Astrosat Picture of the Month

Sharing the excitement of India's first dedicated space observatory, every month!

Image of the Month

The AstroSat Picture of the Month for May 2019 is the near-ultraviolet image of the Jellyfish Galaxy JO201, using ASTROSAT. This image shows young stars formed in the disk of the galaxy. The cross marks the active galactic nucleus (AGN) at the centre of the galaxy. The cavity-like structure around the central AGN is due to a dearth of young stars.

Picture credit: Koshy George and team

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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.

Peering into the heart of the Jellyfish Galaxy

This month, we bring back our friend, the Jellyfish galaxy JO201, that we had introduced to you in an earlier APOM, where we described how this galaxy acquires its tentacles-like shape. However, this time, we do not talk about its outer shape but rather study its interior to understand its anatomy. This galaxy was imaged in near and far UV bands from UVIT on AstroSat and the zoomed-in image of the centre is shown in the picture. When we see the the galaxy closely, we notice that the UV emission is bright at the centre, surrounded by a region where UV light is faint. Thereafter, it is again bright in a broken ring-like structure.

Why is there less ultraviolet light from the region just around the centre? By comparing the UV images from AstroSat with images from other telescopes at different wavelengths, astronomers from India and abroad have shown that the ultraviolet light from the central region of this galaxy is related to the working of Active Galactic Nuclei (AGN) at the centre of this galaxy. Most large galaxies are found to have central regions, called AGN, that are very bright at certain wavelengths. They are believed to be very bright because of the presence of supermassive black holes, whose mass could be hundreds of thousands to billions of times the mass of Sun. The light doesn't come from the black-holes themselves but from gas and dust surrounding the black-hole swirling into its recesses. AGN are considered to have important roles to play in the formation of stars in galaxies, and consequently in their appearance and evolution.

In the case of JO201, the UV from regions in the outer ring and beyond is thought to be due to young stars formed in the last 200 million years, unlike the centre which is bright in UV because of the AGN. Therefore, the cavity region surrounding the centre, that has low UV light, has very little star formation occurring. What halted the star formation here? These researchers suggest that energy is released from the AGN into its surroundings, heating the surrounding cold gas clouds and disrupting the process of star formation here. They also show that the effect of stripping of gas giving the jellyfish galaxy its name, is responsible for the lack of young stars in the broken ring structure. This is evident from the fact that both the broken ring structure and tentacles are seen on the left side of the galaxy image. More details of this work can be found in their paper, accepted for publication in the Monthly Notices of Royal Astronomical Society.

The paper describing the results is accepted for publication by the Monthly Notices of the Royal Astronomical Society and can be found here. The accompanying science story, through India Science Wire, is here.

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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