Free Astronomy Magazine May-June 2018

49 MAY-JUNE 2018 SPACE CHRONICLES — one-tenth the duration of a typi- cal supernova explosion. Over the past decade several FELTs have been discovered with time- scales and luminosities not easily ex- plained by traditional supernova models. And, only a few FELTs have been seen in sky surveys because they are so brief. Unlike Kepler, which collects data on a patch of sky every 30 minutes, most other tele- scopes look every few days. Therefore they often slip through undetected or with only one or two measurements, making understand- ing the physics of these explosions tricky. In the absence of more data, there have been a variety of theories to explain FELTs: the afterglow of a gamma-ray burst, a supernova boosted by a magnetar (neutron star with a powerful magnetic field), or a failed Type Ia supernova. Then along came Kepler with its pre- cise, continuous measurements that allowed astronomers to record more details of the FELT event. “We col- lected an awesome light curve,” said Armin Rest of the Space Telescope Science In- stitute in Baltimore, Maryland. “We were able to constrain the mechanism and the properties of the blast. We could ex- clude alternate theories and arrive at the dense-shell model explana- tion. This is a new way for massive stars to die and distribute material back into space.” T his video illustrates four ways in which a massive star can explode. [NASA] K 2 follow-on mission. Artist concept of Kepler spacecraft and fields of view across our galaxy. [NASA] “With Kepler, we are now really able to connect the models with the data,” he continued. “Kepler just makes all the difference here. When I first saw the Kepler data, and real- ized how short this transient is, my jaw dropped. I said, ‘Oh wow!’” “The fact that Kepler completely captured the rapid evolution really constrains the exotic ways in which stars die. The wealth of data al- lowed us to disentangle the physical properties of the phantom blast, such as how much material the star expelled at the end of its life and the hypersonic speed of the explo- sion. This is the first time that we can test FELT models to a high de- gree of accuracy and really connect theory to observations,” said David Khatami of the University of Califor- nia at Berkeley and Lawrence Berke- ley National Laboratory. This discovery is an unexpected spin- off of Kepler’s unique capability to sample changes in starlight contin- uously for several months. This ca- pability is needed for Kepler to discover extrasolar planets that briefly pass in front of their host stars, temporarily dimming starlight by a small percent. The Kepler ob- servations indicate that the star ejected the shell less than a year be- fore it went supernova. This gives insight into the poorly understood death throes of stars — the FELTs apparently come from stars that un- dergo “near-death experiences” just before dying, belching out shells of matter in mini-eruptions before exploding entirely. !