Space enthusiasts filled The North Door in downtown Austin Tuesday night to hear from UT astronomers about gravitational waves, dark energy and the tremors of old stars over local brews at the 40th monthly Astronomy on Tap event.

Astronomy on Tap is a monthly event that brings astronomers to present their research or talk about astronomy news at The North Door bar. The program began in New York City, but Austin is one of many satellite programs around the U.S. This month, the event featured three speakers, all from UT: astronomy professor Craig Wheeler, astrophysics professor Karl Gebhardt and Barbara Castanheira, a research fellow at the McDonald Observatory.

Wheeler led the night with his talk on gravitational wave findings. Gravitational waves — ripples through space-time caused by the movement of massive objects — were first detected by the Laser Interferometer Gravitational-Wave Observatory in 2015.

More recently last August, scientists observed gravitational waves from two neutron stars, or  dense celestial objects formed from the collapse of a massive star. Previously, gravitational waves had only been detected between two colliding black holes, but no light can escape from black holes, so these collisions gave scientists nothing to see. However, the neutron star collision emitted light as well as gravitational waves, giving the scientific community two ways to analyze the event.   

Wheeler began by asking the audience to put their arms up and wave in specific directions, causing the crowd to laugh at the pleasant oddity of people swinging about. The purpose of the experiment was to illustrate how scientists detect gravitational waves: The LIGO experiment stretches two laser beams two and half miles at a right angle. As the lasers reflect off of a series of mirrors that converge where the two arms connect, the length of the arms of the beams will vary in distance when a gravitational wave is detected, and any changes in the laser beam will measure this change in distance.

After the presentation, an audience member asked what the effect of gravitational waves from these cosmic collisions would be if they occurred closer to Earth.

“Oh, you’d be dead. Most certainly,” Wheeler said.

Gebhardt continued next with his talk about dark energy detection with the Hobby-Ebberly Telescope Dark Energy Experiment, an ongoing research effort at the McDonald Observatory in West Texas. According to their website, HETDEX collects data from galaxies between nine and 11 billion light-years away to measure the precise rate of expansion of the universe, which will help unlock the mystery of dark energy. Dark energy is a theoretical energy proposed by cosmologists to help explain the expansion of the universe, Gebhardt said.

“It may not be dark, and it may not be energy,” he said. “It’s just a way of describing our ignorance.”

He showed the audience a series of dots representing photons millions or billions of years old that contain information about the past universe.

“This is what I’ve become,” Gebhardt said jokingly. “I’m a dot finder.”

These photons are instrumental for Gebhardt’s team to further grasp the elusive qualities of dark energy and the perpetual expansion of the universe, he said.

The night concluded with Barbara Castanheira’s work on asteroseismology, where the vibrations from white dwarf stars can be measured to gain a better understanding of their composition. White dwarfs are the cooling remnants of low-mass stars after they have stopped producing energy. Castanheira demonstrated her work by knocking on a table in front of her on the stage. By knocking on it, she said, she could figure out what the table is made of. The same logic applies to white dwarfs. By analyzing their seismic vibrations, this “knocking” allows her to draw estimates of what elements comprise these ancient objects.