A galactic story of friendship that ends with an explosion: superluminescent supernova gc2017
Published! is a series of chats with women in science highlighting their publications as leading authors. If you know someone who has recently published a scientific manuscript who would like to chat with me, you can get in touch via Twitter @laurenpoppi or email <lauren.poppi@rutgers.edu>.
Congratulations on your recent paper! Could you tell us a little bit about it?
First, I’ll explain what superluminescent supernovae are.
That would be great for those of us who don’t know!
Supernovae are star explosions. There are different kinds, some come from low mass stars - we don’t care about those (laughs) - and others come from supermassive stars that have reached the end of their lives. Their core runs out of fuel and collapses because gravity wins. The implosion of the core causes the explosion of the star and you get a big bright flash - a supernova. Now, that’s the classic picture, but there are some supernovae that have been identified in the past decade to decade-and-a-half that are much brighter than the typical supernovae. That’s why they were called superluminous, because they have much higher brightness than we were accustomed to. Now, to explain these super bright events we couldn’t use the classic mechanism that we understood for supernovae. The classic mechanism for a supernova is: the core collapses, the star explodes, and in the explosion a whole bunch of nickel-56 is released. Nickel-56 is an element that has nearly the same heaviness of iron - it’s in the same group on the Periodic Table. It is super radioactive and has a half-life of 6.1 days. The nuclear decay of nickel-56 keeps the material hot and bright. The peak brightness of these supernovae is powered, say, by nickel-56. For these superluminescent supernovae, if you were to try and explain it with nuclear decay, you would need way too much nickel. It’s just not possible!
So, we are still trying to understand what powers these supernovae. There are a couple of ideas. First, maybe it’s a combination of nickel and other things. Another popular idea is the concept of a magnetar, and it works pretty well. In a magnetar, the core has collapsed and has formed what we call a neutron star. Basically, the density of the core is so high that the electrons and the protons merge together to form neutrons, and you get a big ball of neutrons and other things. The neutron star, if it’s super magnetic and it’s rotating, is called a magnetar. That magnetar can power a supernova because it’s rotating super-fast and it’s magnetized. The rest of the envelope can tap the energy of the magnetar, and as it spins down that energy is transferred to the ejecta. This idea is super popular.
So what got you interested in this particular superluminescent supernova?
We call this supernova ‘2017gci’ because it exploded in 2017, and ‘gci’ is a code used to identify it. We have so many star explosions every year that we need all of the letters of the alphabet three times in order to differentiate them! So, I saw an article on 2017gci in the preprints at the end of December. They did a pretty standard analysis of the object, and included the light curve (which tells us how the brightness changes over time), and the spectroscopy (which tells us what the ejecta material is made of). What they found was that it had very interesting ‘wiggles’ in the light curve at 140 days after maximum light. Also, around that same period, they found traces of hydrogen in the spectrum. That’s not normal (laughs)! These superluminescent supernovae are typically hydrogen-poor - they don’t have hydrogen in their spectrum. We know a few other superluminous supernovae like this, that have wiggles in their light curve, and that have traces of hydrogen around that time as well. These observations could be explained if your light curve is powered by a magnetar. I understand that most people don’t have the superluminescent supernovae light curve in their head...
Um, no we don’t Héloïse!
Well there is a peak followed by a nuclear decay tail. If you know your exponentials, then you know what I’m talking about. The question is, where the hell do these extra wiggles come from?
Ok so… explosion, hot materials, bright light that reaches a peak then decays, but there are wiggles. I think I’m following!
Previous studies from similar supernovae have suggested that it could be extra material, what we call ‘circumstellar’ which is latin for ‘material around the star’. The ejecta shocks and heats up the extra material as it goes past. As this material heats up, it creates extra light which causes bumps in the light curve. If that extra material has hydrogen in it, you will see extra light and hydrogen lines in the spectrum. So that’s one idea. Another idea that has been suggested in the past was that the hydrogen was inside the explosion. Maybe when the star explodes, it has a binary companion. It is super common for stars to have friends, especially supermassive stars! In this case, the binary companion has loads of hydrogen in its envelope left. The star that explodes doesn’t, and that’s why you don’t see hydrogen in the spectrum. As the star explodes, it strips some of that hydrogen off the companion. That hydrogen is kind of stuck inside the ejecta at first, but over time, you get adiabatic cooling, and as it cools you start to see the inner layers of the explosion. Eventually, it reveals the hydrogen.
