by Elton Gomes
Indian astrophysicists have discovered large ultraviolet lobes and jets that were hurled out from a dying star. The discovery was made using data from AstroSat – a space observatory launched by the Indian Space Research Organisation (ISRO) in 2015. The discovery has been featured as the AstroSat Picture of the Month (APOM) for October.
Professor Kameswara Rao from the Indian Institute of Astrophysics (IIA) and his collaborators used the Ultra-Violet Imaging Telescope (UVIT) on board the AstroSat to stare at a planetary nebula named as NGC 6302 – it is popularly known as the Butterfly Nebula.
What is a planetary nebula?
“When hydrogen and helium fuel that kept the star shining gets exhausted, the star expands in size and becomes a red giant star. Such stars shed most of their outer layers which expands outwards, and the inner core, made of carbon and oxygen, shrinks further and becomes hotter. This hot core shines brightly in the ultraviolet, and ionizes the expanding gas. This glowing ionized gas is what is seen as a planetary nebula”, Prof Rao explained, according to a report in the Better India.
A planetary nebula is formed when a star like the Sun is in its dying days. The term was coined by astronomers in the 19th century since the dying nebula looked like planets through their telescopes.
What do we know about the Butterfly Nebula?
Sriram Krishna, a student of Rao, spent several hours analysing the data from the Butterfly Nebula. “Its central star is one of the hottest that we know, at 220,000 degrees celsius. The name itself comes from the shape of the two lobes of expanding gas that look like the wings of a butterfly,” Krishna said, as per a report in the Wire.
One might expect a planetary nebula to be spherical, but in reality it displays a range of complicated structures. “We used the UVIT on AstroSat to make four images of the nebula, each in different ultraviolet ‘colours’, or filters. The image made with the filter centred at 160.8 nm, called F169M, had a surprise in store for us,” Krishna said further, as per the Wire.
Astronomers have assessed the two lobes of the nebula since several years via visible light images. They propose that the more energetic ultraviolet light could be emitted closer to the central star, where the hot stellar wind hits the slowly expanding gas. But this time, Indian astrophysicists discovered the actual size of the lobes. Krishna said, “However, we discovered that the lobes imaged with the F169M filter in ultraviolet were about three times larger than the size of the lobes imaged in visible light.”
Why is this important?
Firoza Sutaria, a co-author involved in the study said, “Our discovery points to an unseen companion star in an orbit with the central star”, as reported by BusinessLine.
In addition, the researchers discovered two faint jets that were blasting out from the centre, at almost right angles to the newly discovered ultraviolet lobes. The team led by Prof Rao has recently discovered a large ultraviolet halo in yet another planetary nebula using AstroSat, and it will be studying many more such objects in the future. They hope that such discoveries could provide an answer to the age old puzzle of the ‘missing mass problem in planetary nebulae’.
The study’s results have been published in the journal Astronomy and Astrophysics, and the study has been co-authored by Kameswara Rao, Sriram Krishna, Jayant Murthy, Firoza Sutaria, and Rekesh Mohan of IIA; Alak Ray of Homi Bhabha Centre for Science Education; and De Marco of Macquarie University in Australia.
Elton Gomes is a staff writer at Qrius
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