NASA image of the supernova remnant Cassiopeia A

Neutron star mini-lecture for supernovaember

Curious about ‘zombie star’ neutron stars and excited for supernovaember? Take a look at the mini-lecture video I made for my Integrative Studies in Physics class! Full transcript below.

Transcript:

Hello everyone, in this mini-lecture we’re going to talk about neutron stars. Neutron stars are the dead remnants left over from the supernovae of stars that were initially 8-20 solar masses. Here’s a picture of a dead star, and the white dot at the center right there is the neutron star. The stuff you see around it is gas that was blown off in the supernova. This is a composite image showing gas emitting visible light in red, orange, yellow, and green, and very hot gas emitting X-ray light in blue.

To understand neutron stars, we’re going to talk about degeneracy pressure, the musical chairs of subatomic particles, because it shows up again in neutron stars. In the mini-lectures on brown dwarfs and white dwarfs, we mentioned two principles of quantum mechanics, which you don’t have to understand in detail, but you should know the general idea. The first is the exclusion principle: it says that two particles in the same position cannot have the same momentum. The other is the uncertainty principle: a particle’s momentum and position cannot both be specified with infinite precision. We’ve already learned that these principles are true for electrons. They give an atom its size, and they even give a white dwarf its size. The fact that these principles also are true for protons and neutrons mean that they determine the size of a neutron star.

It’s the degeneracy pressure of neutrons that is supporting a neutron star against gravity and keeping the thing in gravitational equilibrium. As a reminder, when a massive star dies in a supernova explosion, its core collapses, and the electrons there combined with protons in the core to make neutrons. So that’s why the electron degeneracy pressure went away, because the electrons themselves went away and left neutrons.

Neutron stars aren’t exclusively neutrons, but they’re made up of the nuclei of neutron-rich isotopes of very heavy elements, so for now, we can think of them as a ball of neutrons. In this diagram of a neutron star interior, I want to point out that there are some question marks over here next to labels for what could be in the core. Neutron star matter is an active area of research that people at MSU in astronomy & astrophysics and in nuclear physics are investigating. One funny thing is that these super heavy, super neutron-rich nuclei no longer look like spheres, like we’re used to, but under the immense density and pressure inside neutron stars, the nuclei get stretched and squished into what’s called nuclear pasta. The nuclear pasta and the layers of a neutron star aren’t on the quiz, they’re just really cool. And yes, we do actually refer to them as spaghetti, lasagna, and gnocchi. Since neutrons are a lot more massive than electrons, it means that a ball of mostly neutrons, held up by degeneracy pressure, can be a lot smaller than a white dwarf that’s held up by electron degeneracy pressure. Remember how white dwarfs were about planet-sized?

Well, a neutron star is city-sized! This diagram shows how a neutron star is about the size of greater Lansing, about 20-25 kilometers in diameter, which is about 15 miles across. MSU campus is right about here. This size is downright tiny compared to other astronomical objects like planets and stars! What’s most impressive is how much mass is crammed in to this 15 mile-diameter sphere. The typical neutron star contains about 1.5 to 2 solar masses. This mass, paired with its size, gives neutron stars their incredible density.

To give you some perspective, one cubic centimeter, so like, the size of a marble, of the core of a neutron star has as much mass as all of Mount Everest, around 10^15 grams. Another way to think about the density of this matter is in terms of people. If you were to take every human being on the planet, and imagine not only squishing them into the same country, or same city, or same room, but down into 1 centimeter cubed, that would have the same density as the core of a neutron star. In the next few videos we’ll learn how neutron stars also have magnetic fields thousands of times stronger than anything that’s ever been created in a lab on Earth, and how some of them spin around on their axis faster than a blender. So, neutron stars are absolutely wild, more than anything we’ve ever encountered here on Earth or in the solar system. In the next mini-lecture, we’ll talk about how neutron stars were discovered, and in the lecture after that, you’ll learn how neutron stars are kind of like zombie stars.

Header image: Cassiopeia A (“Cas A”) supernova remnant. Image credit: NASA/CXC/SAO.

Narrowband composite image of a fragment of the Veil supernova remnant, called the Bat Nebula.

