Year: 2018

Doing my MSc in Canada


I wrote a guest post in AstroBetter about doing my MSc in Canada at the University of Alberta! Going abroad for a MSc is quite an uncommon path for US-born students in STEM, but I’m really glad I did it. Read the whole post here!

I knitted a hat!


When I was a kid, my grandma taught me to knit, and I made a few simple little things. In middle school and high school, I’d knit skinny “fashion scarves” with fluffy sparkly yarn, and I did some granny-square blankets, teddy bears, and mittens with the church youth knitting group (I was suuuuper cool /sarcasm). I hadn’t really touched it at all since starting college, but I noticed it becoming popular again among my generation in the past five or so years. So, I finally properly picked it up again earlier this month and knitted a hat!

Checking the circumference and length of the body of the hat. Yes, I’m using a paper clip for my row marker.

At the suggestion of the ladies at Sticks & Strings in Lansing, I joined Ravelry and found a cute, easy pattern for a winter hat (/toque, for Canadians). I used the Bankhead pattern by Susie Gourlay, adult size large. It fits pretty perfectly! Have a look at my project page on Ravelry for the technical details. I’ve noticed that it’s easier now to do “longer” patterns while binge-watching tv shows! I also have a longer attention span as a 28 year old than I did as a 12 year old. I made this hat in probably 5 days (two weekends and a workday evening) working at a leisurely pace. I’d say it was relaxing to work on this, but mostly, it was nice for my anxiety to be channelled in a focused, creative outlet where the input-output relation (so much work for so much result) is basically linear 😊 I’m looking forward to the Fiber Arts Fest in Ann Arbor in October!

CUWiP panel on mental health


If you’re an undergraduate physics/astronomy major in the US or Canada and a gender minority (woman, non-binary, etc.), sign up to attend the Conference for Undergraduate Women in Physics (CUWiP)! It’s a 3-day regional conference Jan 18-20, 2019 held at 12 locations across the US and Canada, so there’ll be one not too far from you. You can look up the CUWiP hosting universities here.

At Michigan State University (for students in Michigan, Indiana, Kentucky, Ohio, and western Pennsylvania) I’ll be involved in a panel/workshop on mental health! Take a look at a seminar I gave in May 2018 at MSU on mental wellbeing for early career researchers (note that many of the university resources are MSU-specific). Mental health issues are alarmingly common for early career researchers (students and postdocs), so raising awareness and connecting people to resources are very important.

Conference networking and self-care

I’m at COSPAR 2018 in Pasadena, CA this week! COSPAR is a giant meeting with 3,500+ attendees from all around the world spanning all aspects of astronomy, astro-particle physics, space physics, solar physics, astrobiology, and any other science from low-Earth-orbit to the edge of the universe. COSPAR 2018 is Pasadena’s largest-ever scientific conference! It can be a bit overwhelming, so here are some tips for networking at and navigating such a meeting.

Networking

“Networking” means making friends/acquaintances with nice people who do interesting science. That’s really all it is! Quick conversation starters: ask them what their latest paper was on, students are working on, and/or side projects are. It’s ok to ask simpler/broader subject questions!

  • Email people you’d like to meet and ask to meet them for lunch or coffee, and tell them when your poster/talk is.
  • If it’s your first time at a very large meeting, attach yourself to someone a little more senior than you who you know well (senior grad student, postdoc) and ask them to introduce you to people at coffee breaks and bring you along for meals the first day.
  • Tag along for meals even if you just met the people! Saying “mind if I join you for lunch?” or “mind if I join you for dinner?” is  a totally normal thing to ask at conferences.
  • Get dinner with colleagues on the majority of the evenings. Mix it up: sometimes with grad students, sometimes some postdocs and profs in the mix. Take evenings for yourself when you need them, but don’t miss out on this part of networking.
  • Attend the keynote talks. They’re often quite interesting, and people will generally be talking about them at coffee breaks and whatnot.
  • Try going to a session block that sounds really interesting and is totally out of your wheelhouse. Also go to a session block or two in a related topic to broaden your understanding of your own subtopic. This is one of those great things you can only do at very large, broad meetings like COSPAR!
  • Prepare an “elevator pitch” (one to two sentence non-jargon summary) if someone asks what your research is on.
  • See this great thread on attending a conference as a student/ECR without your advisor there!

Self-care

Giant 9-day-long conferences can be exhausting, even for the most extroverted among us. Try not to skimp on your usual basic self-care like eating regular healthy meals, getting plenty of sleep at night, and exercising once or twice a week (even just 20 minutes of youtube yoga in your hotel room).

