tue Feb 09, 2021 4:53 pm
...
EDIT: well, 2 bright flashes, and perhaps one dim one between those two. Though that could just as well be an artifact.
...
Subspacetransmitter wrote:
Tue Feb 02, 2021 10:29 am
...
According to my research on the pulsar, it has two maxima in the 33.5ms of its period, one bright and one fainter, both lasting about 5ms. This results in the minimum necessary exposure time (5ms).
...
Pulsar_Animation_Medium[1].gif
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Re: APOD: Flashes of the Crab Pulsar (2021 Feb 09)

Post by johnnydeep » Tue Feb 09, 2021 7:04 pm

bystander wrote:
Tue Feb 09, 2021 6:02 pm
Ann wrote:
Tue Feb 09, 2021 5:20 am
...
viewtopic.php?p=310477#p310477
...
Subspacetransmitter wrote:
Tue Feb 09, 2021 9:42 am
...
There is also the original GIF linked, which runs repetitively, so you can see the flashes much better.
...
johnnydeep wrote:
Tue Feb 09, 2021 4:53 pm
...
EDIT: well, 2 bright flashes, and perhaps one dim one between those two. Though that could just as well be an artifact.
...
Subspacetransmitter wrote:
Tue Feb 02, 2021 10:29 am
...
According to my research on the pulsar, it has two maxima in the 33.5ms of its period, one bright and one fainter, both lasting about 5ms. This results in the minimum necessary exposure time (5ms).
...
Pulsar_Animation_Medium[1].gif
Ok, so apparently I saw the only flashes recorded in the video (and gif)? Is it not possible to record every flash in a video that we could see (and discern the separate flashes if we slowed it down)? Clearly, some fancy processing would be needed, but since we know the period of the flashes, we must be able to determine separate 33.5 ms flashes one way or another.
"To Boldly Go......Beyond The Fields We Know."

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Re: APOD: Flashes of the Crab Pulsar (2021 Feb 09)

Post by Chris Peterson » Tue Feb 09, 2021 7:24 pm

johnnydeep wrote:
Tue Feb 09, 2021 7:04 pm
bystander wrote:
Tue Feb 09, 2021 6:02 pm
Ann wrote:
Tue Feb 09, 2021 5:20 am
...
viewtopic.php?p=310477#p310477
...
Subspacetransmitter wrote:
Tue Feb 09, 2021 9:42 am
...
There is also the original GIF linked, which runs repetitively, so you can see the flashes much better.
...
johnnydeep wrote:
Tue Feb 09, 2021 4:53 pm
...
EDIT: well, 2 bright flashes, and perhaps one dim one between those two. Though that could just as well be an artifact.
...
Subspacetransmitter wrote:
Tue Feb 02, 2021 10:29 am
...
According to my research on the pulsar, it has two maxima in the 33.5ms of its period, one bright and one fainter, both lasting about 5ms. This results in the minimum necessary exposure time (5ms).
...
Pulsar_Animation_Medium[1].gif
Ok, so apparently I saw the only flashes recorded in the video (and gif)? Is it not possible to record every flash in a video that we could see (and discern the separate flashes if we slowed it down)? Clearly, some fancy processing would be needed, but since we know the period of the flashes, we must be able to determine separate 33.5 ms flashes one way or another.
It would be exceedingly difficult to record this object realtime. There simply aren't enough signal photons to rise above the noise floor, even of an extremely low noise system.

At the least, it would require an imaging system with near zero noise and an extremely large aperture.

(The pulsar was first detected with a radio telescope, and its period accurately measured that way, not optically. It was later observed to vary rapidly in the optical range, by using a shuttering technique similar to what I described above.)
Chris

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Re: APOD: Flashes of the Crab Pulsar (2021 Feb 09)

Post by johnnydeep » Wed Feb 10, 2021 3:09 pm

Chris Peterson wrote:
Tue Feb 09, 2021 7:24 pm
johnnydeep wrote:
Tue Feb 09, 2021 7:04 pm
bystander wrote:
Tue Feb 09, 2021 6:02 pm




Pulsar_Animation_Medium[1].gif
Ok, so apparently I saw the only flashes recorded in the video (and gif)? Is it not possible to record every flash in a video that we could see (and discern the separate flashes if we slowed it down)? Clearly, some fancy processing would be needed, but since we know the period of the flashes, we must be able to determine separate 33.5 ms flashes one way or another.
It would be exceedingly difficult to record this object realtime. There simply aren't enough signal photons to rise above the noise floor, even of an extremely low noise system.

At the least, it would require an imaging system with near zero noise and an extremely large aperture.

(The pulsar was first detected with a radio telescope, and its period accurately measured that way, not optically. It was later observed to vary rapidly in the optical range, by using a shuttering technique similar to what I described above.)
Thanks, Chris. Ah, radio waves: is there nothing they're not good for!
"To Boldly Go......Beyond The Fields We Know."

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Re: APOD: Flashes of the Crab Pulsar (2021 Feb 09)

Post by attasm1@mymts.net » Wed Feb 10, 2021 3:33 pm

This achievement is fantastic! Congratulations, Martin.
A few years back I wrote about the possibility of an amateur sky gazer with some ingenuity and equipment successfully imaging the Crab pulsar flashing.
If you're interested, here is the text of the article, from the Journal of the Royal Astronomical Society of Canada, June 2009, pp.97-98.
Best wishes for continued success,
Michael

Heart of the Crab: Variable to the Extreme

Michael Attas
The massive Hubble portrait of the Crab Nebula, my favourite deep-sky object, has decorated my computer desktop since 2005. Recently I stumbled across some amazing historical tidbits about the Crab on the World Wide Web. The highlight was a you-are-there website describing the thrilling discovery of the neutron star at the Crab’s core. Thinking about the advance of observing technology over the years covered by the websites leads me to pose an observing challenge to those among you who track the pulsations of variable stars.