The light at the end of the teaching tunnel

I’m over halfway through my first semester of teaching! I’d been a teaching assistant and ran laboratory physics sections and an observational astronomy practical lab, but never before had I been an instructor-of-record. The [Adjunct] Prof. We’ve gotten through the awkward start and the growing pains, and settled into a nice rhythm for the synchronous class time (it’s virtual). I can see how the next 7 weeks or so will shake out, and it looks like mostly smooth sailing!

I’m teaching one section (out of three) of intro astronomy for non-science majors, with very minimal math. Other prof friends have told me how much they enjoy teaching this class, and I can definitely see why — none of the students are science majors, so they’re just fulfilling their science requirement with the class, but even so, they have so much enthusiasm for outer space! This is also probably the last science class they’ll ever take in their lives, so there’s a non-negligible pressure to instill basic science literacy and math literacy.

I wouldn’t quite say that teaching comes naturally to me, since I’m putting in a ton of work and preparation, but I seem to be good at this, and it’s pretty fun. It’s so rewarding and enjoyable to teach students who actually want to be there! I have big dreams of creating a seminar-style class on astronomy and society with a focus on science literacy (so, blending this class and the preparation I’ve done so far for Citizen Science coming up at Bard). For now though, I’ll not bite off more than I can chew. This one course is only 30% of my contract but about 75% of my time, so I can’t imagine teaching 3 courses for a full-time teaching faculty position.

More on the lessons I’ve learned from surviving this semester to come after I’ve actually finished and survived the semester!

Header image: the Bat Nebula, a region of the Veil supernova remnant, by Josep M. Drudis.

All About Space: What are X-ray binaries?

Earlier this summer, I was asked to contribute to the British popular science magazine All About Space, answering a reader question about X-ray binaries. My write-up was published in the August 2021 issue!

Digital magazine page with text overlaying a picture of a low-mass X-ray binary. Transcript in text on blogpost page. Caption: These pairs can be detected thanks to the X-rays emitted as the smaller star is eaten. Did you know? An X-class solar flare occurred on 2 July 2021 and was the most extreme flare observed since 2017.

What are X-ray binaries?

An X-ray binary has a compact object, like a stellar black hole or a neutron star, and a companion star that is normal like our Sun. The compact object and the companion orbit around each other, bound together by gravity, and they’re close enough that the compact object slowly eats its friend! As it drains material from the companion and gathers it together to eat it, this material gets hotter than the surface of the sun and shines very bright X-ray light.

How the compact object eats its companion depends on how massive the companion is. If the star is bigger than our Sun, it will have big clouds of wind coming off it, and as the compact object passes through the wind, it gobbles up the gas in its path (like Pacman). We cleverly named these systems “high-mass X-ray binaries”, since the companion is big. If the companion is smaller than our Sun, then the compact object swirls the star’s gas around itself, as if the compact object is sitting in the middle of its own dinner plate. This swirling plate of gas is called an accretion disk, and these systems with small companions are called “low-mass X-ray binaries”.

(Header image/inset background credit: ESA. Inset credit: All About Space magazine.)

PhD ring featured in LabX-NAS

My PhD ring was featured in this week’s Scientist Show & Tell for LabX and the National Academy of Sciences. When I first laid eyes on it at Jean Jean Vintage, I thought it looked exactly like a black hole with big jets shooting out of the top and bottom. I would visit it in the store and try it on periodically until I just had to have it. Since the ring looks like the artist’s illustrations of black holes that I use in research talks, it seemed like fate to commemorate getting my PhD.

On the left is a radio image of the giant lobes formed by jets, powered by the supermassive black hole at the center dot. On the right is an artist’s illustration of an accreting stellar black hole with jets shooting out the top and bottom. (Credits: NRAO, me, NASA/CXC/M.Weiss)

You can show LabX’s posts some love on their Instagram, Twitter, and Facebook, and other scientists can submit their favorite object to show & tell here.

Black holes at the end of time in Loki

Now that I’ve pulled myself together after watching the Season 1 finale of Loki (and only barely), I want to mention the brief black hole science we see in the beginning of the episode. (MILD SPOILER AHEAD)

At the beginning of the episode, we fly past black holes and what looks like a rainbow bridge/Einstein-Rosen bridge (/wormhole) as we zoom in to Loki and Sylvie approaching the Citadel at the end of time. At first, I, like everybody else, was like “oooh, space, pretty”, but then my science brain kicked in.

