An illustration showing binary-star system V Hydrae launching balls of plasma into space. Panel 1: the two stars orbit each other. Panel 2: the smaller star’s orbit carries it into the red giant’s expanded atmosphere, where it feeds on surrounding material. Panel 3: this material is eventually ejected as blobs of plasma. Panel 4: 8.5 years later, the companion star makes another pass through the red giant’s atmosphere, causing more blobs to be ejected. Image Credit: NASA/ESA/STScI
Huge ‘cannonball’ blobs of plasma have been observed firing from the direction of a massive dying star.
The balls of plasma are traveling so fast that it would take just 30 minutes for them to travel to the Moon from Earth.
The ejections seem to have been occurring once every 8.5 years for the past 400 years.
The star in question is a massive red giant called V Hydrae about 1,200 lightyears away.
Red giants are stars that are going through the process of dying and using up all the fuel that makes them shine.
As these dying stars reach the end of their life, they shed their outer layers into space.
However, this does not explain where the streams of plasma blobs are coming from.
Astronomers have suggested that the outbursts are coming from an unseen companion star, probably in an elliptical orbit that takes it close to the red giant’s atmosphere every 8.5 years.
As it does so, it feeds on cosmic gas and dust in V Hydrae’s atmosphere, creating a disc that surrounds the companion star.
This disc could be the launch pad from which the blobs are emanating.
Raghvendra Sahai of NASA’s Jet Propulsion Laboratory has led a study on the phenomenon and believes that the star system could be studied to gain more insight into planetary nebulae.
These nebulae are caused when stars reach the end of their lives and shed their outer layers into space.
This material is illuminated by stars and creates a large, expanding shell that looks like a planet from Earth, which is how the nebulae get their name.
The team studying V Hydrae used the Hubble Space Telescope to observe it over an 11-year period, from 2002 to 2004, then from 2011 to 2013.
They found that every blob has a temperature of about 10,000°C.
They were also able to view blobs that had been ejected as far back as 1986, including some that are already 60 billion kilometres away.
Using this data, the team created computer models to get to the bottom of the mysterious plasma blobs, and concluded that they are coming from an accretion disc surrounding a companion star.
“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,” says Sahai.
“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.”
One revelation from the Hubble observations is that the disc does not fire the blobs in the same direction every time.
The direction changes from side to side and back and forth, potentially a result of a wobble in the companion star’s accretion disc.
“This accretion disk engine is very stable because it has been able to launch these structures for hundreds of years without falling apart,” Sahai said.
“In many of these systems, the gravitational attraction can cause the companion to actually spiral into the core of the red giant star.
Eventually, though, the orbit of V Hydrae’s companion will continue to decay because it is losing energy in this frictional interaction.
However, we do not know the ultimate fate of this companion.”