When I was originally looking at the hydrogen wiggles in 2017gci, I thought maybe it's circumstellar material from a binary companion. I was mixing the two ideas. If they were too close just before the explosion, maybe some of the hydrogen exploded outward, not too far from the star, so the star exploded and then encountered the hydrogen. That’s what I was expecting to find in the models.
What kind of models are you using?
I’m using stellar models that were created by my boss. They include a million solar masses worth of stars. It is like a mini-universe with loads of parameters that fit observations of stars as we know them. It also uses a state-of-the-art approach to model the atmosphere of stars and what they look like, etc. It’s a big simulation, and my idea was to go in that simulation and find something that looks like a progenitor of that supernova. The people that had studied it had done a fantastic analysis. I was able to turn their observations into search criteria to look in the simulation. The question was, “does our state-of-the-art simulation predict something that could give us these results?”. I didn’t find what I was expecting to find.
One of the very important criteria was for the star to fully lose its hydrogen before it explodes, but somehow, only just before. This would be necessary for the wiggles to appear on the time scale of 100 days. If you calculate how quickly things have to move, you realize that the star has to lose its hydrogen only a few decades before it dies. This is a time crunch! That star means business! A few decades is nothing in the lifetime of a star which is millions of years in most cases. I went into the simulation and I found some systems. What I didn’t expect was that they don’t lose the hydrogen at the end of their lives because of binary interaction. They did have binary interaction much earlier in their life (and it’s super important to have binary interaction because the single stars can’t create these models) but they need an early binary interaction, and, at the end of their lives they need a field of very strong mass loss from stellar winds. I know I’m introducing so many terms and concepts. Your star gets so bright essentially that light pushes material away. And that’s what we found! We matched these criteria. The star lost its hydrogen just before the explosion, so the hydrogen was still nearby. We found a couple of systems like this. In one system, the star that exploded was born with 30 times the mass of the sun, and the companion star is about 12 solar masses. Or another system that works as well is a 30 solar mass star, with similar evolutions and everything, but the companion is a 25 solar mass black hole, which is pretty cool! The likelihood of the first option compared to the second option is around 110:1. You’re much more likely to have the lower mass star than a black hole, but you know.... it’s still cool!
Whoa! That’s amazing! It’s cool that the black hole is even a possibility. Is this modeling approach you used pretty novel?
The simulations that I use are very broad-scope, they can use loads of different observations, but they don’t do all of the physics in extreme detail. It’s a different approach to that used by others where they take the parameters of the supernova and they try to create a model that will fit that. Those dedicated models are great because they can really look at the physics in a lot of detail. The problem is, they’re not asking, “can stellar evolution as we know it recreate this supernova?”. That’s the approach I took.
What’s interesting is that the other models, such as the circumstellar model idea, don’t work for this particular star. The other binary model that I mentioned earlier - where the hydrogen comes from a companion - also doesn’t work for this particular supernova. Something else is probably going on, or at least we need to understand it better. It is important to use both approaches if we want to fully understand how we get these incredible explosions. We need dedicated models with all of the physics details in order to recreate the spectrum of the light curve. That’s something I can’t do with my models. But we also need models that can recreate a mini universe, self-consistently, based on real observations in the universe combined with an understanding of stellar evolution. It’s all about bridging that gap.
Was there a crunch point in this project where you had to come up with a creative work around?
I’m not an expert in superluminous supernovae. I come from the world of supernovae and I have always kept an eye on them because they are superluminous and shiny and I like them! But we don’t have an expert in-house. I was initially writing this as a single author paper, but in the end I chickened out and I put my boss on it, like “I’m not responsible for this whatever happens!” (laughs). But it was the first time in my scientific career that I went from point A to point Z on my own. The project as I’m describing is not the way that it happened. There were loads of points where I felt like “Oh no! It’s useless!” and then “Oh no it’s not!”. Up and down. My boss is amazing and she was instrumental in helping keep me afloat. It happens with all projects, you reach this point where you have invested time and things just don't pan out. In 2020, this happened a lot and I was tired of it. I just needed a win! “Please, just give me one thing that works!” (laughs)
I feel this viscerally (laughs).
