The recurrent nova RS Ophiuchi just went into outburst — its first burst in 15 years — and it’s bright enough to see with the naked eye.
A star that normally slumbers around 12th magnitude suddenly "woke up" seven magnitudes brighter this past weekend. Now you can see it with the naked eye!
Irish amateur Keith Geary was the first to report the surprise outburst of RS Ophiuchi, one of the few known recurrent novae. He captured photos of it glaring at magnitude 5.0 with his DSLR camera at 22:20 UT on August 8th and confirmed his observation in binoculars. Fellow AAVSO member Alexandre Amorim of Brazil also spotted the eruption 25 minutes earlier.
Since then, the star has brightened up to magnitude 4.5 (August 9.7 UT), making it a relatively easy naked-eye object even from outer suburban areas and a cinch to see in binoculars.
Typically, RS Oph rises steeply and rapidly to maximum and then quickly declines, dropping about two magnitudes over a week's time, before leveling off and fading more gradually. The outburst will make for exciting observing in binoculars and small telescopes in the coming days. Try to catch the star at every opportunity you can because the next blast won't likely recur for another 15 or 20 years!
RS Ophiuchi last blew its top in February 2006 and before that in January 1985. The process that makes a recurrent nova is essentially the same as in the classical variety: A white dwarf and a donor star orbit in a close binary system. As the donor star evolves — a red giant in the case of RS Ophiuchi — it overflows its Roche Lobe and the white dwarf snatches the spilling gas (mostly hydrogen), which forms a spinning accretion disk around the compact star.
Material in the disk funnels to the dwarf's surface, where it's compacted and heated until the base layer reaches about 10 million degrees Celsius. It then ignites in a thermonuclear explosion which blows the envelope of material into space at high speed and makes one heck of a bright blast. According to recent observations reported in the Astronomer's Telegram, RS Ophiuchi is expelling material at around 2,600 kilometers per second.
Recurrent novae repeat the nova process approximately every 10 to 100 years, while nova outbursts are thought to repeat on much longer timescales from around 1,000 to 100,000 years. You can't wait around for a nova to go nova again, but for the approximately 10 recurrent novae (yes, they're rare!), if you live well you can see a repeat or two in a lifetime.
I love it when amateurs discover things. I asked Geary if he would share his discovery account, which you'll find below. I think you'll wholeheartedly agree with his conclusion.
"I have been following this star and many other variables since the year 2003. I regularly submit my observations to the AAVSO," said Geary.
"I had been on a family holiday visiting my parents in Waterford, Ireland. Up to last night I had eight nights of cloudy weather, however I persevered and made my way to a familiar observing spot called Dunbratton County awaiting nightfall. I began my visual and DSLR nova patrol using my APM 20×100 binoculars and Canon 6D at 21:30 UT, until I took a regular shot of the RS Ophiuchi region at 22:20 UT with my Canon 200-mm f/2.8 lens.
I examined the image and immediately thought that I had made an error. I thought I was off target. To my amazement after re-examining my image I could see RS Ophiuchi shining at magnitude 5.0. I was astounded as it was my first ever success! I immediately emailed CBAT and the AAVSO to raise the alert.
Persistence pays off! I would encourage anyone reading this article to take up variable star astronomy, who knows what the heavens will show us all next!"