Astronomers studying the Milky Way’s only known helium nova, V445 Puppis, have discovered high-speed cosmic bullets of gas racing outward at 20 million miles per hour. The ejections emerged after a two-decade-old dust cloud finally cleared, revealing a white dwarf feeding on a rare helium star.
Clearing Dust Reveals a Rare Stellar Pairing at V445 Puppis
For 25 years, one of the Milky Way’s strangest stellar explosions hid its culprit behind its own debris. When the stellar explosion in question is V445 Puppis, which erupted in 2000, much of the phenomena associated with it were shrouded in mystery due to a vast cloud of dusty debris that surrounded this nova.
When this debris finally cleared, a team of researchers was able to peer into V445 Puppis using NASA’s long-serving Hubble Space Telescope, NASA’s exoplanet-hunting spacecraft TESS (Transiting Exoplanet Survey Satellite), and the Earth-based Very Large Telescope (VLT), along with an array of other instruments. This allowed them to discover not only the “bullets”, clumps of potentially oxygen-rich gas it is firing, but also the true nature of this system. That revealed that V445 Puppis consists of a dead star hungrily feeding on a companion star that is, by itself, a rare find. Thus, this system offers scientists a rare chance to study one of the rarest types of binary systems and one of the rarest cosmic explosions.
Novae are sudden, explosive bursts of energy in binary star systems. They happen when a Sun-like star dies and leaves behind a remnant known as a white dwarf, which then pulls gas from its companion star. The material that is pulled off the companion star then gathers on the white dwarf’s surface. That forces the temperature and pressure to increase, culminating in a violent thermonuclear explosion.
It is extremely unusual to have a helium nova, as the vast majority of stars have plenty of hydrogen even in their evolved states, but researchers see no hydrogen here. Scientists from the University of Warwick were able to confirm the real nature of the stellar explosion, known as V445 Puppis. New observations also suggest that the pair has resumed transferring material since its eruption in 2000, potentially restarting the long buildup toward another blast. The findings were presented Wednesday at the National Astronomy Meeting in Birmingham and described in a conference abstract.
Cosmic Bullets and Unexplained Projectiles Crossing the Milky Way
The cleared view also exposed something unexpected: compact knots of possibly oxygen-rich gas hurtling away at nearly 9,000 kilometers per second, or up to 20 million miles per hour (also recorded at 32 million kilometers per hour). These high-speed clumps, nicknamed “bullets,” have never been seen in another nova, and researchers do not yet know what launched them.
The origin of these 'bullets' is a mystery. We suspect that these originated post-outburst, but 'bullets' of this kind have not been observed in any other nova,
team member John Mills, a researcher at the University of Warwick in the UK, said in a statement.
Lead researcher John Mills told IFLScience about the several currently unexplained features in this system. We didn't know an awful lot about this object, even though it erupted about 25 years ago, because this eruption also produced a lot of dust, obscured our view of this central binary,
lead researcher John Mills, from the University of Warwick, told IFLScience. Describing the system, John Mills stated: It’s just such a weird system. It really reminds you that there's so much stuff going on out there.
Implications for Type Ia Supernovae and Cosmic Distance Measurements
The findings offer the clearest look yet at the only confirmed helium nova in our galaxy, while reopening a debate over whether such systems can eventually produce Type Ia supernovae. The dust is now coming off, and with that, new insights and new mysteries around this event.
