What does it mean for a nova event to be “the fastest ever?”
Fastest Nova Ever
On June 12th of last year, astronomers noticed that a star in our night sky had suddenly brightened considerably.
The star in question is a white dwarf called V1674 Herculis with a variable magnitude that can dip as low as 16, which is to say that it’s normally very dim.
The previous record-holder for fastest nova went to a white dwarf called V838 Herculis. V838 was discovered back in March of 1991. It’s lucky that it was discovered, too, because its discoverer had to deal with two factors that would make observing any object in the sky difficult.
For one, George Alcock only had a pair of binoculars, and for two, the sky was very cloudy.
Luckily, in the early hours of the morning, the clouds broke to reveal a clear sky, and Alcock got to see a previously unknown white dwarf erupt in a nova.
At the time, the discovery of V838 Herculis was one of the largest amplitude novae astronomers had seen. The outburst itself was larger than 13 magnitudes, reaching about a 7 in that first observation, and fading to about a 14 by September of 1991.
V838 Herculis is a bit hard to catch, though, as it’s classified as a fast nova. So there have only been about 700 observations of it since its discovery because it typically will dim rapidly after brightening.
But now, V1674 Herculis has outdone V838 Her and in the process has given astronomers some real food for thought.
What exactly is a Nova?
In Latin, nova translates to “new” but in astronomy, a nova specifically refers to any star that suddenly brightens significantly.
You’ve more than likely heard of supernovae, when stars several times more massive than the sun explode, and if you’re a regular Science Getter, you’ve more than likely heard of Kilonovae — that are caused when two neutron stars collide, producing one of the brightest stellar phenomena known.
But novas, or novae, are slightly different because they’re not really explosions. All of the novae that astronomers have observed have involved a white dwarf and three other types of stars: red super giants, main-sequence stars like our own, and subgiants — which are stars that are somewhere between the brightness of main-sequence and giant stars.
Theoretically, the white dwarf and companion star need to be orbiting very closely for a nova to be produced. The white dwarf will draw material off the surface of the larger star, generating an eruption and causing things to get very hot, and very bright.
While fast nova type stars do dim very quickly, all novas eventually dim significantly within 150 days. A fast nova, however, must dim to 1/16th its brightness within 100 days.
Sounds like a wide margin, right? Well, V1674 Herculis is on a whole new level of fast.
Seeding Solar Systems
Last year, V1674 Herculis suddenly brightened to a magnitude of 6.2.
That’s 10,000 times the magnitude it started at. Now, when this white dwarf was originally discovered back in 1991, it took about 3 days to dim, which is still incredibly fast.
But this time, it dimmed significantly within a 24-hour period.
Yeah! Talk about finishing quick, am I right ladies? (I’ll just see myself out.)
That means that V1674 Herculis didn’t just smash V838 Her’s record, it obliterated it! (You might even say that it ushered in a new form of fast nova…the speed runner…okay, I’ve been playing way too much Shredder’s Revenge.)
Mark Wagner, a scientist at Ohio State University and co-author of the study said in a press release that, “The most unusual thing is that this oscillation was seen before the outburst, but it was also evident when the nova was some 10 magnitudes brighter. A mystery that people are trying to wrestle with is what’s driving this periodicity that you would see it over that range of brightness in the system.”
And that wobble seems to be present even when the star isn’t flaring, but because of this discovery, scientists now think that novae like V1674 Herculis may have contributed a large portion of Earth’s Lithium deposits.
This is because in addition to brightening and dimming rapidly, V1674 also ejects a decent amount of material while doing so.
But that’s not all. Because on top of its hashtag #speedrunnerstar status V1674 is also a rare example of a nova that exists between the two different novae classifications, which are Iron 2 and Helium and Nitrogen (Fe ii and He/N on screen).
Sumner Starrfield, another co-author of the study says that, “As best we can tell, because of the 500-second oscillation, [V1674 is] an ‘intermediate polar,’ where the gas is flowing from the secondary into an accretion disk. But because of the strong magnetic field of the white dwarf, it comes down on the poles.”
The astronomers involved with this study hope to use the Large Binocular Telescope in Arizona for future work. And if they do figure out how this record-breaking white dwarf works, they might just figure out an important piece of our own solar system’s origin story and that is how novae like this might have seeded other systems with heavy elements.
The paper authored by C.E. Woodward, R. Mark Wagner, and Sumner Starrfield has been published in Research Notes of the American Astronomical Society, and you can read the paper in full by following the first link in the sources section.