NASA Simulates Space in Millihertz Gravitational Waves, Enhances Our Understanding of the Milky Way Galaxy

Since 2015, ground-based observatories have been used in detecting hundreds of events that represent the mergers of systems. The signals they produce have short durations and high frequencies and can occur anywhere in space. However, these signals originate from sources outside the Milky Way galaxy.

Our galaxy is also filled with binary systems, which are expected to contain compact entities such as white dwarfs, neutron stars, and black holes in tight orbits. Because of this, there is a need for a space observatory that can 'hear' them since their gravitational waves are generated at too low frequencies for ground-based detectors.

What are Gravitational Waves?

Gravitational waves (GW) refer to cosmic ripples in space-time, which are generated by some of the universe's most violent and energetic entities. It can be viewed as the waves produced by gravity itself.

Albert Einstein first described Gravitational waves in his theory of general relativity in 1916. Using mathematical theories, he showed that the acceleration of massive orbiting objects can disrupt space-time so that waves of undulating space-time would propagate in all directions away from the source. These ripples would travel at the speed of light, carrying information about their origins. After decades of effort, the Laser Interferometer Gravitational-Wave Observatory (LIGO) directly detected an astrophysical GW source for the first time in 2015.

Although the processes that generate gravitational waves are extremely violent and destructive in nature, they are thousands of billions of times smaller by the time they reach Earth. They diminish over time and space just as the waves from a stone dropped in a pond get smaller and smaller as they travel away from the source.

A Better Glimpse of the Sky

Using simulated data, astronomers from NASA's Goddard Space Flight Center produced a glimpse of the sky as it would appear in millihertz gravitational waves. The resulting image reveals how space-based gravitational wave observatories to be launched in the next decade can enhance our understanding of our galactic home.

Binary systems called ultracompact binaries (UCBs) are expected to be detected by future observatories such as Laser Interferometer Space Antenna (LISA) led by the European Space Agency (ESA) in collaboration with NASA. UCBs are usually difficult to detect since they are faint in visible light, and astronomers can only identify a handful of these with orbital periods that are shorter than an hour.

After using data that simulates the expected distribution and gravitational wave signals of these binary systems, the NASA team developed a way of combining the data into an all-sky view of UCBs in the Milky Way Galaxy. As Goddard astrophysicist Ira Thorpe described, the image they generated is directly analogous to an all-sky view of space in a particular type of radiation, like visible light, infrared, or X-rays. Thorpe further explains that gravitational waves bring the promise of observing the universe differently, allowing them to see the distribution of matter in the galaxy and how it changes over time.

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