First, the visuals of the black holes are fairly accurate. They have a bit of an accretion disk with some spiral arm structure on the edges, similar to what we see in spiral galaxies. They’re clearly 3-D spherical “holes” instead of 2-D circular “holes” in spacetime, and they even have a bit of a bright photon ring right around the event horizon. Sure, they aren’t verbatim simulations like the one below from NASA, but they’re very pretty and artsy-cool looking. In storytelling, the appeal of the science matters much more than the rigor of it. Checkmarks all around for effort and follow-through!

[GIF of a black hole nearly edge-on, from NASA Goddard/J. Schnittman. All the variants of this simulation are worth oohing and aahing over.]

Einstein-Rosen bridges (or wormholes) are most likely the inspiration for the Bifrost rainbow bridge that Heimdall controls. As an observational astronomer, I feel obligated to point out that although these are mathematically possible, we haven’t seen any observational evidence of them in our universe. Sorry. I still like them in sci-fi.

The other awesome science part is that black holes WILL actually take over at the end of the universe. There’s a Crash Course Astronomy video by the Bad Astronomer himself, Phil Plait, explaining the concept of “deep time” embedded below. In about 10 trillion years, degenerate zombie stars (black holes, neutron stars, and white dwarfs) will be the primary source of energy generation in the universe. After that, protons (one of the primary building blocks of atoms, and all matter) will decay. Anything that isn’t a black hole will dissolve into energy and tiny subatomic particles, and we’ll be left with black holes! That will happen in about 1 duodecillion years (1 with 40 zeroes after it). After that, things get super boring from a visual perspective, and I’m glad they didn’t go with that for Loki.

So, it makes scientific sense that He Who Remains/Kang the Conqueror lives in the black hole-dominated end of the universe. Using the visuals in the establishing shot was 😘👌 *chef’s kiss*

I absolutely love reading and watching science fiction, and it makes my nerdy heart so happy to see my research topic incorporated into the story.

(Header image: Disney+/Marvel Studios)

Podcast playlist for Abtract: The Future of Science

After listening to about 16 hours of podcasts this past weekend for a drive to Rochester and back, I’m putting together playlists of astronomy- and space-themed episodes from science podcasts! These playlists will be a great way to learn more about outer space in an approachable, accessible (read: non-expert, non-academic) way. First up: the podcast Abstract: The Future of Science.

Yes, I was on this one, and my episode is listed below, but you should listen to the other astro episodes, too! I’ve put the episode description beneath them along with a link to the episode pages on Apple Podcasts. I’ll do posts like this in upcoming weeks for more science podcasts, like Ologies (the UFOlogy episode is what sparked this playlist idea), Science Rules! with Bill Nye, Flash Forward, and Sean Carroll’s Mindscape. More ideas are welcome!

Abbie Stevens is an energetic, friendly and curious postdoctoral fellow in Astronomy and Astrophysics at the University of Michigan and Michigan State University. She studies black holes and neutron stars by looking at X-ray light coming from stars they’re gobbling up!
Tune in for answers to questions like…
How do binary systems form?
What is the process of stellar evolution?
What are the different types of black holes and where do we find them?
How do stars die and what kind of remnants do they leave behind?
and many more!
Get the episode on Apple Podcasts.

Lisa Dang is an enthusiastic, outgoing and optimistic PhD student in Astrophysics at McGill University. During her graduate degree, she also held a research position at the NASA Spitzer Science Center at Caltech in Pasadena, California. Right now, she’s studying the diversity of exoplanets and their climate, with a variety of space telescopes, and most excitingly with the upcoming James Webb Space Telescope. She hopes to understand how planets form and evolve, to ultimately uncover the recipe for habitable planets! When she’s not busy scratching her head looking at copious amounts of data, you can find her traveling, drawing, or taking care of her plants!
Tune in for answers to questions like…
Is there life in the universe beyond earth?
How do we define life?
How old are you in “Hot Jupiter” years?
What and how have we learned about exoplanets?
What are the mechanisms behind tidal locking?
and more!
Get the episode on Apple Podcasts.