It’s just part of the process. When you don’t have an expert in-house, and you don’t have the confidence of the average white man (laughs), I don’t think, “Of course it will be very interesting”. I am expecting at any point for someone to say “Oh no, there is **this very obvious thing that you didn’t think about**, everything you did is irrelevant”. So, I’ll only believe it when the reviewer gives it the green light. I recommended one of the leading experts in superluminescent supernovae as a reviewer and I think the article went to that person. I hope I get their seal of approval! I was really my own biggest enemy, to be honest. It’s all about keeping yourself motivated when your brain is trying to sabotage you.
So you have already explained the main findings of your paper… and you have successfully explained them to an outer space-challenged neurobiologist!
I hope so!
How was the writing process? Did you write as you went, or did you wait until the story was all together to write the paper?
I tend to write as I go, even though I know that sections will move around as I find new things. For example, these supernovae are helium poor - you typically don’t see helium in the spectra. So I was using one criteria to check whether there was helium left, and there was plenty of helium left! So I thought, “Oh no! It’s pointless!!!”. But then, a couple of days later as I was starting my discussion… I found another paper that explained how helium can easily be hidden, even in the sort of masses that we find. I then found a mention of it in another supernovae paper that said it’s very likely that these helium-poor explosions do have plenty of helium in their spectra. Our evidence corroborates with what they found. When I started finding models, I started writing. I write in LaTeX, which maybe is not common in neurobiology, are you familiar with the LaTeX editor?
Yeah, I think only the brilliant people use LaTeX. I’m a basic Microsoft Word user. Google Docs is me being fancy.
I have no Microsoft, the computers I have are all Linux or Mac-based, because a lot of our software is homebrew and it’s much easier to run on a Unix-run environment than it is on Windows! I code everything, and use LaTeX. It’s easier for equations. In LaTeX it’s easy to move everything around and you’re not going to mess up your formatting too much because it’s all done for you.
Oh cool, so LaTeX supports your dynamic writing style and allows you to adapt things as you go. You probably don’t have any situations where you’re inserting citations with one of those awful programs?
I’ve NEVER used anything other than BibTeX (laughs). BibTeX is my religion. I love BibTeX, I love LaTeX. It was a bit of a learning curve when I started, but I wouldn’t go back. Especially with things like Overleaf, now it’s easier than ever. For people that don’t want to look at the code, they even have a cute version of the text that is kind of pre-processed. It doesn’t have any of the formatting but it looks marked down essentially. I still look at the code!
Writing as I go helps me to organize my thoughts in a way that doesn’t happen if it’s not written down. Explaining something to someone is the best way to see if you really understand it yourself.
Did you have to generate figures and tables for this article as well?
Yeah. Bullet points and figures are the first things to go in. There are only a couple of figures in this one. I did a little diagram of the stellar evolution in InkScape.
What are the next questions that you want to answer?
I think there are some bigger questions in the field that aren’t going to be answered for a while. One of the biggest unknowns is, the star loses its hydrogen a few decades before the end, but that doesn’t mean it will make circumstellar material that will generate the light curve that you see. It has to be dense enough for you to generate extra light. If it’s just diffuse gas, then nothing is going to happen. I don’t know enough about stellar winds to fully comprehend how that might happen. Based on some references that I looked at, there are things that can happen with bubbles forming when stars are moving at a certain speed, but stellar winds are really not my area of expertise. I would love to hear what stellar wind people think. Maybe it’s not going to work with what we currently understand. What we have in our models/simulations is based on what we know now, but there are still unknown mechanisms. That is something that I both look forward to and dread a little bit, because it could render the current models a little bit irrelevant. It’s part of the process.
I love that there are 'stellar wind people' out there, that makes me happy. Do you remember a specific moment that you realized you wanted to be a scientist?
I always loved learning when I was a kid. I thought I wanted to be a historian. I never thought of myself as taking on an industry job, but the subject kind of changed as I went. I wasn’t aware PhDs were a thing for a long time. I don’t think I had a big differentiation in my mind between science and history, because I liked them both. Science is a creative process, in my experience. Research is a creative process. There is a lot that goes into doing good research and creating communication. There are loads of skills that you only acquire in literature class that come in handy when you are doing science. I don’t see a big separation.
