20,000-Year-Old Explosion Continues Expanding Into Space
The abrupt, explosive death of a massive star, called a supernova, is one of the biggest blasts in the universe since the Big Bang. What’s left behind are shredded stellar remnants resembling a fluffy cotton ball. The explosion expands from a smudge of light into a wispy, entangled cobweb of glowing gasses.
One of the nearest supernova remnants is the Cygnus Loop, located high in the summer sky. It has ballooned to 120 light-years in diameter. The energy needed to inflate such a huge structure is beyond imagination.
If it could be seen with the naked eye, the Cygnus Loop would be the angular diameter of six full Moons stretched across the sky. Put another way, it would appear to be the width of three fingers held at arm’s length. Given its size, the Cygnus Loop is a favorite target of amateur stargazers.
Astronomers used the power of the Hubble Space Telescope to zoom in for a close-up look at one sliver of the nebula. They found gossamer filaments resembling wrinkles in a bedsheet stretched across two light-years. The filaments are at the outer edge of the expanding bubble, plowing into interstellar space.
Analyzing the shock wave’s location, astronomers found that the filaments haven’t slowed down at all in the last 20 years of Hubble observations. The filaments haven’t even changed shape. The material is speeding into interstellar space at over half a million miles per hour – fast enough to travel from Earth to the Moon in less than half an hour!
A blink between Hubble images taken in 2001 (with Wide Field Planetary Camera 2 (WFPC2)) and 2020 (with Wide Field Camera 3 (WFC3)) shows gossamer filaments of glowing hydrogen in orange and cooling ionized oxygen in blue. The hydrogen filaments resemble lines in a wrinkled bedsheet seen from the side. The wrinkles arise as the shock wave encounters more or less dense material in the interstellar medium. Analyzing the shock wave’s location, astronomers found that the filaments have not slowed down at all in the last 20 years of Hubble observations, and they haven’t changed shape. The material is speeding into interstellar space at over half a million miles per hour—fast enough to travel from Earth to the Moon in less than half an hour. The shock wave is moving toward the top of these images. Credit: NASA, ESA, STScI, Ravi Sankrit (STScI)
Supernova Bubble Expands in New Hubble Time-Lapse Movie
Though a doomed star exploded some 20,000 years ago, its tattered remnants continue racing into space at breakneck speeds – and NASA’s Hubble Space Telescope has caught the action.
The nebula, called the Cygnus Loop, forms a bubble-like shape that is about 120 light-years in diameter. The distance to its center is approximately 2,600 light-years. The entire nebula has a width of six full Moons as seen on the sky.
Zooming In on the Supernova
Astronomers used Hubble to zoom into a very small slice of the leading edge of this expanding supernova bubble, where the supernova blast wave plows into surrounding material in space. Hubble images taken from 2001 to 2020 clearly demonstrate how the remnant’s shock front has expanded over time, and they used the crisp images to clock its speed.
By analyzing the shock’s location, astronomers found that the shock hasn’t slowed down at all in the last 20 years, and is speeding into interstellar space at over half a million miles per hour – fast enough to travel from Earth to the Moon in less than half an hour. While this seems incredibly fast, it’s actually on the slow end for the speed of a supernova shock wave. Researchers were able to assemble a “movie” from Hubble images for a close-up look at how the tattered star is slamming into interstellar space.
Astronomers’ Insights
“Hubble is the only way that we can actually watch what’s happening at the edge of the bubble with such clarity,” said Ravi Sankrit, an astronomer at the Space Telescope Science Institute in Baltimore, Maryland. “The Hubble images are spectacular when you look at them in detail. They’re telling us about the density differences encountered by the supernova shocks as they propagate through space, and the turbulence in the regions behind these shocks.”
Credit: NASA, ESA, STScI, Acknowledgment: NSF’s NOIRLab, Akira Fujii, Jeff Hester, Davide De Martin, Travis A. Rector, Ravi Sankrit (STScI), DSS
A very close-up look at a nearly two-light-year-long section of the filaments of glowing hydrogen shows that they look like a wrinkled sheet seen from the side. “You’re seeing ripples in the sheet that is being seen edge-on, so it looks like twisted ribbons of light,” said William Blair of the Johns Hopkins University, Baltimore, Maryland. “Those wiggles arise as the shock wave encounters more or less dense material in the interstellar medium.” The time-lapse movie over nearly two decades shows the filaments moving against the background stars but keeping their shape.
“When we pointed Hubble at the Cygnus Loop we knew that this was the leading edge of a shock front, which we wanted to study. When we got the initial picture and saw this incredible, delicate ribbon of light, well, that was a bonus. We didn’t know it was going to resolve that kind of structure,” said Blair.
Supernova’s Interaction With the Cosmos
Blair explained that the shock is moving outward from the explosion site and then it starts to encounter the interstellar medium, the tenuous regions of gas and dust in interstellar space. This is a very transitory phase in the expansion of the supernova bubble where invisible neutral hydrogen is heated to 1 million degrees Fahrenheit or more by the shock wave’s passage. The gas then begins to glow as electrons are excited to higher energy states and emit photons as they cascade back to low energy states. Further behind the shock front, ionized oxygen atoms begin to cool, emitting a characteristic glow shown in blue.
The Cygnus Loop was discovered in 1784 by William Herschel, using a simple 18-inch reflecting telescope. He could have never imagined that a little over two centuries later we’d have a telescope powerful enough to zoom in on a very tiny slice of the nebula for this spectacular view.
The Hubble Space Telescope
The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency (ESA). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.
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