In many ways, the first item on Monsieur Charles Messier’s list of fuzzy non-comets is the most peculiar. His 1774 list includes many galaxies, globular clusters, and planetary nebulae, but M1 is none of these. The smudge in Taurus received the nickname “Crab Nebula” a century later from Lord Rosse, who saw filaments like crab’s legs extending from the central mass. It looked strange enough, but how strange it actually was became apparent only in the 20th century.

With the gradual understanding of the mechanism of supernovae came the conception of a supernova remnant, or SNR. The debris remaining after a star explodes can take many forms, and naturally it changes over time. Changes in the Crab’s shape were evident over a few decades, with the filaments appearing to be expanding from the centre. Based on the expansion rate, astronomers estimated the supernova occurred almost a millennium ago. Old Chinese records indicate that the Crab Nebula is the remnant of a star that exploded in 1054 -- or at least that’s when the light from the explosion reached Earth. Since then, the puff left behind has been expanding and evolving.

Our understanding of SNRs has also been evolving, thanks to both theoretical advances (especially general relativity) and observations at wavelengths outside the visible range. Observations made using early radio telescopes linked the Crab to a bright radio source. Both X-ray and gamma imaging confirmed there was a compact, energetic enigma there. The hot, bluish 16th-magnitude star named Baade’s Star or CM Tauri at the heart of the Crab was found to have a peculiar light spectrum, but seemed too faint to be the source of all the electromagnetic energy observed. Then, not long after the announcement in early 1968 of the accidental discovery of pulsars, the compact source was found to emit radio pulses at a rate of thirty times a second. That was convincing evidence that the core of the Crab Nebula is a rapidly rotating neutron star, a bizarre object as massive as the Sun but only a dozen kilometers in diameter. As it rotates, emissions from its magnetic poles sweep across the sky, with the radio waves flashing past the Earth like a searchlight beam.

Astronomers immediately wondered if the visible light from the neutron star at the Crab’s core was also flashing. The discovery of the optical pulsations of CM Tauri is an exciting chapter in 1960s astronomy, and one that’s extremely well documented. Thanks to the physicist Philip Morrison and the American Institute of Physics, the website http://www.aip.org/history/mod/pulsar/pulsar1/01.html contains descriptions, interviews, images, and audio from the very moment of discovery. It is a fascinating look at how real science advances, by a combination of enthusiasm, knowledge, risk-taking, and a sense of adventure. John Cocke and Michael Disney, two young theoretical astronomers, found themselves at the University of Arizona’s Steward Observatory on Kitt Peak late in 1968. They needed experience at actually using a telescope and somehow realized that they could put together all the pieces they needed to attempt this challenging observation. Variable stars don’t get much more variable than this. How do you detect a star flashing 30 times a second? You need fast imaging instrumentation, plus electronics to compile data in special ways over an extended period, plus a decent-sized telescope, of course. (The one they used was a 36-incher.)

With electronics expert Don Taylor and night assistant Bob McCallister, the astronomers booked a few nights on the scope and set up to collect data. Even pointing the telescope was a challenge, since the target star was too faint to observe visually. Three nights of observations produced no pulsations, and then cloudy nights scrubbed the next sessions. After some head-scratching they realized they had miscalculated the expected pulse period: they had used the wrong formula to correct for the Doppler effect caused by the earth’s revolution around the sun. A last-minute cancellation on January 15, 1969 gave them access to the telescope once again. The website puts us right in the room with them as they began their observing run that night. What makes the setting so real is that they had a tape recorder running while making their observations, so they could keep track of the data they were collecting. Their voices on the tape reveal a mix of frustration, delight, incredulity, and finally the flash of success as they saw a clear signal rising out of the electronic noise. After the initial thrill, they knew they had to prove to themselves (and others) that the pulse was real. In order to do this, they demonstrated that it disappeared when they changed the target frequency, and also when they moved the telescope off the target star. The website also puts this moment of discovery in context, with transcripts and audio of several recent interviews, and a variety of images and background information. Their observation was quickly confirmed by another group using another telescope, and the papers announcing the results and confirmation appeared in Nature the following month.

And now, a challenge. We’re in 2009, almost half a century after this discovery. Telescopes, even large ones, are much more accessible to amateurs, and modern electronic imaging brings the power of 1960s professional observatories to our own back yards. Can we detect the flashing of that distant neutron star? What would it take to succeed? I picture a clever amateur using some fast pixel shuffling on a sensitive CCD chip attached to a high-end scope to do the trick. Simpler techniques involving a slotted disk spinning in front of the detector at 30 rpm might also work. Seeing the outcome, say as a pair of images with the neutron star “on” and “off,” would make for an awesome Galileo moment for 2009’s International Year of Astronomy. Let me know if you’re up to the challenge.
Last edited by bystander on Wed Feb 10, 2021 4:49 pm, edited 1 time in total.
Reason: added link to journal

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Re: APOD: Flashes of the Crab Pulsar (2021 Feb 09)

Post by Astronymus » Wed Feb 10, 2021 6:12 pm

The Crab Pulsar flashes may have been first noted by an unknown woman attending a public observing night at the University of Chicago in 1957 -- but who was not believed.
Why am I not surprised? :roll:

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Re: APOD: Flashes of the Crab Pulsar (2021 Feb 09)

Post by neufer » Fri Feb 12, 2021 8:20 pm

Click to play embedded YouTube video.
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