Since I was a kid, I have always loved learning how the world works. I can blame a very famous TV show for kids in France called 'C’est pas sorcier' which kind of translates to “It’s not rocket science”. They had all of these dioramas explaining things, they went to different places. It was all things science and astronomy, physics, environmental, biology, the human body; I learned so many things. Even in undergrad, I had an intuitive understanding of certain things because they had explained it so well. I think all of my scientific and science communication endeavours stem from the people who made this show many years ago. Sometimes I watch an episode just because it makes me happy!
Do you have a fun science fact that you would like to share with us?
It’s something that a cosmologist said in one of our journal clubs. I can’t remember the exact number, but black holes evaporate and the smaller they are, the faster they evaporate. A black hole with the mass of the Earth would evaporate in less than a second! That blew my mind! It’s not just a little under a second, it’s way under a second. That’s one of those facts that really blew my mind.
That’s crazy. I’m imagining something the size of the Earth disappearing in under a second?
It would never be the size of the Earth!
Oh the mass of the earth.
Yes it would be the size of a marble. Roughly. Scales in astronomy make no sense.
They make no sense to a neuroscientist! I’m like, “how many micrometers, how many microseconds?” and you’re talking in decades, millions of years!
It’s one of the things I love about astronomy, the incredible scales. It does something weird to my brain where I think in log scales in my daily life, because of my job. For example, if you’re looking at buying a house, there is a big difference between 100,000 pounds and 500,000 pounds (laughs). Sometimes I forget because, well... it’s the same order of magnitude! But this is not how life works (laughs)!
(laughs) So true. That’s classic.
So, science is stressful, what do you do to destress/recalibrate? And what would be some of your advice for a junior scientist chasing that dreamy work/life balance?
I’m less tough on myself about always keeping the same schedule. It’s good to have a schedule, but I’m less afraid of changing it as I need it. I have different phases. On a daily basis, I like starting early and finishing early, but when I’m in writing mode, my schedule shifts a little bit. I take bigger breaks in the middle of the day, work early and work late. Science is hard and exhausting! Work-life balance looks different for everyone but it also might look different for you at different times depending on what you need. It is important to be honest with yourself and to re-assess frequently. You know, “Is this meeting my needs, or is it not meeting my needs?”. If it’s not, tweak a little. Consistency is important to an extent, but re-assessing is just as important.
Find a fun hobby! I do roller derby. Breathing and exercise are so important for mental health. I know people are sick and tired of that kind of advice. I find that breathing and exercise are often the first things to go when my mental health deteriorates, because that’s just how our bodies react. I was diagnosed with hyperventilation syndrome at the end of 2020, and I know that when I exercise regularly and when I’m being more mindful of my breathing, I do better. But it’s this vicious cycle where I can only do these things when my mental health is just good enough. So if it goes below that, then it’s like ***deflating balloon sound***. It’s good to keep that in mind. I like roller derby because there is a team. I’m very social and like talking to and interacting with people. I realize that this is harder right now in America and other countries because of COVID. The team aspect of roller derby really motivates me. There have been plenty of times where I have felt like I could not be bothered to be on skates, but after 20 minutes, you’re with other people and it’s just a completely different environment. You’re talking, falling over, hitting each other… and suddenly you feel better! I really recommend it. I don’t go there for the exercise, I go there to be with my friends and hit them a little bit (laughs).
(laughs) It must be nice to vent some of that science aggression with some shoulder barges and speed!
If you could have a chat with your pre-PhD self, what would you say?
Make sure that if someone recommends a supervisor to you, it’s because that person really knows them and that it’s not just office politics. Ask questions. They’re not just interviewing you, you’re interviewing them too. That would be the biggest advice I would give.
That’s very widely applicable advice for both PhD and postdoc!
Absolutely.
So, I checked out your awesome website. I think every scientist should have a website like yours! Or at least we should try harder. So many webpages of these amazing scientists that do beautiful work, and their pages are lacklustre!
It’s because everyone learned html in 2001 and they haven’t changed it since then! I don’t have the patience, so I just pay Squarespace my monthly subscription. I make it pretty and they make sure it works for me. It’s all drag and drop, so that’s why it can be the way it is. All of the heavy lifting is done by a third party service.
