Bakersfield Night Sky – February 20, 2016
By Nick Strobel
It was 7:50 AM on Thursday and I was looking at a big black square where a gorgeous picture of the cosmos was usually displayed on the Astronomy Picture of the Day website I show at the start of every astronomy lecture. Across that black square was a notice that it would be updated during a press conference from the LIGO (Laser Interferometer Gravitational-Wave Observatory) that was to start at 11:00 AM EST. That was 8:00 AM our time and class was going to get started at that time. Students took their seats and looked at the same black square while I kept refreshing the web browser. 8:00 came and I refreshed the web browser. Still a black square. Two minutes later, 8:02, a refresh of the web browser revealed a picture of two black holes merging with the caption that gravitational waves had been detected by the LIGO detectors in Hanford, WA and Livingston, LA!
The detection was actually on September 14, 2015 but the results were finally made public five months later in the February 11, 2016 issue of Physical Review Letters after the results had been vetted in the peer review process of all reputable scientific journals. I told my students that the discovery will result in a Nobel Prize. Unlike the previous year's announcement in March 2014 about the possible signature of gravitational waves in the cosmic microwave background that would have also been Nobel Prize-worthy if it had been confirmed, this discovery will not "go away" upon further analysis of the data.
Two black holes, one with 36 times the mass of the Sun and the other 26 times the mass of the Sun, spiraled inward toward each other and merged to form a black hole with 62 times the mass of the Sun roughly in the same direction as the Large Magellanic Cloud in the South Hemisphere sky. The source was much further away than that galaxy though, as the gravitational waves had traveled between 700 million years to 1.6 billion years at the speed of light, reaching the LIGO detector in Livingston, LA 7 milliseconds before the LIGO detector in Hanford, WA. Both detectors measured the increasing amplitude and frequency of the spacetime ripples during the last 0.2 seconds of the spiraling in, merger, and ringing as the merged object settled down.
If you check the arithmetic of the two initial black holes and the final result, you'll see that there is a mass of 3 times the mass of the Sun missing. That mass was converted to the energy of gravitational waves. It is a lot of energy: about 50 times more energy released at that time than that produced by all of the stars in the rest of the universe combined!
This detection pushes the testing of General Relativity to about a million times greater strength than the previous test that came from observations of the spiraling inward of two pulsars. That discovery in 1974 netted the two discoverers a Nobel Prize in Physics in 1993. Gravitational waves are a very big deal. That's why I think this discovery is going to earn the three physicists who dreamed up LIGO, Kip Thorne (executive producer and science advisor for the movie "Interstellar"), Ronald Drewer, and Rainer Weiss, each a Nobel Prize. It was also why I kept refreshing my web browser at the start of Thursday's class with eager anticipation!
Several other detections were made in the fall 2015 observing run and many more are expected in future observing runs as the sensitivity of Advanced LIGO is increased even further. Hopefully, with that catalog of detections, we will begin to see discrepancies from the predictions of Theory of General Relativity that will lead us to an even deeper understanding of gravity, particularly at the quantum realm. The LIGO scientists have likened the observation of gravitational waves to being able to "hear the universe", so this detection is the transition from watching silent movies of the universe to watching movies with sound---not just a new window on the universe but a whole new sense to learn about the universe. To find out more about gravitational waves and how the LIGO detectors work, click on over to my webpage about tests of General Relativity at www.astronomynotes.com/relativity/s4.htm .
Back home in Bakersfield, you can now purchase tickets for the "Supervolcanoes" show on March 3rd and the "Black Holes" show on March 17th. You can also see Jupiter begin to lead the procession of planets across the sky starting at about 7:30 PM. It will be below the tail end of Leo. By 1 AM you will be able to see Mars among the dim stars of Libra rising followed by Saturn an hour and a half later between Scorpius and Ophiuchus. The first star chart below shows the view at 2:30 AM looking south with Jupiter on the far right and Saturn low on the far left. By about 5:45 AM, you'll be able to see Venus through the twilight glow low in the southeast (see the second chart below). Though Mercury is nearby, it will be lost in the ever brightening twilight before it gets high enough for us to see. Hopefully, the Waxing Gibbous Moon, just one day from full phase, won't wash out your view of the procession of the planets.
Want to see more of the stars at night and save energy? Shield your lights so that the light only goes down toward the ground. See www.darksky.org for how.
Director of the William M Thomas Planetarium at Bakersfield College
Author of the award-winning website www.astronomynotes.com