The Biggest Explosions of All

I’ve spent a lot of time in my astronomy career pointing telescopes at some of the biggest explosions of all—type 1a supernovae. This kind of supernova starts with a white dwarf star and another star orbiting each other. White dwarfs are very dense stars at the end of their lives. The only objects more dense are neutron stars and black holes. The white dwarf’s gravity draws material off the companion star until it reaches critical mass and the whole thing explodes. One such star that I had the chance to observe in detail in was Supernova 2011fe in the galaxy M101. Here’s an image from the Mayall 4-meter at Kitt Peak, one of the telescopes I used to observe this object. The supernova is the bright blue star outshining everything else in the upper right-hand part of the image.

Image by T.A. Rector (University of Alaska Anchorage), H. Schweiker & S. Pakzad NOAO/AURA/NSF

These cosmic explosions are pretty interesting in their own right. Our own star is expected to end its life as a white dwarf and these explosions give us a glimpse at the hearts of these stellar corpses. These explosions are also one of the ways heavy elements formed in the cores of stars get distributed out into the universe. Supernova 2011fe was, in fact, one of the closest Type 1a supernovae we’ve ever observed. We caught the explosion soon after it happened, watched the supernova brighten to maximum, then start to fade away.

Type 1a supernovae also have another useful property. Because white dwarfs have a fairly uniform mass, the brightness of the explosion is also uniform. So, if every Type 1a supernova observed were placed at the same distance away from you, they would all, more or less, be the same brightness. This means that by measuring the apparent brightness of the supernova, you can figure out how far away it is. This is a bit of an oversimplification, but there are ways to calibrate that information based on the how fast the explosion brightens and fades.

Back in the 1990s, an astronomer named Saul Perlmutter was granted target-of-opportunity time on Kitt Peak telescopes. In this case, it meant if a type 1a supernova went off, he could ask the telescope to point to it and take an image and calibration data. He and his colleagues hoped to get distances to as many galaxies as possible. I helped acquire some of that data which was combined with a lot of other data from a lot of telescopes to provide evidence that the expansion of the universe is accelerating. Perlmutter would go on to share a Nobel prize with Adam Riess and Brian P. Schmidt for this work.

This is one of those discoveries that shows some of the true fun of science. We learned that the expansion of the universe is accelerating, but that raises an even bigger question. Why is it accelerating? Typically that’s attributed to something called “Dark Energy.” This attribution isn’t meant to be an answer in itself. It’s meant to be a placeholder. It’s “Dark” energy because we don’t know precisely what kind of energy it really is, or even if it’s energy at all! Later this year, a new instrument called DESI will be installed on the Mayall 4-meter which will endeavor to get answers to some of those questions. But like all good science, I expect a veritable explosion of new questions raised for every answer we’re able to get.

Cosmos: A Spacetime Odyssey

The autumn of 1980 was perhaps one of the most difficult times of my life. My father died suddenly of a heart attack just about six weeks before my fourteenth birthday. One thing that helped pull me through that difficult time was Carl Sagan’s original Cosmos. It fostered my love of astronomy and set me on a course that would eventually earn me a degree in physics. Thirty-five years later, I’m now sharing Neil deGrasse Tyson’s updated Cosmos with my daughters. My youngest is the same age I was when I discovered Sagan’s original.

Cosmos: A Spacetime Odyssey_titlecard

Overall, I’ve been impressed with the series. I can nitpick some places where they’ve sacrificed precision in how a particular astronomical object or phenomena is depicted in the name of dramatic effect, but for the most part Tyson gets the important things right. The show has allowed me to better explain the importance of spectra in my work at Kitt Peak. I was delighted to see an episode featuring Henrietta Leavitt, Annie Jump Cannon, and Cecilia Payne-Gaposchkin. I was able to discuss how they influenced both my work and how people they worked with directly inspired teachers of mine such as Emilia Belserene at Maria Mitchell Observatory. I also appreciated the discussion about how neutrinos can precede supernova explosions, though I noticed they managed to leave out mention of Stirling Colgate’s important contributions to that work.

Perhaps the most important thing about the series is that I see the same wonder on the faces of my daughters that I had when I watched Carl Sagan’s original series. My oldest daughter has already set her sights on a degree in mathematics and computer science. My youngest still has options wide open. I hold no strict expectation she’ll pursue a career in science, but I do expect she’ll come to respect the process of science and hold an appreciation of it no matter what she does.

