Rare Naked-Eye Nova

August 9, 2021: Every 20 years or so, a thermonuclear explosion occurs on the surface of RS Oph, a white dwarf in the constellation Ophiuchus. Yesterday, it happened again. On Aug. 8th, the brightness of the tiny star increased 600-fold, from magnitude +12 to +5. Keith Geary of Ireland was the first to notice. Hours later, Italian astronomer Ernesto Guido and colleagues photographed the outburst using a remote-controlled telescope in Australia:

This is called a “recurrent nova,” and it is rare. In the whole Milky Way galaxy, only 7 star systems are known to produce such explosions.

RS Oph is actually a binary star–a very lopsided one. On one side is a white dwarf, on the other is a red giant. There’s very little distance between the two, so the gravity of the white dwarf is able to pull gaseous material off the larger star down onto itself. Every couple of decades, enough matter accumulates to trigger an explosion. The last time this happened was back in 2006.

At 5th magnitude, the current outburst is visible to the unaided eye, albeit just barely. Binoculars or a telescope will allow you to see it with ease. Look south after sunset. Ophiuchus hangs high in the sky just above the better known constellations Scorpius and Sagittarius. Sky maps: simple, detailed, really detailed.

Update: Variable star observer Filipp Romanov of Yuzhno-Morskoy, Russia, has just seen RS Oph and estimates that its magnitude has increased further to +4.6.

5 thoughts on “Rare Naked-Eye Nova

  1. Pingback: Rare Naked-Eye Nova – Nelsapy

  2. Dear friends,

    I’d like to inform you that AAVSO recognized 3 (three) observers to detected RS Oph outburst, independently, as we read here:
    https://www.aavso.org/aavso-alert-notice-752

    I, Alexandre Amorim, observed RS Oph at magnitude 5.0 at 21:55 UT and reported to the AAVSO database and to the AAVSO Forum at 22:22 UT.
    https://www.aavso.org/rs-ophiuchi

    It seems that our friend Keith Geary observed RS Oph at 22:20 UT and quickly reported to CBAT, following his this report to VSNET list at 22:35 UT:
    http://ooruri.kusastro.kyoto-u.ac.jp/mailarchive/vsnet-alert/26131

    So, I back to my observation session. After clouds in sky, I back to computer e send an e-mail to Dr. Green who wrote in CBET 5013 including my name as an independent detection:
    http://cbat.eps.harvard.edu/iau/cbet/005000/CBET005013.txt

    and quoted the link to my photo:

    Alex!

    Like

  3. Pingback: NASA’s OSIRIS-REx Finds Bennu Collision Risk Nearly Nonexistent | The Daily Space

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