Hubble spots giant ‘cannonballs’ shooting from star
NASA’s Hubble Space Telescope has discovered blobs of superhot plasma, each twice as large as Mars, being ejected from the binary-star system V Hydrae. These plasma balls are flying through space so fast that it would take only 30 minutes for them to cover the distance from Earth to Mars. Astronomers estimate that this stellar “cannon fire” has occurred once every 8.5 years for at least the last 400 years.
These plasma balls are a puzzle for astronomers because they could not have been ejected by the host star, called V Hydrae. The star is a red giant located about 1,200 light-years from Earth, which has been estimated to have shed at least half of its mass into space. Red giants are bloated, dying stars in the final stages of their lifespan that are exhausting the nuclear fuel that makes them shine. They have ballooned in size and are shedding their outer layers into space.
Researchers theorize that the plasma balls were launched by an unseen companion star. According to this theory, the companion star would be in an elliptical orbit that brings it close to V Hydrae’s atmosphere every 8.5 years. As the companion star moves into the red giant’s outer atmosphere, it gobbles up material. This material settles into a disk around the companion star, which serves as a launching pad for the blobs of plasma.
This theory may also explain a dazzling variety of glowing shapes imaged by Hubble that are seen around dying stars, called planetary nebula. A planetary nebula is an expanding shell of glowing gas expelled by a dying star late in its life.
“We knew this object had a high-speed outflow from previous data, but this is the first time we are seeing this process in action,” said Raghvendra Sahai of NASA’s Jet Propulsion Laboratory in Pasadena, California, lead author of the study. “We suggest that these gaseous blobs produced during this late phase of a star’s life help make the structures seen in planetary nebulae.”
Observations by Hubble over the last two decades have revealed an enormous diversity and complexity of structure in planetary nebulae. High-resolution images captured by the telescope revealed knots of material in the glowing gas clouds around dying stars. Scientists speculated that these knots were actually jets ejected by disks of material around companion stars that were not visible in the Hubble images. The exact details of how the jets were formed are unknown.
“We want to identify the process that causes these amazing transformations from a puffed-up red giant to a beautiful, glowing planetary nebula,” Sahai said. “These dramatic changes occur over roughly 200 to 1,000 years, which is the blink of an eye in cosmic time.”
The scientists used Hubble’s Space Telescope Imaging Spectrograph (STIS) to conduct observations of V Hydrae and the surrounding region over an 11-year period, first from 2002 to 2004, and then from 2011 to 2013. The data revealed a string of enormous, super-hot blobs, each with a temperature of more than 17,000 degrees Fahrenheit (about 9,427 degrees Celsius), nearly twice as hot as the surface of the Sun.
The scientists made a detailed map of the blob’s location, allowing them to trace the first gigantic clumps back to 1986. STIS detected giant blobs as far as 37 billion miles (60 million kilometers) away from V Hydrae.
“The observations show the blobs moving over time,” Sahai said. “The STIS data show blobs that have just been ejected, blobs that have moved a little farther away, and blobs that are even farther away.”
The blobs expand and cool as they move farther away from the red giant and, consequently, are then not detectable by visible light. However, observations taken at longer sub-millimeter wavelengths in 2004, by the Submillimeter Array in Hawaii, revealed fuzzy, knotty structures that may be blobs launched 400 years ago, the scientists said.
Based on the Hubble observations, Sahai and his colleagues Mark Morris of the University of California, Los Angeles, and Samantha Scibelli of the State University of New York at Stony Brook developed a model of a companion star with an accretion disk to explain how the blobs were ejected.
“This model provides the most plausible explanation because we know that the engines that produce jets are accretion disks,” Sahai explained. “Red giants don’t have accretion disks, but many most likely have companion stars, which presumably have lower masses because they are evolving more slowly. The model we propose can help explain the presence of bipolar planetary nebulae, the presence of knotty jet-like structures in many of these objects, and even multipolar planetary nebulae. We think this model has very wide applicability.”
Jim Sharkey is a lab assistant, writer and general science enthusiast who grew up in Enid, Oklahoma, the hometown of Skylab and Shuttle astronaut Owen K. Garriott. As a young Star Trek fan he participated in the letter-writing campaign which resulted in the space shuttle prototype being named Enterprise. While his academic studies have ranged from psychology and archaeology to biology, he has never lost his passion for space exploration. Jim began blogging about science, science fiction and futurism in 2004. Jim resides in the San Francisco Bay area and has attended NASA Socials for the Mars Science Laboratory Curiosity rover landing and the NASA LADEE lunar orbiter launch.