White Dwarf Supernovae: Standard Lampposts on Dark Energy Road

My dear readers,

This special post is part of the Carnival of Cosmology: Dark Energy, hosted by Galileo's Pendulum, a fellow astronomy blog I discovered less than 12 hours ago, as of the writing of this post.

To begin, I'm going to give a very brief background about dark energy in general, and then I'll talk about one of the tools we use to measure this enigmatic stuff.  Most of my research has been investigating the nature of dark energy using Type 1a supernovae (pronounced like "Type One-A Super-no-vee," SNe 1a for short, and also known as white dwarf supernovae.) so it is a topic very dear to my heart as well as my head.

As you may know, the Universe is expanding.  However, what you may not know is that this expansion is not slowing down, as you might think gravity would cause it to do, but it is speeding up.  We can tell this by looking far, far away, deep into space, where the things we see are not quite as bright as we would expect them to be.

One type of candle at many distances - as the candle gets farther away, it appears dimmer. The same goes for white dwarf supernovae and the expanding Universe.  

Image courtesy of Lawrence Livermore National Laboratory/Universe Adventure

To quantify this notion, we use "standard candles," which have a set brightness that we know is the same, no matter where they are in space or when they sent out their light.  A white dwarf supernova is just such a "candle."**  This particular type of exploding star is very special, in that it doesn't care what kind of galaxy it calls home (big, small, elliptical, spiral, etc), and it always has the same pattern of brightening and fading.

Strange, to be sure, but this is all because of the specific type of star associated with this explosion: a white dwarf of about 1.44 times the mass of our Sun (or 1.44 Solar masses).  A star similar to our Sun goes through its life cycle (click here for a very plain-English explanation of stellar evolution) and eventually becomes a white dwarf.  Usually a white dwarf will just burn the rest of its energy, cooling down to become a black dwarf.  However, if it is part of a binary system, or has a companion star, and that companion orbits close enough to our white dwarf, the white dwarf will start sucking mass right off of its companion.

Image courtesy of Science Engine - Space

Once it reaches 1.44 Solar masses, the white dwarf becomes too big for its britches and collapses under the force of its own gravity in an explosion so bright that it can rival the brightness of its host galaxy!

So, you can now see how a particular kind of star in a particular setting makes a particular kind of explosion and doesn't have to be located in a particular type of galaxy.  Even without any constraints on location, this seems like it would be pretty improbable, right?  Well, just remember that there are as many as tens to hundreds of billions of stars in a given galaxy, and with the Hubble Ultra-Deep Field as an indicator, there are billions and billions of galaxies out there, which makes for a lot of potential SNe 1a to be observed.

In 1994, a white dwarf supernova (lower left) occurred in galaxy NGC 4526. The supernova's brightness rivaled that of its host galaxy - one single star explosion rivaled the brightness of billions of stars combined!

Image courtesy of the High-Z Supernova Search Team/HST/NASA

Now, since there are so many SNe 1a out there and they are so standard, they make an excellent tool for measuring distances, which is exactly how the 2011 Nobel Prize in Physics recipients used them to discover dark energy.  They took a theoretical model of how the brightness should vary with distance and compared that with data from dozens of supernovae that they actually observed (today we have hundreds of observations, and soon there will be many, many more, thanks to the advances in telescope cameras and sensors, as well as the growing number of all-sky surveys being performed).  The disparity between the model and the data grew with distance, thus "dark energy" was discovered.
Head on back over to the Carnival to check out the other great posts!

** I should note that SNe 1a are more like standardizable candles.  If you really want to get technical, check out this article from Lawrence Livermore National Laboratory.

Perchance to Dream

My hero.

Dearest readers,

My long-time role model and hero, Sally K. Ride, passed away this week at 61 years old, after a 17-month battle with pancreatic cancer.

The first American woman to go to space, Dr. Ride was also an astrophysicist at University of California San Diego and the co-founder of Sally Ride Science, a company which aims to get kids, especially young girls, interested in science.

With news of Dr. Ride's passing dominating my social media, I have been reflecting on just how she influenced my own life.  My hipster tendencies are screaming, "Hey, I liked Sally Ride before all the hype!" but the rest of me is just glad that even in death, her legacy will inspire people to dream big.

I didn't have many role models/heroes when I was growing up, but a seemingly-innate fascination with the space shuttle made me love Sally Ride from the time I first learned of her existence and accomplishments.  In the 4th grade, during Women's History month, one of my assignments was to write a report on a woman of note.  I remember people choosing Harriet Tubman or Mother Theresa, and I chose Sally Ride.

[Funny, my family had a computer before most others', and I actually remember the font I used to type my little report, Typewrit, because it looked like a typewriter and 9-year-old me just adored it for some reason.  Maybe that's where my love of interesting fonts began!]

I'm sure that report is still laying around in a box somewhere, because my dear mother saves everything, but alas, I cannot put my hands on it at the moment.  Suffice it to say that I can probably give Dr. Ride most of the credit for my wanting to become an astronaut, since I was born only a year before her history-making flight.  I didn't become an astronaut, but that big dream is what fueled my love of astronomy from a very early age, and that is what kept me going all through college and grad school.  It was my goal, my dream, my life-target, and still is all those things.

Perhaps you have veered from the original path to your dream, like I seem to be doing.  I thought that getting my PhD would get me to where I wanted to be, and it may yet (but please, no more school for quite a while!!).  Here's a novel idea, though: other roads can also lead to my dream of exploring the Universe.  It might be a roundabout path I take to get there, but a large portion of traveling is in the journey itself, and so it is with the journey through life.  Who says you have to do what everyone else "always does" to get where you want to be?  I see nothing wrong with marching to the beat of your own drummer.  Go against the grain.  Do something different.  Surprise people.  It may or may not be the path of least resistance, but whatever happens, it will be an adventure!
Finally coming out of hiatus,

Ms. Disarray

The Higgs Discovery, Boiled Down

Hello from hiatus!  I'm still adjusting to my non-student life, still looking for a job, and still TAing for the time being, but I will get back to blogging, I promise.

In the meantime, you have likely heard the buzz about the Higgs boson findings at CERN, and if you're anything like me, you had trouble understanding it.  Yes, I am a physicist, but I do not study High Energy or Particle Physics, so I'm not all up with the lingo.  Thus, I turned to my favorite astronomy blogger, Phil Plait at Bad Astronomy, who seems to know about everything, so I will direct you to his post about the Higgs.

Click HERE, dear reader, and be amazed!

Until next time,

Ms. Disarray <3