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Multiwavelength image of the Crab Nebula, a supernova remnant. Credit: X-ray: NASA/CXC/SAO; Optical: NASA/STScI; Infrared: NASA/JPL/Caltech; Radio: NSF/NRAO/VLA; Ultraviolet: ESA/XMM-Newton

Star Stuff: How to hold a dead star in your hand

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Oct 12, 2017

Star Stuff is a weekly column by rocket scientist & astrophysicist Summer Ash highlighting some amazing things happening every day on and off the planet, especially great science done by and/or for women. She harnesses her science communication powers to smash the patriarchy and advocate for equality and inclusion across all time and space. Throwdowns with pseudoscience may occur.


Have you ever wanted to catch a falling star and put it in your pocket? Well, that’s still pretty hard to do, but what you can do now is hold a dead star in your hand thanks to the work of researchers at the Harvard-Smithsonian Center for Astrophysics. All you need is a 3D printer.

Three dimensional modeling has been around forever(ish), but it’s only within the last decade that astronomers have been able to put together not just 3D models of their datasets, but 3D visualizations as well. The majority of space is space, so it’s not that realistic to try and 3D print the large scale structure of the Universe. However, more compact structures like supernova remnants are a different story.

Kimbery Arcard, Visualization Lead for NASA's Chandra X-ray Observatory, was inspired by the Astronomical Medicine (AstroMed) Project which used applied medical imaging software to astronomical data sets to map the 3D structure of molecular clouds. Arcard told me she immediately made the jump to wanting to see how it might work with Chandra data: “As soon as I saw this project I'm like, ‘This is it.’ I heard her talking about it one day and I just completely fell in love with the idea. I've worked in data my whole career and it's always been 2D.”

Arcand has been with NASA for almost two decades so she suspect Chandra data had enough resolution to lend itself to what AstroMed was doing. So she poured through the data archive in the hopes of finding inspiration. Around the same time, she came across Tracey Delaney, an astronomer studying Cassiopeia A (Cas A for short). 

Supernova remnant Cassiopeia A. Credit: NASA/CXC/SAO

Cas A was one of the first astronomical radio sources detected. It was discovered by radio astronomers in Cambridge, England in 1948 and its optical counterpart was found two years later in 1950. It’s X-ray emission wasn’t detected until the 1960’s and even then it wasn’t fully mapped until Chandra observed it in 1999. Located approximately 11,000 light-years away from us, Cas A is the end stage of life for a star that was once there. That star was massive enough that once it could no longer sustain fusion in its core, its outer layers collapsed in on it, resulting in an explosion we know as a supernova. The central core was destroyed, leaving behind shells of ejecta that are still expanding today. What we see as X-ray emission from Cas A is due to the different chemical composition of these expanding shells and how they are cooling and/or being heated by interacting with each other or the surrounding interstellar medium.

At the time Arcand and Delaney were talking, Delaney had been working on mapping the shape of this ejecta, not just as it was projected on the sky but in three dimensions. Using velocity measurements, she could essentially step into the sky and distinguish the closer side of the remnant from the farther side, and therefore model the explosion in full 3D. Arcand approached her about collaborating with AstroMed and the result was the first 3D model of a supernova remnant. But that wasn’t enough for Arcand. “Within a year I was kind of like, ‘What else can we do?’ I had seed so much of this 3D printing in non-astronomy science. Medicine, manufacturing, etc.,” she recalled. “There was so much that was bubbling up from the surface so I thought, ‘Well, why can't we 3D print this?’”

3D model of Cassiopeia A (left) and 3D printed version (right). Credit: NASA/CXC/SAO, K. Arcand

So they did. And now you can do to. The files for Cas A are freely available to download from Chandra’s website and it doesn’t end there. Arcand and Chandra have gone on to do the same for supernova remnant 1987A (SN 1987A) and another object called V745 Sco, which is not a supernova at all but a peculiar binary star system. And while the overall process remains the same, Arcand says each object requires a different approach. “Each data set is unique. There's no one size fits all. You have to just follow the trail, and see where that one will lead you, and see where that will lend itself to three dimensionality.”

Supernova 1987A is drastically different from Cas A. It is dominated by a ring filled with glowing clumps of matter surrounded by a more diffuse sphere of ejecta. Astronomers believe the ring was made by material the star shed prior to its demise and that the supernova slammed the remains of the star into the ring causing the strong emission we see now. SN 1987A is not actually in our galaxy, but located 168,000 light-years away in the Large Magellanic Cloud, one of our smaller satellite galaxies.

Making the 3D model for SN 1987A actually helped astronomers to better understand why they were seeing what they were seeing. Arcand and her team worked with astronomers who do simulations to model supernova remnants. Showing them the physical 3D printed version of SN 1987A allowed them to see it from all angles, including both inside and out. Holding it in their hands, it suddenly made sense why certain emission looked the way it did. It was as if 3D printing was now another way for astronomers to iterate on their understanding of supernovae.

Supernova 1987A multiwavelength image (left) and 3D printed version (right). Credit: X-ray: NASA/CXC/SAO/PSU/K.Frank et al.; Optical: NASA/STScI; Millimeter: ESO/NAOJ/NRAO/ALMA. Salvatore Orlando (INAF-Osservatorio Astronomico di Palermo) & NASA/CXC/SAO/A.Jubett et al.)

 

Arcand and Chandra recently moved beyond supernova remnants with the binary star system V754 Sco. The two stars in this system, a red giant and a white dwarf, are known to astronomers to produce frequent but irregular outbursts. Their activity was recorded in 1937 and 1989, and when they went at it again in 2014, Chandra was ready. Because the two stars orbit so closely to one another, material from the red giant can be sucked off onto the white dwarf. If the white dwarf accretes enough, it can trigger an explosion known as a nova that doesn’t destroy the white dwarf but increases its brightness by a factor of thousands.

The detailed observations from Chandra allowed astronomers studying V745 Sco to adjust their models of the star system so that they matched the data, and thereby forcing them to reexamine their understanding of the behavior of this particular nova. Arcand told me the new 3D model of V745 Sco is actually in two parts: “We have the shock and the ejecta as separate pieces. You can either print them combined into one unit, or you can print them separately scaled to the right size so that you can kind of fit them into each other like a puzzle piece.”

Binary star system V745 Vsco computer model (left) and 3D printed version (right). Credit: INAF-Osservatorio Astro. di Palermo/S.Orlando; NASA/CXC/M.Weiss

For something so intangible like the Universe, 3D printing is opening up new avenues for how we understand the world around us. It’s hard to believe it’s been less than 100 years since we even realized the full scale of our own galaxy and that so many of the spiral nebulae through our telescopes were actually completely separate galaxies of their own. it’s one thing to know about how matter is distributed in space, but it’s quite another to physically be able to explore it, even if it’s just a scale model.

Arcand says no one really saw the idea of 3D printing in astronomy as being useful at first: “I'm not sure anybody thought this was at all worthwhile at first, but the people around me are very good about letting us play.” To me, this is what science is all about. We “play” by testing things out, seeing how they work, seeing how they change when we do this or that. I’m so grateful that organizations like Chandra (and NASA), give their teams space to play like this. Otherwise, I’d never get to hold the universe in my hand and who doesn’t want to do that?