  • Don’t feel bad about skipping sessions. Acknowledge now that you won’t see All The Talks.
  • Spend time making new conference buddies and seeing old ones.
  • Take a nap if you need to! At one of the big AAS winter meetings, I took a nap every day.
  • Eat a vegetable every day. Your body needs it.
  • Drink plenty of water.
  • Try to not go over your usual caffeine & sugar intake. I know, I know, that’s what coffee breaks are for…but try not to go overboard. Doing this helps me manage anxiety better and sleep reasonably well with the jetlag.
  • Struggling with your mental health at a conference can be more taxing than usual. Reach out to friends (at the conference and at home), and take time to do whatever helps you when you’re at home. Generally people don’t pry and we all know everyone else is busy, but if you need an excuse to get out of something, you’re “not feeling great, but will catch up tomorrow/the next day/after my talk.”

What would you add to the lists?

HEAsoft install on a Mac

Updated Feb 1, 2021

Here are my instructions for how to get HEAsoft, the NASA High Energy Astrophysics Software, set up on a Mac with macOS Catalina (v10.15.7). I learned most of this from HEAsoft’s own documentation (and a lot of trial and error over the years). I work in bash, so adapt as needed if you use c-shell or zsh. Disclaimer: I’m not a HEAsoft developer or maintainer, so follow this advice at your own risk. Actual HEAsoft maintainers should be your first point of contact if something goes wrong.

Step 0

Make a full backup of your machine as-is.

Step 1

Install these things:

Anaconda
Xcode from the App Store
Command Line Tools for Xcode by typing xcode-select –install
homebrew (or another package manager like MacPorts or Fink)

prompted to run these by homebrew:

git -C /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core fetch –unshallow
git -C /usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask fetch –unshallow

Step 2

Using the package manager, install the following (and their dependencies). Some of these are brew upgrade Thing instead of brew install Thing (it will complain and tell you).

brew install gcc@10
brew install x11vnc
brew install perl
brew install wget
brew install automake
brew install mawk
brew install flex
brew install wcslib
brew install lzip
brew install slang
brew install imagemagick
brew install gnuplot
brew install ncurses
brew install pgplot
brew install cfitsio

Step 3

Download the HEAsoft source tarball. The first bullet point, above Step 1 on that page, should have everything you need (and you probably don’t need the extra old XSPEC stuff). This download takes like 30 minutes! I then put it in the directory ~/opt/ and unzip the HEAsoft tarball in there (tar -xvzf). This is a different location than what I’ve previously done! It seems that the new macOS really hates letting the user install things as su.

As it’s downloading, navigate to your old HEADAS directory and rename it to, e.g., old-heasoft6.26. This way there won’t be weird crosstalk. You can also delete your previous old-heasoft and tarball if you still have it. If you’ve never ever installed HEAsoft on your computer, you can skip this part.

Step 4

Follow the instructions for remote CALDB: https://heasarc.gsfc.nasa.gov/docs/heasarc/caldb/caldb_remote_access.html. Remember to save the files in /usr/local/src and put the appropriate export lines in ~/.bashrc!

Step 5

Copy/paste into ~/.bashrc (using homebrew installations of the compilers and the anaconda distribution of python 3):

export CC=/usr/local/bin/gcc-10
export CXX=/usr/local/bin/g++-10
export FC=/usr/local/bin/gfortran-10
export PERL=/usr/local/bin/perl
export PYTHON=/Users/YourUserName/opt/anaconda3/bin/python
unset CFLAGS CXXFLAGS FFLAGS LDFLAGS

Step 6

In the ~/.bash_profile file, be sure that /usr/bin and /usr/local/bin are at the beginning of your PATH environment variable.

Step 7

Restart your computer. I don’t know how necessary this is, but it’s one of the few things that changed in the few days between the install not working and working.

Step 8

To configure, make, and install (your HEAsoft version number might be different when you reference this blog post):

cd ~/opt/heasoft-6.28/BUILD_DIR/
./configure
make > build.log 2>&1
make install > install.log 2>&1

Note that I’m no longer passing the X11 include and library directories to the configure script, as I’ve had to do in previous installs. You should be able to open build.log and install.log as those things are going (from a different terminal window) to see their progress. You can also use tail build.log and tail install.log to view the last 10 lines of the files (though this won’t update, so this is more for occasional checks).

The make line with build.log takes a particularly long amount of time (like 20ish minutes). Since it’ll use a lot of memory and you’ll hear the fans going as it’s makeing, I don’t recommend playing videogames on your computer in the downtime.

Step 9

Copy/paste into ~/.bashrc for general use (again, your HEAsoft version number and system architecture might be different. If you ls in the HEAsoft directory you’ll see what to put for the system architecture thing):

export HEADAS=/Users/YourUserName/opt/heasoft-6.28/x86_64-apple-darwin19.6.0
alias heainit=”. $HEADAS/headas-init.sh”

To start up XSPEC, in a bash terminal session type

heainit
xspec

and it should start up an XSPEC environment! Happy analysis!

Step 10

Once I get PyXSPEC working, I’ll put the steps here.

