Recurring Nova RS Ophiuchi Blows its Top!

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Artist’s conception of the RS Ophiuchi Nova system with the parasitic white dwarf and its Red giant companion. Illustration credit: M. Kornmesser, European Southern Observatory (ESO)

On August 8 and visible now during the summer, the faint cataclysmic variable star RS Ophiuchi at over 6,500 light-years distant brightened from magnitude 11.2 to 4.8 during the August 8-9, 2021 time frame. It went from a threshold small-telescope object to naked-eye visibility within 24 hours.

Irish amateur Astronomer Keith Geary was the first to report the surprise outburst of RS Ophiuchi, one of the few known recurrent novae.

Many may have heard of the more sensational cousin to this type of star, a ‘Supernova’, the spectacular end to a high-mass star or a star in a system similar to this star’s, RS Ophiuchi’s, with one key difference. This later type of supernova involving a white dwarf, a Type Ia supernova, completely obliterates the progenitor star and any companion whereas a nova remains and could repeat between 1,000 and 100,000 years.

According to recent observations reported in the Astronomer’s Telegram, RS Ophiuchi is expelling material at around 2,600 kilometers per second.

What is a Nova?

RS Ophiuchi is a ‘Nova’ or, more specifically, a ‘recurring’ Nova. Translated from the Latin Nova, it means ‘new’ but taken in full context to mean ‘new star’.

There’s a key, intrinsic difference between a nova and a SuperNova. Novae (Latin plural for nova) are in a class of stars known as cataclysmic variables, or variable stars that undergo an explosive outburst without completely obliterating themselves, such as is the case with a supernova.

Nova stellar ‘systems’ consist of a parasitic white dwarf and a ‘regular’ or evolved star in orbit around a common center. As the powerful gravity of the dense white dwarf accretes material from the companion star onto itself, it eventually reaches a critical mass where the inter-layer (layer between the white dwarf’s ‘surface’ and the newly accreted material) tempertue exceed 10 million degrees resulting in a thermonuclear detonation and a runaway chain reaction. In the case of RS Ophiuchi, this process repeats on 10-20 year time scales, hence the ‘Recurring’ designation.

According to recent observations reported in the Astronomer’s Telegram, RS Ophiuchi is expelling material at about 2,600 kilometers per second.


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