Watch for Rare Recurrent Nova Begins

by AMNH on

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In 1998, the star V2487 Ophiuchi erupted into a nova, a massive explosion that registered in the sky as a sudden increase in the star’s brightness, visible from 40,000 light years away. Now, thanks to the work of Dr. Ashley Pagnotta, a postdoctoral researcher at the Museum, summer sky watchers are keeping an eye out to see when the star erupts once more. 

image of V2487 Ophiuchi
An image of V2487 Ophiuchi in 1998, during its last nova.
© Tsukuba Astronomical Observatory

V2487 Ophiuchi is actually a binary system consisting of two stars: a hot, dense white dwarf and its partner, thought to be a larger subgiant star. These two stars orbit one another, and as they do, the white dwarf steals mass from its larger neighbor. That mass piles up, layers and layers of it compressing on the surface of the white dwarf until it becomes so hot and pressurized that the surface layer explodes.

When Nova Ophiuchi erupted in 1998, it didn’t look quite like a garden-variety “classical” nova. Studying the event nearly a decade later, Pagnotta and her colleagues found evidence that 1998 wasn’t the first time that V2487 Ophiuchi went nova. Images from the Harvard College Observatory Plate Collection, a historical library of telescope images, showed that V2487 Ophiuchi had previously erupted in 1900. The finding makes the star one of only 10 known recurrent novas in our galaxy, which erupt on predictable schedules. Pagnotta and colleagues pegged V2487 Ophiuchi’s nova as erupting once every 18 to 20 years—a two-year-long window that begins this summer.

Historical image of a previous nova in V2487 Ophiuchi.
Historical image of a previous nova in V2487 Ophiuchi.
© Harvard College Observatory

Amateur astronomers are already monitoring the sky. The clearest sign of a nova will be that the star suddenly becomes much brighter. During its last eruption, V2487 Ophiuchi went from its usual magnitude of about 17 to a magnitude of 9, which is historically its maximum brightness. (Magnitude numbers get smaller as stars get brighter.)

“Amateurs are very good at keeping an eye on potentially interesting things like this,” says Pagnotta. “Many people are looking at this star a couple of times every week or every month.”

That should allow astronomers to get comprehensive data on every stage of the next nova in V2487 Ophiuchi. This kind of information exists for just a few novas, and will help researchers better understand what happens during these spectacular explosions. When anyone notices the star getting brighter, word will go out in the community, which will get other people looking to confirm it.

Once data is in to suggest that a nova is occurring in V2487 Ophiuchi, Pagnotta and her colleagues will turn an array of more diverse and powerful telescopes on the star system to get a closer look and measure things like the levels of x-rays and ultraviolet light produced during the nova.