X-ray Time-lapse of Cassiopeia A
(Credit: NASA/CXC/RIKEN/T. Sato et al.)
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These images show the location of an event, discovered by Chandra, that likely signals the merger of two neutron stars. Unlike other neutron star mergers, this one was not observed as a gamma-ray burst. This field of view that shows the Chandra image focuses only on the source dubbed XT2. A bright burst of X-rays in XT2 could give astronomers fresh insight into how neutron stars — dense stellar objects packed mainly with neutrons — are built.

Optical Time-lapse of Cassiopeia A
(Credit: NASA/STScI)
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Scientists created a historical record in optical light of Cas A using photographic plates from the Palomar Observatory in California from 1951 and 1989 that had been digitized by the Digitized Access to a Sky Century @ Harvard (DASCH) program, located at the Center for Astrophysics | Harvard & Smithsonian (CfA). These were combined with additional ground-based images obtained in 1996 and 1999 from the MDM Observatory, and with images taken by the Hubble Space Telescope between 2004 and 2011. This long-term look at Cas A allowed astronomers to learn about the physics of the explosion and the resulting remnant from both the X-ray and optical data.

A Tour of the Latest Look at "First Light" from Chandra
(Credit: NASA/CXC/A. Hobart)
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With closed-captions (at YouTube)

Over its two decades in space, NASA's Chandra X-ray Observatory has captured many spectacular images of cosmic phenomena. But perhaps its most iconic is the supernova remnant called Cassiopeia A.

Located about 11,000 light years from Earth, Cas A (as it's nicknamed) is the glowing debris field left behind after a massive star exploded. When the star ran out of fuel, it collapsed onto itself and rebounded explosively as a supernova, possibly briefly becoming one of the brightest objects in the sky.

The shock waves generated by this blast supercharged the stellar wreckage and its environment making it glow brightly in many types of light, particularly X-rays. Shortly after Chandra was launched aboard the Space Shuttle Columbia on July 23, 1999, astronomers directed the observatory to point toward Cas A. The result was a seminal moment for the observatory and the field of X-ray astronomy with the release of Chandra's "First Light" image on August 26, 1999.

Since then, Chandra has repeatedly returned to Cas A to learn more about this important object. A new movie shows the evolution of Cas A over time, enabling viewers to watch as 10-million-degree-Celsius gas in the remnant expands outward. These X-ray data have been combined with data from another of NASA's "Great Observatories," the Hubble Space Telescope, showing delicate filamentary structures of cooler gases with temperatures of about 10,000 degrees Celsius. In this movie, we see Hubble data from a single time period to emphasize the changes in the Chandra data.

The movie shows Chandra observations from 2000 to 2013, or about the time it takes for a child to enter kindergarten and then graduate from high school. This gives astronomers a rare chance to watch as a cosmic object changes on human timescales, giving them new insight into the physics involved. For example, particles in the blue outer shock wave carry more energy than those produced by the most powerful particle accelerators on Earth. As this blast wave hits material in its path it slows down, sending a shock wave backwards at speeds of millions of miles per hour.

Chandra will continue to observe Cassiopeia A in the future, adding to its remarkable legacy of discovery for this supernova remnant.