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!
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.)
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!
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)
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!
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!
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.
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.
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!
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.
In a terrifying departure from my modus operandi, I will be presenting a piece of creative non-fiction at the REO Town Reading Series on Thursday April 22nd! I’ll be telling a story about the brightest little pulsar in our galaxy. Join Mary Fox, Stevie Pipis, Selena Gambrell Anderson, and me with host and curator Matt Rossi on FB live starting at 7:30pm EDT.
UPDATE: Here is the video link for you to watch at your leisure! Thank you to everyone who tuned in. Transcript of my piece:
I’m going to tell you a story about the brightest little pulsar in the Milky Way, named Swift J0243.6+6124, and don’t worry, you don’t have to remember that name, and I’ll tell you what a pulsar is.
On October 3rd 2017 there was a very bright burst of light near the Perseus constellation. It wasn’t close enough to see by eye, but things that go ‘bump’ in the night tend to be interesting to astronomers, so we had telescopes at the ready. The Swift X-ray observatory was the telescope first to detect it, which is why ‘swift’ gets to be first part of its name. The telephone number in the rest of the name, and yes we actually call it a telephone number, is its location in galactic coordinates, which is like latitude and longitude for the night sky. For the next 150 days, taking us into the spring of 2018, we saw this shiny new source get unimaginably bright, then dim again. Not only were there X-rays, but gamma rays, visible light, and radio waves also shone from it during that time, in their own ways.
In the night sky, when something transient shines brightly in X-rays, this light often comes from near the remnant of a dead star, like a black hole. But calling it a dead star doesn’t quite convey its character; calling it a zombie star is far more accurate. Like zombie people, this zombie star is eating living stars, and it’s still quite active and spinning around, and in general, like zombie people, one could argue that its time as a zombie is far more interesting than its time when it was alive.
Many zombie stars have a little star friend that they grew up with. They orbit around each other as they’ve always done, but like we’ve seen too many times in the movies, the little star friend can’t bring itself to leave, which ultimately leads to its untimely demise. The zombie star feeds on its star friend, slowly draining the outer material from the star and forming a disk around itself, like it’s greedily filling its plate. This syphoned star stuff, waiting to be gobbled down by the zombie star, gets very hot, like 100 times hotter than the surface of the sun. It shines its heat light in X-rays, so when we detect these particular colors and shapes of X-rays from a point in the galaxy, we know that this whole zombie scenario is happening.
Now let’s check in with the ‘unimaginably bright’ aspect of this source. First, I need to tell you what we imagined the limit was. As a zombie star is eating, if it eats more stuff, it shines more brightly. But as your intuition may have already told you, things shining light in space cannot be infinitely bright. There reaches a point where the radiation of the light shining out, pushes back and doesn’t allow more material to fall in. If there’s enough material, the system can even sustain this luminosity. In the 1920s, this luminosity limit was worked out in detail by Sir Arthur Stanley Eddington, a British astronomer, physicist, and mathematician. An important detail to keep in mind is that this luminosity limit depends on the mass, or weight, of the object doing the eating.
When we as astronomers are observing X-ray light from these voracious black holes, we often don’t know how massive they are, so we just pretend that they’re all 10 times the mass of the Sun. In the sciences, when we’re trying to figure something out but don’t have all the information (which is how it goes in astronomy, more so than other fields), we simplify, make a plausible assumption, and move on. Some of the sources we see in the night sky are brighter than this luminosity limit for a black hole weighing 10 times the mass of the Sun, and we call them ultra-luminous. Also, if you’ve ever wondered what’s more than ‘ultra’, according to astronomers, it’s ‘hyper’. So, two things could be happening here: either it’s actually more massive than 10 times the Sun, so it’s shining normally for its actual mass, or there’s some funky, fancy stuff going on that is temporarily letting it be brighter than it should be.
But! Here’s the twist. You didn’t know there’d be a twist, but there is. When we were observing the X-rays from J0243, we instantly noticed pulses in the brightness of the X-ray light, nearly perfectly precise like the ticking of a clock. Black holes can’t pulse. There is no mechanism to get a signal this precise from them. However, neutron stars do, and some of them are so good at pulsing that we call them pulsars. Neutron stars are another type of zombie star, left over when a medium-big star is massive enough to die in a supernova, but not massive enough to collapse into a black hole.
A pulsar is a neutron star with two bright spots on the surface at the north and south magnetic pole, off-kilter with how it spins. It’s like if a neutron star were a light house, in that it’s always shining beams of light, but you only see it when they point in your direction. Pulsars are effectively cosmic clocks that are stunningly accurate out to many decimal places, and NASA is testing a technology to use them like reference points for interplanetary GPS.
So, knowing that J0243 is a pulsar, only a fraction the mass we first assumed for the luminosity limit, it is very super ultra hyper bright. It sounds like it shouldn’t be possible, but nature begs to differ. What’s probably happening is that the pulsar’s magnetic fields, which are thousands of times stronger than anything we can create on Earth, are holding things in place like Spanx, so it can eat even more and radiate even more. I think there’s an analogy here about Spanx holding stuff in, letting the star shine extra bright, but I prefer a more body-positive ethos so I’m going to let that slip away.
What does this mean?
I’ve been studying X-rays from this source, and one really interesting thing about it has to do with its iron levels. Though gas in space tends to be mostly hydrogen, there are trace amounts of other chemicals like oxygen, silicon, magnesium, and iron. If the gas gets hot enough (spoiler: it does), the iron can light up and fluoresce like neon lights. This shows up in cool shapes that we can see with extremely fancy and expensive X-ray detectors on satellites in space. If we want to know where this gas with iron is, like geometrically in the system, we can’t just take a picture because the whole system (zombie star, star friend, plate of stuff it’s eating) are way too small and way too far away.
Instead we need to figure it out from the physics, like a more boring, yet higher stakes, version of Clue. We know the weapon and the victim and the murderer, but not the room, and the room is important. The big weird wrench in the gears here is that the iron doesn’t know that it’s around a pulsar. It doesn’t see the pulsations. And like, How can you not know with such a stupidly bright pulsar, but anyways. The two possibilities are that it has a wall of stuff blocking its direct line-of-sight with the pulsar, or it has a cozy cocoon of dust and gas wrapped around it, diffusing the pulses into a strong, steady light.
I don’t have an answer to this yet. Scientific research is trial and error and error, ad nauseam, and I am in the thick of it. A very helpful colleague suggested some calculations I can do, but I haven’t done that yet, and instead I wrote this.
As part of the MSU Science Festival, I’m giving a public talk on alien worlds (“exoplanets”) this Saturday April 17 at 11am EDT. It’ll be fun for adults as well as kids. Here’s the link to join the webcast. You’ll need to register on the virtual platform (it’s quick and free) to access the details. See you there!
Thank you Skype A Scientist for having me speak yesterday! As one of the finalists for the No Time Like The Presentation contest, I gave a 10-minute presentation on my research for a general audience. It was the first time in ages that I’ve given a talk with almost entirely new slides. I was so nervous and excited, and it was so fun! The talks were recorded and posted to YouTube (see embedded below). I spoke first, but you should stick around for all the talks. I loved learning about everyone’s research.
First order of business now is to make a sign reminding myself to SPEAK SLOWER and hang it just above my monitors…
Last week I submitted a 90-second video abstract of my research to the No Time Like The Presentation competition from Skype A Scientist. And I was selected to give a 10-minute talk on my research!!
The full-length presentations (from me and the other scientists selected) will be in April and streamed live to their Youtube page (and saved for later viewing).