You have also made a lot of content available. You’ve made it really easy to find how to get in touch with you, to see your publications, your GitHub, your illustrations, and your Twitter handle (@Sydonahi)... Everything is just one click from this page. Sometimes it’s hard to find someone’s LinkedIn or publications if they have a common name, for example.
Oh yeah, at least my name is pretty unique, I’m the only one!
(laughs) Same here!
At least in astronomy and astrophysics. I don’t know about biology. If there is a publication by HF Stevance, it’s probably me.
You do a lot of science communication. I think this is super cool, and it’s obviously something you enjoy. Do you think we should be doing a better job of communicating our science?
I think, to an extent, but also I know how much time it takes. So, there is this conversation like, “Everyone should make an effort to communicate!”, but I think, “No, not everyone!”. It takes a lot of time to do, and to do it well. It should be more valued. We shouldn’t change the people, we should change the system so that it values science communication more. Then for the people who do spend time on it, it’s not just a hobby. It’s not just a little thing they do on the side, it’s something that is valued by the community as a whole. That is what I would change.
I fully understand that some people don’t have the patience to deal with internet trolls and make content that is relatable to people who did science class once 25 years ago, I get that. Some of us are massive nerds, and all we want to do is talk to other massive nerds and not have to worry. That’s fine. These people have their place in science, absolutely. The system needs to recognise the value of giving back to the community and sharing science widely in a digestible way. Science is losing the connection to people because of disinformation and clickbait. That’s something I see a lot as a science communicator, I can’t compete. I have bright orange hair, and I don’t get as many likes as someone who posts, “We found bones on Mars”, and it’s like “OH MY GOD!” (laughs).
(laughs) “What do I have to do to get through to you people?!”
Exactly, it’s a losing battle, and an exhausting one. I think that science as a whole should do a better job of communicating, but that doesn’t mean making everyone a science communicator. It means giving credit to the people who spend the time to do it well. Science communication is not valued by the system that I am trying to make a career in. That’s a problem. That’s how you end up with people at the top that are antisocial and can’t talk to students… it’s a mess. Maybe it’s because we don’t value these other skills.
It is a skill being able to make something like a superluminescent supernova accessible to people!
I’m a big supporter of not making people do stuff they don’t want to do. Some people are better at other things. That’s why you want to build well-rounded teams. It should be the case when you build your department or research groups, making sure that you have diversity in every sense of the word. That’s just going to be better for everyone.
So what is it like being a scientist in New Zealand?
I think it’s very similar to the UK. I don’t know what it’s like in America. We hear these things like “Americans have no work-life balance, they have no holidays, they are supposed to work 80 hours a week”. It’s so weird to us. We sometimes make fun of y’all. You often see people at conferences that don’t go to the social events after the conference, they do more work, or they’re just on their laptop all the time not talking to anyone. But conferences are for talking to interesting people! That’s where you get noticed and can share your ideas. That’s something that I think we have more of here.
So, you have a bit more balance and a more social approach?
Yeah, I think so. Science is a team sport. Even if you’re doing your projects basically solo, you still benefit from the social aspects, like talking to people and bouncing ideas off of each other. It’s something that scientists don’t think about a lot, just because of the nerd culture, I think. There is so much to be gained from social interactions.
I guess the question we need to ask ourselves is, “Am I achieving more in 60-70 hours than I would in a supercharged 8-9 hour/day schedule? Is it enough of an increase in productivity to warrant my health and other things disintegrating?” Sometimes the answer is yes, temporarily, but maybe the answer should be no - it's not worth it.
We have to ask ourselves this question constantly. People are used to it, too. I didn’t grow up in this work culture, so I don’t have the same stamina. I’m still learning how to manage it. It is also important to set your own limits and to be OK with them. Sometimes you have to go, “You can do the 11PM thing, good on you, but I’m just gonna **whistles, points to door**, because that’s not me today”.
That just blows my mind. I don’t think I would do anything valuable if I stayed at the office 70 hours a week. I have the attention span of a pickle! I need to do something else to get back the attention I need to solve that bug. Sometimes, if there is something that is really buggy and doesn’t work, and I haven’t fixed it before lunch, I know that I’m not going to fix it in the afternoon because I do my best work in the morning. I’ll work on something else, talk to students, work on admin, do some other less ‘thinky’ work. I know if I look at it all afternoon, I might fix it in 4 hours. If I wait until 9 AM tomorrow morning, I’ll fix it in 5 minutes. This has happened to me so many times. I come back and look at it with fresh eyes and realise “I just didn’t fix that variable name”, and it’s fixed. It just doesn’t seem valuable to me. I can spend four hours on it today, or 5 minutes on it tomorrow!