PhD thesis!!!


Presenting: my PhD thesis!! The whole thesis is downloadable here on the UvA Digital Academic Repository. The cover is an accreting black hole with a jet, seen through a light curve with quasi-periodic variability. Design by Libby Taggart Singh, image by NASA/JPL-Caltech.

In the Netherlands it’s traditional to print up like 200 copies of the thesis in soft-bound B5-size (6.8-9.8 in) and hand them out to everyone at the institute (the API has 100+ people), your close friends and family, and mail some to collaborators and close colleagues. It’s almost like your business card. I have about 20 PhD theses of people who graduated from API before me while I was there, and it’s really nice to finally get to pass out a thesis of my own.

My public PhD defense, reception, and party are Thursday April 19th in Amsterdam! If you’re around and would like to come, please contact me via email or Twitter to get the details! Only 6 more days to go!!!

Amsterdam Science-Art Slam

Image description: Pink-hued image of a galaxy with many stars and dust filaments. Overlaid with cut-outs of a person hunched over playing a wind instrument, a fuzzy photo of a dancer, and a close-up of hands playing a violin. Image from Science-Art Slam facebook page.

Back in May 2017, I was part of a Science-Art Slam in Amsterdam, organized by Claudia Mignone. Three astronomers/astrophysicists (David Gardenier, me, and Daniele Gaggero) gave 20ish-minute talks about our research, while at the same time musicians were creating free-improvisation music and a visual artist was mixing live projections of related scientific images. It was a super fun and different outreach-type event to both experience and participate in!

I talked about neutron stars, black holes, and their extreme environments. The transcript is below the embedded video. Enjoy!

Transcript:
I’m Abbie Stevens, I’m doing a PhD at the University of Amsterdam, and I’m going to tell you a bit about what I’m doing it on. So I’m gong to tell you about neutron stars and black holes and the weird space around them. Black holes you’ve probably heard of, but neutron stars you maybe haven’t. David [the previous speaker] talked a little bit about neutron stars. This will be a story in two parts: first, what neutron stars and black holes are, and second, how we learn about them and how we know the things that we know.

Part 1: What are they?
When a star dies, it will turn into one of three things, depending on how massive it is: a white dwarf, neutron star, or black hole. if it’s up to 8 times as big as our Sun, it turns into a white dwarf. Most stars fall under this category and will become white dwarfs (including our Sun). A white dwarf is roughly the size of the Earth, but it has almost as much stuff as in our Sun.

If the star is a bit more massive than that, up to about 20 times the mass of the Sun, the star will go supernova and what’s left is a neutron star. A neutron star is very dense. It’s only 25 kilometers in diameter, but has 1.5 to 2 times the mass of the Sun inside it. It’s average density (how compact it is; the amount of stuff per volume) is on par with an atomic nucleus, and it’s inner core is denser than an atomic nucleus. To get an intuition for this kind of density, imagine taking every person on Earth, and squishing them into a 1 centimeter cube. I’ve calculated it, and it gets you in the right ballpark. This extreme density causes the neutron star to warp spacetime. Albert Einstein’s theory of general relativity, which is the leading theory of how gravity works, says that matter tells spacetime how to bend, and the fabric of spacetime tells matter how to move. So in this framework, a neutron star is massive enough and dense enough to bend spacetime by a decent amount. And then, the curved spacetime causes the light and matter near the neutron star to behave in strange ways.

So let’s talk about a neutron star’s gravitational field. The acceleration due to gravity, which is a way of measuring the strength of a gravitational field, at the surface of a neutron star, is 100 billion times stronger than at the surface of the earth. If you dropped your phone on earth from 1 meter up (or if you’re Dutch, 2 meters up), it hits the ground in a couple milliseconds. If you did that from 1 meter off the surface of a neutron star, it would drop so fast, from the strong gravity, that it would hit the surface in 1 billionth of a second. Also, your phone would break. The work that you do against gravity hiking Mt. Everest on the surface of the Earth, is the same as what it would take to hike 1 thousandth of a millimeter on the surface of a neutron star (assuming you had a magical space suit that allowed you to not be totally pancaked to start with).

And then, black holes are weirder than that. A black hole is the remnant of a massive normal star, more than 20 times the mass of our Sun or even bigger. The black hole is what’s left over after it’s gone supernova.

Some black holes are 6 to 10 times as massive as our Sun — these are the small ones, stellar black holes. These ones are a few kilometers across in diameter typically, maybe 2 or 3 kilometers. The first black holes discovered by LIGO, the gravitational wave detector, were about 30 times the mass of our Sun, and they combined to make a black hole that was about 60 times the mass of our sun. Remember, there’s a lot of stuff in the Sun to start with, and this is 60 times that! And then there are the supermassive black holes at the centers of galaxies, that are millions or billions of times the mass of our Sun. The supermassive black hole at the center of the Milky Way, called Sagittarius A* (said “A star”), and it’s about 4 million times the mass of the sun, but only about 30 times the size of the Sun.

