I’m currently watching two novae in the night sky, both within range of binoculars and small telescopes.
‘Nova’ is Latin for ‘new,’ as in ‘new star.’ But, a nova is not a new star. A nova is an event involving a white dwarf star (a small, dense remnant of a red giant star, no longer producing nuclear fusion) and a younger star converting hydrogen atoms into helium atoms through nuclear fusion.
When a white dwarf and a fusion-generating (a.k.a., main sequence) star orbit one another, gravity pulls them closer to one another. When sufficiently close, the dense white dwarf will gravitationally steal matter from its less massive companion. The white dwarf uses this accreted matter to create an atmosphere around it, mostly comprised of hydrogen.
The newly formed atmosphere is heated by the white dwarf to a temperature in which runaway hydrogen fusion begins. This fusion blows the atmosphere into space where the heated gas can be seen in visible light.
From Earth, we see a star that’s significantly brighter than before. This increase in brightness can last for weeks or even months. This event is known as a ‘classical nova.’ Some white dwarf-main sequence star binaries can repeat the process of accretion, fusion, and eruption. These are known as ‘recurrent novae.’
V1405 Cas is a current nova in the constellation Cassiopeia. This nova was discovered at magnitude 9.6 on March 18th (depending on your location in the Santa Fe area, stars are visible to the unaided eye down to around magnitude 5.0 – 6.5). Earlier in March, an astronomer’s photograph of the area, including stars down to magnitude 13, showed nothing in the nova’s location. Currently, the nova shines between magnitudes 7 and 8.
Before dawn on April 8th, I photographed Cassiopeia as it rose in the northeast. I easily identified V1405 Cas, using the nearby open star cluster Messier 52 (M52) as a guide.
It’s worth noting that, initially, I didn’t find the nova in photos I took the previous evening (April 7th), when Cassiopeia was low above the northern horizon and well inside the Santa Fe area light dome. Due to these circumstances, my guidepost, M52, was not visible in the photo. However, once I found the nova in my pre-dawn photo of April 8th, I went back and discovered it in my photo of April 7th by comparing the star fields of the two photos.
A potential nova, identified as PNV J17581670-2914490, is currently under observation in the constellation Sagittarius. It was discovered just five days ago (April 4th) at magnitude 8.8. Spectroscopic analysis performed at Kyoto University confirmed that this is a classical nova. Official designation as a nova has yet to be given.
I photographed this object before dawn on April 8th at about magnitude 7.7.
This object was more difficult to find because it’s located within the Large Sagittarius Star Cloud, where faint stars are abundant. I finally located it by laboriously comparing star locations in my April 8th photo with a photo of the same area I’d taken in February.
Nobody knows how long the novae in Cassiopeia and Sagittarius will remain at their brighter levels, but astronomers are observing them and recording data nightly, trying to learn more about novae and the conditions that lead to these violent events.