Gravitational waves open new window to cosmos
By Amanda Jermyn



Guest column by Adam Jermyn

For eons, two black holes slowly orbited one another, each some thirty times the mass of our Sun. As they moved, they pushed and pulled on the fabric of space-time, causing ripple-like waves of compression and tension to radiate away. Over time, the distance between the black holes shrank as these gravitational waves carried away some of their energy. The closer they got, the faster they orbited, and the more powerful these waves became. Then, roughly one billion years ago, for several milliseconds, they emitted more radiation in gravitational waves than the entire rest of the observable universe does in light. In the middle of this emission the two black holes merged together, forming a single massive black hole.

This past September those waves reached Earth, vastly weaker after the long journey, and were observed by scientists at the recently commissioned and incredibly sensitive Laser Interferometric Gravitational-Wave Observatory (LIGO). Each LIGO detector has two 4-kilometer long arms at right angles to each other. As the gravitational waves passed by they stretched one arm and shrank the other, and it is the difference in arm length that was detected. The signal these waves produced was tiny, one part in one thousand trillion trillion, so LIGO detecting them was the equivalent of looking up and spotting a single atom on the surface of Mars. This unfathomably precise observation was not only the first time in human history that we have observed the merger of black holes, but also the first direct detection of gravitational waves. It is a tremendous achievement for the Caltech- and MIT-led LIGO collaboration, as well as for the National Science Foundation, which funded the project.

Looking past this detection, the implications for the future of astronomy are profound. For the first time we will learn about populations of pairs of black holes that orbit one another. We will find out how many of them there are, how massive they are, and what their orbits are like. All this will provide us with crucial information about how they form, and about the lives and deaths of massive stars. We will hear gravitational waves from neutron star mergers slightly before the light from them arrives on Earth, letting us point telescopes at the right place at the right time to see them. This will let us probe their composition, examine the properties of matter under the most extreme circumstances, and test the laws of physics at energies that cannot be reached in even the largest Earth-based particle colliders. These and many other observations are expected from gravitational wave astronomy in the coming years.

Even more exciting than the things we expect to see are the things we haven’t even thought of. The invention of radio telescopes led to the discovery of pulsars, rapidly spinning neutron stars with extreme magnetic fields. X-ray telescopes shed light on the interiors of galaxies and the supermassive black holes they contain. Every time astronomers have been given a new window on the Cosmos amazing and completely unimagined things have been discovered. Gravitational waves are likely to be no different.

Join the Springfield Stars Club on Tuesday, March 22nd at 7:00pm at the Springfield Science Museum for a talk by Tim Connolly on “Apps for Stargazing.” Discover how apps can help you find the locations of stars, planets, satellites, space stations, galaxies and comets. Find night sky targets for astro-imaging and learn how to remotely operate GoTo computer telescopes. Connolly is employed by Baystate Medical Center’s Pathology Department, performing diagnostic electron microscopy, and is active in the Stars Club and Amherst Area Amateur Astronomers Association. Refreshments will be served, and the public is welcome. The meeting is free of charge for members, with a suggested donation of $2 per non-member.

Adam Jermyn, of Longmeadow, is studying for a PhD in astrophysics at Cambridge University in England; he is the son of Reach for the Stars columnist Amanda Jermyn, who invited him to write this guest column in the wake of the recent detection of gravitational waves.