NASA’s Cosmic Vision: Simulating Our Galaxy Through Gravitational Waves

Astronomers using simulated data have produced a glimpse of the sky as it would appear in gravitational waves, cosmic ripples in space-time generated by orbiting objects. The image shows how space-based gravitational wave observatories expected to launch in the next decade will enhance our understanding of our galactic home.

Since 2015, ground-based observatories have detected about a hundred events representing the mergers of systems that pair stellar-mass black holes, neutron stars, or both. The signals typically last less than a minute, have relatively high frequencies, can appear anywhere in the sky, and their sources lie far beyond our galaxy.

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Watch as gravitational wavesGravitational waves are distortions or ripples in the fabric of space and time. They were first detected in 2015 by the Advanced LIGO detectors and are produced by catastrophic events such as colliding black holes, supernovae, or merging neutron stars.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>gravitational waves from a simulated population of compact binary systems combine into a synthetic map of the entire sky. Such systems contain white dwarfs, neutron stars, or black holes in tight orbits. Maps like this using real data will be possible once space-based gravitational wave observatories become active in the next decade. Brighter spots indicate sources with stronger signals and lighter colors indicate those with higher frequencies. Larger colored patches show sources whose positions are less well known. The inset shows the frequency and strength of the gravitational signal, as well as the sensitivity limit for LISA (Laser Interferometer Space Antenna), an observatory now being designed by ESA (European Space AgencyThe European Space Agency (ESA) is an intergovernmental organization dedicated to the exploration and study of space. ESA was established in 1975 and has 22 member states, with its headquarters located in Paris, France. ESA is responsible for the development and coordination of Europe's space activities, including the design, construction, and launch of spacecraft and satellites for scientific research and Earth observation. Some of ESA's flagship missions have included the Rosetta mission to study a comet, the Gaia mission to create a 3D map of the Milky Way, and the ExoMars mission to search for evidence of past or present life on Mars.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>European Space Agency) in collaboration with NASAEstablished in 1958, the National Aeronautics and Space Administration (NASA) is an independent agency of the United States Federal Government that succeeded the National Advisory Committee for Aeronautics (NACA). It is responsible for the civilian space program, as well as aeronautics and aerospace research. Its vision is "To discover and expand knowledge for the benefit of humanity." Its core values are "safety, integrity, teamwork, excellence, and inclusion." NASA conducts research, develops technology and launches missions to explore and study Earth, the solar system, and the universe beyond. It also works to advance the state of knowledge in a wide range of scientific fields, including Earth and space science, planetary science, astrophysics, and heliophysics, and it collaborates with private companies and international partners to achieve its goals.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>NASA for launch in the 2030s. Credit: NASA’s Goddard Space Flight Center

“Binary systems also fill the Milky WayThe Milky Way is the galaxy that contains our Solar System and is part of the Local Group of galaxies. It is a barred spiral galaxy that contains an estimated 100-400 billion stars and has a diameter between 150,000 and 200,000 light-years. The name "Milky Way" comes from the appearance of the galaxy from Earth as a faint band of light that stretches across the night sky, resembling spilled milk.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>Milky Way, and we expect many of them to contain compact objects like white dwarfs, neutron stars, and black holes in tight orbits,” said Cecilia Chirenti, a researcher at the University of Maryland, College Park, and NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “But we need a space observatory to ‘hear’ them because their gravitational waves hum at frequencies too low for ground-based detectors.”

Astronomers call these systems UCBs (ultra-compact binaries), and they expect that future observatories like LISA (Laser Interferometer Space Antenna), which is led by ESA (European Space Agency) in collaboration with NASA, will detect tens of thousands of them. UCBs are typically difficult to spot – they are usually faint in visible light, and astronomers currently know of only a handful with orbital periods shorter than an hour. Discovering many new UCBs is one of LISA’s main objectives.

Artist’s impression of LISA Pathfinder, ESA’s mission to test technology for future gravitational-wave observatories in space. LISA is a space-based gravitational wave observatory building on the success of LISA Pathfinder and LIGO. Credit: ESA–C.Carreau

Using data simulating the expected distribution and gravitational wave signals of these systems, the team developed a way to combine the data into an all-sky view of the galaxy’s UCBs. A paper published in The Astronomical Journal describes the technique.

“Our image is directly analogous to an all-sky view of the sky in a particular type of light, such as visible, infrared, or X-rays,” said Goddard astrophysicist Ira Thorpe. “The promise of gravitational waves is that we can observe the universe in a totally different way, and this image really brings that home. I hope one day I can see a version made with real LISA data on a poster or T-shirt.”

Reference: “Imaging the Milky Way with Millihertz Gravitational Waves” by Kaitlyn Szekerczes, Scott Noble, Cecilia Chirenti and James Ira Thorpe, 15 June 2023, The Astronomical Journal.
DOI: 10.3847/1538-3881/acd3f1/meta