Our guest this week, Shaziana Kaderali, is a Master’s candidate at McGill University in Aerospace Engineering. Her research is focused on Space Situational Awareness and Spaceflight Dynamics. She helps satellite operators avoid collisions, among much else! She’s a jack of all trades and a master of all of them, and we’ve got her on the show to talk all things aerospace!
Questions Answered:
What’s an aerospace engineer thinking about first thing in the morning?
What do we mean by dynamics and specifically aerospace dynamics?
What’s going on up there in orbit around our lovely little planet?
Should we be worried about the exponential increase in orbital objects and debris in freefall around the earth?
What is the future of aerospace engineering going to look like?
How do we dispose of dead or defunct spacecraft and what’s the end-of-life process?
and many, many, many more!
Get the episode on Apple Podcasts.

Our guest this week, Bryce Cyr, is completing his PhD in Cosmology at McGill University. He’s studying the theoretical structures known as cosmic strings (unrelated to string theory, but we discuss that too). They might shed light on the nature of the early universe and the origin of dark matter!
Questions Answered:
How did the universe begin? Where did it come from and where is it going How far back can we look?
What’s the big idea with the cosmic microwave background?
Why is gravity problematic?
What’s the goal of string theory? What about cosmic strings, are they the key unification?
What’s the big hold up on the grand unified theory of physics?
and many, many, many more!
Get the episode on Apple Podcasts.

Our guest this week, Mitchell Kurnell, just started his PhD in Mechanical Engineering in the Aerospace Mechatronics lab (yeah you know the one, he’s worked alongisde Eitan Bulka (Ep.11) and Ali Safaei (Ep.39)). Our discussion is split between his master’s research on nuclear physics, and his PhD research on cube sats.
Questions Answered:
Is nuclear energy a safe energy alternative and can we entrust our future in these fission reactors?
How can we use lasers to learn about a material’s composition?
How big and how small are the satellites in orbit above our heads? What are they doing up there?
What is space junk and does it pose a problem to other satellites in orbit around the earth?
and many, many, many more!
Get the episode on Apple Podcasts.

Our guest this week, Andrew Saydjari, is midway through his PhD in Astrophysics at Harvard University. Andrew’s research lies at the intersection of Astrophysics and Machine Learning, and he’s studying the massive dust clouds in our very own galaxy. Tune in to tap into the wealth of knowledge that Andrew’s bringing to Episode 31!
On this week’s episode we answer questions like:
Why should you care about interstellar dust clouds that are a million times as wide as the earth’s orbit around the sun?
What do spectra of light tell us about the molecular make-up of these clouds?
How much information can I glean from just a single image of a molecular cloud out there in space?
And how does the symmetry of molecules factor into all this?
Get the episode on Apple Podcasts.

Interview for the podcast Abstract: The Future of Science

I was interviewed by Jeremy Ullman for his podcast Abstract: The Future of Science! We had SO MUCH FUN talking about black holes, neutron stars, supernovae, the Milky Way galaxy, the recent outbursting black hole named 4U 1543-47 (which I talk about in this twitter thread), and more. It’s 30 minutes long, available on Spotify (embedded above), Apple Podcasts, and wherever else you like to listen. My in-laws have already listened to it, and they said that both the science and my talking speed are understandable 😊

I’ve realized that not many people know that I stutter. My speech is usually fine these days, but it used to be very bad and very, very noticeable. I’ve been through years of speech therapy, and I think my early interest in music and singing was in part to help me get over my stuttering. Of course, I didn’t let it get in the way of doing and loving theater throughout school, though it partially informed why I didn’t seriously pursue acting beyond college. So, it feels QUITE momentous to be featured in an audio-only medium, and to have loved every bit of it. Jeremy can confirm that I didn’t stutter during the recording and he had no troubles editing.

I got myself a fancy Yeti mic and learned the basics of Audacity, and now I want to be on everyone’s podcast. Let’s talk!

The Science of Star Wars

Tomorrow on May the 4th I’ll be a panelist for a discussion on the science of Star Wars with Skype A Scientist! Join us at 1pm EDT (registration is free) 🤓 here’s the event info page with more about our host Dr. Dyanna Louyakis, biologist Dr. Morgan Halane, and me.

Comment (on Facebook, Twitter, or LinkedIn) with questions you have (silly and serious) about the biology and astronomy/physics in Star Wars, and I’ll put them on the list!

Update: Here’s the recording on Youtube (pardon the technical difficulties at the beginning). Keep an eye out for my lightsaber chopsticks.