Exactly. It’s maybe different in terms of the style of work as well? A lot of your work would be high-level thinking, coding, and problem solving, which you need to be 100% refreshed and switched-on for. Whereas, that’s maybe 30% of my work in the lab.
Oh yeah, because there is the physical aspect of being in the lab? Yeah, I can see that.
Yeah a lot of repetitive tasks and simple procedures. Some of it you can be on autopilot with music playing because you’re just repeating the same thing 400 times.
That doesn’t sound too tortuous!
Sometimes I’m a bit homesick for Australia, my old workmates send me pictures of the department having Friday social drinks at 5PM on a Friday!
Well I have in my calendar today we are going for beer at 4 to celebrate my boss being appointed to head of department!
Congratulations to your boss, that is the coolest!
So, my last question has to do with the mission of GWIS. How do you hope to see the scientific landscape change for women-identifying scientists going forward, especially within your field?
I don’t know how we can change it. I feel a bit blasé because I’ve seen a few things and I have seen the apathy. Unfortunately, we are in a position where change will need to happen to peoples’ mindset, not just to the system. Universities tend to hide things and allies need to be in your immediate community for things to change. It needs to be an active act, from everyone involved; including all of the majority groups. I have seen a lot of people being very active, and I’ve seen a lot of the more senior people not understanding their position and the power they have.
I have been in a position where there was a colleague who was extremely problematic, and in my mind it was a mix of ageism, misogyny, and power imbalance. Power dynamics can be very subtle. When you’re aware of unconscious biases, you recognize things straight away. For example, you might be called aggressive when you just point out that someone is wrong. That’s textbook misogyny. But other people, especially senior level individuals, who are not bathed in all of this stuff don’t understand, and they have different goals. Their goal isn’t necessarily to understand unconscious biases and to address them in a way that can move things forward. Their goal is to keep the peace and make sure that not many waves are made. I often hear things like, “Can we just focus on the science?” and we’re over here like “I wish we could!”. You might be able to turn a blind eye, but I cannot. What makes it difficult is that these are often really nice people. These are nice people who help in many other ways, who have supported me in many other ways. So you have that cognitive dissonance where they are good people that are doing the wrong thing, they just don’t understand why, and I don’t have the words to explain it to them. I have no immediate solution for this.
I’m putting this out there... I wish that we were in a position in a few decades where people are more aware and more willing to have difficult conversations when they are in a position of power, because that is what is necessary. When you are in a position of power, you should be the one having the difficult conversations. It shouldn’t be your students, trying to advocate for themselves, because they are very vulnerable. They can be retaliated against very easily. Also, some people do not understand that your experience with someone is not necessarily the student’s experience with that person, because of power differentials. That’s something I see in older generations, not understanding the intrinsic power dynamics.
I also wish that senior collaborators in science didn’t have the emotional intelligence of a turtle. That is my goal for the next few decades. To make sure that our scientists have emotionally matured a bit and understand human interactions a little more, so that they are better managers, better leaders, and better equipped to deal with difficult human relationships. That’s my wish. It will require a culture shift. I think we are still too complacent with antisocial behaviours. We often hear things like “Oh well, he’s a bit aloof isn’t he? He’s a bit funny, doesn’t really like people, doesn’t really talk to people”. Um, there are ten other people who do fantastic science and are not problematic, so can we pick those people instead?
Yeah definitely, I see what you mean. Let's make social and emotional intelligence part of the value system in how we hire and promote people, not ignoring all the red flags just because someone is a good scientist.
Exactly, because you can have an excellent scientist who stunts the growth of ten other scientists around them. Just because they’re doing great science doesn’t mean that you’re not losing in the end. If they’re taking that energy away from the community around them, in the end you are still losing.
Do you have anything else you would like to add?
I’d like to thank my boss, JJ Elrich (@astro_jje), because she’s amazing!
If you are looking for more of the juicy physics details surrounding 2017gci, you can read an illustrated discussion on Héloïse's blog here.
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