Unlike Neil deGrasse Tyson, I hold no Ph.D. My career in astronomy diverged from a strictly academic path into more of an engineering and support path. Despite that, I feel it’s important to convey my love of science in classrooms as well as science fiction and steampunk conventions. In fact, I think there’s value in showing that you don’t need a Ph.D. to appreciate, use, and act on scientific discovery. Because of my interest in communicating about science, I’ve been paying close attention to Tyson’s presentations. He is a good, clear communicator and I’ve especially enjoyed seeing how he introduces subjects such as stellar spectroscopy, supernovae, and black holes.

In the most recent episode I watched, Tyson presented the sobering evidence for climate change. There’s been a lot of debate about it, but as he notes there’s well over a century of solid evidence that carbon dioxide is increasing and global temperatures are warming. He notes that weather is hard to predict and there are lots of minute variations. He demonstrated this by walking a dog. The dog goes all over the place, attracted by different things. However, climate is like the man holding the leash. There may be random variations, but there’s also an overall path. Although climate change is a sobering reality, I appreciated that Tyson showed that there is hope. We have to work hard and make solar and wind energy a reality and we need to do it much faster than we have been.

Now some will say addressing climate change is just too big a problem to address. I watched this episode after visiting New Orleans ten years after Hurricane Katrina. Ten years ago, some people said rebuilding New Orleans was just too big a challenge, we should let the city go. Although Katrina still echoes in New Orleans, it’s returned to being a bright and vibrant city. Researchers at Tulane University are working on finding ways to restore the gulf coast and perhaps even find ways to make New Orleans much safer should another hurricane strike. We humans are amazing and we can solve the big problems when we set our minds to it.

I appreciate the effort Neil deGrasse Tyson, Ann Druyan, and Seth MacFarlane have put into bringing a new version of the show back. I hope it inspires a new generation to look at the world with wonder and to take the scientific process seriously.

Remembering Stirling Colgate

My graduate advisor, Stirling A. Colgate, passed away last weekend. He was a colorful character, president of New Mexico Tech from 1965-1974, and physicist at Los Alamos National Laboratory. Here we see him as he appeared in the PBS Nova episode “Death of a Star” which was filmed around the time I worked for him. In the background is the Digitized Astronomy Supernova Search Telescope that he developed and I worked on for two years.

Stirling Colgate

Perhaps Stirling’s most famous contribution to astrophysics was predicting that there would be a neutrino burst during a supernova explosion. This idea was borne out by the explosion of Supernova 1987A. Stirling once told me that the reason he went into physics was that he enjoyed watching things explode. Of course supernovas are the biggest explosions in the universe.

One of Stirling’s other major accomplishments was his attempt to build a supernova search telescope. He started this telescope in the 1960s, during the era when astronomers sat out in the dome with the telescope, often taking photos on glass plates or counting photons with photoelectric photometers. Stirling’s supernova search never worked as hoped, but the papers that came from the project helped to drive further development in robotic and automated astronomy. It paved the way for remote operation of telescopes. This in turn allowed for better image quality, because astronomers didn’t have to be out at the telescope. It allowed for real-time analysis of data, because astronomers could use a computer to collect data and look at it at the same time. What’s more, because of this work, astronomers don’t always have to travel to the telescope that’s collecting their data, they can work over the internet. Among other things, this work allowed for the development of robotic space-based telescopes such as the Hubble Space Telescope and Kepler.

As I said, Stirling was a colorful character. His last name was not coincidence. He was an heir to the Colgate family of Colgate toothpaste fame. There are many stories I could tell that really aren’t appropriate here, but one thing he did tell a friend upon meeting him was, “You’ve no doubt heard many stories about me. Let me assure you that each and every one of them is true, even the contradictory ones!”

While I was working for Stirling in 1989, William Fowler came to give a lecture at New Mexico Tech. In 1983, Fowler won the Nobel Prize in Physics for theoretical and experimental studies of the nuclear reactions of importance in the formation of the chemical elements in the universe. Fowler had also been one of Stirling’s postdoctoral advisors. The three of us, along with Stirling’s wife, Rosie, sat around a table in Socorro’s Capitol Bar, shooting the breeze. I remember Stirling turning to Willy Fowler and asking what he thought about recent studies that showed the possibility of global warming. Fowler said if it bore out, it would have tremendous impact. It’s amazing to me that over twenty years later, we’re just starting to see the scale of the impact.

Unfortunately, over the years, Stirling’s work and mine carried us in different directions. It has been a while since I’ve had a chance to communicate with him, but he still sticks with me as an important and influential teacher. He taught me how to solder electronics, how to read an oscilloscope and how to repair cryogenic systems. He taught me about the physics of exploding stars and he taught me about statistical analysis. He taught me to always ask why things work and not just how they work.

Free of his mortal coil, I picture Stirling in a swimsuit, waiting to dive into a distant supernova and ride the waves of the explosion as far they’ll carry him.