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This spectacular image of the large spiral galaxy NGC 1232 was obtained on September 21, 1998, during a period of good observing conditions. It is based on three exposures in ultra-violet, blue and red light, respectively. The colours of the different regions are well visible : the central areas contain older stars of reddish colour, while the spiral arms are populated by young, blue stars and many star-forming regions. Note the distorted companion galaxy on the left side, shaped like the greek letter "theta". NGC 1232 is located 20º south of the celestial equator, in the constellation Eridanus (The River). The distance is about 100 million light-years, but the excellent optical quality of the VLT and FORS allows us to see an incredible wealth of details. At the indicated distance, the edge of the field shown corresponds to about 200,000 light-years, or about twice the size of the Milky Way galaxy. The image is a composite of three images taken behind three different filters: U (360 nm; 10 min), B (420 nm; 6 min) and R (600 nm; 2:30 min) during a period of 0.7 arcsec seeing. The field shown measures 6.8 x 6.8 arcmin. North is up; East is to the left. #L

Indian scientists discover new way of powering radio sources in universe

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In a first, a team of Indian astronomers has discovered some sources in the universe capable of emitting radio waves in a never-before-known mechanism, using the Giant Metrewave Radio Telescope (GMRT) located at Khodad in Junnar, about 80 km from Pune.

The team, led by TIFR-National Centre for Radio Astronomy (NCRA), which operates the GMRT, said they found a rare source named ‘Extremely Inverted Spectrum Extragalactic Radio Sources’. This discovery, according to the team, could open up avenues for further studies regarding an alternate theory suggesting radio sources to be powered outside the power law.

“In case of special cluster sources, the magnetic flux drops to low frequencies and capturing this sudden fall is extremely challenging. This was possible only due to the high sensitivity of the GMRT and its low range feature. We took accurate measurements as such emissions were captured at frequencies around 150 MHz (megahertz),” senior NCRA scientist Ishwar Chandra told The Indian Express.

Radio galaxies are a small subset of galaxies that emit exceptionally powerful emissions at radio frequencies. Up until now, astronomers believed that all these sources emitted radio waves due according to the power law. But a section of scientists, including astronomer Mark Henry from Cambridge University in 1967, had proposed that not all sources were powered as per this law. “So, if a radio spectrum was found declining at a speed larger than +2.5, it was ruled out under the power law. But now, there is an alternate theory and it will begin to emerge as we can confirm that not all sources need to be classified under the power law. However, the number of such sources is still small,” said Chandra.

The NCRA team, comprising Gopal Krishna from Aryabhatta Research Institute of Observational Science; Mukul Mhaskey, Surajit Paul and Sameer Salunke from Savitribai Phule Pune University; Pratik Dhabadhe from Inter University Centre for Astronomy and Astrophysics; Sandeep Sirothia from Square Kilometre Array, South Africa, and former scientist at NCRA, is presently involved in an advanced study in tracing more such sources using the upgraded GMRT (uGMRT).

 Source: Indian Express

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