Scientists are tracking an interesting binary star named RS Ophiuchi (RS Oph), located approximately 5,000 light-years away from the earth that exploded on August 8, 2021 --four years earlier than expected. The study can give lead to the structure of the Universe.
Researchers have been tracking this star system as its recurrent explosions could give clues to the formation of Type I Supernovae, which has so far remained a mystery. Type I Supernovae is used to measure distances in the space, and tracing its formation can help understand the structure of the Universe and its rate of expansion.
Scientists at the S. N. Bose National Centre for Basic Sciences SNBNCBS, Kolkata, an autonomous research institute under the Department of Science and Technology (DST) who are studying the evolution of the different elements and other parameters of this binary star in the constellation “Ophiuchus” may soon unravel the formation of Type 1.
The RS Oph star system stands out as one of the stars in it is a tiny, compact and super-dense white dwarf (WD), while the other component is a large red giant star. These two stars are orbiting each other, and the white dwarf orbits close to the red giant is accumulating hydrogen-rich mass from its companion giant star and forming an accretion disc around itself.
The accreted matter gets compressed and heated by the dwarf's powerful gravity. When the bottom-most layer of this disc reaches a temperature around 10 million degrees Celsius, it ignites the hydrogen fusion reactions in a brilliant thermonuclear flash that blows all the accumulated gas into space at a tremendous speed of few thousand of kilometres a second. During the explosion, huge amount of energy (brightness of about 105 Suns) is released, making it visible from a large distance.
Such explosions in binary star systems are called “Novae”, which means “new stars”. Few of them explode every few tens of years because of the high WD mass (near Chandrasekhar limit of 1.4 solar mass) and high accretion rate. They are known as “Recurrent Novae”. RS Oph is one among ten such novae identified in our galaxy that show multiple explosions in human lifetime.
In the past, RS Oph was observed to erupt with an average recurrence period of about 20 years. This happens because the companion star in the RS Oph system is a late-type star which ejects huge amount of material from its surface and the high mass of the WD (about 1.4 times solar mass).
It is being studied by Indian astronomer’s aiming to unravel the physics of “Recurrent Novae” and their connection with Type Ia supernovae.
Scientists estimated that RS Ophiuchi would explode, giving birth to a Type Ia supernova when the WD in the RS Oph system exceeds the Chandrasekhar limit. Hence it can help to solve the mystery of related to the progenitor of Type Ia supernovae.
The temperature, luminosity, and change in physical and chemical parameters having been studied earlier, the team of scientists at SNBNCBS is now working with international astronomers to probe more about this interesting star aiming to unravel mysteries about the expansion of the Universe.
Figure 1: Artist view of a nova system where a white dwarf (left) accumulates hydrogen-rich gas from its companion star. The material spirals down to the white dwarf surface and forms an accretion disk around the dwarf. The bottom layer is compressed and ignites in a thermonuclear blast. Image credit: ESO
Figure 2: Previously observed outbursts of RS Oph. The brightness increases (magnitude decreases) during the outbursts. The average recurrence time is about 20 years.
Figure 3: Image of RS Oph observed 155 days after the 2006 outburst by Hubble Space Telescope (HST) through the F502N filter show a double ring structure. (Ribeiro et. al., 2009, Astrophysical Journal, 703, 1955).
For more details, contact Ramkrishna Das (ramkrishna[dot]das[at]bose[dot]res[dot]in, dr[dot]ramkrishna[dot]das[at]gmail[dot]com), Department of Astrophysics & Cosmology, S N Bose National Centre for Basic Sciences.
