All posts for the month February, 2016



Nothing. They just waved.

Led by physics major Tyler Wade, this week’s astronomy journal club discussed the very exciting result from the LIGO collaboration, the first detection of gravitational waves.

Einstein predicted the existence of gravitational waves back in 1916. (If your differential geometry and German are any good, you can read the original paper here.) Essentially, gravitational waves are a consequence of that fact that mass can distort the shape of space (that’s what we call gravity).

The upshot of this is that any massive object in motion can excite gravitational waves, but only very massive objects (like, black hole-sized) produce waves big enough that we have any hope of measuring them.

And so for the last few decades, the LIGO project, along with other gravitational observatories, has been monitoring the space-time continuum, looking for tiny distortions due to rapid, oscillatory motion of massive celestial bodies.

LIGO attempts to detect these distortions by sending two laser beams, one each, out and back along two orthogonal 4-km tunnels. By measuring the travel time for each laser beam down each tunnel, they can determine their lengths to a ridiculous precision. A passing gravitational wave would VERY slightly modify the tunnel lengths in a particular way.

How slightly? The signal reported last week by LIGO corresponds to a change in the tunnel length by 0.0000000000000000000001 meters. That’s the equivalent of a change in the width of the Milky Way galaxy by 1 meter.

At two different observatory sites, one in Washington state and the other in Louisiana, the LIGO collaboration measured the distinctive signature of gravitational waves generated by two black holes, many times the mass of the Sun, as they completed their death spiral, merging into an even bigger black hole and radiating an enormous amount of energy.

Why is this important? Well, seeing gravitational waves is not going to allow us to control gravity (at least not yet), and the fact that they exist is not surprising. Instead, LIGO has provided us a brand-new way of doing astronomy.

It’s as if, up until now, we were doing astronomy colorblind, and suddenly LIGO built a color telescope. Of course, being able to see in color would open up vast and unexpected vistas on the universe. The detection of gravitational radiation is the same kind of revolutionary achievement.

NYT has a really great animation and video describing how the detection worked, which I’ve embedded below.

The red dots show the observations, with the dips due to asteroid chunks transiting the white dwarf. The inset shows an artist's conception of the disruption process.

The red dots show the observations from this study, with the dips due to asteroid chunks transiting the white dwarf. The inset shows an artist’s conception of the disruption process.

For our second journal club meeting this semester (didn’t manage to blog the first one), we discussed a study from Saul Rappaport and colleagues on observations of the white dwarf WD 1145+017, which continues to show evidence that it is eating a small asteroid.

A study last year from Vanderburg and colleagues (which we discussed last semester) presented observations from the K2 Mission showing distinctive but highly-variable transit signals coming from WD 1145+017. That group conducted follow-up observations that pointed to the presence of an asteroid very close to the star, being ripped apart by the star’s gravity.

As crazy as it sounds, the idea that some white dwarfs are eating asteroids is fairly well-established, but Vanderburg’s study was the first to present observations of the process clearly in action. The variability of the transit signals indicates that the violent process is dynamic and complicated.

This new study from Rappaport and colleagues continues the saga of WD 1145+017 and finds that the disruption process persists more than a year after the initial observations. And using the apparent drift rates of the different chunks of asteroid, Rappaport is able to constrain the mass of the parent asteroid to be about 1% that of Ceres in our solar system.

One of the most exciting aspects of this study for me is that the observations were made using a network of small, amateur telescopes. Some of the scopes used in the study were 25-cm, and so I’m hopeful that, in the near future, we will be able to use Boise State’s own Challis Observatory to conduct follow-up. Just gotta wait for a clear night.

Boise State’s Institute for STEM and Diversity Initiatives is hosting Aerospace Day here on campus today, a day to explore the science, engineering, and applications of aerospace technology.

I volunteered to give a talk on our group’s research looking for short-period exoplanets, and it seemed well-received. Lots of interesting questions afterward. I’ve posted the talk below.

During my talk, I mentioned the website, where the public can help find new exoplanets using data from the Kepler mission.

Thanks to Christine Chang Gillespie, Donna Llewellyn, and all the other organizers for the invitation to speak.