As you’ve maybe figured out, black holes are more massive and even denser than neutron stars, so they bend spacetime even stronger than a neutron star, and then again, light and matter behave even more strangely around them. But unlike neutron stars, black holes don’t have a hard surface. The size I’m referring to here is for the event horizon. This is the point, or rather, the surface, of no return, where the gravity is so strong that not even light can escape. So while black holes have stronger gravitational effects, there reaches a point where we have no hope of ever knowing what is inside it, so in some senses, neutron stars are more interesting to look at.

Now I’m going to take a step back and tell you how we know this, and how we learn more about neutron stars and black holes.

Part 2: How do we learn about them?
Black holes and neutron stars tend to exist in binaries with normal-type stars like our Sun. So you’ll have a neutron star or a black hole and a normal star that are pretty close together and orbit each other (kind of like the Earth and the Moon orbiting each other). But the gravity of the neutron star or black hole is really strong, so if it’s close enough to the normal star, the outer stuff of the normal star becomes more gravitationally attracted to the neutron star or black hole than it is to it’s own star, and the star stuff falls towards and swirls around the neutron star or black hole. So this process of draining the normal star and feeding the black hole or neutron star is called accretion, and accretion is a very powerful astrophysical process.

The star stuff that’s being accreted forms a disk around the black hole or neutron star (almost like the rings of Saturn, but thicker and bigger), and there’s a lot of friction within the disk that makes it get really hot. Now when anything is hot, it shines energy. For the human body, we shine most of our heat energy as infrared radiation. Like with infrared cameras or night-vision goggles, people glow brightly because of the infrared heat. The sun is hotter, and it shines most of its heat energy in visible light. And this accretion disk of hot star stuff, the inner part that’s close to the black hole or neutron star, is so hot that it shines most of its heat energy as X-ray radiation. The same energy the doctor uses to take pictures of your bones. This X-ray-hot part of the accretion disk is also the part that is sitting in the bent spacetime, the strong gravitational field close to the black hole or neutron star. We’re talking within hundreds of kilometers. So if we study the X-ray radiation, it can tell us how the stuff is moving and behaving in strong gravitational fields.

But, we can’t just take a picture, because this interesting region around black holes and neutron stars is both very small, and very far away. If you take a typical distance for one in our galaxy, it would be like trying to resolve the width of a human hair on Mars at closest approach. We can’t do that. So on the sky this looks like a single dot, or a single pixel. But, the X-rays aren’t constant – they flicker and wiggle and vary in brightness, and these variations are fast – tens to hundreds of times per second.

If you look at a particular black hole of neutron star with an x-ray telescope for a few hours, you can build a variability picture of these flickers and wiggles in X-rays, and some interesting patterns emerge. There’s noise that can look flat or like some weird lumps, and we think this is from stuff in the accretion disk gently flaring in brightness as it moves its way in toward the black hole or neutron star. There are pulsations in some neutron star systems that David talked about, from very regular brightness changes. Neutron stars have really strong magnetic fields (thousands of times stronger than anything that’s ever been created in a lab on earth), and the magnetic field can cause a lighthouse effect where you see regular bright flashes when the north or south pole is pointed towards you. Some of the pulsations happen hundreds of times per second, so you have a neutron star that’s 25 kilometers across spinning hundreds of times per second! Neutron stars that show pulsed light like this are called pulsars, and Claudia [Mignone] will tell us about the discovery of pulsars in the last session.

Then for both neutron stars and black holes, there are quasi-periodic oscillations. So they have a bit of a period, but they’re not very precise. Not quite periodic, not quite noise. But you could almost think of it like a changing heartbeat in the accretion flow. There are lots of types of quasi-periodic oscillations, so that the combination of quasi-periodic oscillations and noise in the variability picture is almost like a fingerprint. I have one colleague who has an nearly photographic memory for the variability pictures. You can show her one, and she says “that’s that black hole from 2010” or you show her another one and “oh it’s this neutron star from 2002”. And we think that the quasi-periodic oscillations are telling us about a hot fluffy flow of star stuff that’s piling onto the neutron star or black hole, and it’s wobbling around from being in the really strong gravitational field.

So we have these X-rays that are coming from this hot star-stuff that’s around neutron stars and black holes, and it’s spinning in curved spacetime. So by looking at these X-rays, they can tell us more about what black holes and neutron stars are, and how they make matter do weird stuff.

If you’re interested, I have some 3D-printed accretion disks that you can play with during the break.

I’m a Michigander!

We’re getting settled in Lansing, Michigan, and I’m now just under a week away from submitting the bulk of my PhD thesis. If we’re friends IRL, contact me for my new US phone number and address!