In Search of the Stars
By Evans Owusu, MSC
Look up into the beautiful night skies anywhere in the world and you see dazzling, bright and shining stars. What are they made of? How were they formed? Let’s explore the subject. Stars are to the Universe what cells are to the human body-the building blocks of life. They are the fundamental unit of luminous matter in the Universe. Stars are made up of mainly dust and gas (hydrogen) held together by its gravity. They vary in size, mass, temperature and brightness. Stars are either classified as small, intermediate or large (massive) depending on their masses. Like all living things, stars are born and they die, hence, they are time bound. The closest star to us in our Solar System is the Sun. The mass of other stars are measured in relation to the mass of the Sun-known as the Solar Mass (Msun). By definition, a massive star is any star that has a mass greater or equal to 8 times the mass of the Sun (8Msun). Intermediate mass stars have masses less than 8Msun, and low mass stars have masses less than 1.5Msun. The bigger the mass of a star, the shorter their lifespan, that is, they die more quickly compared to low and intermediate stars.
Low and intermediate mass stars are formed when cold, dense, and dusty molecular clouds collapse under their own gravity. This formation paradigm is the generally acceptable theory for most stars by the astronomy community. However, the formation process of massive stars is still a widely debatable subject. As a result, it is an active area of research in astrophysics. In light of this, I studied some massive protostars to ascertain their mode of formation at radio frequency. Protostars are stars in their early developing phase i.e. a fetus star developing into a baby.
Over the years, astronomers have used the EM spectrum to probe and aid our understanding of the Universe. From radio wavelengths, where the Universe is transparent all the way to x-rays and gamma rays, which provides a glimpse of the violent, high-energy Universe. In between these two extremes, the optical band reveals a most inspiring view of stars and galaxies. I examined the stars at radio frequency ~ 25 GHz using data from the Australia Telescope Compact Array. The stars were studied at both radio continuum (broad ranges of wavelengths) and spectral lines (at specific wavelength). Massive stars generally play an important role in injecting energy and turbulence into the interstellar medium. I observed 4 massive protostellar objects. The continuum data were used to characterize the properties (such as luminosities, positional angles, and sizes) of the detected radio jets emanating from the massive protostars. I used water masers to confirm active star formation. Ammonia, an interstellar polyatomic molecular gas tracer was used to look for evidence of an accreting disc which can confirm the formation of massive stars.
The sizes of the objects from the continuum reveal intermediate size scales that can be compared with emissions from large scale and small scale emission. The water maser data tell us about jet/outflow properties when compared with the location and directions of known jets. The ammonia data also reveal the molecular envelopes on ~2 arcsec scales that are contrasted with what is known on large scales with data from single-dish telescopes, revealing extended molecular emission. The results further reveal that the water masers were farther apart on average of 2 km/s from their known rest velocity of massive protostars, with luminosities of the water masers found to be in the outer region of massive protostars, where water masers are found to have luminosity in the order of 10−6LSun. I categorized the morphology of the massive protostars, as either brightly compact or elongated.
From the figure above, I report the first ever detection of water maser in the observed massive protostar. Double maser peaks indicate the likelihood of active star formation, In search of the stars, I have successfully identified the mode of formation of observed massive protostars and determined their size, luminosity and morphology.
CONFLICT OF INTEREST
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ABOUT THE AUTHOR
Evans Owusu, was a MRes student at the University of Leeds researching on the evolution of radio jets from massive young stellar objects under the supervision of Dr Stuart Lumsden and Prof Melvin Hoare. He was sponsored by the Development in Africa with Radio Astronomy Fund. His expertise spans physics, mathematics, and astronomy. He obtained his undergraduate degree in Physics at Kwame Nkrumah University of Science and Technology (KNUST), followed by a masters in Mathematical Sciences at the African Institute for Mathematical Sciences (AIMS) Ghana campus under full scholarship. AIMS is a network of specialized institutes focused on training high potential young African scientists in the mathematical sciences, preparing them for high-profile research careers and ultimately solving big regional and global problems. He was part of the second cohort of the Royal Society radio astronomy training programme at the Ghana Space Science and Technology Institute.
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