Love Professor Mike Merrifield. Always, a joy to watch his videos. On a side note, I just searched and noticed there are no videos on Phoenix A* (or TON 618 for that matter)... just a hint, hint, nudge, nudge. Would be fascinating hearing the DeepSkyVideos' crew talking about these mind-blowing objects.
So fun, the theory, the research, but also your interaction and professors enthusiasm! I once tried to get a picture of it with my 6‘‘-SC telescope. If you know what it is you recognize it, but it is definitely on my bucket list to do better!
The ability to do red/blue-shifting to the degree of accuracy with sufficient granularity to discern the difference for that many points of the nebula to reconstruct as a three dimensional representation is a massively impressive amount of data gathering and processing. Would have been impossible not too many years ago.
It is heartening to me that there exist such people who can take such pleasure in the visualisation of the nature of reality. I think it counts as Art, for what else is a painting?
In addition to the Chinese, Native American tribes also reported it. We have paintings of it depicted as a brand new star next to the crescent moon and it was later confirmed with moon cycle retracing the first night it appeared, it was next to the crescent moon. Also several Islamic reports also list it's appearance.
Awesome video, as always! Getting a Deep Sky Video with Prof Merrifield is like a little Christmas every time. However at 5:07 I think the answer misses the question. You don't get a doppler shift when material is moving left and right in view, this is true, so a blob that got ejected to the "left" from our perspective would have zero doppler shift and this method (Z-from-doppler) would not work. But you don't need it - we can see the distance of the blob to the center of the nebula just by looking at it. So that blob can have its XYZ coordinates too. It's a blend of doppler data for blobs that are in front or back and non-doppler observations for things that are left or right.
It's more complex than that though. At any given point on the surface of the picture, you get the X,Y coordinate from the location on that picture. But you'll still have blobs that are (for example) right and towards us, right and away from us, and everything in between. You need the doppler data along each pixel of the picture get get Z, along with the location of the pixel to get X & Y.
@@LeoSutic The way you phrase that makes me think you still don't get it. Along each XY point on the sky, they take a spectrum. In that spectrum, they spot multiple features with different doppler shifts. From those doppler shifts, they determine the Z of each blob of gas. That gives them X, Y, and Z of each blob. It requires the position on the sky *and* the doppler shift to get all 3 coordinates. At no point are they getting "doppler from xy".
@@jursamaj imagine a point at the edge of the nebula. The Doppler shift will be zero. But based on the distance from the center and the known time of boom you know the speed and can get you Doppler data, if you'd want it (which you probably don't). That was what I was alluding to.
Does one need to correct for the expansion of the universe when analyzing these Doppler shifts, or are the velocities from the explosion much higher and other factors are nearly negligible?
I don't think you need to take it into account, since it's in our own galaxy (thus "very close" to us), typically you only need to take it into account when looking at distant galaxies.
Expansion of the universe is measured over millions of parsecs. The Crab Nebula is only 2000 parsecs away, but more importantly, only 3 parsecs across. The difference caused by universal expansion is absolutely trivial, about .21 meters (8.25 inches) per second between the front and back of the nebula.
scientific data visualization, especially 3D point clouds or density data is really interesting. I work on some python libraries that runs them on your GPU
I'm not sure if you have already encountered it, but it might be very interesting to talk with the people behind the PLATO spacecraft project - it may become the first space telescope to regularly find earth-like exoplanets around sun-like stars!
I actually tried to make a 3D map of the infrared light echo around Cassiopeia A, but there are so many challenges for me that I gave up for now. Got a noisy 3D map. The map is also very “flat“ and the 2D map/animation is in the end more enjoyable. (uploaded on wikimedia)
But wait, deriving position from speed only works if we assume that the speed hasn't changed. And the heating effects described mean precisely that the speed of the material _has_ changed. What am I missing?
1:30 Why is this not true for the universe? The fastest stars (relative to us) are the furthest. Why do we want to explain it with some unknown dark energy?
at 2:20 Prof. Merrifield mentions that most of the material is Hydrogen....but i thought supernovas occur after the star has exhausted its hydrogen, helium, and everything else lighter than iron. or is that only in the core of the star?
what a great question! hope u found your answer already, but here's what i found: The core collapse supernovae are called Type II if they display hydrogen, Type Ib if they show helium, and Type Ic if neither hydrogen nor helium are present. There's also a type 1a for absent H and He but with absorption lines of Si and some Fe. So what i gather is yeah, if the star is 20M (solar masses) or less, there's still a bunch of H in the outer star layers, but any more massive and it gets all used up or gets blown away during one of its stages.
I hate it when people use "CE" instead of "AD", the people who came up with the system we use to record time used AD and it works well, so out of respect we should use AD since we are still using their system
well... a 1000 yrs ago ppl on Earth first saw the beginning of it. But don't forget that the nebula is over 6500 light yrs away. So earthling knowledge may be 1000 yrs old, but if u want to get technical of its actual real time existence then it's over 7500 yrs, but then u have to wonder does it even exist anymore if u could magically transport there and try to view it?
@@y2kenh Didn't ask you and that's not in the video. I'm clearly asking a rhetorical question meant to highlight the derp here, but of course, anyone as smart as you would know that...
