The New York Times News Service
"The past is never dead,” William Faulkner once wrote. "It’s not even past.” Nobody knows this better than astronomers. Everything that has ever happened in the universe's history has left a mark on the sky; with the right technology, much of it is now decipherable.
For the past quarter-century, NASA’s Chandra X-ray Observatory has been recording the roiling aftermath of two mighty supernova explosions that occurred hundreds of years ago, far out in space. This spring, the astronomers who operate Chandra combined its X-ray images into videos that document the evolution of two astrophysical landmarks: the Crab nebula, in the constellation Taurus, and Cassiopeia A, a gas bubble and hub of radio noise in the constellation Cassiopeia.
The videos show twisting, drifting ribbons of the remains of the star being churned by shock waves and illuminated by radiation from the dense, spinning cores left behind.
They were made to celebrate the 25th anniversary of the observatory, which was launched into space in 1999 and has been a workhorse of cosmology and astrophysics ever since.
The anniversary comes at a poignant moment. Earlier this year NASA proposed cutting Chandra’s operating funds. More than 700 astronomers signed a protest letter and created a website asking the agency to change its mind. Federal lawmakers from Massachusetts also joined the protest.
Lately things have been looking up. In July, a draft of a House appropriation bill for NASA’s 2025 budget expressed support for the continued operation of Chandra, "which continues to deliver discoveries addressing a wide range across astrophysics.”
Chandra was one of four "Great Observatories” that NASA launched in the 1990s. The others were the Compton Gamma Ray Observatory and the infrared Spitzer Space Telescope, both of which have since been shut down, and the Hubble Space Telescope, which remains on duty.
Chandra’s job is to observe the cosmos through X-ray goggles and study its hottest and most violent phenomena, like black holes, exploding stars and blazing-hot intergalactic gas. Because X-rays are blocked by Earth’s atmosphere, these astrophysical events can be studied only from space.
Chandra was the dream-child of Riccardo Giacconi, a physicist who pioneered the field of X-ray astronomy and won the Nobel Prize in physics in 2002.
Astronomers now have a multispectral view of some of the weirdest events in the universe thanks to Chandra, the Hubble Space Telescope, which sees ordinary visible light, and the James Webb Space Telescope, which sees infrared light.
In 2003, astronomers using Chandra discovered a singing black hole that had been periodically blowing bubbles in the hot, diffuse gas pervading a cluster of galaxies some 250 million light years away. The activity was producing sound waves - an eternal note of B flat belted into intergalactic plasma.
Chandra’s X-ray observations have also revealed that enigmatic flecks of light in the early universe, initially detected by the Webb telescope, were actually quasars, young galaxies harbouring supermassive black holes. That finding caused some astrophysicists to reconsider their ideas about how and when such massive black holes form.
In June, Chandra scientists announced the discovery of a black hole with a mass of 80 million suns that was kicking up a rumpus back when the universe was only a half-billion years old. Scientists can’t explain how it got so big so fast.
Chandra has also long-tracked exploding stars.
The Crab nebula was created in the year 1054 in an explosion that was seen by Chinese and Japanese astronomers and recorded in Native American pictographs. The nebula harbours one of the first known pulsars - a spinning neutron star that flicks a pulse of radio energy 30 times per second like a superfast lighthouse beam.
Cassiopeia A, located about 11,000 light-years away from Earth, is the remains of a star that exploded as a supernova about 340 years ago. Nobody seems to have observed it at the time, but astronomers have recently pinpointed a bright dot at its centre, a dense neutron star that is the squished leftover core of the original star.
As Chandra’s time-lapse movies show, these stars are still exploding, in a sense. Newly minted elements like iron, oxygen, calcium and silicon are still being shed into space to fertilise the next generations of stars.
Chains of supernova explosions have acted as thermonuclear foundries throughout cosmic history, progressively transforming a simple baby universe of hydrogen and helium into a more complex mix of the heavier elements needed for life as we know it. The past marches on in our cells as well as in the sky.