Astrosat Picture of the Month

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Image of the Month

The AstroSat Picture of the Month for June 2019 is the far-ultraviolet image of the Dwarf Galaxy IC2574, using ASTROSAT. The far-ultraviolet traces young massive stars in the galaxy.

(Picture Credits: Chayan Mondal and collaborators)

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“AstroSat Picture of the Month” is an initiative of the Public Outreach and Education Committee of the Astronomical Society of India and the AstroSat Training and Outreach Team.

Star formation around bubbles in the Dwarf galaxy IC2574

In the APOM this month, we bring you the dwarf galaxy IC2574. As the name suggests, dwarf galaxies are smaller, fainter and less massive than galaxies such as the Milky Way or Andromeda. While dwarf galaxies host hundreds of millions to a few billion stars, the larger galaxies can have nearly hundred to thousand times more number of stars. It has been found that these small dwarf galaxies are more in number as compared to larger galaxies like Milky Way in the Universe.

IC2574 is also known as Coddington's nebula, after Edwin Foster Coddington who discovered it in 1898. It is located at a distance of approximately 12 million light years away and can be found in the Ursa Major constellation in the north. It is irregular in shape like the Wolf-Lundmark-Melotte (WLM) galaxy, presented in our very first APOM. IC2574 was imaged in ultraviolet by Chayan Mondal and collaborators using the Ultraviolet Imaging Telescope (UVIT) on-board AstroSat. They wanted to study the regions where young massive stars in this galaxy are located. Hot massive stars are those stars which weigh more than 10 times the mass of Sun and they emit significant fraction of their light in ultraviolet.

These researchers have identified sites of most massive stars in IC2574 using the ultraviolet images. They find that about one-third of them could have been formed as a result of previous supernova explosions. When massive stars die in supernova explosions, the outer layers are blown outwards into the surrounding gas, and form spherical shells. These expanding bubbles compress the gas between them which could initiate star formation in the rims of the bubble structures, leading to a new generation of stars. The authors suggest that in IC2574, one of the mechanisms to form young stars is gas compression following shell expansion. Unlike spiral galaxies like Milky Way, where stars are formed mostly in the spiral arms, it is possible that formation of later generations of stars in dwarf galaxies could be because of these bubble structures.

More details of this work can be found in their paper, which has been submitted to the Astrophysical Journal.

Click here for the entire APOM archive.


AstroSat, India's first dedicated multi-wavelength space observatory, was launched by ISRO on 28 September, 2015. It has five instruments on board – the Ultra Violet Imaging Telescope, the Soft X-ray Telescope, the Large Area X-ray Proportional Counter, the Cadmium-Zinc-Telluride Imager and the Scanning Sky Monitor.

Get answers to your common queries about ASTROSAT in English, in हिंदी, and in मराठी.


  1. Pale Blue Dot (EARTH): Look again at that dot. That’s here. That’s home. That’s us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every “superstar,” every “supreme leader,” every saint and sinner in the history of our species lived there-on a mote of dust suspended in a sunbeam.

    The Earth is a very small stage in a vast cosmic arena. Think of the rivers of blood spilled by all those generals and emperors so that, in glory and triumph, they could become the momentary masters of a fraction of a dot. Think of the endless cruelties visited by the inhabitants of one corner of this pixel on the scarcely distinguishable inhabitants of some other corner, how frequent their misunderstandings, how eager they are to kill one another, how fervent their hatreds.

    Our posturings, our imagined self-importance, the delusion that we have some privileged position in the Universe, are challenged by this point of pale light. Our planet is a lonely speck in the great enveloping cosmic dark. In our obscurity, in all this vastness, there is no hint that help will come from elsewhere to save us from ourselves.

    The Earth is the only world known so far to harbor life. There is nowhere else, at least in the near future, to which our species could migrate. Visit, yes. Settle, not yet. Like it or not, for the moment the Earth is where we make our stand.

    It has been said that astronomy is a humbling and character-building experience. There is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world. To me, it underscores our responsibility to deal more kindly with one another, and to preserve and cherish the pale blue dot, the only home we’ve ever known.


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